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Hydrogen fluoride addition reactions and a fluorinated cathode catalyst support material for fuel cells
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Hydrogen fluoride addition reactions and a fluorinated cathode catalyst support material for fuel cells
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Content
HYDROGEN FLUORIDE ADDITION REACTIONS AND A FLUORINATED CATHODE
CATALYST SUPPORT MATERIAL FOR FUEL CELLS
by
Amanda F. Baxter
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements of the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
August 2020
Copyright 2020 Amanda F. Baxter
ii
Dedicated to my mother, Julianne.
iii
ACKNOWLEDGEMENTS
It is surreal to reflect on where I was when I started this journey. I am filled with gratitude thinking
about the many people who have helped me along the way. First, I would like to thank my advisors.
I would like to thank Prof. Karl Christe for the wisdom he has shared with me and for his
unwavering support. I would like to thank Prof. Ralf Haiges for always being there to answer my
questions and being patient and kind while doing so. I would like to thank Prof. Surya Prakash for
teaching me how to think about the bigger picture and keep things in perspective. It was truly a
privilege to work with these professors the last several years.
I would like to thank Prof. Antonio Togni of ETH in Zürich for being so welcoming and
kind when I visited his group. I would also like to thank Profs. Fokion Egolfopoulos, Travis
Williams and Alex Benderskii for serving on my committees. I would like to thank Prof. Megan
Fieser who has been a mentor to me recently through her involvement with Women in Chemistry.
Her encouragement and advice has been instrumental in helping me get to the next stage of my
career.
Next, I would like to thank my friends and colleagues. Guillaume Bélanger-Chabot helped
to train me when I was first getting started. I recognize this took a huge amount of time, effort and
patience, for which I am extremely grateful. I would also like to thank Ewa Pietrasiak. I am so glad
I got the opportunity to learn from Ewa during my time in Prof. Togni’s group at ETH. Finally, I
would like to thank Vicente Galvan who trained me when I joined the fuel cell lab. He has always
been willing to answer my questions, help me troubleshoot and has made my transition to the fuel
cell lab very enjoyable.
iv
I would like to thank my other colleagues including Piyush Deokar, Nicolas Hilgert, Jonas
Schaab, Igor Martin, Vanda Dašková, Sebastian Küng, Eugene Kong, Bo Yang, Dean Glass, Adam
Ung, Sahar Roshandel, Nazanin Entesari, Huong Dang, Raktim Sen, Sayan Kar, Archith
Nirmalchandar, Kavita Belligund, Colby Barrett, Vinayak Krishnamurti, Xanath Ispizua-
Rodriguez, Fang Fu, Alain Goeppert, Patrice Batamack and Thomas Mathew who have all made
this experience more enjoyable.
I would like to thank the Women in Chemistry community including Betsy Melenbrink,
Caitlin DeAngelo, Arunika Ekanayake, Sahar Roshandel, Renata Rezende Miranda, Cay Yu, Ariel
Vaughn, Nazanin Entesari and Negar Kazerouni. I would like to thank those who contributed their
technical support with instrumentation including Ralf Haiges (X-ray crystallography), Allan
Kershaw (NMR), Andrew Clough and Jeremy Intrator (XPS), and Matt Mecklenburg and Tom
Orvis (TEM). I would also like to thank Robert Aniszfeld, Michele Dea and Jessie May whose
critical work behind the scenes makes all of this possible.
I was fortunate to have amazing teachers and mentors in chemistry early on who inspired
me down the path toward pursuing my Ph.D. in chemistry. I am grateful for Prof. Allan van Asselt
who provided me with the critical information, advice and encouragement I needed to transition
from undergraduate to graduate school. I would also like to thank my high school chemistry teacher
Amy Derting, who introduced me to and got me excited about chemistry in the first place. Her
impact on my life cannot be overstated.
Last but certainly not least I would like to thank my (non-colleague) friends and my family.
I would like to thank my partner, A.J. Cooper whose constant support and encouragement keeps
me grounded. I would like to thank Lauren Martin and Lizette Guzman for all the great times we
had that allowed me to fully unwind. I also would like to thank my parents, Julianne and Stewart,
v
for their endless support all of these years. They taught me how to embrace failure and encouraged
me to stay curious when I was a little girl filled with questions, both of which have supported my
development as a scientist. Finally, a big thanks to the rest of my family: Andrew, Austin, Danielle,
Steven, Tony, Sandy, Bernie and Chiara. I am grateful I was always just a short drive away and
was able to spend lots of quality time with them during graduate school.
vi
CONTRIBUTIONS
The experimental work in Chapter 2 was completed by Ralf Haiges and me. The following paper
is rewritten in Chapter 2 with permission from Wiley. (Baxter, A. F.; Christe, K. O.; Haiges, R.
“Convenient Access to α-Fluorinated Alkylammonium Salts” Angew. Chem. Int. Ed. 2015, 54,
14535.)
Much of the experimental work in Chapter 3 was performed by me. I later learned Joachim
Axhausen had also prepared these compounds while he was a Ph.D. student in Andreas Kornath’s
group at LMU Munich. We decided we will combine our data and publish a manuscript together.
Ralf Haiges and I obtained the X-ray crystal structures. I performed the synthesis and NMR
experiments while Joachim independently performed the synthesis and vibrational analysis. The
manuscript is not yet submitted.
The synthesis of perfluorinated primary alcohols (Chapter 4) was a group effort. The work
was initiated many years ago by Joachim Hegge, but the data was incomplete. The experimental
work including the equilibria data was performed by my mentee, Jonas Schaab, and me. Thomas
Saal contributed the detailed NMR analysis which was needed to distinguish the alcohols from
their oxonium salts. Karl Christe was involved with the data analysis and writing and editing of
the manuscript. This chapter was reproduced from the following manuscript with permission from
Wiley. (Baxter, A. F.; Schaab, J.; Hegge, J.; Saal, T.; Vasiliu, M.; Dixon, D. A.; Haiges, R.;
Christe, K. O. "α‐Fluoroalcohols: Synthesis and Characterization of Perfluorinated Methanol,
Ethanol and n‐Propanol, and their Oxonium Salts" Chem. Eur. J. 2018, 24, 16737.)
The crystal structures of heptaflurocyclobutanol and hexafluorocyclobutane-1,1-diol
(Chapter 6) were performed by Jonas Schaab under my supervision, as well as Ralf Haiges. The
vii
three of us contributed to the following manuscript which was reproduced with permission from
Wiley. (Baxter, A. F.; Schaab, J.; Christe, K. O.; Haiges, R. “Perfluoroalcohols: The Preparation
and Crystal Structures of Heptafluorocyclobutanol and Hexafluorocyclobutane-1,1-diol” Angew.
Chem. Int. Ed. 2018, 57, 8174.)
The experimental work in Chapter 6 was mostly done by me with a couple of important
exceptions. Vicente Galvan and Sahar Roshandel performed the TEM measurements. Vicente also
performed the fuel cell testing. Vicente Galvan, Bo Yang and Surya Prakash contributed valuable
discussions during the course of this work.
viii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ........................................................................................................ iii
CONTRIBUTIONS...................................................................................................................... vi
TABLE OF CONTENTS .......................................................................................................... viii
LIST OF FIGURES .................................................................................................................... xii
LIST OF TABLES ................................................................................................................... xviii
LIST OF SCHEMES ................................................................................................................. xxi
ABSTRACT ............................................................................................................................... xxii
CHAPTER 1: INTRODUCTION .................................................................................................1
Motivation ..................................................................................................................................1
Fluorine: A Small Atom with a Big Ego .............................................................................1
Bioactivity of Fluorine-Containing Molecules ....................................................................2
Fluoropolymers ....................................................................................................................4
Experimental Methods ...............................................................................................................5
Reactions with Hydrogen Fluoride ......................................................................................5
Safety ...................................................................................................................................6
References ..................................................................................................................................9
CHAPTER 2: THE SYNTHESIS OF α-FLUORINATED ALKYLAMMONIUM SALTS.11
Abstract ....................................................................................................................................11
Introduction ..............................................................................................................................11
Synthesis ..................................................................................................................................13
NMR Spectroscopy ..................................................................................................................15
X-ray Crystallography .............................................................................................................18
Conclusion ...............................................................................................................................20
References ................................................................................................................................21
CHAPTER 3: THE SYNTHESIS OF [NH2CFNH2]
+
AND [NH2CNH]
+
................................24
Abstract ....................................................................................................................................24
Introduction ..............................................................................................................................24
Results and Discussion ............................................................................................................25
Experimental ............................................................................................................................35
ix
Conclusion ...............................................................................................................................36
References ................................................................................................................................36
CHAPTER 4: THE SYNTHESIS OF PRIMARY PERFLUORINATED ALCOHOLS ......39
Abstract ....................................................................................................................................39
Introduction ..............................................................................................................................39
Synthesis ..................................................................................................................................42
Thermodynamics......................................................................................................................45
NMR Spectroscopy ..................................................................................................................47
Conclusion ...............................................................................................................................51
References ................................................................................................................................51
CHAPTER 5: THE CRYSTAL STRUCTURES OF HEPTAFLUOROCYCLOBUTANOL
AND HEXAFLUOROCYCLOBUTANE-1,1-DIOL ..........................................................55
Abstract ....................................................................................................................................55
Introduction ..............................................................................................................................55
Results and Discussion ............................................................................................................56
Conclusion ...............................................................................................................................64
Experimental ............................................................................................................................64
References ................................................................................................................................64
CHAPTER 6: PARTIALLY FLUORINATED GRAPHENE AS A CATHODE CATALYST
SUPPORT IN PROTON EXCHANGE MEMBRANE FUEL CELLS ............................68
Abstract ....................................................................................................................................68
Introduction ..............................................................................................................................68
Motivation ..........................................................................................................................68
Introduction to Fuel Cells ..................................................................................................70
Background ........................................................................................................................73
Results and Discussion ............................................................................................................75
Synthesis ............................................................................................................................75
Characterization .................................................................................................................75
Half-cell Testing ................................................................................................................84
Fuel Cell Testing ................................................................................................................87
Conclusion ...............................................................................................................................90
Experimental ............................................................................................................................90
Preparation of fluorinated graphene ...................................................................................90
Preparation of Pt supported on fluorinated graphene ........................................................91
Characterization .................................................................................................................91
Half-cell Testing ................................................................................................................92
x
Fuel Cell Testing ................................................................................................................93
References ................................................................................................................................94
APPENDIX 1: ADDITIONAL INFORMATION FOR THE SYNTHESIS OF α-
FLUORINATED ALKYLAMMONIUM SALTS (CHAPTER 2) ....................................99
Experimental Details ................................................................................................................99
Materials and apparatus .....................................................................................................99
Crystal Structure determinations......................................................................................100
[HCF2NH3][MF6] .............................................................................................................100
[CF3NH3][MnF5n+1] ..........................................................................................................100
[CF3CF2NH3][AsF6] .........................................................................................................101
[HCF2CF2NH3][AsF6] ......................................................................................................101
[NH3CF2CF2NH3][AsF6]2 ................................................................................................102
CF3NH2: ...........................................................................................................................103
NMR experiments with RCN + HF (R = CH3, CH3CH2, CF3CH2) .................................103
Crystallographic Details.........................................................................................................105
References ..............................................................................................................................118
APPENDIX 2: ADDITIONAL INFORMATION FOR THE SYNTHESIS OF [NH2CFNH2]
+
AND [NH2CNH]
+
(CHAPTER 3) ........................................................................................120
Experimental Details ..............................................................................................................120
Vibrational Analysis ..............................................................................................................124
Crystallographic Details.........................................................................................................126
References ..............................................................................................................................136
APPENDIX 3: ADDITIONAL INFORMATION FOR THE SYNTHESIS OF PRIMARY
PERFLUORINATED ALCOHOLS (CHAPTER 4) ........................................................138
Experimental Details ..............................................................................................................138
Materials and apparatus ...................................................................................................138
General Procedure 1 (GP1) ..............................................................................................138
COF2 + HF CF3OH .....................................................................................................139
COF2 + HF CF3OH .....................................................................................................140
CF3COF + HF C2F5OH ...............................................................................................142
C2F5COF + HF C3F7OH ..............................................................................................143
C2F5COF + HF C3F7OH ..............................................................................................144
NMR Results ..........................................................................................................................145
Preparation of CF3OH, CF3CF2OH and CF3CF2CF2OH NMR samples .........................145
Preparation of CF3OH2
+
, CF3CF2OH2
+
and CF3CF2CF2OH2
+
NMR samples .................145
CF3OH..............................................................................................................................146
CF3OH/CF3OH2
+
..............................................................................................................148
CF3OH2
+
...........................................................................................................................150
CF3CF2OH .......................................................................................................................151
CF3CF2OH2
+
....................................................................................................................153
xi
CF3CF2CF2OH .................................................................................................................155
CF3CF2CF2OH2
+
..............................................................................................................157
HF ....................................................................................................................................160
HF/SbF5............................................................................................................................161
References ..............................................................................................................................162
APPENDIX 4: ADDITIONAL INFORMATION FOR THE CRYSTAL STRUCTURES OF
HEPTAFLUOROCYCLOBUTANOL AND HEXAFLUOROCYCLOBUTANE-1,1-
DIOL (CHAPTER 5) ...........................................................................................................163
Experimental Details ..............................................................................................................163
Crystallographic Details.........................................................................................................166
APPENDIX 5: ADDITIONAL INFORMATION FOR PARTIALLY FLUORINATED
GRAPHENE AS A CATHODE CATALYST SUPPORT IN PROTON EXCHANGE
MEMBRANE FUEL CELLS (CHAPTER 6) ...................................................................177
XRD ....................................................................................................................................177
XPS ....................................................................................................................................178
SEM-EDS ..............................................................................................................................183
Half-Cell Data ........................................................................................................................188
Electrochemical Impedance Spectroscopy ............................................................................190
xii
LIST OF FIGURES
Figure 1.1. Some biologically active fluorinated molecules. 1 = 5’-fluoro-5’-deoxyadenosine, the
compound formed by the enzyme fluorinase; 2 = Fludrocortisone, the first fluorine-containing
pharmaceutical, first synthesized in 1954. 3 = Lipitor (Atorvastatin) inhibits cholesterol
biosynthesis; 4 = Advair Diskus (Fluticasone propionate + Salmeterol) anti-asthma; 5 = Crestor
(Rosuvastatin) inhibits cholesterol biosynthesis. 3-5 are three of the top ten best selling drugs. .. 3
Figure 1.2. Examples of some common fluoropolymers. .............................................................. 4
Figure 1.3. Photograph of the stainless steel/Teflon-FEP high vacuum line used in this work. ... 7
Figure 1.4. Photograph of a typical stainless steel/Teflon-FEP reactor used in this work. ........... 7
Figure 2.1. The
14
N NMR spectrum of a 0.2 mol% CH3CN solution in HF after 7 days at ambient
temperature. .................................................................................................................................. 16
Figure 2.2.
19
F NMR spectrum of CF3NH2 at -30°C. .................................................................. 18
Figure 2.3. The asymmetric unit in the crystal structure of [HCF2NH3][AsF6]. Thermal ellipsoids
are set at 50% probability. Hydrogen atom positions were determined from the electron density
map and are depicted as spheres of arbitrary radius. Selected bond lengths [Å] and angles [˚]: C1-
F2 1.326(3), C1-F1 1.338(3), C1-N1 1.470(3), C2-F3 1.325(3), C2-F4 1.342(3), C2-N2 1.475(3),
F2-C1-F1 108.4(2), F2-C1-N1 107.5(2), F1-C1-N1 106.9(2), F3-C2-F4 108.7(2), F3-C2-N2
107.7(2), F4-C2-N2 106.8(2). ....................................................................................................... 19
Figure 2.4. The asymmetric unit in the crystal structure of [CF3NH3][Sb2F11]. Hydrogen atom
positions were determined from the electron density map and are depicted as spheres of arbitrary
radius. Thermal ellipsoids are set at 50% probability. Selected bond lengths [Å] and angles [˚]:
F9-C1 1.307(3), F10-C1 1.312(5), N1-C1 1.469(6), F9-C1-F9 110.7(4), F9-C1-F10 110.1(3), F9-
C1-N1 108.3(3), F10-C1-N1 109.5(4). ......................................................................................... 20
Figure 3.1. Low temperature IR (top) and Raman (bottom) spectra for [NH2CFNH2][AsF6] (blue:
a, f), [NH2CFNH2][Sb2F11] (green: b, e), [ND2CFND2][AsF6] (red: c, d). ................................... 28
Figure 3.2. The asymmetric unit in the crystal structure of [NH2CFNH2][SbF6]. Thermal ellipsoids
are set at 50% probability. Hydrogen atom positions were determined from the electron density
map and are depicted as spheres of arbitrary radius. Selected bond lengths [Å] and angles [˚]: C1-
N1 1.301(3), C1-N2 1.296(3), F1-C1 1.313(3) ; N1-C1-N2 128.3(2), N2-C1-F1 116.0(2), N1-C1-
F1 115.8(2). ................................................................................................................................... 30
Figure 3.3. (Top) The
14
N NMR spectrum of NH2CN in CH3CN at 25 ˚C. (Bottom) The
14
N NMR
spectrum of [NH2CNH][SbF6] in SO2 at -65˚C. ........................................................................... 31
xiii
Figure 3.4. Low temperature IR (top) and Raman (bottom) spectra for [NH2CNH][AsF6] (blue: a,
f), [NH2CNH][SbF6] (green: b, e), [ND2CND][AsF6] (red: c, d). ................................................ 33
Figure 3.5. The asymmetric unit in the crystal structure of [NH2CNH][SbF6]. Thermal ellipsoids
are set at 50% probability. Hydrogen atom positions were determined from the electron density
map and are depicted as spheres of arbitrary radius. Selected bond lengths [Å] and angles [˚]: C1-
N11.158(3), C1-N2 1.275(3); N1-C1-N2 173.6(2).
....................................................................................................................................................... 34
Figure 4.1. Temperature dependence of the COF2+HF⇌CF3OH equilibrium measured by area
integration of the corresponding
19
F NMR signals for two different mole ratios of HF/COF2.
Reproduced from reference 31...................................................................................................... 41
Figure 4.2. Temperature dependence of the COF2 + HF CF3OH equilibrium. Each data point
was measured, approaching the equilibrium from above and below the desired temperature.
Equilibrium was reached when both values coincided. ................................................................ 42
Figure 4.3. Plot of C2F5OH Formation as a Function of Temperature and Initial Concentration.
....................................................................................................................................................... 44
Figure 4.4. Plot of C3F7OH Formation as a Function of Temperature and Initial Concentration.
....................................................................................................................................................... 44
Figure 4.5. van ’t Hoff plots for the equilibrium RfCOF+HF RfCF2OH (Rf=F, CF3, CF3CF2).
Equations for the lines are as follows: (Rf=F) y=1798.3x+11.237, R
2
=0.9913; (R=CF3)
y=1634.4x+11.524, R
2
=0.99284; (R=CF3CF2) y=1087.7x+11.481, R
2
=0.98735. ....................... 46
Figure 5.1. Asymmetric unit of the heptafluorocyclobutanol crystal structure. Ellipsoids are set at
50% probability except for the hydrogen atoms being shown as spheres of arbitrary radius.
Hydrogen atom positions were determined from the difference electron density map. Selected bond
distances [Å] and angles [°]: C1–O1 1.358(5), C1–O1 1.358(5), C1–C2 1.564(5), C2–C3 1.553(5),
C3–C4 1.563(5), C1–C4 1.558(5), C5–C6 1.566(5), C6–C7 1.560(5), C7–C8 1.555(5), C5–C8
1.572(6); C1-C2-C3 90.4(3), C2-C3-C4 897(3), C3-C4-C1 90.3(3), C4-C1-C2 89.5(3), C5-C6-C7
90.0(3), C6-C7-C8 89.7(3), C7-C8-C5 90.0(3), C8-C5-C6 88.9(3), F1-C1-O1 112.4(3) F8-C5-O2
112.6(3), F2-C2-F3 109.5, F9-C6-F10 109.5(3). .......................................................................... 57
Figure 5.2. A) Crystal packing of heptafluorocyclobutanol projected down the b axis. B) Part of
an hfcb helix parallel to the b axis. The fluorine atoms have been omitted for clarity. Selected
distances [Å]: O1H1···O2 2.825(3), O2-H2···O1 2.810(3), F1–F10 2.876(3), F2–F11 2.923(3),
F3–F10 2.836(3), F6–F14 2.924(3), F7–F8 2.889(3), F7–F14 2.897(3), F10–F12 2.812(3) F11–
F13 2.926(3). ................................................................................................................................. 60
Figure 5.3. The hfcbd molecule in the crystal structure. Ellipsoids are set at 50% probability except
for the hydrogen atoms being shown as spheres of arbitrary radius. Hydrogen atom positions were
determined from the difference electron density map. Selected bond distances [Å] and angles [°]:
xiv
C1–O1 1.393(4), C1–O2 1.378(3), C1–C2 1.576(3), C2–C3 1.560(4), C3–C4 1.563(3), C4–C1
1.576(4), C2–F1 1.335(3), O1-C1-O2 115.1(2), C1-C2-C3 90.2(2), C2-C3-C4 89.8(2), C3-C4-C1
90.1(2), C4-C1-C2 88.7(2), F1-C2-F2 109.5(2). .......................................................................... 62
Figure 5.4. A) Crystal packing of hfcbd·HF projected down the b axis. B) Part of the hydrogen
bonding network in hfcbd·HF viewed down the c axis. Some fluorine atoms have been omitted for
clarity. Selected distances [Å]: O1H1···O2 2.750(3), O1···H3-F7 2.576(3), O2H2···F7 2.697(3),
O2H2···F7’ 2.968(3), F1–F5 2.923(2), F4–F4’ 2.871(3). ............................................................ 63
Figure 6.1. United States energy consumption based on fuel type as of 2018. ........................... 69
Figure 6.2. Schematic of a proton-exchange membrane fuel cell (PEMFC). Image courtesy of
user: CFA213FCE, Wikimedia Commons, CC BY-SA 3.0, URL:
https://commons.wikimedia.org/w/index.php?curid=26261005 .................................................. 72
Figure 6.3. Raman spectra (top) and XRD patterns (bottom). ..................................................... 77
Figure 6.4. Deconvoluted C1s spectra of FG1 (a) and FG2 (b). Deconvoluted F1s spectra of FG1
(c), FG2 (d), PtFG1 (e), and PtFG2 (f). All other spectra along including survey spectra are
provided in Appendix 5. ............................................................................................................... 80
Figure 6.5. SEM-EDS mapping of FG2 (top) red C, blue F, green O, yellow S. SEM-EDS mapping
of PtFG2 (bottom) red C, blue F, green O, yellow Na, pink Pt. Additional SEM images and EDS
maps can be found in the supporting information. ....................................................................... 81
Figure 6.6. TEM, HRTEM and particle size distribution of Pt/FG1 (top), Pt/FG2 (middle) and
Pt/G (bottom). Pt/FG1: 4.0 ± 1.1 nm; Pt/FG2: 4.2 ± 0.9 nm; Pt/G: 3.5 ± 0.6. ............................. 82
Figure 6.7. TGA under N2 (left) and air (right). ........................................................................... 83
Figure 6.8. a) CV under N2 at 50 mV/s b) LSV under O2 1600 rpm, 10 mV/s, positive going
direction c) Effect of rotation rate on LSV for Pt/FG2 under O2 positive going direction d)
Koutecky-Levich plot of the different catalysts at 0.80 V v. RHE (triangles) and 0.85 V v. RHE
(circles) e) Plot of specific activity vs. potential f) Electrochemical Impedance Spectroscopy under
O2, 1600 rpm, 0.7 V v. RHE, Raw data is given by symbols whereas the solid line is the data fitted
according to the equivalent circuit. Full details regarding the EIS fitting parameters are provided
in Appendix 5. ............................................................................................................................... 85
Figure 6.9. Fuel Cell Testing Results
a
Effect of cathode catalyst loading. 70°C 100 sccm H2 250
sccm O2.
b
Effect of adding a carbon black spacer to the cathode catalyst ink. 70°C 100 sccm H 2
250 sccm O2.
c
Effect of fluorination of the graphitic support. 70°C 100 sccm H2 250 sccm O2.
d
Constant potential 0.3V. 70°C 50 sccm H2 50 sccm O2.
e
EIS at OCV, 70°C. The dots represent
the raw data while the solid line represents the fit. ....................................................................... 88
Figure A1.1. Packing diagram of [HCF2NH3][AsF6]. View along the 001 direction. ............... 105
xv
Figure A1.2. Packing diagram of [HCF2NH3][AsF6]. View along the 010 direction. ............. 105
Figure A1.3. Packing diagram of [HCF2NH3][AsF6]. View along the 100 direction. ............... 106
Figure A1.4. Packing diagram of [CF3NH3][Sb2F11]. View along the 001 direction. ............... 112
Figure A1.5. Packing diagram of [CF3NH3][Sb2F11]. View along the 010 direction. ............... 113
Figure A1.6. Packing diagram of [CF3NH3][Sb2F11]. View along the 100 direction. ............... 113
Figure A2.1. Packing diagram of [NH2CFNH2][SbF6]. View normal to the 100 direction. ...... 126
Figure A2.2. Packing diagram of [NH2CFNH2][SbF6]. View normal to the 010 direction. ...... 126
Figure A2.3. Packing diagram of [NH2CFNH2][SbF6]. View normal to the 001 direction. ...... 127
Figure A2.4. Packing diagram of [NH2CNH][SbF6]. View normal to the 100 direction. ......... 132
Figure A2.5. Packing diagram of [NH2CNH][SbF6]. View normal to the 010 direction. ......... 132
Figure A2.6. Packing diagram of [NH2CNH][SbF6]. View normal to the 001 direction. ......... 133
Figure A3.1.
1
H NMR spectrum COF2 + HF CF3OH. .......................................................... 146
Figure A3.2.
13
C NMR spectrum COF2 + HF CF3OH. ......................................................... 147
Figure A3.3.
19
F NMR spectrum COF2 + HF CF3OH. .......................................................... 147
Figure A3.4.
19
F-
13
C HSQC spectrum COF2 + HF CF3OH. ................................................. 148
Figure A3.5.
1
H NMR spectrum 2COF2 + 3HF + SbF5 CF3OH + [CF3OH2][SbF6]............. 148
Figure A3.6.
13
C NMR spectrum 2COF2 + 3HF + SbF5 CF3OH + [CF3OH2][SbF6]. .......... 149
Figure A3.7.
19
F NMR spectrum 2COF2 + 3HF + SbF5 CF3OH + [CF3OH2][SbF6]. ........... 149
Figure A3.8.
1
H NMR spectrum COF2 + 2HF + SbF5 [CF3OH2][SbF6]. .............................. 150
Figure A3.9.
13
C NMR spectrum COF2 + 2HF + SbF5 [CF3OH2][SbF6]. ............................. 150
Figure A3.10.
19
F NMR spectrum COF2 + 2HF + SbF5 [CF3OH2][SbF6]. ........................... 151
Figure A3.11.
1
H NMR spectrum CF3COF + HF CF3CF2OH. ............................................. 151
Figure A3.12.
13
C NMR spectrum CF3COF + HF CF3CF2OH. ............................................ 152
Figure A3.13.
19
F NMR spectrum CF3COF + HF CF3CF2OH. ............................................ 152
xvi
Figure A3.14.
19
F-
19
F COSY spectrum CF3COF + HF CF3CF2OH. ..................................... 153
Figure A3.15.
1
H NMR spectrum CF3COF + 2HF + SbF5 [CF3CF2OH2][SbF6]. ................. 153
Figure A3.16.
13
C NMR spectrum CF3COF + 2HF + SbF5 [CF3CF2OH2][SbF6]. ................ 154
Figure A3.17.
19
F NMR spectrum CF3COF + 2HF + SbF5 [CF3CF2OH2][SbF6]. ................ 154
Figure A3.18.
1
H NMR spectrum CF3CF2COF + HF CF3CF2CF2OH. ................................. 155
Figure A3.19.
13
C NMR spectrum CF3CF2COF + HF CF3CF2CF2OH. ................................ 155
Figure A3.20.
13
C NMR spectrum CF3CF2COF + HF CF3CF2CF2OH. ................................ 156
Figure A3.21.
19
F NMR spectrum CF3CF2COF + HF CF3CF2CF2OH. ................................ 156
Figure A3.22.
19
F-
13
C HSQC spectrum CF3CF2COF + HF CF3CF2CF2OH. ........................ 157
Figure A3.23.
1
H NMR spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6]. .... 157
Figure A3.24.
13
C NMR spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6]. ... 158
Figure A3.25.
13
C NMR spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6]. ... 158
Figure A3.26.
19
F NMR spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6]. ... 159
Figure A3.27.
19
F-
13
C HSQC spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6].
..................................................................................................................................................... 159
Figure A3.28.
1
H NMR spectrum of HF at -60°C. .................................................................... 160
Figure A3.29.
19
F NMR spectrum of HF at -60°C. .................................................................... 160
Figure A3.30.
19
F NMR spectrum of HF (33.3 mmol) and SbF5 (1.5 mmol) at -60°C. ............ 161
Figure A3.31.
1
H NMR spectrum of HF (33.3 mmol) and SbF5 (1.5 mmol) at -60°C. ............. 161
Figure A4.1. Packing diagram of C4F7OH. View along the 001 direction. ............................... 166
Figure A4.2. Packing diagram of C4F7OH. View along the 010 direction. ............................... 166
Figure A4.3. Packing diagram of C4F7OH. View along the 100 direction. .............................. 167
Figure A4.4. Packing diagram of C4F6(OH)2. View along the 001 direction. ........................... 174
Figure A4.5. Packing diagram of C4F6(OH)2. View along the 010 direction. ........................... 175
Figure A4.6. Packing diagram of C4F6(OH)2. View along the 100 direction. ........................... 175
xvii
Figure A5.1. XRD pattern of heat treated graphene. ................................................................. 177
Figure A5.2. XPS survey spectra. .............................................................................................. 178
Figure A5.3. Deconvoluted C1s XPS spectrum of Pt/FG1. ....................................................... 179
Figure A5.4. Deconvoluted C1s XPS spectrum of Pt/FG2. ....................................................... 179
Figure A5.5. Deconvoluted C1s XPS spectrum of G. ............................................................... 180
Figure A5.6. Deconvoluted C1s XPS spectrum of Pt/G. ........................................................... 180
Figure A5.7. Deconvoluted Pt4f XPS spectrum of Pt/FG1. ...................................................... 181
Figure A5.8. Deconvoluted Pt4f XPS spectrum of Pt/FG2. ...................................................... 181
Figure A5.9. Deconvoluted Pt4f XPS spectrum of Pt/G. ........................................................... 182
Figure A5.10. SEM-EDS spectrum and maps FG1. Red C, Blue F, Green O. .......................... 183
Figure A5.11. SEM-EDS spectrum of FG2. .............................................................................. 184
Figure A5.12. SEM-EDS spectrum and maps PtFG1. Red C, Blue F, Yellow Na, Green O, Pink
Pt. ................................................................................................................................................ 185
Figure A5.13. SEM-EDS spectrum PtFG2. ............................................................................... 186
Figure A5.14. SEM-EDS spectrum and maps of Pt/G; Red C, Green O, Blue Pt. .................... 187
Figure A5.15. Effect of rotation rate Pt/G under O2 10 mV/s, positive going direction. .......... 188
Figure A5.16. Effect of rotation rate Pt/FG1 under O2 10 mV/s, positive going direction. ...... 188
Figure A5.17. Kinetic current vs. Potential ............................................................................... 189
Figure A5.18. Mass activity v. Potential. ................................................................................... 189
xviii
LIST OF TABLES
Table 2.1. Final product ratio for the reaction of nitriles with aHF. ............................................ 17
Table 4.1. Summary of the thermodynamic quantities derived from the van‘t Hoff plots for the
RfCOF + HF RfCF2OH (Rf = F, CF3, CF3CF2) equilibria. a) enthalpies of reaction (kcal/mol).
b) entropies of reaction (cal/molK) c) Gibbs free energies at 298 K (kcal/mol). ......................... 46
Table 4.2. Summary of the
19
F-,
13
C-, and
1
H-NMR shifts and
1
JCF coupling constants of CF3OH
and CF3OH2
+
. ................................................................................................................................ 49
Table 4.3. The
19
F and
13
C-NMR shifts and the corresponding coupling constants of
perfluoroethanol, CF3CF2OH, recorded at -60 °C in HF, and of its protonated cation. The
CF3CF2OH2
+
spectra were recorded at -50 °C for a 1:3 molar mixture of CF3COF and SbF5 in HF.
....................................................................................................................................................... 50
Table 4.4. The
19
F and
13
C-NMR shifts and the corresponding coupling constants of perfluoro-n-
propanol, CF3CF2CF2OH, and its protonated cation, CF3CF2CF2OH2
+
, recorded in HF solution at
-55 °C and -50 °C, respectively . .................................................................................................. 50
Table 6.1. Summary of Raman and XRD data. ............................................................................ 77
Table 6.2. Summary of deconvoluted C1s XPS spectra. ............................................................. 79
Table 6.3. Summary of deconvoluted F1s spectra. ...................................................................... 79
Table 6.4. F/C ratios determined by XPS and SEM-EDS ............................................................ 80
Table 6.5. Summary of half-cell data ........................................................................................... 86
Table 6.6. Summary of results from fuel cell testing. .................................................................. 88
Table A1.1. The effect of concentration on the RCN + HF reaction. Ratio of products after 7 days
with different concentrations of CH3CN in HF. ......................................................................... 104
Table A1.2. The effect of reaction time on the RCN + HF reaction. Ratio of products from a 5%
solution of CH3CH2CN in HF after varying lengths of time. ..................................................... 104
Table A1.3. The effect of R on the RCN + HF reaction. Ratio of products after 7 days from a 5%
solution of RCN in HF. ............................................................................................................... 104
Table A1.4. Sample and crystal data for [HCF2NH3][AsF6]...................................................... 106
Table A1.5. Data collection and structure refinement for [HCF2NH3][AsF6]. .......................... 107
Table A1.6. Atomic coordinates and equivalent isotropic atomic displacement parameters (Å
2
) for
[HCF2NH3][AsF6]. ...................................................................................................................... 108
xix
Table A1.7. Bond lengths (Å) for [HCF2NH3][AsF6]. ............................................................... 109
Table A1.8. Bond angles (°) for [HCF2NH3][AsF6]. ................................................................. 110
Table A1.9. Anisotropic atomic displacement parameters (Å2) for [HCF2NH3][AsF6 ............. 111
Table A1.10. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
) for
[HCF2NH3][AsF6]. ...................................................................................................................... 112
Table A1.11. Sample and crystal data for [CF3NH3][Sb2F11]. ................................................... 113
Table A1.12. Data collection and structure refinement for [CF3NH3][Sb2F11]. ......................... 115
Table A1.13. Atomic coordinates and equivalent isotropic atomic displacement parameters (Å
2
)
for [CF3NH3][Sb2F11]. ................................................................................................................. 116
Table A1.14. Bond lengths (Å) for [CF3NH3][Sb2F11]. ............................................................. 116
Table A1.15. Bond angles (°) for [CF3NH3][Sb2F11]. ................................................................ 116
Table A1.16. Anisotropic atomic displacement parameters (Å
2
) for [CF3NH3][Sb2F11]. .......... 118
Table A1.17. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
) for
[CF3NH3][Sb2F11]. ...................................................................................................................... 118
Table A2.1. Summary of the experimental and computational vibrational spectra and their
assignments. (*) denotes frequencies due to incompletely deuterated isotopomers.
1
indicates
vibrational mode due to [NH2CNH]
+
due to incomplete reaction. ............................................. 124
Table A2.2. Summary of the experimental and computational vibrational spectra and their
assignments. (*) denotes frequencies due to incompletely deuterated isotopomers. .................. 125
Table A2.3. Crystal data and structure refinement for [NH2CFNH2][SbF6]. ............................. 128
Table A2.4. Atomic coordinates (x10
4
) and equivalent isotropic displacement parameters (Å
2
x10
3
)
for [NH2CFNH2][SbF6]. .............................................................................................................. 129
Table A2.5. Bond lengths (Å) and angles (°) for [NH2CFNH2][SbF6]. ..................................... 130
Table A2.6. Anisotropic displacement parameters (Å
2
x10
3
) for [NH2CFNH2][SbF6]. ............. 131
Table A2.7. Hydrogen coordinates (x10
4
) and isotropic displacement parameters (Å
2
x10
3
) for
[NH2CFNH2][SbF6]. ................................................................................................................... 131
Table A2.8. Sample and crystal data for [NH2CNH][SbF6]. ..................................................... 133
Table A2.9. Data collection and structure refinement for [NH2CNH][SbF6]. ........................... 134
xx
Table A2.10. Atomic coordinates and equivalent isotropic atomic displacement parameters (Å
2
)
for [NH2CNH][SbF6]. ................................................................................................................. 135
Table A2.11. Bond lengths (Å) for [NH2CNH][SbF6]. .............................................................. 135
Table A2.12. Bond angles (°) for [NH2CNH][SbF6]. ................................................................ 135
Table A2.13. Anisotropic atomic displacement parameters (Å
2
) for [NH2CNH][SbF6]. .......... 136
Table A2.14. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
) for
[NH2CNH][SbF6]. ....................................................................................................................... 136
Table A3.1. Summary of temperature-dependent equilibrium data for COF2 + HF CF3OH
(higher concentration). ................................................................................................................ 139
Table A3.2. Summary of temperature-dependent equilibrium data for COF2 + HF CF3OH
(lower concentration). ................................................................................................................. 140
Table A3.3. Summary of temperature-dependent equilibrium data for CF3COF + HF
CF3CF2OH (higher concentration). ............................................................................................. 141
Table A3.4. Summary of temperature-dependent equilibrium data for CF3COF + HF
CF3CF2OH (lower concentration). .............................................................................................. 142
Table A3.5. Summary of temperature-dependent equilibrium data for CF3CF2COF + HF
CF3CF2CF2OH (higher concentration). ...................................................................................... 143
Table A4.1. Sample and crystal data for C4F7OH. ..................................................................... 167
Table A4.2. Data Collection and Structure Refinement for C4F7OH. ........................................ 167
Table A4.3. Atomic coordinates and equivalent isotropic atomic displacement parameters (Å
2
) for
C4F7OH. ...................................................................................................................................... 169
Table A4.4. Bond lengths (Å) for C4F7OH. ............................................................................... 169
Table A4.5. Bond angles (°) for C4F7OH. .................................................................................. 171
Table A4.6. Torsion angles (°) for C4F7OH. .............................................................................. 172
Table A4.7. Anisotropic atomic displacement parameters (Å
2
) for C4F7OH............................. 173
Table A4.8. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
) for
C4F7OH. ...................................................................................................................................... 174
Table A4.15. Anisotropic atomic displacement parameters (Å
2
) for C4F6(OH)2. ..................... 175
Table A4.16. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
) for
C4F6(OH)2. .................................................................................................................................. 176
xxi
Table A5.1. EIS fitting details for Pt/FG1 in 0.5M H2SO 4 under O2 at 0.7 V v. RHE. .............. 190
Table A5.2. EIS fitting details for Pt/FG2 in 0.5M H2SO4 under O2 at 0.7 V v. RHE. .............. 190
Table A5.3. EIS fitting details for Pt/G in 0.5M H2SO4 under O2 at 0.7 V v. RHE. .................. 191
Table A5.4. EIS Fitting details for Pt/G fuel cell, 70°C at OCV. .............................................. 191
Table A5.5. EIS fitting details for Pt/FG2 fuel cell, 70°C at OCV. ........................................... 192
LIST OF SCHEMES
Scheme 2.1. Preparation of CF3OCl and CF3NCl2. ...................................................................... 12
Scheme 2.2. Mechanism for the stepwise HF addition across C≡N triple bonds of nitriles. ....... 16
Scheme 3.1. The proposed pathway of the stepwise addition of HF to NH2CN. ......................... 27
xxii
ABSTRACT
Broadly, this dissertation explores fluorination reactions. Chapters 2-5 involve the synthesis of
fluorinated molecules, specifically exploring hydrogen fluoride addition reactions. The inspiration
for this work came from the knowledge that α-fluoroalcohols and α-fluoroalkylamines are
thermally unstable due to facile HF elimination and the question of whether the reverse reaction
could be performed to prepare these compounds under certain conditions. Chapters 2 and 3 study
HF addition reactions across the C≡N bond of cyanides and nitriles to synthesize α-fluoroalkyl-
ammonium and -iminium salts. In this case, addition of a strong Lewis acid allowed for the
isolation of thermally stable ammonium or iminium salts. Chapters 4 and 5 study HF addition
reactions across the C=O bond of carbonyl fluorides to synthesize perfluorinated alcohols. In
Chapter 4, primary perfluorinated alcohols were synthesized at low temperature. While in Chapter
5, heptafluorocyclobutanol (hfcb) was isolated. Hfcb is the exception to the rule of thermally
unstable α-fluoroalcohols as it is stabilized by its substantial ring strain. This molecule was
characterized by its single crystal X-ray structure and is the first example of a crystallographically
characterized α-fluoroalcohol. Chapter 6 investigates the synthesis of partially fluorinated
graphene by reaction with xenon difluoride. This fluorinated material was investigated as a catalyst
support for the oxygen reduction reaction in proton exchange membrane fuel cells and compared
to a non-fluorinated analogue.
1
CHAPTER 1: INTRODUCTION
Motivation
Fluorine: A Small Atom with a Big Ego
Fluorine is the most electronegative element on the periodic table, has a small size (van der Waals
radius 1.47Å), and forms strong C-F bonds.
1
Because of these unique characteristics, fluorinated
molecules and materials have interesting properties. Fluorinated molecules are extremely
important in the pharmaceutical, agrochemical and polymer industries. Additionally, fluorine is
becoming increasingly important in materials science as fluorinated materials are utilized in
electronic devices
2
such as liquid crystal displays, OLEDs, touchscreens and photovoltaics as well
as electrochemical energy systems.
3
The field of synthetic fluorine chemistry has profoundly
impacted our daily lives during the last century.
Fluorine is the 13
th
most abundant element by weight percent 0.054% in the Earth’s crust,
ahead of carbon at 0.02%. However, owing to the low solubilities of its salts in water, it is rare in
the oceans (1.3 ppm), and organofluorine compounds are scarce in nature. In 1944, the first
naturally occurring organofluorine compound, monofluoroacetate, was isolated from the plant D.
cymosum in South Africa.
4,5
Monofluoroacetate was found to be the source of the plants’ toxicity
and has since been identified at high levels in other toxic plants in Central Africa, South West
Australia and South America.
6
The other examples of naturally occurring organofluorine
compounds can be traced to a single precursor, 5’-fluoro-5’-deoxyadenosine (1, Figure 1.1) which
is produced by the only enzyme known to form a C-F bond, fluorinase.
6–8
Although over 4,000
naturally occurring organohalogen (F, Cl, Br, I) compounds are known, only 30 naturally occurring
organofluorine compounds are known.
9
2
Bioactivity of Fluorine-Containing Molecules
The lack of diversity in fluorine-containing natural products as well as the toxicity associated with
many of them meant that prior to the 1950s, organofluorine compounds were not considered for
pharmaceutical applications.
10
This changed after the 1954 discovery of fludrocortisone (2, Figure
1.1) which is used to treat low glucocortocoid levels in patients with adrenal gland diseases.
11
Initially, the authors studied the other halogenated derivatives (I, Br and Cl) and did not consider
fluorine until they observed that the anti-inflammatory properties were improved with decreasing
size of halogen, prompting them to study the smallest halogen, fluorine.
12
Since this initial
discovery, the importance of fluorine chemistry in drug discovery continues to increase.
13,14
As of
2014, about 25% of pharmaceuticals on the market as well as a significant amount of new drugs
introduced each year contain at least one fluorine atom.
10
Three of the top ten best selling drugs
also contain fluorine,
15
Lipitor (3, Figure 1.1) and Crestor (5, Figure 1.1) are prescribed to treat
high cholesterol and Advair Diskus (4, Figure 1.1) an asthma medication.
There are many ways the presence of fluorine can alter the bioactivity of a molecule. Owing
to its high electronegativity, fluorine can strongly affect the acidity or basicity of nearby functional
groups. This modulation of pKa can in turn can affect the binding affinity, pharmacokinetics and/or
bioavailability of a drug.
16
Fluorination can also alter lipophilicity which is a crucial parameter for
membrane permeability.
16
Additionally, the introduction of fluorine will alter the steric and
electronic properties of the molecule which can strongly affect protein-ligand interactions.
16
Poor
metabolic stability is often problematic in drug discovery since the physiological response is to
eliminate the drug. It is well established that substituting a hydrogen atom for a fluorine atom on
an aromatic ring can improve metabolic stability by inhibiting oxidation of the drug by enzymes.
16
3
Figure 1.1. Some biologically active fluorinated molecules. 1 = 5’-fluoro-5’-deoxyadenosine, the
compound formed by the enzyme fluorinase; 2 = Fludrocortisone, the first fluorine-containing
pharmaceutical, first synthesized in 1954. 3 = Lipitor (Atorvastatin) inhibits cholesterol
biosynthesis; 4 = Advair Diskus (Fluticasone propionate + Salmeterol) anti-asthma; 5 = Crestor
(Rosuvastatin) inhibits cholesterol biosynthesis. 3-5 are three of the top ten best selling drugs.
15
The global agrochemicals market was valued at $215 billion in 2016.
17
This value is
projected to grow as the global population continues to grow, and maximizing crop production
becomes an increasingly important issue.
18
Similar to trends in the pharmaceutical industry, 25%
of licensed herbicides contain at least one fluorine atom.
18
Many reasons for the enhanced
biological activity of agrochemicals are similar to those described above for pharmaceuticals, such
as the strength of the C-F bond improving metabolic stability, modulation of lipophilicity and
tuning electronic and steric effects to improve target-ligand binding.
4
Fluoropolymers
Aside from interesting biological activity, fluorine chemistry has revolutionized the
plastics industry and hence, the many other industries that rely on the plastics industry. This started
with the accidental discovery of polytetrafluoroethylene (Figure 1.2) by Dr. Roy Plunkett of
DuPont in 1938 when he noticed the pressure of the autoclave containing gaseous
tetrafluoroethylene had decreased with concomitant formation of a white, waxy solid that was
insoluble in just about everything.
19
Since then many other variations of fluorinated polymers have
been prepared such as fluorinated ethylene propylene (FEP) and polyvinylidene fluoride (PVDF)
(Figure 1.2). Fluoropolymers exhibit unique properties such as low friction, exceptional thermal
and chemical stability, and low surface energies and dielectric constants.
20
As such, they are used
widely for various applications including household appliances and cookware as well as in the
aerospace, medical and electronic industries.
20
Global fluoropolymer sales exceeded $2 billion in
2000 and continues to grow.
21
Figure 1.2. Examples of some common fluoropolymers.
Although the synthetic work in Chapters 2-5 is fundamental in nature, studies on
fluorination reactions and specifically C-F bond forming reactions may find applications in these
5
industries where fluorine is becoming increasingly important. The small fluorinated molecules
reported here have reactive functional groups (amines or alcohols), and thus may serve as building
blocks to prepare other molecules that can be used for applications such as those described above.
Experimental Methods
Reactions with Hydrogen Fluoride
The experiments described in Chapters 2-5 involve the use of anhydrous hydrogen fluoride (aHF).
aHF is highly corrosive, volatile, and it reacts with many materials including glass. All experiments
were performed using specialized custom equipment made in our laboratory that will be briefly
described here. Experiments are performed under anhydrous conditions using a high-vacuum line
and glovebox techniques. The high-vacuum line is made of stainless steel with Teflon-FEP U-
traps and a Heise pressure gauge (Figure 1.3). The stainless steel high-vacuum line is passivated
with ClF3 prior to use in order to replace any metal oxides on the surface with more inert metal
fluorides. Once passivation with ClF3 is complete, it must be conditioned with HF to remove any
chlorine-containing compounds. The ClF3 or HF can be condensed in a U-trap to determine the
color, and passivation and conditioning are considered complete when the compounds are
colorless. A unique feature of this high-vacuum line is the four U-traps in series which permit a
separation technique called fractional condensation. The U-traps can be cooled to different
temperatures, allowing for the separation of volatile compounds based on the temperature at which
their vapor pressure becomes negligible which can often be approximated as the melting point.
Figure 1.4 shows a typical reactor used in this work. The reactor is fabricated from two
different types of Teflon-FEP tubing that are manipulated with an open flame or a heat gun. It
consists of a thin-walled slightly transparent Teflon-FEP bottom (A) so that reactions can be
6
monitored visually. The thin-walled Teflon-FEP is fused to a thicker-walled more opaque Teflon-
FEP upper portion (B). The more sturdy thicker-walled Teflon-FEP is required to form the flare
which connects the Teflon-FEP portion to the stainless steel portion of the reactor. The top cap (C)
can be removed so that manipulations such as transferring liquids by cannulation or syringe can
be performed under N2. NMR experiments are performed in a reactor made from 4 mm o.d. Teflon-
FEP tubing. After all the materials are added to the 4 mm Teflon-FEP tube, the contents of the
tube are cooled to -196°C, and the tube is sealed by gently twisting while heating with a heat gun
under dynamic vacuum. When the 4 mm tube is sealed, it can be placed inside a standard 5 mm
NMR glass tube for measurements.
The volume of each segment of the high-vacuum line is calibrated by measuring the
pressure decrease upon the expansion of a known volume of N2 and calculated using the ideal gas
law. Thus, gases which obey the ideal gas law can be quantified by measuring their pressure in a
segment with a known volume. AsF5, for example, was quantified in this way. SbF5 is a highly
viscous liquid and was handled in a glove box and quantified by mass. HF boils at 20°C, so it is
condensed on the high-vacuum line. However, since HF exhibits hydrogen bonding, it does not
obey the ideal gas law and is quantified by mass or volumetrically.
Safety
HF is extremely corrosive and can cause severe burns that can be fatal. In addition to standard
chemistry laboratory personal protective equipment such as a lab coat, gloves and safety goggles,
extra precautions must be taken when working with HF, including the use of Neoprene or leather
gloves and a face shield. In particular, the eyes are extremely vulnerable to HF burns and may
suffer irreversible damage including loss of sight if exposed to HF in liquid or vapor form.
22
7
Therefore, it is recommended to use both safety goggles and a face shield as an extra layer of
protection.
Figure 1.3. Photograph of the stainless steel/Teflon-FEP high vacuum line used in this work.
Figure 1.4. Photograph of a typical stainless steel/Teflon-FEP reactor used in this work.
8
It is important to note that HF chemical burns are unique from other acid burns. This is
because like other acids, HF dissociates to the corrosive H
+
, however, it also dissociates to the
highly reactive F
-
ion. The action of the corrosive H
+
is similar to other strong acid burns resulting
in immediate, visible tissue damage. Unlike other acids, HF is highly lipophilic and readily
penetrates the skin into deep tissue where F
-
can react with cations including Ca
2+
and Mg
2+
ultimately causing liquefactive necrosis.
23
HF burns are also characterized by intense pain. This is
believed to be the result of increased membrane permeability to potassium due to local depletion
of Ca
2+
as well as direct inhibition of Na
+
K
+
pumps caused by fluoride.
23
These two phenomena
result in local hyperkalemia, neuronal depolarization and intense pain. Importantly, with aHF or
concentrated aqueous HF solutions, symptoms are usually felt immediately, resulting in the
individual seeking immediate treatment. However, with burns caused by dilute aqueous HF
solutions (<20%), symptoms may be delayed up to 1 day. This often delays treatment which can
result in complications. Proper treatment includes thorough rinsing of the skin with water to
remove HF from the skin and prevent additional penetration through the skin. Then calcium
gluconate gel should be applied to neutralize the HF burn by supplying additional Ca
2+
to react
with excess F
-
. Emergency room treatment for severe burns includes calcium gluconate injection.
23
Other chemicals used in this work require extra safety precautions. Some of the main
hazards are provided here. AsF5 is a highly toxic gas, poisonous to liver cells. SbF5 hydrolyzes in
air to HF. Thus, its use requires the same safety precautions as HF. ClF3 reacts explosively with
water. This can be problematic if any air leaks into the waste trap containing ClF3. Therefore, it is
recommended to remove the waste trap containing ClF3 immediately when passivation is
complete.
9
References
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https://doi.org/10.1038/416279a.
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561–565. https://doi.org/10.1038/nature02280.
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Introduced to the Market in the Last Decade (2001–2011). Chem. Rev. 2014, 114 (4), 2432–2506.
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HYDROCORTISONE. J. Am. Chem. Soc. 1954, 76 (5), 1455–1456.
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9α-HALO DERIVATIVES FROM 11-EPI-17α-HYDROXYCORTICOSTERONE. J. Am. Chem.
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10
(14) O’Hagan, D. Fluorine in Health Care: Organofluorine Containing Blockbuster Drugs.
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11
CHAPTER 2: THE SYNTHESIS OF α-FLUORINATED
ALKYLAMMONIUM SALTS
Abstract
A series of novel a-fluoroalkyl ammonium salts was obtained from the corresponding cyano
compounds or nitriles by reaction with anhydrous HF. Room-temperature stable trifluoromethyl
ammonium salts were obtained in quantitative yield in a one-step reaction at ambient temperature
from the commercially available starting materials BrCN or ClCN. The novel cations
[CF3CF2NH3]
+
, [HCF2CF2NH3]
+
, and [(NH3CF2)2]
2+
were obtained from CF3CN, HCF2CN, and
(CN)2, respectively, and anhydrous HF. The aforementioned fluorinated ammonium cations were
isolated as room temperature stable [AsF6]
-
and/or [SbF6]
-
salts, and characterized by multi-nuclear
NMR and vibrational spectroscopy. The salts [HCF2NH3][AsF6] and [CF3NH3][Sb2F11] were
characterized by their X-ray crystal structure.
Introduction
Similar to α-fluoroalcohols, α-fluoroalkylamines are unstable at room temperature and undergo
facile HF elimination. Both the simplest perfluorinated alcohol and amine, namely,
trifluoromethanol and trifluoromethylamine, were first prepared by Seppelt in 1977 from the
corresponding chloro-derivatives, CF3OCl and CF3NCl2, with HCl at low temperature [Eqs. (1)
and (2)].
1–3
(1)
(2)
12
The thermally unstably compounds CF3OCl and CF3NCl2 are not readily available and were
prepared according to relatively cumbersome procedures starting from COF2 and ClF or BrCN and
SF4 (Scheme 2.1).
Scheme 2.1. Preparation of CF3OCl and CF3NCl2.
3,4
Small amounts of CF3NH2 and C2F2NH2 have also been obtained from the corresponding N-chloro
compounds and Me3SiH
5
or the corresponding perfluoroalkylsulfinylamines, Rf-NSO (Rf =
perfluorinated alkyl group) and HCl.
6
Since the initial syntheses of CF3OH and CF3NH2, a wealth
of computational work has been published relating to α-fluoroalkyl alcohols and amines
7–18
demonstrating the relevance of these compounds to the scientific community. By comparison,
however, there has been a lack of reports relating to the bulk syntheses of these or higher primary,
perfluorinated analogs,
5,19–21
which is likely due to the cumbersome preparation of the precursor
compounds. Herein, a convenient and versatile method to prepare α-fluorinated alkylammonium
salts is reported based on an HF addition reaction across C≡N bonds of cyano compounds or
nitriles.
Only a few examples of HF additions to C≡N bonds have been reported in the literature so
far.
22–24
Solutions of HCN in anhydrous HF were reported as unstable at 20 °C and to form the
[HCF2NH3]
+
cation, which was isolated as the [AsF6]
-
salt and was characterized by NMR and
vibrational spectroscopy.
22,25
While small amounts of CF3NH2 were identified by IR spectroscopy
13
in the reaction products when FCN was added to anhydrous HF at -78 °C,
23
it was found that HF
catalyzes the explosive polymerization of FCN.
26
Herein, the isolation and characterization by multi-nuclear NMR and vibrational
spectroscopy of the following room-temperature stable α-fluorinated alkylammonium salts
[HCF2NH3][MF6] (M = As, Sb), [CF3NH3][MnF2n+1] (n = 1, 2), [HCF2CF2NH3][AsF6],
[CF3CF2NH3][AsF6] and [(CF2)2(NH3)2][AsF6]2 is reported. Additionally, the salts
[HCF2NH3][AsF6] and [CF3NH3][Sb2F11] were characterized by their X-ray crystal structures. The
cations [CH3CF2NH3]
+
, [CH3CH2CF2NH3]
+
, and [CF3CH2CF2NH3]
+
could not be isolated as
[MF6]
-
salts, but were observed by NMR spectroscopy.
Synthesis
The [HCF2NH3]
+
cation was prepared by dissolving HCN in a large excess of anhydrous HF and
stirring of the resulting solution at ambient temperature for three days. While the resulting
polybifluoride [HCF2NH3][HF2·nHF] is only stable in HF solution and decomposed upon removal
of the solvent, a room temperature stable [MF6]
-
(M = As, Sb) salt is obtained after the addition of
a stoichiometric amount of MF5 (Eq. 3).
(3)
Removal of the volatile compounds in vacuo resulted in colorless, crystalline solids that
was identified as [HCF2NH3][MF6] by its multi-nuclear NMR and vibrational spectra which were
in good agreement with the ones previously reported.
22,25
In addition, [HCF2NH3][AsF6] was
characterized by its X-ray single crystal structure.
In analogy to the synthesis of [HCF2NH3]
+
, the simplest perfluoroalkyl ammonium cation,
[CF3NH3]
+
should be accessible by reacting FCN with HF. Cyanogen fluoride, however, is not
14
readily available and must be prepared by the thermolysis of cyanuric fluoride.
27
Furthermore it is
unstable at ambient temperature and tends to polymerize explosively. We therefore explored the
possibility of synthesizing [CF3NH3]
+
through an in situ generation of FCN through fluorination
of HCN. However, when a freshly prepared solution of HCN in HF was exposed to an excess of
100% fluorine at room temperature, only the [HCF2NH3]
+
cation was obtained and no evidence
for the formation of [CF3NH3]
+
could be found. Therefore, it must be concluded that the HF
addition to HCN proceeds faster than its fluorination to FCN, and that [HCF2NH3]
+
does not react
with F2 at ambient temperature and pressure.
Ultimately we were able to find a practical method for the preparation of the [CF3NH3]
+
cation employing the commercially available starting materials XCN (X = Br, Cl). The reaction of
cyanogen bromide or cyanogen chloride with an excess of anhydrous HF results in the release of
HX and a HF solution of the polybifluoride [CF3NH3][HF2·nHF] is obtained (Eq. 4).
(4)
This reaction proceeds fastest with ClCN, requiring about six hours reaction time, while
four days are required in the case of BrCN as starting material. After the addition of stoichiometric
amounts of MF5 (M = As, Sb) followed by the removal of volatile materials in vacuo, the resulting
salts [CF3NH3][MF6] or [CF3NH3][Sb2F11] were obtained in quantitative yields (Eq. 5-6).
(5)
(6)
These novel [CF3NH3]
+
salts were identified and characterized by multi-nuclear NMR and
vibrational spectroscopy. Additionally, [CF3NH3][Sb2F11] was structurally characterized by
single-crystal X-ray diffraction.
[CF
3
NH
3
][HF
2
·nHF] + MF
5
[CF
3
NH
3
][MF
6
]
-(n+1) HF
[CF
3
NH
3
][HF
2
·nHF] + 2 SbF
5
[CF
3
N][Sb
2
F
11
]
-(n+1) HF
15
In order to probe the generality of our method of adding HF across C≡N triple bonds, we
attempted HF addition reactions with a variety of other fluorinated and non-fluorinated nitriles.
The reactions of CF3CN and HCF2CN with HF afforded the expected, novel fluorinated higher
ammonium cations [CF3CF2NH3]
+
and [HCF2CF2NH3]
+
which, after addition of AsF5, were
isolated in >90 % yield as the corresponding [AsF6]
-
salts (Eq. 7-8).
(7)
(8)
(9)
The perfluorinated diammonium salt [(NH3CF2)2][AsF6]2 was obtained as an off-white
solid in near quantitative yield from cyanogen (CN)2 and anhydrous HF, followed by the addition
of AsF5 (Eq. 10). The aforementioned α-fluoroalkylammonium salts [HCF2NH3][MF6],
[CF3NH3][MF6], [CF3NH3][Sb2F11], [CF3CF2NH3][MF6], [HCF2CF2NH3][MF6], and
[H3NCF2CF2NH3][MF6] are moisture sensitive but room temperature stable solids that can be
stored in the dry nitrogen atmosphere of a glove box for at least several months. Further details
and synthetic procedures are provided in Appendix 1.
NMR Spectroscopy
When the non-fluorinated nitriles CH3CN and C2H5CN and the partially fluorinated compound
CF3CH2CN were dissolved in anhydrous HF and the reaction followed by multi-nuclear NMR
spectroscopy, the corresponding ammonium cations [RF2C-NH3]
+
were not the exclusive reaction
products. Even after reaction times of several days at ambient temperature, mixtures of the
corresponding nitrilium cations [RC≡NH]
+
, iminium cations [RFC=NH2]
+
and ammonium cations
were obtained (Figure 2.1), indicating the equilibria shown in Scheme 2.2.
CF
3
CN [CF
3
CF
2
NH
3
][AsF
6
]
1. xs HF, 48 h
2. +AsF
5
HCF
2
CN [HCF
2
CF
2
NH
3
][AsF
6
]
1. xs HF, 48 h
2. +AsF
5
(CN)
2
[H
3
NCF
2
CF
2
NH
3
][AsF
6
]
2
1. xs HF, 48 h
2. +AsF
5
16
Figure 2.1. The
14
N NMR spectrum of a 0.2 mol% CH3CN solution in HF after 7 days at ambient
temperature.
Scheme 2.2. Mechanism for the stepwise HF addition across C≡N triple bonds of nitriles.
The nitriles are immediately protonated in anhydrous HF solution and form the
corresponding nitrilium cations. Even at temperatures as low as -70°C it was not possible to
observe any unprotonated nitrile in HF solution. The following stepwise HF addition proceeded
slower and resulted in the formation of an equilibrium between the corresponding nitrilium,
iminium and ammonium cations. While the final equilibrium concentrations were influenced by
+ HF R
NH
2
NH R N
R NH
R
F
-F
-
+ HF
NH
2
R
F
+ HF
R = Me, Et, CF
3
CH
2
NH
3
R
F
F
17
the nature of the nitrile (Table 2.1), the -fluoroammonium species were formed in only 12 – 33
% yield in the case of CH3CN, C2H5CN and CF3CH2CN. The major species in the equilibrium was
the -fluoroiminium ion in case of acetonitrile and propionitrile and the nitrilium cation in case of
CF3CH2CN. This is in stark contrast to the reactions of HCN, BrCN, ClCN, CF3CN, HCF2CN or
(CN)2 in anhydrous HF for which the corresponding -fluoroammonium species were the sole
reaction products.
Table 2.1. Final product ratio for the reaction of nitriles with aHF.
[a]
R = [RCNH]
+
[RCFNH2]
+
[RCF2NH3]
+
CH3 13 % 75 % 12 %
C2H5 n.o. 85 % 15 %
CF3CH2 60 % 7 % 33 %
CF3 n.o. n.o. 100 %
HCF2 n.o. n.o. 100 %
H n.o. n.o. 100 %
[a]
Determined by NMR spectroscopy from a solution of 5% RCN in HF after 7 days at ambient
temperature. n.o. = not observed.
The iminium cations showed sharper triplet resonances (20 Hz line width) at about -230
ppm in the
14
N NMR spectra. While the
14
N NMR resonances of unprotonated nitriles are generally
observed at about -130 ppm, the resonances of the nitrilium ions were broad singlets at about -170
to -180 ppm with line widths of about 150 Hz. The
1
J(
1
H
14
N) coupling constants of the -
fluoroammonium and -fluoroiminium cations are in the range of 50 Hz, while
1
J(
1
H
14
N)
couplings could not be observed in the case of the nitrilium ions.
18
The free amine, CF3NH2, was prepared by reacting [CF3NH3][MF6] with trimethylamine
at -30°C, however, the yields were very low (~1%). CF3NH2 was identified by its
19
F NMR
spectrum as a triplet at -52 ppm with
3
JFH = 10.0 Hz (Figure 2.2).
Figure 2.2.
19
F NMR spectrum of CF3NH2 at -30°C.
X-ray Crystallography
Details of the crystallographic data collection and refinement parameters for the structurally
characterized compounds [HCF2NH3][AsF6] and [CF3NH3][Sb2F11] are given in Appendix 1.
[HCF2NH3][AsF6] crystallizes in the triclinic space group P1
̅
with two formula units in the
asymmetric unit (Z = 4, Z’ = 2). The crystal structure contains [HCF2NH3]
+
cations and [AsF6]
-
anions (Figure 2.3) that are associated through hydrogen bonding between the NH3 groups of the
cations and the F atoms of anions. The shortest N-H···F distances are found at 2.787(2) Å. The
[HCF2NH3]
+
cation exhibits a staggered conformation, with a pseudo-tetrahedral substituent
arrangement around the carbon and nitrogen atoms.
19
Figure 2.3. The asymmetric unit in the crystal structure of [HCF2NH3][AsF6]. Thermal ellipsoids
are set at 50% probability. Hydrogen atom positions were determined from the electron density
map and are depicted as spheres of arbitrary radius. Selected bond lengths [Å] and angles [˚]: C1-
F2 1.326(3), C1-F1 1.338(3), C1-N1 1.470(3), C2-F3 1.325(3), C2-F4 1.342(3), C2-N2 1.475(3),
F2-C1-F1 108.4(2), F2-C1-N1 107.5(2), F1-C1-N1 106.9(2), F3-C2-F4 108.7(2), F3-C2-N2
107.7(2), F4-C2-N2 106.8(2).
[CF3NH3][Sb2F11] crystallizes in the monoclinic space group P21/m with two symmetry-
related formula units per unit cell. The solid-state structure contains isolated [CF3NH3]
+
cations
and [Sb2F11]
-
anions (Figure 2.4) that are associated through hydrogen bonding between the H
atoms of the cations and the F atoms of anions. The shortest N-H···F distances are found at
2.754(5) Å. As expected and similar to the [HCF2NH3]
+
cation, the [CF3NH3]
+
cation exhibits a
staggered conformation. While the average C-F distance of the [CF3NH3]
+
cation is significantly
shorter (0.023 Å) than in [HCF2NH3]
+
cation, the C─N bond distances remain constant within one
standard deviation.
20
Figure 2.4. The asymmetric unit in the crystal structure of [CF3NH3][Sb2F11]. Hydrogen atom
positions were determined from the electron density map and are depicted as spheres of arbitrary
radius. Thermal ellipsoids are set at 50% probability. Selected bond lengths [Å] and angles [˚]:
F9-C1 1.307(3), F10-C1 1.312(5), N1-C1 1.469(6), F9-C1-F9 110.7(4), F9-C1-F10 110.1(3), F9-
C1-N1 108.3(3), F10-C1-N1 109.5(4).
Conclusion
In summary, the HF addition across C ≡N triple bonds of nitriles is a versatile and convenient
method for the preparation of -fluoroalkylammonium salts. In anhydrous HF, the cyano
compounds are immediately protonated under formation of nitrilium ions. The successive stepwise
HF addition across the C ≡N triple bond results in the formation of fluoroiminium and, ultimately,
-fluoroalkylammonium ions. The reactions of HCN, CF3CN, HCF2CN, and (CN)2 with
anhydrous HF resulted in the formation of the corresponding -fluoroalkylammonium ions
[HCF2NH3]
+
, [CF3CF2H3]
+
, [HCF2CF2NH3]
+
, and [H3NCF2CF2NH3]
2+
, respectively. Cyanogen
21
bromide and -chloride, XCN (X = Br, Cl) reacted under HX evolution and formation of [CF3NH3]
+
while the nitriles CH3CN, CH3CH2CN and CF3CH2CN, formed mixtures of the corresponding
nitrilium, iminium and ammonium ions in anhydrous HF. Room-temperature stable but moisture
sensitive -fluoroalkylammonium salts were obtained and isolated after the addition of
stoichiometric amounts of the Lewis acids AsF5 or SbF5. All isolated species were fully
characterized by multi-nuclear NMR and vibrational spectroscopy. In addition, the crystal
structures of [HCF2NH3][AsF6] and [CF3NH3][Sb2F11] were obtained. The free amine, CF3NH2,
was obtained by deprotonation of [CF3NH3][AsF6] with (CH3)3N and isolated by sublimation,
albeit in a low yield.
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18 (3), 259–268. https://doi.org/10.1016/S0022-1139(00)82616-0.
(24) Wiechert, K. ; H., H. H. ;. Mohr, P. Über das Verhalten von Nitrilen in wasserfreiem,
flüssigem Fluorwasserstoff. Z. Für Chem. 1963, 3 (8), 308–309.
https://doi.org/10.1002/zfch.19630030808.
(25) Dove, M. F. A.; Hallett, J. G. Hydrogen Cyanide as a Ligand towards Copper(I) and
Silver(I) in Liquid Hydrogen Fluoride. J. Chem. Soc. Inorg. Phys. Theor. 1969, No. 0, 2781–2787.
https://doi.org/10.1039/J19690002781.
(26) Lutz, W.; Sundermeyer, W. Darstellung und Reaktionen des Trifluormethylisocyanats.
Chem. Ber. 1979, 112 (6), 2158–2166. https://doi.org/10.1002/cber.19791120623.
(27) Fawcett, F. S.; Lipscomb, R. D. Cyanogen Fluoride. J. Am. Chem. Soc. 1960, 82 (6), 1509–
1510. https://doi.org/10.1021/ja01491a064.
24
CHAPTER 3: THE SYNTHESIS OF [NH
2
CFNH
2
]
+
AND
[NH
2
CNH]
+
Abstract
The [NH2CFNH2]
+
cation was prepared and isolated as [MF6]
-
(M = As, Sb) salts by reacting
NH2CN or ((CH3)3SiN)2C with a superacidic solution of anhydrous HF and MF5. The novel
fluoroformamidinium cation was characterized by multinuclear NMR and vibrational
spectroscopy. Additionally, [NH2CFNH2][SbF6] was characterized by its X-ray crystal structure.
Reacting NH2CN or ((CH3)3SiN)2C with HF and MF5 at -78°C resulted in the protonated species
[NH2CNH][MF6]. The protonation occurs exclusively at the nitrogen of the nitrile rather than the
amino group as determined by
14
N NMR and vibrational spectroscopy. Additionally,
[NH2CNH][SbF6] was characterized by its X-ray crystal structure.
Introduction
The tetramethyl fluoroformamidinium cation is a synthetically useful reagent, particularly for
peptide coupling
1–3
and deoxyfluorination reactions.
4
This synthetic utility has driven the
discovery of new insecticides,
5
antimicrobial silver complexes
6
and drug candidates for
neurological disorders.
7
Other derivatives such as bis(tetramethylene)fluoroformamidinium and
1,3-dimethyl-2-fluoro-4,5-dihydro-1H-imidazolium were also prepared;
8
however, the simplest
fluoroformamidinium cation, [NH2CFNH2]
+
, has until now remained unknown.
Recently, work in our laboratory showed anhydrous HF could be added across the C≡N triple
bond of various nitriles affording α-fluorinated alkylammonium salts.
9
In one example, HF was
added across both of the C≡N triple bonds of (CN)2 resulting in the first example of an α-
25
fluorinated diammonium dication, [NH3CF2CF2NH3]
2+
. With this result in mind, we postulated an
analogous HF addition reaction to NH2CN may yield the simplest perfluoroalkyl diammonium
dication [NH3CF2NH3]
2+
. However, following the typical procedure for the preparation of α-
fluorinated alkylammonium salts led to a different result.
Results and Discussion
When NH2CN was reacted with a large excess of anhydrous HF at ambient temperature for two
days, the fluoroformamidinium cation, [NH2CFNH2]
+
, was obtained, and subsequent addition of a
strong Lewis acid MF5 (M = As, Sb) resulted in the isolation of the corresponding [MF6]
-
salts in
quantitative yields. The fluoroformamidinium cation can also be prepared by reacting a superacidic
MF5/HF mixture with cyanamide or bis(trimethylsilyl)carbodiimide at 0°C for 15 min [Eq. (1-
2)].
10
These [NH2CFNH2][MF6] salts are colorless crystalline solids that are stable at ambient
temperature under a dry nitrogen atmosphere for at least several weeks. This stability is somewhat
surprising. Typically compounds that feature the F-C-NH2 connectivity, such as the perfluorinated
primary amines CF3NH2 and CF3CF2NH2, decompose rapidly at ambient temperature via HF
elimination.
11–13
Even the bis(trifluoromethyl)ammonium cation, [(CF3)2NH2][MF6] decomposes
at ambient temperature to (CF3)2NH and MF5.
14
Uniquely in the [NH2CFNH2]
+
cation is the partial
double bond character of both C-N bonds which may allow for its enhanced resistance to HF
elimination.
(1)
(2)
26
The [NH2CFNH2][MF6] salts were characterized by multinuclear NMR and vibrational
spectroscopy. The
13
C NMR spectrum showed a doublet at 160 ppm with a large
1
JCF = 271 Hz.
The
19
F NMR spectrum showed a triplet at -58.2 ppm with a
3
JFH(trans) = 33.3 Hz indicating the non-
equivalency of the protons in solution due to hindered rotation around the partial double bonds.
Coupling information could not be deduced from the
1
H NMR spectrum as only a broad unresolved
peak is observed at 7.2 ppm because of the quadrupolar
14
N nucleus and potentially fast exchange
in HF solution. The
14
N NMR spectrum of the [NH2CFNH2]
+
cation also showed only a single
resonance, a triplet at -300 ppm with a
1
JNH = 60 Hz. The NMR spectra were recorded in HF
solution, and in addition to the peaks assigned to [NH2CFNH2]
+
, peaks due to [CF3NH3]
+
and
[NH4]
+
were also observed. The concentrations of [CF3NH3]
+
and [NH4]
+
increased over time
relative to [NH2CFNH2]
+
, and this was suppressed at lower temperatures. These findings led us to
conclude that [NH2CFNH2]
+
can continue to add HF, ultimately leading to its dissociation to
[CF3NH3]
+
and NH3.
Assuming the HF addition proceeds stepwise, one can envision a reaction pathway as shown
in Scheme 3.1. The first HF addition results in the protonated species which was also isolated and
is described in detail in the subsequent discussion. The second HF addition results in the title
compound, and the next HF addition would yield the [NH2CF2NH3]
+
cation which could not be
observed presumably because its reaction with HF to form [CF3NH3]
+
and NH3 occurs faster than
the NMR timescale.
27
Scheme 3.1. The proposed pathway of the stepwise addition of HF to NH2CN.
The deuterated analogue [ND2CFND2][AsF6] was also synthesized by reacting
bis(trimethylsilyl)carbodiimide with deuterium fluoride and arsenic pentafluoride at 0°C for 15
min. The low-temperature vibrational spectra of [NH2CFNH2][AsF6], [NH2CFNH2][Sb2F11] and
[ND2CFND2][AsF6] are shown in Figure 1. To facilitate the assignment of the vibrational modes,
quantum chemical calculations were performed for the [NH2CFNH2]
+
and [ND2CFND2]
+
cations
using the PBE1PBE level of theory and 6-311G (3df, 3pd) basis set. The calculations resulted in a
cation with C2v symmetry and identical CN bond distances of 1.2936 Å in excellent agreement
with the crystallographically determined CN bond distances 1.301(3) Å and 1.296(3) Å to be
discussed in the subsequent section.
28
Figure 3.1. Low temperature IR (top) and Raman (bottom) spectra for [NH2CFNH2][AsF6] (blue:
a, f), [NH2CFNH2][Sb2F11] (green: b, e), [ND2CFND2][AsF6] (red: c, d).
For a C2v symmetric cation with eight atoms, 18 vibrations are expected (7A1 + 2A2 + 3B1
+ 6B2). The full list of calculated and experimental frequencies for [NA2CFNA2][MF6] (A = H,D)
as well as the assignment of vibrational modes are given in Table S1. The IR spectrum of
[NH2CFNH2][Sb2F11] exhibits sharp features in the 3000-3500 cm
-1
region allowing for the
assignment of the symmetric (3299 cm
-1
and 3192 cm
-1
) and asymmetric (3427 cm
-1
and 3350 cm
-
29
1
) NH2 stretching modes. A CN stretching mode is observed in the IR spectra of
[NH2CFNH2][AsF6] at 1725 cm
-1
, of [NH2CFNH2][Sb2F11] at 1754 cm
-1
and of
[ND2CFND2][AsF6] at 1693 cm
-1
. A second CN stretching mode is observed in the IR spectrum
of [NH2CFNH2][Sb2F11] at 1635 cm
-1
and of [ND2CFND2][AsF6] at 1511 cm
-1
. These values are
in good agreement with the calculated frequencies which indicate these also include δ(NA2):
ν(CN) + δ(NA2) [NH2CFNH2]
+
= 1746 cm
-1
, 1639 cm
-1
; ν(CN) + δ(NA2) [ND2CFND2]
+
= 1717
cm
-1
, 1547 cm
-1
. The CF stretching mode is calculated at 926 cm
-1
and 1006 cm
-1
for [ND2CFND2]
+
and [NH2CFNH2]
+
, respectively. These are in good agreement with the observed frequencies
for[NH2CFNH2][Sb2F11] 982 cm
-1
(IR), 990 cm
-1
(Ra) and for [ND2CFND2][AsF6] 940 cm
-1
(IR),
927 cm
-1
(Ra).
Additionally, [NH2CFNH2][SbF6] was characterized by single crystal X-ray structure
determination. [NH2CFNH2][SbF6] crystallizes in the monoclinic spacegroup P21/c with one
formula unit in the asymmetric unit (Figure 3.2) and four in the unit cell. The CN bond distances
are nearly equivalent, consistent with the NMR and vibrational spectroscopic data which indicate
a symmetrical cation. The bond angles are slightly distorted from the trigonal planar shape with
the NCF angles at 116° and the N2-C1-N1 at 128° due to the partial double bond character of the
CN bonds. The N2···F3 distance is quite short at 2.770(3) Å (sum of van der Waals radii = 3.02
Å), indicating an interaction between the cation anion pair of the asymmetric unit. However, the
NH···F interaction is too weak to be deemed a hydrogen bond with bond angles deviating
significantly from 180°, N2-H4···F3 110(3)°, 3.4(1) Å and N2-H3···F3 96(4)°, 3.22(8) Å. However,
there is an extensive hydrogen bonding network within the unit cell (Figure A2.1-3). Each N-H
bond participates in NH···F bonding with an anion of a different asymmetric unit. These N-H···F
30
bond distances and angles are N2-H3···F2 2.9(1) Å, 170(5)°; N2-H4···F6 3.04(8) Å,147(3)°; N1-
H2···F7 2.9(1) Å, 159(5)°; and N1-H1···F5 3.0(1) Å, 160(4)°.
Figure 3.2. The asymmetric unit in the crystal structure of [NH2CFNH2][SbF6]. Thermal ellipsoids
are set at 50% probability. Hydrogen atom positions were determined from the electron density
map and are depicted as spheres of arbitrary radius. Selected bond lengths [Å] and angles [˚]: C1-
N1 1.301(3), C1-N2 1.296(3), F1-C1 1.313(3) ; N1-C1-N2 128.3(2), N2-C1-F1 116.0(2), N1-C1-
F1 115.8(2).
When a superacidic solution of MF5 in HF was reacted with NH2CN at -78˚C, the
protonated nitrile was obtained, [NH2CNH][MF6] (Equation 3).
15
Additionally, reaction of
bis(trimethylsilyl)carbodiimide with the superacidic HF/MF5 mixture at -78˚C resulted in the same
product [Eq. (4)]. The salts are colorless, moisture and thermally sensitive solids that are stable up
to -40°C. The protonation occurs exclusively on the nitrile, rather than the amino group as can be
observed clearly from the
14
N NMR spectrum (Figure 3.3). Upon protonation, the chemical shift
of the nitrile shifts 69 ppm upfield relative to NH2CN while the chemical shift corresponding to
the amino group remains relatively unchanged. Furthermore, the peak corresponding to the nitrile
31
splits to a doublet with a coupling constant of 78 Hz. Based on these data it is clear that in solution
the nitrogen of the nitrile is protonated, rather than the nitrogen of the amino group.
Figure 3.3. (Top) The
14
N NMR spectrum of NH2CN in CH3CN at 25 ˚C. (Bottom) The
14
N
NMR spectrum of [NH2CNH][SbF6] in SO2 at -65˚C.
(3)
(4)
The deuterated analogue [ND2CND][AsF6] was prepared by reacting
bis(trimethylsilyl)carbodiimide with DF and AsF5 at -78°C. Figure 3.4 shows the low
temperature IR and Raman spectra of [NA2CNA][MF6] (A = H, D; M = As, Sb). To facilitate
assignment of the vibrational modes, quantum chemical calculations were performed at the
32
PBE1PBE/6-311G (3df, 3pd) level of theory for the cations [H2NCNH(3HF)]
+
and
[D2NCND(3HF)]
+
. A summary of the observed and calculated frequencies along with
vibrational mode assignments are provided in Table S2. The IR spectra of [H2NCNH][MF6]
show bands for the symmetric and asymmetric NH2 stretching modes, νas(NH2) = 3384 cm
-1
[AsF6]
-
, 3576 cm
-1
[SbF6]
-
; νs(NH2) = 3384 cm
-1
[AsF6]
-
, 3440 cm
-1
[SbF6]
-
. The NH stretching
mode is detected in both the IR and Raman spectra. For [NH2CNH][AsF6] ν(NH) is observed at
3265 cm
-1
(Ra) and 3331 cm
-1
(IR) and for [NH2CNH][SbF6] at 3265 cm
-1
(Ra) and 3356 cm
-1
(IR). For the deuterated analogue [ND2CND][AsF6], ν(ND) is shifted to lower wavenumbers
2163 cm
-1
(IR), 2149 cm
-1
(Ra). [NH2CNH]
+
exhibits two CN stretching modes, which can be
assigned to each of the nonequivalent CN bonds. ν(CN) of the CN group to which only one
hydrogen atom is attached to the nitrogen is calculated at a higher wavenumber (2357 cm
-1
) than
the CN group to which two hydrogen atoms are attached to the nitrogen ν(CN) + δ(NH2) = 1225
cm
-1
. The experimental values are in good agreement with 2268 cm
-1
(IR) and 2281 cm
-1
(Ra),
as well as at 1212 cm
-1
(Ra) for [NH2CNH][SbF6], and 2278 cm
-1
(IR), 2281 cm
-1
(Ra), 2306
cm
-1
(Ra) and 1112 cm
-1
(Ra) for [NH2CNH][AsF6]. For the deuterated analogue, these CN
stretches are calculated and observed at higher wavenumbers: ν(CN) = 2623 cm
-1
(calc.), 2535
cm
-1
(obs. IR), 2528 (obs. Ra); ν(CN) + δ(NH2) = 1304 cm
-1
(calc.), 1255 cm
-1
(obs. IR), 1263
cm
-1
(obs. Ra).
33
Figure 3.4. Low temperature IR (top) and Raman (bottom) spectra for [NH2CNH][AsF6] (blue:
a, f), [NH2CNH][SbF6] (green: b, e), [ND2CND][AsF6] (red: c, d).
34
Figure 3.5. The asymmetric unit in the crystal structure of [NH2CNH][SbF6]. Thermal ellipsoids
are set at 50% probability. Hydrogen atom positions were determined from the electron density
map and are depicted as spheres of arbitrary radius. Selected bond lengths [Å] and angles [˚]:
C1-N1 1.158(3), C1-N2 1.275(3); N1-C1-N2 173.6(2).
Additionally, [NH2CNH][SbF6] was characterized by its X-ray crystal structure (Figure
3.5). [NH2CNH][SbF6] crystallizes in the triclinic space group P1
̅
with two symmetry-related
formula units in the unit cell. The protonated nitrile exhibits hydrogen bonding within the
asymmetric unit N1-H1···F1 2.85(8) Å, 150(4)˚, and to a lesser extent F3 of the other
asymmetric unit N1-H1···F3 3.24(8) Å, 124(3)˚. The amino group also exhibits hydrogen
bonding N2-H3···F5 2.88(6) Å, 159(3)˚ and N2-H2···F2 2.91(6) Å, 155(3)˚. Upon protonation,
the C1-N1 bond distance is slightly elongated to 1.158(3) Å from 1.152(1) Å in NH2CN
indicating that it retains much of its triple bond character.
16
The C1-N2 bond distance, however,
contracts signficantly from 1.315(1) to 1.275(3), which seems to indicate that the resonance
structure may play a minor role as partial double bond character could explain this difference
[Eq. (5)]. The protonated nitrile group is bent with a C1-N1-H1 bond angle of 136(3)˚.
35
(5)
Experimental
Caution! Anhydrous HF can cause severe burns and contact with the skin must be avoided. AsF5
is volatile and highly poisonous and should only be handled in a well ventilated fume hood.
Appropriate safety precautions should be taken when working with these materials.
Materials and apparatus: All reactions were carried out in either Teflon-FEP ampules or
NMR tubes that were closed by stainless steel valves. Volatile materials were handled in a stainless
steel/Teflon-FEP vacuum line.
17
Reaction vessels and the vacuum line were passivated with ClF3
followed by conditioning with HF prior to use.
Crystal Structure determinations: The single-crystal X-ray diffraction data were collected
on a Bruker SMART APEX DUO 3-circle platform diffractometer, equipped with an APEX II
CCD, using Mo Kα radiation (TRIUMPH curved-crystal monochromator) from a fine-focus tube.
The diffractometer was equipped with an Oxford Cryosystems Cryostream 700 apparatus for low-
temperature data collection. The frames were integrated using the SAINT algorithm to give the hkl
files corrected for Lp/decay.
18
The absorption correction was performed using the SADABS
program.
19
The structures were solved by the direct method and refined on F
2
using the Bruker
SHELXTL Software Package and ShelXle.
20–24
All nonhydrogen atoms were refined
anisotropically. ORTEP drawings were prepared using the ORTEP-3 for Windows V2.02
program.
25
For further experimental details, please see Appendix 2.
36
Conclusion
In conclusion, NH2CN or ((CH3)3SiN)2C reacts with HF to form the novel [NH2CFNH2]
+
cation, which was isolated as room temperature stable [MF6]
-
salts and characterized by
multinuclear NMR and vibrational spectroscopy. Reaction of NH2CN or ((CH3)3SiN)2C with a
superacidic HF/MF5 solution at low temperature results in the protonated species
[NH2CNH][MF6], which were also characterized by multinuclear NMR and vibrational
spectroscopy. Protonation occurs exclusively at the nitrile rather than the amino group in solution
and in the solid state. The [SbF6]
-
salts of both cations were also characterized by single-crystal X-
ray structure determination.
References
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Rapid-Acting Peptide Coupling Reagent for Solution and Solid Phase Peptide Synthesis. J. Am.
Chem. Soc. 1995, 117 (19), 5401–5402. https://doi.org/10.1021/ja00124a040.
(2) Boas, U.; Pedersen, B.; Christensen, J. B. Tetramethyl Fluoro Formamidinium
Hexafluorophoshate – An Improved Synthesis and Some New Uses. Synth. Commun. 1998, 28
(7), 1223–1231. https://doi.org/10.1080/00397919808005964.
(3) El-Fahm, A.; Abdul-Ghani, M. TFFH AS A USEFUL REAGENT FOR THE
CONVERSION OF CARBOXYLIC ACIDS TO ANILIDES, HYDRAZIDES AND AZIDES.
Organic Preparations and Procedures International 2003, 35 (4), 369–374.
https://doi.org/10.1080/00304940309355842.
(4) Bellavance, G.; Dubé, P.; Nguyen, B. Tetramethylfluoroformamidinium
Hexafluorophosphate (TFFH) as a Mild Deoxofluorination Reagent. Synlett 2012, 23 (04), 569–
574. https://doi.org/10.1055/s-0031-1290336.
(5) Lambert, W. T.; Buysse, A. M.; Wessels, F. J. Discovery of Novel Insecticidal 3‐
aminopyridyl Ureas. Pest. Manag. Sci. 2019, ps.5537. https://doi.org/10.1002/ps.5537.
(6) Abu-Youssef, M. A. M.; Soliman, S. M.; El-Faham, A.; Albering, J.; Sharaf, M. M.; Gohar,
Y. M.; Diana, E.; Gatterer, K.; Kettle, S. F. A. A New Triazoloquinoxaline Ligand and Its
Polymeric 1D Silver( I ) Complex: Synthesis, Structure, and Antimicrobial Activity. New J. Chem.
2018, 42 (9), 7197–7205. https://doi.org/10.1039/C7NJ02886E.
(7) Bleicher, K.; Cueni, A.; Puentener, K.; Shiina, J. Processes for the Preparation of Oxytocin
Analogues. US 2017/0174725 A1.
37
(8) El-Faham, A. NEW SYNTHESES OF
Bis(TETRAMETHYLENE)FLUOROFORMAMIDINIUM HEXAFLUOROPHOSPHATE
(BTFFH) AND 1,3-DIMETHYL-2-FLUORO-4,5-DIHYDRO-1H-IMIDAZOLIUM
HEXAFLUOROPHOSPHATE (DFIH). UTILITY IN PEPTIDE COUPLING REACTIONS.
Organic Preparations and Procedures International 1998, 30 (4), 477–481.
https://doi.org/10.1080/00304949809355316.
(9) Baxter, A. F.; Christe, K. O.; Haiges, R. Convenient Access to α-Fluorinated
Alkylammonium Salts. Angewandte Chemie International Edition 2015, 14535–14538.
https://doi.org/10.1002/anie.201507177.
(10) Axhausen, J., A. H. Basicity of Amino and Carbonyl Groups in Small Molecules, Ludwig
Maximilian University of Munich, 2013.
(11) Kloter, G.; Lutz, W.; Seppelt, K.; Sundermeyer, W. Trifluoromethylamine, CF3NH2.
Angew Chem Int Edit 1977, 16 (10), 707–708. https://doi.org/10.1002/anie.197707072.
(12) Kloter, G.; Seppelt, K. Trifluoromethanol (CF3OH) and Trifluoromethylamine (CF3NH2).
J Am Chem Soc 1979, 101 (2), 347–349.
(13) Kumar, R. C.; Shreeve, J. M. F-Ethylamine and F-Ethylimine. J Am Chem Soc 1980, 102
(15), 4958–4959. https://doi.org/10.1021/ja00535a022.
(14) Minkwitz, R.; Lamek, D.; Jakob, J.; Preut, H.; Mack, H. G.; Oberhammer, H. Contribution
to the Chemistry of Bis(Trifluoromethyl)Amines: Preparation of Bis(Trifluoromethyl)Ammonium
Hexafluorometalates (CF3)2NH2+MF6- (M = As, Sb). Crystal Structure of(CF3)2NH2+AsF6-
and Gas-Phase Structures of (CF3)2NX (X = H, Cl). Inorganic Chemistry 1994, 33 (9), 1817–
1821. https://doi.org/10.1021/ic00087a016.
(15) Buzek, P.; von Ragué Schleyer, P.; Klapötke, T. M.; Tornieporth-Oetting, I. C. Das
Reaktionsverhalten Der N-Basen NH3, NC NH2 Und NC CN Gegenüber EF5 Und EF5/HF (E
= As, Sb). Journal of Fluorine Chemistry 11, 65 (1–2), 127–132. https://doi.org/10.1016/S0022-
1139(00)80483-2.
(16) Denner, L.; Luger, P.; Buschmann, J. X-Ray Structure of Cyanamide at 108 K. Acta
Crystallographica Section C 1988, 44 (11), 1979–1981.
https://doi.org/10.1107/S0108270188007851.
(17) K. O. Christe, R. D. W., C. J. Schack, D. D. Desmarteau. In Inorganic Syntheses; Wiley:
New York, 1986; pp 3–6.
(18) SAINT +; Bruker AXS: Madison, WI, 2011.
(19) SADABS; Bruker AXS: Madison, WI, 2012.
(20) C. B. Hubschle, G. M. S., B. Dittrich. J. Appl. Crystallogr. 2011, No. 44, 1281–1284.
(21) Sheldrick, G. M. Acta Crystallogr. Sect. A 2008, No. 64, 112–122.
(22) Sheldrick, G. M. Acta Crystallogr. Sect. C 2015, No. 71, 3–8.
(23) Sheldrick, G. M. SHELXL; 2012.
38
(24) SHELXTL; Bruker AXS: Madison, WI, 2014.
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39
CHAPTER 4: THE SYNTHESIS OF PRIMARY
PERFLUORINATED ALCOHOLS
Abstract
The thermally unstable, primary perfluoroalcohols, CF3OH, C2F5OH, and n-C3F7OH, were
conveniently prepared from the corresponding carbonyl compounds in anhydrous HF solution.
Experimental values for the reaction enthalpies and entropies were derived from the temperature
dependence of the RfCOF + HF RfCF2OH (Rf=F, CF3, CF3CF2) equilibria by NMR
spectroscopy. Protonation of these alcohols in HF/SbF5 produced the perfluoroalkyl oxonium salts
[RfCF2OH2][SbF6].
Introduction
Under normal conditions, primary perfluorinated alcohols are unstable due to facile HF
elimination.
1
Despite this instability, the simplest primary perfluorinated alcohol, CF3OH, is
generated in the atmosphere as a by-product of the degradation of hydrofluorocarbons (HFCs)
including HFC-23, HFC-125, and HFC-134a.
2
The mechanism of the atmospheric formation of
CF3OH has been established as a reaction between CF3 radicals and oxygen forming CF3O2
3,4
which in turn reacts with NO to form CF3O radicals.
5
Then, the CF3O radicals can react with a
hydrocarbon
6–12
or with H2O
13,14
to form CF3OH. The atmospheric degradation of CF3OH,
however, is much less understood despite extensive computational studies.
2,15–22
In the laboratory, CF3OH was first synthesized by Seppelt in 1977.
23
He used a low-
temperature dichlorine elimination from two starting materials containing a positively and a
40
negatively polarized chlorine atom. The reaction was done in three steps [Eqs. (1-3)] and involved
the formation of shock-sensitive CF3OCl as an intermediate.
(1)
(2)
(3)
Since this initial report, experimental studies relating to CF3OH have been lacking, and the
synthesis of higher perfluorinated primary alcohols has until now remained unknown. Secondary
perfluorinated alcohols, however, are more thermally stable, and one article on the
13
C NMR of
perfluorinated isopropanol was published.
24
Perfluorocyclobutanol, which is room temperature
stable due to its ring strain, was first published in 1961
25
and its X-ray crystal structure is discussed
in detail in chapter 5. Tertiary β-fluoroalcohols, such as perfluoro-tert-butanol, are thermally stable
due to the absence of α-fluorine atoms.
26
Despite the lack of literature on primary perfluorinated alcohols, they are well known to
form stable RfCF2O
-
salts.
27–29
Although an additional paper entitled “Perfluoroalcohols” implies
the synthesis of these alcohols, evidence for the presence of the free alcohols was not firmly
established.
30
The authors reacted a [HN(CH3)3]
+
F
-
equivalent with acyl fluorides and obtained
COF2, CF3CF2CFO and (CF3)2CFCFO products, which were formulated as adducts of the
corresponding perfluoroalcohols with N(CH3)3 and characterized according to the
19
F and
1
H NMR
spectra. Their product showed a signal in the
19
F NMR spectrum at -33.18 ppm, whereas CF3OH
resonates at -54.5 ppm and CF3O
-
at -20 ppm.
29
The possibility for the existence of an equilibrium
between a donor–acceptor system and an ionic salt has already been suggested,
30
but more work
remains to establish the exact nature of the products.
41
In 2007, Christe and co-workers published a more convenient route to CF3OH, exploiting
the temperature-dependent equilibrium shown in Equation 4.
31
The temperature dependence of the
equilibrium as determined by
19
F NMR spectroscopy is shown in Figure 4.1. An unusual
relationship was found for the equilibrium concentrations against temperature and as a result, the
relevant thermodynamic data could not be derived. An increase in CF3OH concentration with
decreasing temperature was observed in the temperature range 25°C to -5°C, followed by a
decrease in CF3OH concentration with decreasing temperature from -5°C to -45°C. This is
unexpected considering the decomposition of CF3OH to COF2 and HF is endothermic. In the
present study, we report the synthesis and thermodynamic properties of perfluoroethanol and
perfluoro-n-propanol, as well as a re-investigation of the trifluoromethanol equilibrium in
Equation 4 which could not be explained satisfactorily.
31
(4)
Figure 4.1. Temperature dependence of the COF2+HF⇌CF3OH equilibrium measured by area
integration of the corresponding
19
F NMR signals for two different mole ratios of HF/COF2.
Reproduced from reference 31.
31
42
Synthesis
Carbonyl fluoride was added to liquid anhydrous HF in a fluorinated ethylene propylene (FEP)
NMR tube, and the
19
F NMR spectra were recorded at various temperatures after equilibrium had
been achieved. The equilibrium concentrations of carbonyl fluoride and trifluoromethanol were
measured by integrating the areas of the
19
F NMR signals and by using the temperature-sensitive
shift of the
1
H signal of methanol to determine the temperature.
32
It was found that the molar ratio
of CF3OH/COF2 increased with decreasing temperature from 0.37 at 10°C to 2.52 at -62°C (Figure
4.2). Thus, we propose the previously reported anomaly in Figure 4.1
31
was due to the long time
required to reach equilibrium at low temperatures.
Figure 4.2. Temperature dependence of the COF2 + HF CF3OH equilibrium. Each data point
was measured, approaching the equilibrium from above and below the desired temperature.
Equilibrium was reached when both values coincided.
43
To ascertain that the system had truly reached equilibrium, each temperature point was
approached from above and below the desired temperature, and only when the points had
converged within an acceptable margin of experimental error were these data points accepted. At
higher temperatures, equilibration was fast, and at temperatures ≥0°C, it occurred in less than ten
minutes. At temperatures ≤-50°C however, reaching equilibrium required 24 h or longer.
Even at the lowest measured temperatures, we still observed signals due to COF2, and it
was not possible to shift the equilibrium completely towards the alcohol. Higher conversion to
CF3OH could be achieved by continuously removing the alcohol from the reaction mixture either
by conversion into CF3OH2
+
salts through addition of strong Lewis acids or by trapping it as an
ether through a Lewis acid-catalyzed reaction with an alkyl fluoride.
31
Due to the large excess of
HF used in our study, the change from a 75- to a 116-fold excess of HF had little impact on the
amount of CF3OH formed in the reaction. Also, solubilities do not influence the equilibrium if HF
is used in a large enough excess as a solvent. Furthermore, no evidence was found in the present
study to support the previously suggested hypothesis that the increase in the self-association of HF
at lower temperatures plays a significant role in the slow formation of CF3OH.
31
The successful synthesis of CF3OH from COF2 and HF prompted us to extend this
approach to the longer-chain primary perfluoroalcohols, pentafluoroethanol and heptafluoro-
npropanol. Both compounds were obtained in the same manner as trifluoromethanol, albeit with
lower yields. As was the case for CF3OH, the concentrations of C2F5OH and n-C3F7OH increased
with decreasing temperature (Figures 4.3-4). There is a trend of decreasing alcohol formation with
increasing chain length. The maximum observed RfCF2OH/RfCOF molar ratios were 0.993 and
0.0809 for Rf=CF3 and CF3CF2, respectively, as compared to 2.52 for CF3OH.
44
All three alcohols were characterized in anhydrous HF solution by
19
F and
13
C NMR
spectroscopy. The proton resonances for the hydroxyl groups of the primary perfluoroalcohols are
expected to occur in the range of 7–10 ppm, based on the value of 8.65 ppm observed for neat
CF3OH.
23
However, the resonance of HF also falls in this range and the alcohol undergoes a fast
exchange with HF on the NMR timescale, preventing direct observation of the hydroxyl proton.
(5)
Figure 4.3. Plot of C2F5OH Formation as a Function of Temperature and Initial Concentration.
Figure 4.4. Plot of C3F7OH Formation as a Function of Temperature and Initial Concentration.
45
When the HF solutions of these perfluorinated alcohols were acidified by the addition of
strong Lewis acids, such as SbF5, the alcohols were protonated affording the corresponding
oxonium salts [Eq. (5)]. The perfluorinated alcohols and oxonium salts were characterized
extensively by NMR spectroscopy and the discussion is provided in a subsequent section.
Thermodynamics
Using the known initial concentrations of RfCOF (Rf=F, CF3, CF3CF2), the known amounts of HF
used and the relative equilibrium concentrations from the integrated
19
F NMR signals, the
equilibrium constant Keq was calculated for each temperature (Tables A3.1-6). These equilibrium
constants were then used to construct van ’t Hoff plots to determine the enthalpies ∆H and
entropies ∆S of reaction
33
according to Equation 6.
𝑙𝑛 𝐾 𝑒𝑞
= −
Δ𝐻 𝑅𝑇
+
ΔS
𝑅 (6)
The van ’t Hoff plots for the formation of the three alcohols are shown in Figure 4.5, and
the thermochemical quantities derived from these are listed in Table 4.1. The reaction enthalpies
from these plots are slightly exothermic, and the entropy values are negative, as expected from the
formation of one molecule of alcohol from two molecules of reactants, making the -T∆S term
positive. Therefore, the free energy values ∆G = ∆H - T∆S pass through zero and becomes
increasingly more positive with increasing temperature, consistent with the favored formation of
the alcohols at low temperature and their decomposition at higher temperatures. The
decomposition of gaseous CF3OH is slow and has a high activation energy barrier of about 43–45
kcal mol
-1
, but is substantially lowered in the presence of HF, other CF3OH molecules, or H2O.
2,16
46
Table 4.1. Summary of the thermodynamic quantities derived from the van‘t Hoff plots for the
RfCOF + HF RfCF2OH (Rf = F, CF3, CF3CF2) equilibria. a) enthalpies of reaction (kcal/mol).
b) entropies of reaction (cal/molK) c) Gibbs free energies at 298 K (kcal/mol).
R f = F R f = CF 3 R f = CF 3CF 2
∆H
a
-3.6 -3.2 -2.2
∆S
b
-22.3 -22.9 -22.8
∆G
c
(298 K) 3.1 3.6 4.6
Figure 4.5. van ’t Hoff plots for the equilibrium RfCOF+HF RfCF2OH (Rf=F, CF3, CF3CF2).
Equations for the lines are as follows: (Rf=F) y=1798.3x+11.237, R
2
=0.9913; (R=CF3)
y=1634.4x+11.524, R
2
=0.99284; (R=CF3CF2) y=1087.7x+11.481, R
2
=0.98735.
The slopes of the van’t Hoff plots depend only on the temperature dependence of the
equilibrium constants. Considering that the equilibrium concentrations were measured for each
compound on the same sample, most systematic errors canceled out. Therefore, we expect the
values of ∆H to be quite accurate. The ∆S values, obtained from the extrapolated intercepts of the
47
curves with the ordinate, are much less accurate because any systematic errors do not necessarily
cancel out. The observed ∆H value of -3.6 kcal mol
-1
for the formation of CF3OH from COF2 in
HF solution is in good agreement with the most reliable calculated gas-phase values of -5.7
19
and
-6.5 kcal mol
-1
.
16
These experimental and computational values are consistent with the
experimental value of -2.8
+1.1
−1.7
kcal mol
-1
from a photoionization study.
34
The enthalpies of reaction
become less negative with increasing chain length, whereas the entropy term is similar in all three
cases. Therefore, ∆G becomes more positive explaining our observed decrease in alcohol
formation with increasing chain length at all temperatures.
NMR Spectroscopy
Considering that the identification and characterization of the alcohols and their corresponding
oxonium salts relied on NMR spectroscopy and that the differences in their NMR parameters are
quite small, it is important to measure these spectra with high accuracy, that is, with the same
instrument under identical conditions and using the same methods for referencing.
35
In the present
study, we measured the
19
F and
13
C NMR spectra of trifluoromethanol, pentafluoroethanol,
heptafluoro-n-propanol and their corresponding oxonium cations in anhydrous HF solution,
utilizing the substitution method with 80% CFCl3 in 20% CDCl3 as the external standard. Details
of the NMR data are provided in Tables 4.2-4, and all NMR spectra are provided in Appendix 3.
The results showed that protonation of the -OH group influences the signals of the
fluorocarbon backbones only very weakly. The most pronounced changes were slightly increased
shielding of the
19
F and
13
C signals of the α-CFn groups and the increase of their
1
JC-F coupling
constants upon protonation. This increase in the coupling constants agrees with previous
experimental and computational results for CF3OH/CF3OH2
+
.
31
Observation of the proton
48
chemical shift was complicated by the alcohols undergoing rapid exchange with the HF solvent
and by the oxonium salts exchanging with both the alcohols and HF. Furthermore, the chemical
shift of the proton resonance of HF depends strongly on the temperature and the acidification with
SbF5. Therefore, no conclusions can be drawn concerning the proton shifts of these alcohols and
their oxonium salts in HF solution.
In the protonation reactions of the alcohols, only one set of signals was always observed.
This fact might be explained by the alcohol and its oxonium salt undergoing a fast exchange on
the NMR timescale. This was verified experimentally by using only half a molar equivalent of
SbF5 in the protonation reaction. In the absence of a fast exchange, two sets of signals, one for the
alcohol and one for the oxonium salt, should be observed, whereas, for a fast exchange, only one
set of signals should be seen with chemical shift and coupling constant values between those of
the pure alcohol and the pure oxonium salt. This second case is shown in the experimental data in
the last column of Table 4.2, which are proof of a rapid exchange between CF3OH and CF3OH2
+
.
We also investigated to what extent the protonation of CF3OH shifts the COF2 + HF CF3OH
equilibrium towards the products. Although a complete conversion of COF2 to CF3OH2
+
at -60°C
was not observed under our reaction conditions, the concentration of unreacted COF2 was reduced
from 27.6 to 5.7% upon addition of a five-fold molar excess of SbF5 to the alcohol solution. The
difficulty to observe a complete shift of the equilibrium to the right might be caused by the slow
conversion of COF2 to CF3OH at low temperature, compared to the fast protonation reaction of
the alcohol.
The
19
F spectra of CF3OH, C2F5OH, and C3F7OH were very similar to those of CF4, C2F6,
and C3F8, respectively,
36
demonstrating that the OH group behaves as a pseudo-fluorine atom.
37
Furthermore, the signals of -CF2OH groups did not appear in the typical CF2 region of 120–130
49
ppm but closer to the CF3 region between 80–90 ppm. The
19
F NMR signals of perfluoro-n-
propanol showed an interesting through-space coupling
38
between the terminal CF3
-
and the
CF2OH-groups with
4
JF-F=8.0 Hz. By analogy with closely related CF3-CF2-CF3,
39
the internal CF2
group coupled only weakly with the fluorine atoms of the terminal CF3- and CF2OH-groups, and
therefore, no additional fine structure was observed. In C3F8, the
3
JF-F is only 0.7 Hz, whereas
4
JF-
F is 7.31 Hz.
39
The above NMR data show the following general trends. 1) The
19
F chemical shifts of the
a-perfluoroalcohols mirror closely those of the corresponding perfluorocarbons,
36,39
showing that
the OH group can be treated as a pseudo-fluorine atom. 2) As expected, the influence of the -OH
or -OH2
+
group is the strongest on the α-fluorine atoms; however, the observed changes are rather
subtle. Protonation of the alcohol increases the one-bond coupling constant,
1
JC-F, only by 3–15
Hz. 3) The
1
H NMR spectra are not useful for distinguishing the free alcohols from the oxonium
salts due to exchange reactions with each other and with HF as well as to a strong temperature and
concentration dependence.
Table 4.2. Summary of the
19
F-,
13
C-, and
1
H-NMR shifts and
1
JCF coupling constants of CF3OH
and CF3OH2
+
.
CF3OH
(neat)
23
CF3OH (in
HF)
a
CF3OH2
+
(in
HF)
b
CF3OH / CF3OH2
+
(in
HF)
c
δ
19
F [ppm] -54.5 (s) -57.8 (s) -59.37 (s) -58.70
δ
13
C [ppm] 118 (q) 120.92 (q) 118.40 (q) 119.84 (q)
1
JCF [Hz] 256 254.9 270.0 262.8
δ
1
H [ppm]
8.65 (s) (9.39)
d
(10.29)
e
(10.98)
f
a) this study, recorded at -60 °C; b) data for the SbF6
-
•nSbF5 salt, recorded at -60 °C, using a large
excess of SbF5; c) using 0.5 equivalents of SbF5; d) concentration-dependent exchange of HF and
CF3OH; the chemical shift of pure HF was found to be strongly temperature dependent and was
observed at 8.77 ppm and 9.46 ppm at 25 °C and -60 °C, respectively; e) concentration- and
temperature-dependent exchange of HF and CF3OH2
+
; the addition of SbF5 to neat HF resulted in
a downfield shift of its proton resonance from 8.77 ppm to 9.23 ppm and from 9.46 ppm to 10.03
ppm at 25 °C and -60 °C, respectively; f) concentration-and temperature-dependent exchange of
HF,CF3OH and CF3OH2
+
.
50
Table 4.3. The
19
F and
13
C-NMR shifts and the corresponding coupling constants of
perfluoroethanol, CF3CF2OH, recorded at -60 °C in HF, and of its protonated cation. The
CF3CF2OH2
+
spectra were recorded at -50 °C for a 1:3 molar mixture of CF3COF and SbF5 in HF.
*s = singlet, t = triplet, q = quartet,
Table 4.4: The
19
F and
13
C-NMR shifts and the corresponding coupling constants of perfluoro-n-
propanol, CF3CF2CF2OH, and its protonated cation, CF3CF2CF2OH2
+
, recorded in HF solution at
-55 °C and -50 °C, respectively .
*s = singlet, t = triplet, q = quartet,
CF3CF2OH
CF3CF2OH2
+
δ
19
F obs [ppm]* -CF2-
-CF3
-86.00 (q)
-89.89 (t)
-87.50 (q)
-89.49 (t)
δ
13
C obs [ppm] -CF2-
-CF3
114.39 (t of q)
117.25 (q of t)
114.04 (t of q)
116.63 (q of t)
1
JCF [Hz] -CF2-
-CF3
268.3
282.7
273.6
283.5
2
JCF [Hz]
3
JFF [Hz]
-CF2-
-CF3
-CF2-
-CF3
43.0
46.6
2.5
2.5
43.8
45.1
2.5
2.5
CF3CF2CF2OH CF3CF2CF2OH2
+
δ
19
F obs [ppm]* -CF2OH
-CF3
-CF2-
-80.64 (q of d)
-84.43 (t of d)
-132.84 (s)
-81.82 (q)
-84.51 (t)
-132.78 (s)
δ
13
C obs [ppm] -CF2OH
-CF3
-CF2-
115.73 (t of t)
117.72 (q of t)
109.22 (t)
115.54 (t of t)
117.40 (q of t)
108.90 (t)
1
JCF (
1
JFC) [Hz] -CF2OH
-CF3
-CF2-
269.4 (270.1)
284.5 (286.7)
(263.1)
272.8 (275)
284.3 (286)
(264.7)
2
JCF [Hz]
4
JFF [Hz]
-CF2OH
-CF3
-CF2-
-CF2OH
-CF3
30.7
32.4
40.6
8.0
8.0
31.3
32.5
39.1
8.0
8.0
51
Conclusion
In conclusion, the previously reported convenient access to CF3OH from carbonyl fluoride and HF
was extended to the syntheses of CF3CF2OH and CF3CF2CF2OH from HF and CF3COF or
CF3CF2COF, respectively. All three alcohols exhibit similar equilibrium characteristics although
there is a trend of decreasing alcohol formation with increasing chain length. They are thermally
unstable molecules that decompose under ambient conditions back to the acyl fluorides and HF.
The equilibrium can be shifted towards the alcohol by protonation, forming the perfluorinated
oxonium salts RfOH2
+
SbF6
-
. All three perfluorinated alcohols and corresponding oxonium salts
were characterized by multinuclear NMR spectroscopy, and the previously reported anomalous
temperature dependence of the COF2/HF equilibrium
31
was found to be caused by its slow rate at
low temperature. From the temperature dependence of the equilibrium and van’t Hoff plots, the
reaction enthalpies were experimentally determined and the values for CF3OH are in good
agreement with calculated values in the literature. The ready access to perfluoroalcohols could
transform them from exotic laboratory curiosities to useful compounds of significant scientific and
industrial interest.
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Angew. Chem.-Int. Ed. Engl. 2007, 46 (32), 6155–6158. https://doi.org/10.1002/anie.200701823.
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chemistry; Wiley: Chichester, 1995; p 338.
54
(33) Atkins, P. W. Physical Chemistry, 6th ed.; Freeman: New York, 1998.
(34) Asher, R. L.; Appelman, E. H.; Tilson, J. L.; Litorja, M.; Berkowitz, J.; Ruscic, B. A
Photoionization Study of Trifluoromethanol, CF3OH, Trifluoromethyl Hypofluorite, CF3OF, and
Trifluoromethyl Hypochlorite, CF3OCl. J. Chem. Phys. 1997, 106 (22), 9111–9121.
https://doi.org/10.1063/1.474017.
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Irreproducibility in Fluorine NMR Spectroscopy. Angew. Chem. Int. Ed. 2018, 57 (30), 9528–
9533. https://doi.org/10.1002/anie.201802620.
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Chemical Shifts, 1951 to Mid-1967; Wiley-Interscience: New York, 1970.
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Pure Appl. Chem. 1991, 63 (11), 1577–1590. https://doi.org/10.1351/pac199163111577.
(38) Sutcliffe, L. H.; Taylor, B. 19F NMR Spectra and 13C Satellite Spectra of Some
Fluorochloroacetones. Spectrochim. Acta Part Mol. Spectrosc. 1972, 28 (4), 619–626.
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(39) Tiers, G. V. D. FLUORINE N.M.R. SPECTROSCOPY. VIII. COUPLING CONSTANTS
IN NORMAL AND ISOTOPIC C 3 F 8. J. Phys. Chem. 1962, 66 (5), 945–946.
https://doi.org/10.1021/j100811a505.
55
CHAPTER 5: THE CRYSTAL STRUCTURES OF
HEPTAFLUOROCYCLOBUTANOL AND
HEXAFLUOROCYCLOBUTANE-1,1-DIOL
Abstract
The first X-ray crystal structure of an a-fluoroalcohol is reported. Heptafluorocyclobutanol was
obtained in quantitative yield from hexafluorocyclobutanone by HF addition in anhydrous
hydrogen fluoride. The compound was characterized by its X-ray single crystal structure.
Heptafluorocyclobutanol readily undergoes hydrolysis to hexafluorocyclobutane-1,1-diol, which
was also structurally characterized by X-ray diffraction.
Introduction
Alcohols possessing α-fluorine atoms are inherently unstable and undergo facile HF elimination.
1–
4
While α-fluoroalcohols have been studied extensively by computational methods,
5–14
complementary experimental studies are lacking, and several attempts to prepare them have been
unsuccessful.
15–19
In fact, only a limited number of α-fluoroalcohols have been observed, and even
fewer have been isolated. Fluoromethanol was first obtained by the reduction of ethyl
fluoroformate or formyl fluoride with LiAlH4.
20
For a microwave spectroscopic study, relatively
pure samples of fluoromethanol were prepared from formaldehyde and anhydrous hydrogen
fluoride (aHF).
21
The simplest perfluoroalcohol, trifluoromethanol, was synthesized from
trifluoromethyl hypochlorite and HCl at -110°C.
2
The compound is unstable and decomposes to
carbonyl fluoride and HF at ambient temperature. It was found that CF3OH, COF2, and HF exist
in equilibrium at lower temperatures, and the equilibrium was studied by variable-temperature
56
NMR spectroscopy.
1
Heptafluoroisopropanol has been observed by NMR spectroscopy in
solutions of hexafluoroacetone in aHF. However, this secondary perfluorinated alcohol has not
been isolated.
22,23
An exception to the rule of the inherent instability of α-fluoroalcohols is
heptafluorocyclobutanol (hfcb), which was first reported by Andreades and England in 1961.
24
Despite its relatively high stability (liquid at room temperature, b.p. of 57–58°C with partial
decomposition), the crystal structure of hfcb has never been established. Herein we report the
single crystal X-ray structure of hfcb, the first example of a crystallographically characterized α-
fluoroalcohol as well as that of its hydrolysis product hexafluorocyclobutan-1,1-diol.
Results and Discussion
Hfcb was prepared by stirring hexafluorocyclobutanone with an excess of anhydrous HF
at ambient temperature for 15 minutes [Eq. (1)]. Slow removal of the aHF solvent at -78°C in a
dynamic vacuum resulted in the isolation of hfcb in quantitative yield as colorless crystals suitable
for single crystal X-ray diffraction. Heptafluorocyclobutanol was characterized by its multi-
nuclear NMR and vibrational spectra as well as its X-ray single-crystal structure.
(1)
The
19
F NMR spectrum of the perfluorocyclobutanone starting material in CDCl3 solution
is already rather complex (AA’MM’M’’M’’’ spin system) and displays 98 transitions that fall into
two groups at -127.0 ppm and -136.3 ppm, respectively, with an area ratio of 4:2.
25
The spectrum
of heptafluorocyclobutanol in aHF solution is equally complex. The fluorine atoms of the molecule
constitute an ABMM’NN’X spin system, resulting in a complex multi-line splitting pattern at -
134.5 ppm to -137.5 ppm. The
13
C spectrum of hfcb in aHF shows a doublet of multiplets at 104.9
57
ppm with
1
JCF = 284 Hz for the CF(OH) group. The carbon resonances of the three CF2 groups
appear as a single triplet of multiplets at 112.3 ppm with
1
JCF = 294 Hz. A further analysis of the
spectra was not attempted. The proton signal of the OH group was not observed in the
1
H NMR
spectrum in aHF solution, even at temperatures as low as -60°C. In the IR spectrum of hfcb, a band
at 3616 cm
-1
for the ν(OH) vibration confirms the presence of an alcohol. Based on the absence of
the carbonyl vibration of perfluorocyclobutanone in the IR and Raman spectra, the conversion of
the ketone to the alcohol was complete. The complete list of observed IR and Raman bands and
their intensities is given in the Supporting Information.
Figure 5.1. Asymmetric unit of the heptafluorocyclobutanol crystal structure. Ellipsoids are set at
50% probability except for the hydrogen atoms being shown as spheres of arbitrary radius.
Hydrogen atom positions were determined from the difference electron density map. Selected bond
distances [Å] and angles [°]: C1–O1 1.358(5), C1–O1 1.358(5), C1–C2 1.564(5), C2–C3 1.553(5),
C3–C4 1.563(5), C1–C4 1.558(5), C5–C6 1.566(5), C6–C7 1.560(5), C7–C8 1.555(5), C5–C8
1.572(6); C1-C2-C3 90.4(3), C2-C3-C4 897(3), C3-C4-C1 90.3(3), C4-C1-C2 89.5(3), C5-C6-C7
90.0(3), C6-C7-C8 89.7(3), C7-C8-C5 90.0(3), C8-C5-C6 88.9(3), F1-C1-O1 112.4(3) F8-C5-O2
112.6(3), F2-C2-F3 109.5, F9-C6-F10 109.5(3).
58
Details of the crystallographic data collection and refinement parameters are given in
Appendix 4. The single crystals of hfcb were manipulated and mounted at -110°C using a custom-
made low-temperature device. Hfcb crystallizes in the monoclinic space group P21/c with two
crystallographic independent molecules in the asymmetric unit (Z = 8, Z’ = 2). The α axis and the
unique β axis of the unit cell are of similar length (7.458(2) Å and 7.798(2) Å, respectively), while
the c axis is more than 2.5 times longer (20.307(4) Å). Both crystallographically independent
molecules are approximately perpendicular to one another and exhibit intermolecular hydrogen
bonding (Figure 5.1). While the analogous non-fluorinated cyclobutanol displays a puckered
butterfly conformation in which one carbon atom forms a 30° angle with the plane containing the
other three carbon atoms of the carbocycle,
26
the four carbon atoms in the perfluorinated analog
are almost coplanar. The carbocycle of one hfcb molecule (C1-C2-C3-C4) is almost planar with
an angle of just 4.2(6)° between the two planes containing C1, C2, C4 and C2, C3, C4. The second
hfcb molecule (C5-C6-C7-C8) deviates more from planarity with an angle of 12.6(6)° between the
two planes containing C5, C6, C8 and the C6, C7, C8. The C-C-C bond angles of both
crystallographically different molecules fall into the range 89.4(3)°–90.5(3)° and are only very
slightly larger than the values of 87.3(2)°–89.3(2)° reported for cyclobutanol at 100 K.
26
The C-C bond distances in hfcb range between 1.553(5)Å (C2-C3) and 1.572(6)Å (C5-
C8). These are rather long compared to the average C(sp
3
)-C(sp
3
) single bond distance of 1.530
Å,
27
but in line with the distances observed for other polyfluorinated cyclobutane derivatives, such
as cis- and trans-1,2-bis(methoxycarbonylphenoxy)hexafluorocyclobutane with C-C bond
distances of 1.563(5)-1.587(4) Å and 1.542(9)-1.565(9) Å, respectively.
28
The C-O bond distances
of 1.358(5)Å in both crystallographically independent hfcb molecules are significantly shorter than
the average C(sp
3
)-O single bond distance in alcohols (1.432 Å)
27
or the C-O distance in
59
cyclobutanol of 1.413(3) Å to 1.424(3) Å.
26
The observed C-F distances in the two
heptafluorocyclobutanol molecules range between 1.325(4) Å (C8-F13) and 1.361(4) Å (C1-F1)
and agree well with the average C-F distance of 1.351 Å in known crystal structures.
27
The F-C-F
angles are very close to the ideal tetrahedral angle and fall within the range of 109.5(3)° to
110.2(3)°.
In the solid state (Figure 5.2), the hfcb molecules are associated via intermolecular OH···O
hydrogen bonding. O2 serves as the hydrogen bond donor to O1 of the same asymmetric unit (O2-
H2···O1 2.810(3) Å, 166.33°) while also serving as a hydrogen bond acceptor to O1 of a different
asymmetric unit (O1-H1···O2 2.825(3) Å, 149.34°). Based on the observed O-H···O distances,
the strength of these hydrogen bonds can be estimated to be approximately 30– 35 kJ mol
-1
.
29,30
The unit cell contains four asymmetric units stacked along the long c axis (Figure 5.2). The
hydrogen bonding arranges the molecules into helices running parallel to the b axis and along the
two twofold screw axes within the unit cell at (1=2,y,1=4) and (1=2,y,3=4). The helices are
associated through intermolecular F···F interactions with distances of 2.812(3) Å–2.926(3) Å,
which are equal or slightly shorter than twice the Van der Waals radius of fluorine (1.46 Å).
31
Heptafluorocyclobutanol is moisture sensitive and it has previously been reported that the
compound reacts vigorously and quantitatively with water under liberation of HF.
24
Water vapor
can slowly diffuse through the walls of thinwalled Teflon-FEP containers.
32
We were therefore
not surprised that liquid hfcb when held for a prolonged period inside thin-walled FEP reaction
vessels at ambient temperature hydrolyzed quantitatively to solid hexafluorocyclobutan-1,1-diol
(hfcbd). Colorless single crystals of hfcbd·HF suitable for X-ray diffraction were obtained from
an aHF solution at -78°C by slow evaporation of the solvent in a dynamic vacuum. The crystal
60
structure of hfcbd is also of interest as it is only the fifth example of a structurally characterized
geminal cyclobutandiol.
33–36
Figure 5.2. A) Crystal packing of heptafluorocyclobutanol projected down the b axis. B) Part of
an hfcb helix parallel to the b axis. The fluorine atoms have been omitted for clarity. Selected
distances [Å]: O1H1···O2 2.825(3), O2-H2···O1 2.810(3), F1–F10 2.876(3), F2–F11 2.923(3),
F3–F10 2.836(3), F6–F14 2.924(3), F7–F8 2.889(3), F7–F14 2.897(3), F10–F12 2.812(3) F11–
F13 2.926(3).
61
(2)
Like perfluorocyclobutanone, the
19
F NMR spectrum of hexafluorocyclobutan-1,1-diol in
aHF exhibits the complex pattern of an AA’MM’M’’M’’’ spin system. Again, the signals fall
within two groups at -133.1 ppm and -134.3 ppm, respectively, with an area ratio of 4:2. The
13
C
resonances of the three CF2 groups are observed as a triplet of multiplets at 110.6 ppm with a
1
J(CF)
coupling constant of 299 Hz. The C(OH)2
13
C resonance is observed at 101.1 ppm. No
1
H NMR
resonances could be observed for the protons of the OH groups. Further analysis of the NMR
spectra of hfcbd was not attempted because of their complexity. Like hfcb, hfcbd·HF crystallizes
in the monoclinic space group P21/c with a = 6.8319(12) Å and b = 5.4873(10) Å and a long c axis
of 18.633(3) Å. Unlike hfcb, the solid-state structure of hfcbd·HF contains only one formula unit
in the asymmetric unit and four formula units in the unit cell (Z = 4, Z’ = 1).
With an angle of 11.4(6)° between the planes containing the four carbon atoms, the
polyfluorinated carbocycle in hexafluorocyclobutan-1,1-diol is more planar than that in
cyclobutanol (Figure 5.3).
26
The C-C-C angles of 88.7(2)–90.2(2)° in the diol are very similar to
the values found for heptafluorocyclobutanol. The C-C bond distances involving the C(OH)2 group
are slightly longer than the one between the CF2 groups (1.576(4) Å and 1.560(4)/1.576(3) Å) and
are again like the values found for heptafluorocyclobutanol. The C-O bond distances of 1.378(3)
Å and 1.393(4) Å are longer than the ones in hfcb but still significantly shorter than the average
C(sp
3
)-O single bond distance in alcohols (1.432 Å).[10] The observed CˇF distances in the hfcbd
range between 1.331(4) Å (C3-F3) and 1.347(3) Å (C2-F2) and agree well with the average C-F
62
distance of other known perfluorocarbon crystal structures (1.351 Å).
27
The F-C-F angles are very
close to the ideal tetrahedral angle and fall within 109.4(2)° and 109.5(2)° while the O-C-O angle
of 115.1(2)° is significantly larger.
Figure 5.3. The hfcbd molecule in the crystal structure. Ellipsoids are set at 50% probability except
for the hydrogen atoms being shown as spheres of arbitrary radius. Hydrogen atom positions were
determined from the difference electron density map. Selected bond distances [Å] and angles [°]:
C1–O1 1.393(4), C1–O2 1.378(3), C1–C2 1.576(3), C2–C3 1.560(4), C3–C4 1.563(3), C4–C1
1.576(4), C2–F1 1.335(3), O1-C1-O2 115.1(2), C1-C2-C3 90.2(2), C2-C3-C4 89.8(2), C3-C4-C1
90.1(2), C4-C1-C2 88.7(2), F1-C2-F2 109.5(2).
In the solid state, the molecules are associated through hydrogen bridges between the OH
groups and the residual HF molecule (Figure 5.4). O1 serves as hydrogen bond donor to O2 and
acceptor to the HF molecule. Besides acting as acceptor to O1, O2 serves as a hydrogen donor to
one HF molecule as well as acceptor to a second HF molecule. As was the case with the hfcb unit
cell, the OH groups of hfcbd point toward each other inside the unit cell, maximizing their
hydrogen bonding potential, which creates a region in the center of the unit cell with a cluster of
63
fluorine atoms (Figure 5.4). The shortest F···F contact in the hfcbd unit cell is 2.871(3) Å, which
is again slightly shorter than twice the Van der Waals radius of fluorine (1.46 Å).
31
Figure 5.4. A) Crystal packing of hfcbd·HF projected down the b axis. B) Part of the hydrogen
bonding network in hfcbd·HF viewed down the c axis. Some fluorine atoms have been omitted for
clarity. Selected distances [Å]: O1H1···O2 2.750(3), O1···H3-F7 2.576(3), O2H2···F7 2.697(3),
O2H2···F7’ 2.968(3), F1–F5 2.923(2), F4–F4’ 2.871(3).
64
Conclusion
In summary, heptafluorocyclobutanol was obtained in quantitative yield from
hexafluorocyclobutanone by HF addition in anhydrous hydrogen fluoride solution. With the X-ray
single crystal structure of heptafluorocyclobutanol, the first example of a structurally characterized
a-fluoroalcohol is reported. The alcohol readily hydrolyzes under formation of
hexafluorocyclobutan-1,1-diol. The X-ray crystal structure of the diol was also determined.
Experimental
Caution! Anhydrous HF can cause severe burns. Contact with the skin must be avoided and the
compound should be handled only in a well-ventilated fume hood. Appropriate safety precautions
should be taken when working with HF. All reactions were carried out in either Teflon-FEP
ampules that were closed by stainless steel valves or NMR tubes that were heatsealed. Volatile
materials were handled in a stainless steel/TeflonFEP vacuum line.
37,38
Anhydrous HF (Galaxy
Chemicals) was dried by storage over BiF5.
39
Hexafluorocyclobutanone was prepared according
to a previous report.
40
CCDC 1832670 and 1832671 contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre. For further experimental details, see Appendix 4.
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1-Ones from Both Intra-Molecular Diels–Alder Adducts of the Claisen Rearrangement Reaction
from the 4-Me Derivative: Mechanistic Implications of a Thermal Retro Π4s + Π2s Reaction of
One of the Adducts and Recyclisations by Π4s + Π2s and/or Π2s + Π2a Routes. Journal of
Fluorine Chemistry 2002, 113 (1), 123–131. https://doi.org/10.1016/S0022-1139(01)00503-6.
(35) Bock, C. M. The Crystal and Molecular Structure of Octahydroxycyclobutane. Journal of
the American Chemical Society 1968, 90 (11), 2748–2751. https://doi.org/10.1021/ja01013a002.
(36) Ebead, A.; Fournier, R.; Lee-Ruff, E. Synthesis of Cyclobutane Nucleosides. Nucleosides,
Nucleotides and Nucleic Acids 2011, 30 (6), 391–404.
https://doi.org/10.1080/15257770.2011.584513.
(37) K. O. Christe, R. D. W., C. J. Schack, D. D. Desmarteau. In Inorganic Syntheses; Wiley:
New York, 1986; pp 3–6.
(38) Haiges, R. Preparation of Transition Metal Fluorides Using ClF 3. In Efficient Preparations
of Fluorine Compounds; Roesky, H. W., Ed.; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2012;
pp 100–107. https://doi.org/10.1002/9781118409466.ch18.
(39) Christe, K. O.; Wilson, W. W.; Schack, C. J. On the Syntheses and Properties of Some
Hexafluorobismuthate (V) Salts and Their in the Metathetical Synthesis of NF+4 Salts. Journal of
Fluorine Chemistry 1978, 11 (1), 71–85. https://doi.org/10.1016/S0022-1139(00)81599-7.
(40) England, D. C. PERFLUOROCYCLOBUTANONES. Journal of the American Chemical
Society 1961, 83 (9), 2205–2206. https://doi.org/10.1021/ja01470a046.
68
CHAPTER 6: PARTIALLY FLUORINATED GRAPHENE
AS A CATHODE CATALYST SUPPORT IN PROTON
EXCHANGE MEMBRANE FUEL CELLS
Abstract
Graphene was partially fluorinated by reaction with XeF2 at 150°C. XPS revealed that increasing
the amount of XeF2 used resulted in a greater degree of fluorination as well as an increase in the
covalent character of the C-F bonds. Pt particles were deposited onto the partially fluorinated
graphene (FG) by ethylene glycol reduction. Fluorination was found to have an adverse effect on
the size and size distribution of Pt particles. Pt supported on FG had higher specific activities
compared to non-fluorinated graphene for the oxygen reduction reaction (ORR) in 0.5M H 2SO4.
Furthermore, Pt supported on FG was superior to the non-fluorinated control as a cathode catalyst
in proton exchange membrane fuel cell testing with a 35% improvement to the peak power density
and a 56% improvement to the maximum current density.
Introduction
Motivation
Since the Industrial Revolution, the average global temperature has increased by nearly 1°C. The
Intergovernmental Panel on Climate Change (IPCC) urges we stay below a 1.5°C increase to
minimize damage to life on Earth.
1
Global fossil fuel-derived CO2 emissions were 37.1 Gt in
2018.
2
The IPCC suggests a total CO2 emissions budget of 580 Gt for a 50% chance of remaining
under the 1.5°C target. Therefore, if global CO2 emissions remain constant, there would be a 50%
69
chance we would reach 1.5°C within 15.6 years. Unfortunately, however, global CO2 emissions
are projected to continue to increase.
3
Due to the increasing global population as well as increasing energy consumption per
capita in developing countries, global energy consumption is increasing at an alarming rate.
2
The
U.S. Energy Information Administration predicts global energy consumption to increase by nearly
50% from 2018 to 2050.
4
As of 2018, nearly 80% of energy consumption in the U.S. is derived
from fossil fuels in the form of oil, coal and natural gas (Figure 6.1).
5
Clearly, radical, immediate
change to our global energy infrastructure is required.
Figure 6.1. United States energy consumption based on fuel type as of 2018.
5
One solution to reduce our dependence on fossil fuels is to better harness the nearly
limitless potential of renewable energy sources, however, the intermittency and unpredictability
of these sources is problematic. Electrochemical conversion of renewable energy to chemical fuels
is a promising avenue to address this since the fuel can be produced when renewable energy is
abundant and used anytime. A promising fuel is hydrogen which is potentially a carbon-free
renewable energy carrier. Hydrogen can be produced by renewable-powered water electrolysis
70
then used in fuel cells to produce energy and water. This is the basis for a carbon-free hydrogen
economy.
6
Introduction to Fuel Cells
A fuel cell is an electrochemical energy conversion system consisting of an anode where oxidation
of a fuel occurs, and a cathode, where a reduction reaction takes place. The anode and cathode are
separated by an electrolyte, thereby allowing electrons to flow from the anode to the cathode
through an external circuit, producing an electrical current. There are different types of fuel cells,
which can be distinguished based on the type of electrolyte and operating temperature. Molten
carbonate fuel cells operate at temperatures over 600°C and use molten carbonate salt mixtures as
the electrolyte. Solid oxide fuel cells operate at temperatures over 700°C and use a solid oxide or
ceramic electrolyte. Because these fuel cells operate at high temperatures, the oxidation and
reduction reactions at the anode and cathode can be performed more efficiently relative to lower
temperature fuel cells. However, high temperature fuel cells have longer start-up times, are
susceptible to corrosion and are more suited to stationary applications. The polymer electrolyte
membrane fuel cell operates at the lowest temperatures, typically less than 90°C, and thus is the
most operationally simple and suitable for mobile applications, such as transportation.
The most well developed polymer electrolyte membranes are proton exchange membranes
(PEM). A proton exchange membrane fuel cell (PEMFC) is depicted in Figure 6.2. PEMs are
proton conducting, but not electrically conductive to prevent a short circuit. Nafion membranes by
Chemours are the industry standard and are made of a perfluorosulfonic acid co-polymer. Anion-
exchange membranes (AEMs) are another type of polymer-electrolyte membrane which conduct
anions, usually hydroxide ions, rather than protons. However, this technology is not as well
established and AEMs often suffer from limited stability relative to PEMs.
71
Most commonly, hydrogen is oxidized at the anode and oxygen is reduced at the cathode.
However, this is not a prerequisite, and there are many other reactions that can be considered. For
example, direct liquid fuel cells are advantageous with respect to the ease of transport and storage
of a liquid fuel compared to a gas such as hydrogen.
7
Of the liquid fuels, the direct methanol fuel
cell (DMFC) is the most well studied. Notably, a collaboration between our group and NASA’s
Jet Propulsion Laboratory during the 1990s resulted in some key findings that ultimately led to the
commercialization of DMFCs.
8
DMFCs are particularly suited for portable devices with low to
medium power requirements as the kinetics are much slower for the six electron methanol
oxidation reaction (MOR) compared to the two electron hydrogen oxidation reaction (HOR)
(Equations 1-2).
(1)
(2)
(3)
Catalysts are required at the anode and cathode to overcome the activation energy barrier
for the MOR or HOR and oxygen reduction reactions (ORR) (Equations 1-3). One disadvantage
of the PEMFC is the acidic environment it induces. This limits which metals are available for use
as catalysts since lower cost first-row transition metals have limited thermodynamic stability in
the acidic media. Platinum is the catalyst of choice for HOR and ORR in PEMFCs, and the high
cost of this precious metal is a disadvantage of PEMFCs. Therefore, much research is aimed at
developing stable Pt-free catalysts or reducing the amount of platinum required. To address the
latter point, platinum is most frequently deposited as small nanoparticles (<5 nm) onto a
conductive carbon support (Pt/C) in order to maximize the surface area. In addition to the high
72
cost of the catalyst, stability is a major issue. Common stability problems for the state-of-the-art
Pt/C catalysts include carbon corrosion, platinum dissolution and Ostwald ripening.
9
Figure 6.2. Schematic of a proton-exchange membrane fuel cell (PEMFC). Image courtesy of
user: CFA213FCE, Wikimedia Commons, CC BY-SA 3.0, URL:
https://commons.wikimedia.org/w/index.php?curid=26261005
In addition to challenges regarding the catalysts, water management is a critical issue for
PEMFCs. At the cathode, two moles of water are produced for each mole of oxygen consumed
(Equation 3). Since oxygen has a very limited solubility in water, cathode flooding can occur
73
whereby the cathode can become starved of oxygen.
10
This is particularly problematic at high
currents when the most water is produced. However, if there is too little water, the fuel cell will
suffer as well. This is because the Nafion membrane must be humidified in order to maintain its
proton conductivity.
11
Despite the challenges still associated with PEM fuel cells, they have many advantages
over conventional combustion-based energy technologies. Hydrogen fuel cells emit only water,
and thus are better for the environment. Additionally, there are fewer moving parts, so fuel cells
can operate very quietly. Finally, fuel cells involve the direct conversion of chemical energy into
electricity, so they have the potential to be more efficient.
12
The theoretical maximum hydrogen
fuel cell efficiency, defined as the ratio between hydrogen consumed and electricity produced, is
above 90%.
12
Fuel cells have some advantages over battery technologies as well. For example,
there is no need for a potentially long recharging time. Hydrogen fuel cell vehicles can be refueled
with hydrogen in about the same amount of time as conventional gasoline-powered vehicles.
Currently, there are three hydrogen fuel cell vehicles that are commercially available to the public
the Toyota Mirai, Hyundai Nexo and Honda Clarity.
Background
The oxygen reduction reaction (ORR) is kinetically limiting compared to the hydrogen oxidation
reaction in proton exchange membrane fuel cells (PEMFCs). Despite the high cost of Pt, it remains
the state-of-the-art ORR catalyst, particularly in the acidic environment of a PEMFC.
13
To
maximize surface area and minimize Pt loading, Pt nanoparticles are generally deposited onto a
high surface area carbon support such as Vulcan XC72. The nature of the support material can
strongly affect the activity and stability of the Pt-based ORR catalyst.
14,15
Additionally, under
operating conditions, especially during start-up and shut-down, corrosion of the carbon support is
74
problematic.
16,17
Graphitized carbon is more corrosion resistant compared to amorphous carbon
such as carbon black.
18,19
Thus, using graphene or heteroatom-doped graphene as a catalyst support
is a promising strategy since graphene has a high surface area, electrical conductivity and its
electronic properties can be tuned by doping.
20–23
Furthermore, a stronger Pt-C interaction in Pt
supported on graphene compared to Pt supported on carbon black has been observed leading to
enhanced stability.
24
We are specifically interested in exploring the effect of fluorination of graphene as a
catalyst support material. For a fuel cell cathode, PTFE and other fluorinated materials are used in
the gas diffusion layer and microporous layer as a means to reduce flooding.
25,26
Furthermore,
since oxygen is highly soluble in perfluorinated solvents, we hypothesize that fluorination within
the catalyst layer may facilitate mass transport of oxygen. However, formation of covalent C-F
bonds may also reduce the conductivity of the support, reducing fuel cell performance. Thus, it is
of interest to systematically study the effect of fluorinating carbon supports as a means to enhance
ORR at Pt-based catalysts.
Fluorinated graphene is of interest as a material for optical, electronic and energy storage
devices.
27–31
However, for these applications generally a large degree of fluorination is sought
after. We sought a method which was scalable and allowed for a tunable degree of fluorination.
We found methods that utilized aqueous dispersions of graphene oxide with HF as a fluorinating
agent to be unscalable with our 40-mL autoclave as dilute solutions are required for the fluorination
reaction to occur.
32
Ultimately, we were able to find a convenient, scalable, solvent-free method
using XeF2 as the fluorinating reagent under mild conditions at 150°C for 12h. The graphene/XeF2
ratio was modified to tune the amount of fluorine in the product. After the fluorinated graphene
75
support was prepared, the Pt particles were deposited onto it by the polyol method using ethylene
glycol (EG) as a solvent and reducing agent.
Previously, it has been found that fluorographene with covalent C-F bonds is unstable to
reductive defluorination in the presence of NaOH
33
or KI
34
. Indeed, we found that the fluorinated
graphene was partially defluorinated upon the polyol synthesis of Pt nanoparticles, which is
performed under alkaline conditions. Nevertheless, we found that the varying amount of fluorine
as well as the nature of the C-F bond led to a difference in ORR performance.
Results and Discussion
Synthesis
Partially fluorinated graphene was prepared by reacting graphene with XeF2 under N2 at 150°C
for 12h. The degree of fluorination was controlled by varying the amount of XeF2. The sample that
was prepared with more XeF2 is referred to as FG1, and the sample prepared with less XeF2 is
referred to as FG2. Additionally, a control experiment was conducted without XeF2 and is referred
to as G. Pt nanoparticles were deposited onto the graphene-based support materials by ethylene
glycol reduction at 140°C for 3.5h. It was noted that the fluorinated graphene materials underwent
partial defluorination during the reduction of Pt nanoparticles.
Characterization
Raman spectroscopy is a powerful tool to study graphitic materials.
35,36
The D-band (~1350 cm
-1
)
is a measure of the disorder in the graphitic structure due to the installation of functional groups
or other defects. The G-band (~1582 cm
-1
) is due to the E2g symmetric sp
2
hybridized carbon of
ordered graphene. Thus, the intensity ratio ID/IG is used as a measure of the disorder of graphene.
76
The ID/I G ratio increases with increasing degree of fluorination as expected (Table 6.1 and
Figure 6.3). Comparing the FG samples to the Pt/FG samples, a decrease in ID/IG is observed
consistent with the other data which show that some fluorine is lost during the polyol synthesis of
Pt nanoparticles. This is in contrast to the non-fluorinated control experiment, in which an increase
in ID/IG is observed upon embedment of the Pt nanoparticles, from 0.068 to 0.144, indicating some
physical or chemical defects were introduced during the polyol reduction process. Thus the ID/IG
of Pt/G is comparable to the lesser fluorinated sample Pt/FG2 (0.193).
The nature of the graphitic materials was further examined by X-ray diffraction (XRD).
The peak corresponding to the (002) diffraction of graphitic carbon appears at 2Θ of about 26.5°
(Table 6.1 and Figure 6.3). The intensity of this peak is related to the degree of stacking of
graphene sheets.
31
The intensity of the (002) peak is G >> FG2 > FG1, indicating that fluorination
had a favorable effect in hindering the stacking of graphene sheets. This trend is maintained after
Pt reduction, Pt/G > Pt/FG2 > Pt/FG1.
The (002) peak becomes increasingly broadened with increasing fluorine content
indicating a decrease in crystallite size along the c-axis.
37
Interestingly, this broadening trend is
retained after deposition of the Pt particles, indicating that this structural change is maintained
even after the partial defluorination that takes place during the Pt reduction in ethylene glycol.
Additionally, the (002) peak position, and hence d-spacing, is nearly unchanged indicating the
distance between layers is unaffected by these mild fluorination conditions. In the XRD pattern of
FG1, a broad peak begins to emerge around 13° which has previously been observed in fluorinated
graphite
38
and fluorinated reduced graphene oxide,
32
however its assignment remains unclear. This
peak is no longer present in Pt/FG1, further evidence of partial defluorination during the polyol Pt
77
reduction. Finally, peaks due to the Pt (111), (200) and (220) Miller indices are observed in Pt/G,
Pt/FG1 and Pt/FG2.
Table 6.1. Summary of Raman and XRD data.
a
Intensity ratio of the D and G bands in the Raman spectra.
b
Position of the D band.
c
Position of
the G band.
d
position of the (002) peak in the XRD pattern.
e
d spacing in the (002) direction
f
relative intensity of the (002) peak.
g
Full width half maximum of the (002) peak.
h
XRD is shown
in Figure A5. 1.
Figure 6.3. Raman spectra (top) and XRD patterns (bottom).
X-ray Photoelectron Spectroscopy (XPS) studies were performed to determine the degree
of fluorination at the surface of the graphitic materials as well as give insight into the nature of the
C-F bond. The C1s spectra can be deconvoluted to five peaks (Table 6.2, Figure 6.4a-b and A5.3-
Id/Ig
a
D (cm
-1
)
b
G (cm
-1
)
c
2Θ
d
d(Å)
e
rel int
f
FWHM
g
G
h
0.068 1361.2 1586.4 26.64 3.34 100 0.56
FG1 0.744 1352.0 1593.4 26.56 3.35 10 0.92
FG2 0.366 1360.2 1588.1 26.72 3.33 18 0.77
Pt/G 0.144 1354.7 1588.1 26.64 3.34 18 0.56
Pt/FG1 0.602 1357.5 1593.4 26.49 3.36 2 0.86
Pt/FG2 0.193 1352.0 1588.1 26.64 3.34 7 0.72
78
6). Peak 1 (~284 eV) is attributed to sp
2
hybridized C-C bonds and was fitted asymmetrically.
Peaks 2 and 3 may be due to defective or sp
3
carbon.
39
Peak 4 is attributed to the C-F bonds, and
at ~288 eV is typical for graphitic materials with a low fluorine content.
40
Peak 5 is due to the π-
plasmon often observed in graphitic materials.
Deconvoluting the F1s spectra can be useful in determining the nature of the C-F bond as
higher binding energies indicate a more covalent bond. Previously, peaks observed at 687 eV, 685
eV and 683 eV were determined to be semi-covalent, semi-ionic and ionic, respectively.
40
The F1s
spectra of FG1 and FG2 deconvoluted to 3 peaks (Table 6.3 and Figure 6.4c-d). The %
concentration of peak 1 (687-688 eV) which can be attributed to the semi-covalent C-F bond is
greater for FG1 compared to FG2. This is in agreement with previous work showing that more
harsh fluorination conditions lead to an increase in the quantity as well as covalency of C-F
bonds.
37
Looking at the Pt/FG samples (Figure 6.4e-f), the peak at the lowest binding energy is no
longer present indicating the weakest ionic bonds have been removed during the polyol reduction.
It is observed that Pt/FG1 deconvolutes to two peaks at 689 and 687 eV with 38 and 62%,
respectively. Whereas, Pt/FG2 deconvolutes to a single peak at 687 eV, suggesting the Pt/FG1
contains significantly more covalent character in the C-F bonding compared to Pt/FG2. Survey
spectra are shown in Figure A5.2. High resolution Pt4f spectra are provided in Figure A5.7-9 and
can be deconvoluted to Pt
0
with no noticeable differences between the three samples.
Elemental Analysis was also performed with Energy Dispersion X-ray Spectroscopy (EDS),
which can penetrate deeper into the material (1-3 µm) compared to XPS (<5 nm). This allows for
a comparison of the fluorination at the surface compared to bulk. The atomic F/C ratios determined
by both methods are reported in Table 6.4. In the fluorinated graphene samples, the F/C ratio is
greater at the surface compared to the bulk. This is consistent with what has been observed
79
previously for the direct fluorination of graphite under mild conditions.
37
Surprisingly, the F/C
ratio determined by XPS is similar between Pt/FG1 (4.1%) and PtFG2 (3.4%). However, the F/C
ratio determined by EDS is much greater for Pt/FG1 (7.6%) compared to Pt/FG2 (2.7%).
Table 6.2. Summary of deconvoluted C1s XPS spectra.
peak 1 peak 2 peak 3 peak 4 peak 5
FG1 Binding Energy (eV) 283.81 283.76 284.93 288.18 290.7
fwhm 0.586 1.004 2.362 1.923 2.714
%conc 11.52 41.7 22.95 18.11 5.72
FG2 Binding Energy (eV) 283.97 283.86 284.94 288.02 290
fwhm 0.545 0.874 2.927 1.918 3.73
%conc 37.2 20.26 23.86 7.49 11.19
Pt/FG1 Binding Energy (eV) 284.19 284.18 285.12 288 291.22
fwhm 0.466 0.899 2.136 3 2.75
%conc 13.71 50.18 21.53 11.19 3.4
Pt/FG2 Binding Energy (eV) 284.27 284.65 286.37 288.64 290.24
fwhm 0.529 1.442 2.448 1.252 3.011
%conc 33.66 38.61 16.33 4.92 6.48
G Binding Energy (eV) 283.8 283.8 285.06
290
fwhm 0.558 1.254 2.796
3.003
%conc 63.51 17.44 13.29
5.76
Pt/G Binding Energy (eV) 284.25 284.62
fwhm 0.611 1.998
%conc 63.64 36.36
Table 6.3. Summary of deconvoluted F1s spectra.
Peak 1 Peak 2 Peak 3
FG1 Binding Energy (eV) 687.34 685.97 684.08
fwhm 2.204 1.368 2.5
%conc 86.55 6.04 7.41
FG2 Binding Energy (eV) 687.94 686.86 685.56
fwhm 2.116 1.271 4.43
%conc 72.47 17.24 10.3
PtFG1 Binding Energy (eV) 688.96 687.36
fwhm 1.950 3.580
%conc 38.33 61.67
PtFG2 Binding Energy (eV)
687.58
fwhm
2.721
%conc
100.00
80
\
Figure 6.4. Deconvoluted C1s spectra of FG1 (a) and FG2 (b). Deconvoluted F1s spectra of FG1
(c), FG2 (d), PtFG1 (e), and PtFG2 (f). All other spectra along including survey spectra are
provided in Appendix 5.
Table 6.4. F/C ratios determined by XPS and SEM-EDS
F/C % (XPS) F/C % (EDS)
FG1 28.0 15.1
FG2 13.6 7.8
PtFG1 4.1 7.6
PtFG2 3.4 2.7
c) d)
e) f)
a)
b)
81
Figure 6.5. SEM-EDS mapping of FG2 (top) red C, blue F, green O, yellow S. SEM-EDS mapping
of PtFG2 (bottom) red C, blue F, green O, yellow Na, pink Pt. Additional SEM images and EDS
maps can be found in the supporting information.
82
Figure 6.6. TEM, HRTEM and particle size distribution of Pt/FG1 (top), Pt/FG2 (middle) and
Pt/G (bottom). Pt/FG1: 4.0 ± 1.1 nm; Pt/FG2: 4.2 ± 0.9 nm; Pt/G: 3.5 ± 0.6.
83
Figure 6.7. TGA under N2 (left) and air (right).
Additionally the distribution of the F and Pt atoms on the carbon surface can be visualized
by SEM-EDS mapping (Figure 6.5 and A5.10-14). Both the F and Pt are distributed evenly on the
carbon. It should be noted that traces of sulfur were also detected by EDS, but not by XPS
indicating the sulfur contamination is deeper in the material and not at the surface. Sulfur was
detected in the starting material and could not be removed by base treatment, indicating it is likely
an inorganic sulfate rather than organosulfur.
41
Additionally, traces of Na were found in the Pt-
containing samples since NaOH was used in the synthesis. Based on the SEM-EDS mapping, the
sodium seems to be coordinated to the oxygen which can be due to sodium ions bound to anionic
oxygen-containing functional groups on the graphene.
Transmission electron microscopy (TEM) was used to determine the size, morphology and
distribution of the Pt particles (Figure 6.6). Generally, the Pt particles are relatively small, round
and well dispersed. High resolution TEM shows diffraction lines with a lattice spacing of 0.22 –
0.23 nm corresponding to the Pt (111) plane. Notably, the size and size distribution for the particles
on the fluorine-containing support are higher (Pt/FG1: 4.0 ± 1.1 nm, Pt/FG2: 4.2 ± 0.9 nm)
compared to the non-fluorinated graphene (Pt/G: 3.5 ± 0.6 nm). This is most likely due to the fact
that the support undergoes partial reductive defluorination during the polyol synthesis. Therefore,
84
the solution will contain free fluoride species which seem to inhibit the formation of small particles
with a narrow size distribution. Halide additives have been used to impart changes in nanoparticle
size and/or morphology. For example, the effect of Br
-
and I
-
was examined during the synthesis
of Pd nanowires.
42
The thermal stability of the materials was analyzed using TGA (Figure 6.7). Generally the
weight loss before 200°C or 250°C is attributed to loss of oxygen-containing functional groups
within the graphitic structure. Consistent, with what has been previously reported for fluorinated
carbon materials, the weight loss for the fluorine-containing functional groups is observed at a
higher temperature 300-500°C.
43
The weight loss percentage increases with increasing fluorine
content as expected. However, since the non-fluorinated graphene also exhibits weight loss in this
region, the exact amount of fluorine cannot reliably be determined by this method. The metal
loading was determined by TGA in air, assuming that only Pt metal remains at 800°C. The values
determined were 24% Pt/FG1, 21% Pt/FG2 and 20% Pt/G.
Half-cell Testing
Figure 6.8a shows the cyclic voltammograms of the three catalysts under N2 in 0.5M H2SO4
electrolyte. The electrochemically active surface area (ECSA) in Table 6.5 is determined by the
hydrogen underpotential deposition. The non-fluorinated catalyst Pt/G has the highest ECSA of
134 m
2
/g. This is in agreement with the TEM results which clearly demonstrate that the
fluorination adversely affected the particle size and distribution.
85
Figure 6.8. a) CV under N2 at 50 mV/s b) LSV under O2 1600 rpm, 10 mV/s, positive going
direction c) Effect of rotation rate on LSV for Pt/FG2 under O2 positive going direction d)
Koutecky-Levich plot of the different catalysts at 0.80 V v. RHE (triangles) and 0.85 V v. RHE
(circles) e) Plot of specific activity vs. potential f) Electrochemical Impedance Spectroscopy under
O2, 1600 rpm, 0.7 V v. RHE, Raw data is given by symbols whereas the solid line is the data fitted
according to the equivalent circuit. Full details regarding the EIS fitting parameters are provided
in Appendix 5.
c)
d)
e)
f)
a)
b)
86
Table 6.5. Summary of half-cell data
ECSA
a
Onset
b
SA
c
(0.8V)
SA
d
(0.85V)
MA
e
(0.8V)
MA
f
(0.85V)
ΩCT
g
ΩMT
h
Pt/G 134 0.95 59 27 79 36 128±34 241±39
Pt/FG2 96 0.95 71 35 68 34 253±29 243±33
Pt/FG1 115 0.90 25 10 29 11 370±45 227±48
a
Electrochemically active surface area (m
2
/g) determined by integrating the hydrogen
underpotential region.
b
Onset potential (V v. RHE) defined as the potential at -0.1 mA/cm
2
.
c
Specific Activity (µA/cm
2
Pt) at 0.8 V v. RHE
d
Specific Activity (µA/cm
2
Pt) at 0.85 V v. RHE.
e
Mass Activity (A/g Pt) at 0.8 V v. RHE
f
Mass Activity (A/g Pt) at 0.85 V v. RHE.
g
Charge
transfer resistance determined by EIS at 0.7 V v. RHE. .
h
Mass transport resistance determined by
EIS at 0.7 V v. RHE
To evaluate the catalytic performance for ORR, linear sweep voltammetry (LSV) was used
under O2 flow at 1600 rpm for each catalyst and is shown in Figure 6.8b. The onset potential for
ORR for both the Pt/G and Pt/FG2 catalysts are 0.95 V while the Pt/FG1 is 0.90 V. This high
overpotential for Pt/FG1 may be due to the higher concentration of fluorine in the bulk as well as
a larger covalency in the C-F bond resulting in poorer conductivity and catalytic performance,
compared to Pt/FG2.
By measuring the LSVs as a function of rotation rate of the RDE, a Koutecky-Levich plot
was constructed (Figure 6.8c-d). This allowed for the determination of the potential-dependent
kinetic currents as well as specific and mass activities, which are normalized to the
electrochemically active surface area (ECSA) and mass of Pt, respectively.
44
The Pt/G and Pt/FG2
catalysts have comparable kinetic currents in the potential range 0.87-0.80 V while those of Pt/FG1
are substantially lower (Figure A5.17). The Pt/FG2 catalyst has the lowest ECSA and thus the
highest specific activities (Figure 6.8e). However, Pt/G which has the highest ECSA, has the
highest mass activities at 0.80 and 0.85 V (Table 6.5) although Pt/FG2 has a higher mass activity
>0.85 V (Figure A5.18). Thus Pt/FG2 has similar ORR performance to the Pt/G catalyst, despite
suffering from a lower ECSA. Thus, if the synthesis were improved so that the size and size
87
distribution of Pt particles were not adversely affected by fluorination, and the ECSA improved,
the ORR performance would likely improve further. Specific and mass activities are low relative
to other Pt-based catalysts, which may be due to the size and quality of the graphene starting
material (average thickness 11-15 nm, average diameter 15 µm). It was found previously that
although Pt particles had a similar ECSA regardless of the size of the graphene starting material
that the ORR activities were drastically reduced with larger graphene particles.
45
Electrochemical Impedance Spectra (EIS) were fitted to the circuit in Figure 6.8f from
which the resistances due to charge transfer and mass transport can be distinguished.
46
The charge
transfer resistance increases with increasing fluorination due to the presence of semi-covalent C-
F bonds which disrupts the sp
2
conjugation and decreases the conductivity. However, the mass
transport resistance is similar in all three cases within experimental error. Full details regarding
the EIS fitting are provided in Tables A5.1-3.
Fuel Cell Testing
To further assess the catalytic performance of Pt/G and Pt/FG2 for ORR, single fuel cell testing
was performed. First the cathode catalyst layer (CCL) was optimized with the non-fluorinated
catalyst, Pt/G. Reducing the catalyst loading results in drastically improved power and current
when normalized for the catalyst loading (Figure 6.9a). This is due to the propensity of graphene
for π-π stacking which forms a dense network and severely limits mass transport. Adding a spacer
such as carbon black, has been shown to improve fuel cell performance by limiting this π-π
stacking and increasing Pt utilization
47,48
which we have also shown here (Figure 6.9b). Thus the
optimized CCL includes a low catalyst loading of 114 µg Pt/cm
2
along with a 1:1 ratio of
catalyst:carbon black.
88
a)
Figure 6.9. Fuel Cell Testing Results
a
Effect of cathode catalyst loading. 70°C 100 sccm H2 250
sccm O2.
b
Effect of adding a carbon black spacer to the cathode catalyst ink. 70°C 100 sccm H 2
250 sccm O2.
c
Effect of fluorination of the graphitic support. 70°C 100 sccm H2 250 sccm O2.
d
Constant potential 0.3V. 70°C 50 sccm H2 50 sccm O2.
e
EIS at OCV, 70°C. The dots represent
the raw data while the solid line represents the fit.
Table 6.6. Summary of results from fuel cell testing.
OCV
a
Peak Power
b
Maximum Current
c
RCT
d
Pt/G 0.72 1.10 5.9 475±4
Pt/FG2 0.65 1.46 9.0 231±2
a
Open circuit voltage (V).
b-
(W/mg Pt)
c
(A/mg Pt).
d
Charge transfer resistance (mΩ)
d)
c)
e)
b)
e)
89
Using the optimized CCL formulation, Pt/FG2 was implemented as the cathode catalyst
allowing for a direct comparison on the effect of fluorination on the graphene catalyst support.
Fluorination resulted in a dramatic improvement in power density (from 1.10 to 1.46 W/mg Pt)
and current density (from 5.9 to 9.0 A/mg Pt). To compare the stabilities of the cells, a constant
potential of 0.3 V was applied for 1h. The Pt/FG2 catalyst steadily increases the first 20 min. after
which a constant current of 455±5 mA/cm
2
is achieved. This is in contrast to the Pt/G catalyst
which steadily decreases from 344 mA/cm
2
to 325 mA/cm
2
over the course of 1h. The OCVs are
low in both cases, and even lower for the Pt/FG2 catalyst. This may be due to the low surface area
of the graphene starting material (50-80 m
2
/g) which on the larger scale of catalyst used in the fuel
cell compared to the half-cell results in an exacerbated effect of high overpotential.
EIS were measured at 70°C at OCV with 10 mV AC amplitude and were fitted according
to the equivalent circuit shown in Figure 6.9. L1 and L2 are inductance due to the cables and wires
of the testing system, Rmem and RCT are the resistances due to the membrane and charge transport,
respectively. CPE1 is the constant phase element that arises from the pseudo-capacitive nature of
the catalyst layers, and Ws1 is the Warburg element for the diffusion of reactants through the
porous catalyst layers. Full details on the EIS fitting are provided in Tables A5.4-5. In contrast to
what was observed in the half-cell studies, the charge transfer resistance (Table 6.6) for Pt/G is
double of that for Pt/FG2, explaining the improved power curve for Pt/FG2 despite the lower OCV.
Perhaps this discrepancy is due to enhanced water management with Pt/FG2 since this is an issue
unique to fuel cells. Also, although a low catalyst loading was used in the fuel cell tests, it is still
three times the amount used in the half-cell testing. Finally, carbon black was added as a spacer
only in fuel cell testing, but not in half-cell testing. Thus, the fluorination could provide a favorable
interaction between Pt/FG2 and carbon black.
90
Conclusion
To conclude, graphene was fluorinated under mild conditions, using XeF2 as a fluorinating reagent.
Two samples were prepared with different fluorine concentrations by changing the amount of
XeF2. Pt nanoparticles were deposited onto the fluorinated graphene supports, as well as a non-
fluorinated control, by ethylene glycol reduction. Notably, the fluorination adversely affected the
size and size distribution of the Pt particles, compared to the non-fluorinated control. This resulted
in a lower ECSA for the fluorinated samples.
The fluorinated graphene underwent partial defluorination during the Pt reduction under
basic conditions. This resulted in the two catalysts having a similar concentration of fluorine at the
surface, but different concentrations in the bulk. Additionally, the Pt/FG sample with the greater
degree of fluorination (PtFG1) also exhibited more covalency in the C-F bonding as determined
by XPS. Both of these phenomena resulted in poor ORR performance for Pt/FG1. The Pt/FG with
a lower degree of fluorination (Pt/FG2) had similar ORR performance to the non-fluorinated
analogue (Pt/G) in half-cell testing. However, Pt/FG2 was the superior cathode catalyst in PEMFC
experiments with a 33% improvement to the peak power density and a 53% improvement to the
maximum current density. We propose that partially fluorinating the carbon support of the cathode
catalyst is a way to improve fuel cell performance, perhaps by facilitating mass transport of O 2
through the catalyst layer or by improving water management. However, too much fluorination
results in more covalent C-F bonds and poor ORR performance.
Experimental
Preparation of fluorinated graphene
“Graphene” refers to commercial graphene nanopowder 11-15nm, from Skyspring Nanomaterials.
XeF2 (2.15 g, FG1; 0.400 g, FG2; 0 g G) along with graphene (0.40 g) was placed into a Teflon
91
lined autoclave (45 mL). The autoclave was purged in a dry box under N2 for 30 min. then sealed
and heated to 150°C (1h ramp time, 12h hold time). The autoclave was allowed to cool naturally.
Then the fluorinated graphene was removed and heated under vacuum at 70°C for several hours to
remove any residual volatile materials.
Preparation of Pt supported on fluorinated graphene
49
200 mg of the graphene support (G, FG1 or FG2) and ethylene glycol (20 mL) was added to a two-
neck 100 mL round bottom flask with a magnetic stir bar. The mixture was placed in a sonicating
bath for 8 min. H2PtCl6·6H2O in ethylene glycol (11.2 mL of a 9.5 mg/mL solution) was added
followed by an additional 16 min of sonication. Then with stirring, NaOH in ethylene glycol (~1M)
was added until the pH was 12. The flask was connected to a reflux condenser and purged with N2
for 15 min. Then it was placed in a preheated oil bath (140°C) and refluxed under N2 for 3.5h.
After the reaction time, the flask was removed from the oil bath, allowed to cool to ambient
temperature and then vacuum filtered. The solid was washed with 25 mL water x5, then dried
under vacuum 55°C for several hours.
Characterization
Raman measurements were performed on a Horiba XploRA ONE Raman microscope with a 532
nm wavelength laser excitation. Powder X-Ray Diffraction (XRD) measurements were performed
on a Rigaku X-Ray diffractometer with a Cu-Kα (0.154056 nm) radiation source and a scan rate
of 6° min
-1
from a 2θ value of 10° to 80°. Scanning Electron Microscopy (SEM) images were
obtained from a JEOL JSM-7001F electron microscope with an acceleration voltage of 15 keV.
Transmission Electron Microscopy (TEM) images were taken on a JEOL JEM 2100F with an
acceleration voltage of 200 keV. The particle size distribution was determined by measuring 50
92
particles using the ImageJ software. Thermogravimetric analysis (TGA) was performed on a TGA-
50 Thermogravimetric analyzer (Shimadzu) at a heating rate of 10°C/min. X-ray Photoelectron
spectroscopy (XPS) data was collected on a Kratos Axis Ultra DLD using a mono Al anode (5
mA, 10 kV) with a pass energy of 160 keV for the survey scans and 20 keV for the high resolution
scans. For the graphene samples without Pt, the charge neutralizer was used (1.9 A filament
current, 4.2 V charge balance, 1 V filament bias). The XPS data were fitted using the CasaXPS
software using a Shirley background. The graphitic sp
2
carbon peak in the C1s spectra (peak 1 in
Table 6.2) was fitted asymmetrically A(0.35,0.3,0)GL(0). The Pt 4f peaks were fitted with an
asymmetric Lorentzian lineshape (α = 1.2, β = 85, m = 70). All other peaks were fitted
symmetrically GL(30).
Half-cell Testing
Half-cell electrochemical testing was performed in a glass cell with a rotating disk electrode
(RDE). A Teflon wrapped glassy carbon RDE (0.196 cm
2
, Pine Instruments) was used as the
working electrode, a Pt wire in a fritted compartment was used as the counter electrode and a
mercury sulfate electrode (saturated K2SO4, Pine Research) was used as the reference electrode.
Measured potentials are converted to the reversible hydrogen electrode. The catalyst ink was
prepared with 2.0 mg catalyst, 10 mg Nafion solution (5 wt%, Ion Power), 800 μL H2O, 100 μL
ethanol and 100 μL isopropanol. The catalyst dispersion was homogenized via probe sonication
10% amplitude 10s pulses for 1 min. 20 µL of the catalyst ink was dropcast onto the glassy carbon
and dried in air (catalyst loading = 8.0-9.6 μg Pt, 41-49 μg/cm
2
, based on 20-24 wt% catalyst as
determined by TGA). 0.5M H2SO4 was used as the electrolyte in all half-cell testing and was
purged with N2 for 20 min prior to use. The catalyst surface was electrochemically cleaned by
cyclic voltammetry (CV) (100 mV/s x30) from 0.03 to 1.1 V v. RHE prior to measurements.
93
Electrochemically active surface area (ECSA) was determined by CV in 0.5M H2SO4 at 50 mV/s
from 0.03 to 1.1 V v. RHE and averaging the charge derived by integration of the hydrogen
adsorption and desorption regions using the ADVC software.
50
210 μC/cm
2
was used to convert
the integrated charge to the ECSA. The solution resistance was determined by Electrochemical
Impedance spectroscopy (EIS) measured from 1E5 to 10 Hz, 10 mV AC amplitude at OCV and
used for IR drop corrections. Linear sweep voltammograms (LSV) were measured under N2 in the
region 1.1 to 0.03 V v. RHE at 10 mV/s with no rotation and subtracted from the LSVs under O2
as the capacitance correction. Then the cell was purged with O2 for at least 20 minutes after which
LSVs were measured at different rotation rates (100 rpm, 400 rpm , 900 rpm, 1600 rpm) from 1.1
to 0.03 V v. RHE at 10 mV/s. EIS was measured at 0.70 V v. RHE from 1E5 to 0.1 Hz, 10 mV
AC amplitude. Specific and mass activities were calculated from the kinetic currents normalized
to the ECSA or mass of Pt, respectively.
44
Fuel Cell Testing
The cathode catalyst was the prepared Pt/G or Pt/FG2 while the anode catalyst was commercial
Pt/C (40 wt%, Etek). In both cases, the catalyst ink was formulated with the designated amount of
catalyst and 5 wt% Nafion solution in a weight ratio 1:3, respectively. Additional water and
isopropanol were added and the dispersion sonicated for 8 min. The homogenous ink was painted
onto 5 cm
2
Toray carbon paper (10% teflonized). After drying in the oven at 60°C, the catalyst
loading was determined by mass. To ensure the cathode was limiting, the anode catalyst loading
was maintained at 1.4 mg Pt/cm
2
while the cathode catalyst loading was varied between 68-252
µg Pt/cm
2
. In some experiments, carbon black (Vulcan XC72) was added to the cathode catalyst
ink as a spacer in a catalyst:carbon black ratio of 1:1. The membrane electrode assembly was
94
prepared by sandwiching the Nafion 211 membrane between the two electrodes and hot pressing
at 120°C for 5 min using 500 kilograms of force.
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99
APPENDIX 1: ADDITIONAL INFORMATION FOR THE
SYNTHESIS OF α-FLUORINATED
ALKYLAMMONIUM SALTS (CHAPTER 2)
Experimental Details
Caution! Anhydrous HF can cause severe burns and contact with the skin must be avoided.
Materials and apparatus: All reactions were carried out in either teflon-FEP ampules or NMR
tubes that were closed by stainless steel valves. Volatile materials were handled in a stainless
steel/teflon-FEP vacuum line. Reaction vessels were passivated with ClF3 prior to use. Nonvolatile
materials were handled in the dry nitrogen atmosphere of a glove box. HF was dried by storage
over BiF5. HCN was prepared from NaCN and stearic acid using a modified literature procedure.
1
ClCN was prepared according to the literature procedure from NaCN and Cl 2.
2,3
(CN)2 was
prepared according to the literature procedure from CuSO4 and KCN.
4
AsF5 was prepared from
AsF3 and F2.
5
SbF5 (Ozark Mahoning) was freshly distilled before use. BrCN (Aldrich), CF3CN
(Synquest), HCF2CN (Synquest) and CF3CH2CN (Synquest) were used as received. CH3CN and
CH3CH2CN were dried over sieves and freshly distilled prior to use. The NMR spectra were
recorded at 298 K on a Bruker AMX-500, Varian NMRS-600, or a Varian NMRS-500. Spectra
were externally referenced to neat nitromethane for
14
N NMR spectra, neat tetramethylsilane for
1
H and
13
C NMR spectra, and to 80% Freon-11 in chloroform-d for
19
F NMR spectra. Raman
spectra were recorded directly in the Teflon reactors or in a J. Young tube in the range 4000–80
cm
-1
on a Bruker Equinox 55 FT-RA spectrophotometer, using a Nd-YAG laser at 1064 nm.
100
Infrared spectra were recorded in the range 4000-400 cm
-1
on Bruker Alpha, Bruker Vertex 70 or
Midac M Series FT-IR spectrometers using KBr pellets.
Crystal Structure determinations: The single-crystal X-ray diffraction data were collected on a
Bruker SMART APEX DUO 3-circle platform diffractometer, equipped with an APEX II CCD,
using Mo Kα radiation (TRIUMPH curved-crystal monochromator) from a fine-focus tube. The
diffractometer was equipped with an Oxford Cryosystems Cryostream 700 apparatus for low-
temperature data collection. The frames were integrated using the SAINT algorithm to give the hkl
files corrected for Lp/decay.
6
The absorption correction was performed using the SADABS
program.
7
The structures were solved by the direct method and refined on F
2
using the Bruker
SHELXTL Software Package and ShelXle.
8–12
All nonhydrogen atoms were refined
anisotropically. ORTEP drawings were prepared using the ORTEP-3 for Windows V2.02
program.
13
[HCF2NH3][MF6] HCN (1.00 mmol) and HF (2.0 mL) were added in vacuo at -196˚C into a
Teflon-FEP ampule. The colorless solution was allowed to warm to ambient temperature and
stirred for 72 h. AsF5 (1.00 mmol) or SbF5 (1.00 mmol) was added to the reaction mixture and
allowed to warm to ambient temperature for 0.5 h. Removal of the volatile compounds in vacuo,
first at -64˚C, then at ambient temperature resulted in a colorless crystalline solid.
[CF3NH3][MnF5n+1] XCN (1.00 mmol) and HF (2.0 mL) were added in vacuo at -196˚C into a
Teflon-FEP ampule. The colorless solution was allowed to warm to ambient temperature, and
react for 6 h when X = Cl and 4 days when X = Br. When X = Br, over time the solution became
colored orange due to the formation of Br2. After the reaction was complete AsF5 (1.00 mmol) or
SbF5 (1.00 or 2.00) mmol was added to the reaction mixture and allowed to warm to ambient
101
temperature and stirred for 0.5 h. Removal of the volatile compounds in vacuo, first at -64˚C, then
at ambient temperature resulted in a colorless, crystalline solid.
[CF3CF2NH3][AsF6] CF3CN (2.18 mmol) and HF (3.0 mL) were added in vacuo at -196˚C into a
Teflon-FEP ampule. The colorless solution was allowed to warm to ambient temperature and
stirred for 48 h. AsF5 (2.20 mmol) was added to the reaction mixture at -196˚C in vacuo, and the
solution was allowed to warm to ambient temperature and stirred for 0.5 h. Removal of the volatile
compounds in vacuo, first at -64˚C, then at ambient temperature resulted in a colorless solid (0.664
g). Yield: 93.7%
Raman (200 mW) 𝑉 ̅
= 1772, (0.44), 1589 (0.71), 1408 (0.55), 885 (0.70), 812 (2.07), 792 (5.06),
758 (0.44), 692 (10.00), 613 (0.89), 585 (1.78), 563 (0.93), 373 (4.83) cm
-1
.
IR (KBr) 𝑉 ̅
= 3491 (w), 3331 (vw), 3183 (s), 2919 (m), 2850 (w), 2105 (vw), 1816 (w), 1729 (s),
1677 (w), 1606 (m), 1525 (s), 1441 (m), 1401 (m), 1287 (m), 1211 (vs), 1038 (m), 900 (m), 829
(w), 702 (vs), 528 (w) cm
-1
.
1
H NMR: (HF, unlocked, 25˚C) δ = 8.2 ppm (HF); In this case a peak could not be observed for
the [CF3CF2NH3]
+
, but there is a shoulder in the HF peak which is likely due to these ammonium
protons;
13
C NMR: (HF, unlocked, 25˚C) δ = 108.6 ppm (t of q,
1
JCF = 280 Hz,
3
JCF = 46 Hz
[CF3CF2NH3]
+
), 115.2 ppm (q of t,
1
JCF = 285 Hz,
3
JCF = 34 Hz, [CF3CF2NH3]
+
);
14
N NMR: (HF,
unlocked, 25˚C) δ = -328.1 ppm (s, Δυ1/2 = 88 Hz);
19
F NMR: (HF, unlocked, 25˚C) δ = -68.1
ppm (m, br [AsF6]
-
), -86.2 ppm (s, [CF3CF2NH3]
+
), -102.8 ppm (s, [CF3CF2NH3]
+
).
[HCF2CF2NH3][AsF6] HCF2CN (1.32 mmol) and HF (3.0 mL) were added in vacuo at -196˚C
into a Teflon-FEP ampule. The colorless solution was allowed to warm to ambient temperature
and stirred for 48 h. AsF5 (1.38 mmol) was added to the reaction mixture at -196˚C in vacuo, and
102
the solution was allowed to warm to ambient temperature and stirred for 0.5 h. Removal of the
volatile compounds in vacuo, first at -64˚C, then at ambient temperature resulted in a colorless
solid (0.382 g). Yield: 93.9%
Raman (200 mW) 𝑉 ̅
= 3172 (0.18), 3025 (1.87), 2865 (0.24), 2697 (0.27), 1573 (0.27), 1432
(0.25), 1361 (0.61), 1294 (0.44), 1198 (0.21), 1135 (0.98), 1023 (0.60), 924 (0.20), 810 (3.94), 691
(10.00), 582 (2.55), 566 (0.52), 533 (0.33), 512 (0.19), 409 (0.21) cm
-1
.
IR (KBr) 𝑉 ̅
= 3175 (m), 2986 (vw), 1702 (vs), 1624 (m), 1560 (w), 1525 (m), 1426 (w), 1341 (m),
1255 (m), 1185 (w), 1131 (s), 983 (vw), 925 (w), 803 (w), 701 (vs), 563 (w), 536 (vw) cm
-1
.
1
H NMR: (HF, unlocked, 25˚C) δ = 7.2 ppm (s, br, [HCF2CF2NH3]
+
, 6.9 ppm (t,
2
JHF = 51.7 Hz),
[HCF2CF2NH3]
+
;
13
C NMR: (HF, unlocked, 25˚C) δ = 107.3 ppm (t of t,
1
JCF = 253 Hz,
3
JCF = 37
Hz, [HCF2CF2NH3]
+
), 112.1 ppm (t of t,
1
JCF = 273 Hz,
3
JCF = 33 Hz, [HCF2CF2NH3]
+
);
14
N NMR:
(HF, unlocked, 25˚C) δ = -330.2 ppm (q,
1
JNH = 53 Hz, Δυ1/2 = 103 Hz);
19
F NMR: (HF, unlocked,
25˚C) δ = -61.1 ppm (m, br [AsF6]
-
), -101.9 ppm (s, [HCF2CF2NH3]
+
), -137.4 ppm (d,
2
JFH = 51.6
Hz, [HCF2CF2NH3]
+
).
[NH3CF2CF2NH3][AsF6]2 NCCN (3.60 mmol) and HF (2.0 mL) were added in vacuo at -196˚C
into a Teflon-FEP ampule. The colorless solution was allowed to warm to ambient temperature
and stirred for 48 h. AsF5 (7.27 mmol) was added to the reaction mixture at -196˚C in vacuo, and
the solution was allowed to warm to ambient temperature and stirred for 0.5 h. Removal of the
volatile compounds in vacuo, first at -64˚C, then at ambient temperature resulted in a colorless
solid (1.546 g). Yield: 83.9%
Raman (200 mW) 𝑉 ̅
= 3088 (0.72), 2986 (0.31), 2859 (0.31), 2338 (0.71), 1564 (0.65), 1402
(0.34), 1222 (0.59), 1024 (0.62), 756 (3.39), 692 (10.00), 608 (0.47), 569 (2.45), 374 (5.23) cm
-1
.
103
IR (KBr) 𝑉 ̅
= 3398 (s), 3313 (m), 3199 (w), 2987 (vw), 1673 (vs), 1585 (vw), 1510 (m), 1401
(vw), 1351 (w), 1317 (s), 1238 (s), 1148 (s), 1109 (m), 1016 (w), 702 (vs), 625 (m), 514 (m) cm
-
1
.
1
H NMR: (HF, unlocked, 25˚C) δ = 6.6 ppm (s, br);
13
C NMR: (HF, unlocked, 25˚C) δ = 110.4
ppm (t of t,
1
JCF = 282 Hz,
3
JCF = 40 Hz);
14
N NMR: (HF, unlocked, 25˚C) δ = -328.9 ppm (s,
Δυ1/2 = 200 Hz);
19
F NMR: (HF, unlocked, 25˚C) δ = -68.3 ppm (m, br [AsF6]
-
), -98.8 ppm (s,
[NH3CF2CF2NH3]
2+
).
CF3NH2: Variable temperature
19
F NMR was conducted of [CF3NH3][AsF6] in neat
trimethylamine. Integrating the peak against CFCl3 as an internal standard, the yield did not
surpass 1%. Pure CF3NH2 could be isolated by reacting [CF3NH3][AsF6] and NMe3 at -30°C for
30 min. Then at -30°C, the volatile materials (CF3NH2 and NMe3) could be transferred under static
vacuum to a new reactor at -196°C. The NMe3 could then be removed under dynamic vacuum at
-78°C. CF3NH2 reacts with SO2, but is soluble and stable in DCM or trimethylamine. CF3NH2 was
identified by its
19
F NMR spectrum as a triplet at -52 ppm with
3
JFH = 10.0 Hz.
NMR experiments with RCN + HF (R = CH3, CH3CH2, CF3CH2) Solutions of various
concentrations of RCN and HF were prepared in teflon-FEP NMR tubes closed with stainless steel
valves. The
14
N NMR spectra clearly show the existence of the three cations: the protonated
nitrile, iminium and ammonium species. Integrating these spectra yields the data summarized in
Tables A1.1-A1.3.
104
Table A1.1. The effect of concentration on the RCN + HF reaction. Ratio of products after 7 days
with different concentrations of CH3CN in HF.
Ratio of 3 products after 1 week
% CH3CN in HF [CH3CNH]
+
[CH3CFNH2]
+
[CH3CF2NH3]
+
10 2 5 1
5 1 10 2
0.2 1 5 1
Table A1.2. The effect of reaction time on the RCN + HF reaction. Ratio of products from a 5%
solution of CH3CH2CN in HF after varying lengths of time.
Relative Intensity
Reaction Time [CH3CH2CNH]
+
[CH3CH2CFNH2]
+
[CH3CH2CF2NH3]
+
40 h 0.62 1.00 0.14
65 h 0.26 1.00 0.15
93 h 0.15 1.00 0.17
161 h 0.00 1.00 0.18
184 h 0.00 1.00 0.17
Table A1.3. The effect of R on the RCN + HF reaction. Ratio of products after 7 days from a 5%
solution of RCN in HF.
Relative Intensity
R = [RCNH]
+
[RCFNH2]
+
[RCF2NH3]
+
CH3 0.17 1.00 0.16
CH3CH2 0.00 1.00 0.18
CF3CH2 1.00 0.12 0.56
105
Crystallographic Details
Figure A1.1. Packing diagram of [HCF2NH3][AsF6]. View along the 001 direction.
Figure A1.2. Packing diagram of [HCF2NH3][AsF6]. View along the 010 direction.
106
Figure A1.3. Packing diagram of [HCF2NH3][AsF6]. View along the 100 direction.
Table A1.4. Sample and crystal data for [HCF2NH3][AsF6].
Chemical formula CH4AsF8N
Formula weight 256.96
Temperature 100(2) K
Wavelength 0.71073 Å
Crystal size 0.040 x 0.070 x 0.420 mm
Crystal habit clear colorless rod
Crystal system triclinic
Space group P -1
Unit cell dimensions a = 7.5182(12) Å α = 96.553(2)°
b = 8.8287(14) Å β = 92.696(2)°
c = 9.3535(15) Å γ = 91.042(2)°
Volume 615.93(17) Å
3
Z 4
Density (calculated) 2.771 g/cm
3
Absorption coefficient 5.628 mm
-1
F(000) 488
107
Table A1.5. Data collection and structure refinement for [HCF2NH3][AsF6].
Diffractometer Bruker APEX DUO
Radiation source fine-focus tube, MoKα
Theta range for data collection 2.19 to 30.56°
Index ranges -10<=h<=10, -12<=k<=12, -13<=l<=13
Reflections collected 14852
Independent reflections 3675 [R(int) = 0.0329]
Coverage of independent reflections 97.2%
Absorption correction multi-scan
Structure solution technique direct methods
Structure solution program SHELXTL XT 2013/6 (Sheldrick, 2013)
Refinement method Full-matrix least-squares on F
2
Refinement program SHELXTL XLMP 2014/1 (Bruker AXS, 2013)
Function minimized Σ w(Fo
2
- Fc
2
)
2
Data / restraints / parameters 3675 / 16 / 231
Goodness-of-fit on F
2
1.065
Δ/σmax 0.001
Final R indices 3207 data; I>2σ(I) R1 = 0.0410, wR2 = 0.1112
all data R1 = 0.0467, wR2 = 0.1158
Weighting scheme
w=1/[σ
2
(Fo
2
)+(0.0844P)
2
+0.0857P]
where P=(Fo
2
+2Fc
2
)/3
Largest diff. peak and hole 3.870 and -1.172 eÅ
-3
R.M.S. deviation from mean 0.221 eÅ
-3
108
Table A1.6. Atomic coordinates and equivalent isotropic atomic displacement parameters (Å
2
)
for [HCF2NH3][AsF6].
U(eq) is defined as one third of the trace of the orthogonalized U ij tensor.
x/a y/b z/c U(eq)
As1 0.25612(3) 0.86479(3) 0.09913(3) 0.00819(10)
As2 0.22992(3) 0.42387(3) 0.73485(3) 0.00887(10)
C1 0.2667(4) 0.3581(3) 0.2732(3) 0.0146(5)
C2 0.7871(4) 0.0960(3) 0.4437(3) 0.0141(5)
F1 0.1302(2) 0.2701(2) 0.3035(2) 0.0246(4)
F2 0.4168(2) 0.2892(2) 0.3048(2) 0.0227(4)
F3 0.6372(3) 0.1530(2) 0.4926(2) 0.0251(4)
F4 0.8069(2) 0.95601(19) 0.48479(19) 0.0208(4)
F5 0.0963(2) 0.9224(2) 0.2193(2) 0.0165(4)
F6 0.0923(2) 0.7882(2) 0.9751(2) 0.0167(4)
F7 0.4145(2) 0.8118(2) 0.9770(2) 0.0165(4)
F8 0.4196(2) 0.9468(2) 0.2200(2) 0.0162(4)
F9 0.2746(3) 0.6951(2) 0.1699(2) 0.0168(4)
F10 0.2362(2) 0.0365(2) 0.0263(2) 0.0151(3)
F11 0.3862(3) 0.3812(2) 0.6120(2) 0.0229(4)
F12 0.3948(2) 0.4895(2) 0.8647(2) 0.0159(4)
F13 0.0740(2) 0.4706(2) 0.8635(2) 0.0157(4)
F14 0.0602(3) 0.3618(2) 0.6129(2) 0.0212(4)
F15 0.2141(2) 0.60575(19) 0.6841(2) 0.0159(3)
F16 0.2457(2) 0.24648(19) 0.7941(2) 0.0162(4)
N1 0.2558(3) 0.3638(3) 0.1165(3) 0.0116(4)
N2 0.7679(3) 0.0764(3) 0.2849(3) 0.0116(4)
109
Table A1.7. Bond lengths (Å) for [HCF2NH3][AsF6].
As1-F9 1.7112(18) As1-F8 1.7215(18)
As1-F7 1.7228(18) As1-F6 1.7250(18)
As1-F5 1.7277(18) As1-F10 1.7375(18)
As2-F11 1.6988(19) As2-F14 1.7103(18)
As2-F16 1.7242(17) As2-F15 1.7301(17)
As2-F12 1.7374(18) As2-F13 1.7402(18)
C1-F2 1.329(3) C1-F1 1.336(3)
C1-N1 1.471(4) C1-H1 1.00(3)
C2-F3 1.322(3) C2-F4 1.344(3)
C2-N2 1.476(4) C2-H5 1.00(3)
N1-H2 0.83(2) N1-H3 0.83(2)
N1-H4 0.83(2) N2-H6 0.84(2)
N2-H7 0.84(2) N2-H8 0.83(2)
110
Table A1.8. Bond angles (°) for [HCF2NH3][AsF6].
F9-As1-F8 90.79(9) F9-As1-F7 90.88(9)
F8-As1-F7 90.28(9) F9-As1-F6 91.16(9)
F8-As1-F6 178.04(8) F7-As1-F6 89.48(9)
F9-As1-F5 90.68(9) F8-As1-F5 89.87(9)
F7-As1-F5 178.43(7) F6-As1-F5 90.32(9)
F9-As1-F10 179.58(8) F8-As1-F10 89.63(9)
F7-As1-F10 89.08(9) F6-As1-F10 88.42(9)
F5-As1-F10 89.35(9) F11-As2-F14 92.09(10)
F11-As2-F16 91.55(9) F14-As2-F16 91.76(9)
F11-As2-F15 90.46(9) F14-As2-F15 90.13(9)
F16-As2-F15 177.19(8) F11-As2-F12 90.65(10)
F14-As2-F12 177.26(9) F16-As2-F12 88.32(9)
F15-As2-F12 89.69(9) F11-As2-F13 178.49(9)
F14-As2-F13 89.35(9) F16-As2-F13 88.85(9)
F15-As2-F13 89.09(9) F12-As2-F13 87.91(9)
F2-C1-F1 108.1(2) F2-C1-N1 107.3(2)
F1-C1-N1 106.9(2) F2-C1-H1 108.(3)
F1-C1-H1 118.(3) N1-C1-H1 108.(3)
F3-C2-F4 109.1(2) F3-C2-N2 107.5(2)
F4-C2-N2 106.7(2) F3-C2-H5 111.5(18)
F4-C2-H5 108.2(18) N2-C2-H5 113.8(19)
C1-N1-H2 112.(3) C1-N1-H3 108.(3)
H2-N1-H3 111.(4) C1-N1-H4 112.(3)
H2-N1-H4 104.(4) H3-N1-H4 110.(4)
C2-N2-H6 110.(3) C2-N2-H7 115.(3)
H6-N2-H7 106.(4) C2-N2-H8 115.(3)
H6-N2-H8 106.(4) H7-N2-H8 104.(4)
111
Table A1.9. Anisotropic atomic displacement parameters (Å2) for [HCF2NH3][AsF6].
The anisotropic atomic displacement factor exponent takes the form: -2π
2
[ h
2
a
*2
U 11 + ... + 2 h k a
*
b
*
U 12 ]
U11 U22 U33 U23 U13 U12
As1 0.01028(16) 0.00635(15) 0.00773(15) 0.00026(10) -0.00005(10) -0.00093(10)
As2 0.01260(15) 0.00615(15) 0.00760(15) 0.00000(10) 0.00005(10) -0.00060(10)
C1 0.0209(13) 0.0139(13) 0.0086(12) 0.0003(9) 0.0004(10) 0.0003(10)
C2 0.0210(13) 0.0122(12) 0.0090(12) 0.0009(9) -0.0019(9) 0.0035(10)
F1 0.0191(8) 0.0371(11) 0.0205(10) 0.0135(8) 0.0051(7) -0.0018(8)
F2 0.0179(8) 0.0327(11) 0.0189(9) 0.0109(8) -0.0042(7) 0.0018(7)
F3 0.0291(9) 0.0308(10) 0.0166(9) 0.0038(8) 0.0071(7) 0.0145(8)
F4 0.0343(10) 0.0144(8) 0.0143(8) 0.0054(6) -0.0021(7) 0.0048(7)
F5 0.0157(8) 0.0199(9) 0.0139(9) 0.0007(7) 0.0046(7) 0.0021(7)
F6 0.0155(8) 0.0175(9) 0.0162(9) 0.0006(7) -0.0041(7) -0.0044(6)
F7 0.0174(8) 0.0169(9) 0.0153(9) 0.0009(7) 0.0051(7) 0.0018(7)
F8 0.0140(8) 0.0195(9) 0.0145(9) 0.0017(7) -0.0039(6) -0.0048(6)
F9 0.0224(9) 0.0102(8) 0.0188(9) 0.0069(7) -0.0001(7) 0.0005(6)
F10 0.0225(9) 0.0081(8) 0.0151(8) 0.0036(6) -0.0007(7) 0.0004(6)
F11 0.0276(10) 0.0246(10) 0.0176(9) 0.0025(8) 0.0108(7) 0.0060(8)
F12 0.0140(8) 0.0177(9) 0.0161(9) 0.0048(7) -0.0034(6) -0.0041(6)
F13 0.0141(8) 0.0170(9) 0.0164(9) 0.0020(7) 0.0036(6) 0.0018(6)
F14 0.0254(10) 0.0195(9) 0.0168(9) -0.0006(7) -0.0095(7) -0.0042(7)
F15 0.0222(8) 0.0090(8) 0.0171(9) 0.0051(6) -0.0003(7) -0.0001(6)
F16 0.0227(9) 0.0078(8) 0.0185(9) 0.0037(6) 0.0000(7) 0.0010(6)
N1 0.0139(11) 0.0116(12) 0.0096(10) 0.0036(8) 0.0002(8) 0.0003(9)
N2 0.0149(11) 0.0101(11) 0.0096(10) 0.0008(8) -0.0001(8) 0.0002(8)
112
Table A1.10. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
) for
[HCF2NH3][AsF6].
x/a y/b z/c U(eq)
H1 0.275(6) 0.465(4) 0.322(5) 0.037(12)
H2 0.259(5) 0.277(3) 0.071(4) 0.024(10)
H3 0.163(4) 0.408(4) 0.096(4) 0.025(10)
H4 0.343(4) 0.409(4) 0.089(4) 0.022(10)
H5 0.893(4) 0.160(3) 0.483(3) 0.006(7)
H6 0.675(4) 0.025(4) 0.258(5) 0.037(12)
H7 0.759(5) 0.158(3) 0.247(4) 0.029(11)
H8 0.851(4) 0.032(4) 0.243(4) 0.027(11)
Figure A1.4. Packing diagram of [CF3NH3][Sb2F11]. View along the 001 direction.
113
Figure A1.5. Packing diagram of [CF3NH3][Sb2F11]. View along the 010 direction.
Figure A1.6. Packing diagram of [CF3NH3][Sb2F11]. View along the 100 direction.
Table A1.11. Sample and crystal data for [CF3NH3][Sb2F11].
114
Chemical formula CH3F14NSb2
Formula weight 538.54
Temperature 100(2) K
Wavelength 0.71073 Å
Crystal size 0.04 x 0.05 x 0.26 mm
Crystal habit clear colourless needle
Crystal system monoclinic
Space group P 1 21/m 1
Unit cell dimensions a = 7.4682(14) Å α = 90°
b = 7.5587(14) Å β = 100.566(3)°
c = 9.6784(18) Å γ = 90°
Volume 537.08(17) Å
3
Z 2
Density (calculated) 3.330 Mg/cm
3
Absorption
coefficient
5.211 mm
-1
F(000) 488
115
Table A1.12. Data collection and structure refinement for [CF3NH3][Sb2F11].
Diffractometer Bruker APEX II CCD
Radiation source fine-focus tube, Mo
Theta range for data collection 2.14 to 30.73°
Index ranges
-10<=h<=10, -10<=k<=10, -
13<=l<=13
Reflections collected 9364
Independent reflections 1735 [R(int) = 0.0498]
Coverage of independent reflections 97.4%
Absorption correction multi-scan
Max. and min. transmission 0.8186 and 0.3444
Structure solution technique direct methods
Structure solution program SHELXS-97 (Sheldrick, 2008)
Refinement method Full-matrix least-squares on F
2
Refinement program SHELXL-97 (Sheldrick, 2008)
Function minimized Σ w(Fo
2
- Fc
2
)
2
Data / restraints / parameters 1735 / 0 / 104
Goodness-of-fit on F
2
1.033
Δ/σmax 0.001
Final R indices
1480 data;
I>2σ(I)
R1 = 0.0245, wR2
= 0.0589
all data
R1 = 0.0322, wR2
= 0.0623
Weighting scheme
w=1/[σ
2
(Fo
2
)+(0.0349P)
2
+0.0000P
]
where P=(Fo
2
+2Fc
2
)/3
Largest diff. peak and hole 1.827 and -1.260 eÅ
-3
R.M.S. deviation from mean 0.199 eÅ
-3
116
Table A1.13. Atomic coordinates and equivalent isotropic atomic displacement parameters (Å
2
) for
[CF3NH3][Sb2F11].
U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
x/a y/b z/c U(eq)
Sb1 0.24843(4) 0.25 0.47662(3) 0.01258(9)
Sb2 0.50366(4) 0.25 0.16342(3) 0.01248(9)
F1 0.0858(4) 0.25 0.3071(3) 0.0240(6)
F2 0.2644(3) 0.4959(3) 0.4642(2) 0.0224(4)
F3 0.4528(3) 0.25 0.3615(3) 0.0178(5)
F4 0.5304(4) 0.25 0.9764(3) 0.0232(6)
F5 0.6735(3) 0.4243(3) 0.2218(2) 0.0250(4)
F6 0.3203(3) 0.0767(3) 0.1325(2) 0.0208(4)
F7 0.0680(4) 0.25 0.5857(3) 0.0233(6)
F8 0.4401(4) 0.25 0.6291(3) 0.0184(5)
F9 0.0543(3) 0.3922(3) 0.8627(2) 0.0360(6)
F10 0.9195(4) 0.25 0.0060(3) 0.0279(7)
N1 0.7939(5) 0.25 0.7736(4) 0.0158(7)
C1 0.9615(6) 0.25 0.8802(5) 0.0181(9)
Table A1.14. Bond lengths (Å) for [CF3NH3][Sb2F11].
Sb1-F1 1.853(3) Sb1-F7 1.858(3)
Sb1-F8 1.858(3) Sb1-F2#1 1.868(2)
Sb1-F2 1.868(2) Sb1-F3 2.048(2)
Sb2-F5 1.844(2) Sb2-F5#1 1.844(2)
Sb2-F4 1.857(3) Sb2-F6 1.8791(19)
Sb2-F6#1 1.8791(19) Sb2-F3 2.022(3)
F9-C1 1.307(3) F10-C1 1.312(5)
N1-C1 1.469(6) N1-H1 1.00(9)
N1-H2 0.79(4) C1-F9#1 1.307(3)
Symmetry transformations used to generate equivalent atoms:
#1 x, -y+1/2, z
Table A1.15. Bond angles (°) for [CF3NH3][Sb2F11].
F1-Sb1-F7 94.42(13) F1-Sb1-F8 170.88(12)
F7-Sb1-F8 94.69(12) F1-Sb1-F2#1 88.98(6)
117
F7-Sb1-F2#1 95.62(6) F8-Sb1-F2#1 90.13(6)
F1-Sb1-F2 88.98(6) F7-Sb1-F2 95.62(6)
F8-Sb1-F2 90.13(6) F2#1-Sb1-F2 168.69(12)
F1-Sb1-F3 87.22(11) F7-Sb1-F3 178.36(11)
F8-Sb1-F3 83.66(11) F2#1-Sb1-F3 84.40(6)
F2-Sb1-F3 84.40(6) F5-Sb2-F5#1 91.21(14)
F5-Sb2-F4 96.19(9) F5#1-Sb2-F4 96.19(9)
F5-Sb2-F6 170.78(8) F5#1-Sb2-F6 89.47(10)
F4-Sb2-F6 92.89(9) F5-Sb2-F6#1 89.47(10)
F5#1-Sb2-
F6#1
170.77(8) F4-Sb2-F6#1 92.89(9)
F6-Sb2-F6#1 88.41(13) F5-Sb2-F3 86.99(8)
F5#1-Sb2-F3 86.99(8) F4-Sb2-F3 175.44(11)
F6-Sb2-F3 83.85(8) F6#1-Sb2-F3 83.85(8)
Sb2-F3-Sb1 143.52(14) C1-N1-H1 116.(5)
C1-N1-H2 108.(3) H1-N1-H2 108.(4)
F9#1-C1-F9 110.7(4) F9#1-C1-F10 110.1(3)
F9-C1-F10 110.1(3) F9#1-C1-N1 108.3(3)
F9-C1-N1 108.3(3) F10-C1-N1 109.5(4)
Symmetry transformations used to generate equivalent atoms:
#1 x, -y+1/2, z
118
Table A1.16. Anisotropic atomic displacement parameters (Å
2
) for [CF3NH3][Sb2F11].
The anisotropic atomic displacement factor exponent takes the form:
-2π
2
[ h
2
a
*2
U11 + ... + 2 h k a
*
b
*
U12 ]
U11 U22 U33 U23 U13 U12
Sb1 0.01194(14) 0.01405(15) 0.01242(14) 0 0.00399(10) 0
Sb2 0.01343(14) 0.01008(14) 0.01545(14) 0 0.00665(10) 0
F1 0.0163(12) 0.0401(18) 0.0147(12) 0 0.0002(10) 0
F2 0.0265(10) 0.0147(9) 0.0269(10) 0.0027(7) 0.0069(9) 0.0028(8)
F3 0.0143(12) 0.0239(14) 0.0164(12) 0 0.0062(10) 0
F4 0.0290(15) 0.0248(15) 0.0189(13) 0 0.0125(12) 0
F5 0.0221(9) 0.0243(11) 0.0300(10) -0.0046(9) 0.0082(8) -0.0117(9)
F6 0.0213(9) 0.0161(9) 0.0259(10) -0.0030(8) 0.0072(8) -0.0066(8)
F7 0.0194(13) 0.0328(16) 0.0209(13) 0 0.0124(11) 0
F8 0.0188(13) 0.0202(14) 0.0151(12) 0 0.0002(10) 0
F9 0.0301(12) 0.0469(15) 0.0323(12) -0.0084(11) 0.0096(10) -0.0237(11)
F10 0.0245(14) 0.0430(19) 0.0167(13) 0 0.0053(11) 0
N1 0.0148(17) 0.0149(18) 0.0169(18) 0 0.0012(14) 0
C1 0.0147(19) 0.026(2) 0.015(2) 0 0.0051(16) 0
Table A1.17. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
) for
[CF3NH3][Sb2F11].
x/a y/b z/c U(eq)
H1 0.810(12) 0.2500 0.674(10) 0.07(3)
H2 0.737(5) 0.166(6) 0.786(5) 0.027(12)
References
(1) Christe, K. O.; Wilson, W. W.; Sheehy, J. A.; Boatz, J. A. N5+: A Novel Homoleptic
Polynitrogen Ion as a High Energy Density Material. Angew. Chem. Int. Ed. 1999, 38 (13–14),
2004–2009. https://doi.org/10.1002/(SICI)1521-3773(19990712)38:13/14<2004::AID-
ANIE2004>3.0.CO;2-7.
(2) Coleman, G. H.; Leeper, R. W.; Schulze, C. C.; Scortt, L. D.; Fernelius, W. C. Cyanogen
Chloride. In Inorganic Syntheses; John Wiley & Sons, Inc., 2007; pp 90–94.
https://doi.org/10.1002/9780470132333.ch25.
119
(3) Jennings, W. L.; Scott, W. B. The Preparation of Cyanogen Chloride. J. Am. Chem. Soc.
1919, 41, 1241–1248. https://doi.org/10.1021/ja02229a011.
(4) McMorris, J.; Badger, R. M. The Heat of Combustion, Entropy and Free Energy of
Cyanogen Gas. J. Am. Chem. Soc. 1933, 55, 1952–1957. https://doi.org/10.1021/ja01332a025.
(5) Mercier, H. P. A.; Sanders, J. C. P.; Schrobilgen, G. J.; Tsai, S. S. The
Oxotrifluoroxenon(VI) Cation: X-Ray Crystal Structure of XeOF3+SbF6- and a Solution Oxygen-
17 and Xenon-129 Nuclear Magnetic Resonance Study of the O-17, O-18-Enriched XeOF3+
Cation. Inorg. Chem. 1993, 32 (4), 386–393. https://doi.org/10.1021/ic00056a009.
(6) SAINT +; Bruker AXS: Madison, WI, 2011.
(7) SADABS; Bruker AXS: Madison, WI, 2012.
(8) C. B. Hubschle, G. M. S., B. Dittrich. J Appl Crystallogr 2011, No. 44, 1281–1284.
(9) Sheldrick, G. M. Acta Crystallogr Sect A 2008, No. 64, 112–122.
(10) Sheldrick, G. M. Acta Crystallogr Sect C 2015, No. 71, 3–8.
(11) Sheldrick, G. M. SHELXL; 2012.
(12) SHELXTL; Bruker AXS: Madison, WI, 2014.
(13) Farrugia, L. J. ORTEP-3 for Windows - a Version of ORTEP-III with a Graphical User
Interface (GUI). J. Appl. Crystallogr. 1997, 30 (5–1), 565–565.
https://doi.org/10.1107/S0021889897003117.
120
APPENDIX 2: ADDITIONAL INFORMATION FOR THE
SYNTHESIS OF [NH
2
CFNH
2
]
+
AND [NH
2
CNH]
+
(CHAPTER 3)
Experimental Details
Caution! Anhydrous HF can cause severe burns and contact with the skin must be avoided. AsF5
is volatile and highly poisonous and should only be handled in a well ventilated fume hood.
Appropriate safety precautions should be taken when working with these materials.
Materials and apparatus: All reactions were carried out in either teflon-FEP ampules or NMR
tubes that were closed by stainless steel valves. Volatile materials were handled in a stainless
steel/Teflon-FEP vacuum line.
1
Reaction vessels were passivated with ClF3 then conditioned with
HF prior to use. Nonvolatile materials were handled in the dry nitrogen atmosphere of a glove box.
HF was dried by storage over BiF5. AsF5 was prepared from AsF3 and F2.
2[3]
SbF5 (Ozark
Mahoning) was freshly distilled before use. NH2CN (Alfa Aesar) was dried in vacuo overnight
prior to use. SO2 (Matheson) was dried over CaH2 before use.
The NMR spectra were recorded on a Bruker AMX-500, Varian NMRS-600, or a Varian NMRS-
500. Spectra were externally referenced to neat nitromethane for
14
N NMR spectra, neat
tetramethylsilane for
1
H and
13
C NMR spectra, and to 80% CFCl3 in chloroform-d for
19
F NMR
spectra.
Crystal Structure determinations: The single-crystal X-ray diffraction data were collected on a
Bruker SMART APEX DUO 3-circle platform diffractometer, equipped with an APEX II CCD,
121
using Mo Kα radiation (TRIUMPH curved-crystal monochromator) from a fine-focus tube. The
diffractometer was equipped with an Oxford Cryosystems Cryostream 700 apparatus for low-
temperature data collection. The frames were integrated using the SAINT algorithm to give the hkl
files corrected for Lp/decay.
3
The absorption correction was performed using the SADABS
program.
4
The structures were solved by the direct method and refined on F
2
using the Bruker
SHELXTL Software Package and ShelXle.
5–9
All nonhydrogen atoms were refined
anisotropically. ORTEP drawings were prepared using the ORTEP-3 for Windows V2.02
program.
10
[NH2CFNH2][AsF6]: Method 1: NH2CN (119 mg, 2.83 mmol) was added to a Teflon-FEP ampule
after which HF (4.0 mL) was added in vacuo at -196˚C. The colorless solution was allowed to
warm to ambient temperature and stirred for 48 h. AsF5 (2.87 mmol) was added to the reaction
mixture in vacuo at -196 ˚C and allowed to warm to ambient temperature for 0.5 h. Removal of
the volatile compounds in vacuo, first at -64˚C, then at ambient temperature resulted in a colorless
crystalline solid. (710 mg, mass expected for 2.83 mmol [NH2CFNH2][AsF6] = 713 mg) Method
2: AsF5 (255 mg, 1.50 mmol) and HF (3 g) were condensed into a Teflon-FEP ampule at -196°C.
The superacidic mixture was briefly warmed to 10°C. Then it was cooled back to -196°C and
bis(trimethylsilyl) carbodiimide was added under N2 (186 mg, 1.00 mmol). The reaction mixture
was warmed to 0°C for 15 min then cooled to -78°C and the volatile materials removed in vacuo
at -78°C resulting in a colorless crystalline solid in quantitative yield.
1
H NMR: (HF, unlocked, -40˚C) δ = 7.21 (t, broad); 6.74 (1:1:1 t,
1
JNH = 55 Hz, [
[7]
NH4]
+
).
13
C
NMR: (HF, unlocked, -40˚C) δ = 160.3 (d,
1
JCF = 271 Hz, [NH2CFNH2]
+
); 116.2 (q,
1
JCF = 278
Hz, [CF3NH3]
+
).
14
N NMR: (HF, unlocked, -30˚C) δ = -300.5 (t, J = 60 Hz, Δυ1/2 = 170 Hz
122
[NH2CFNH2]
+
); -321.4 (s, Δυ1/2 = 158 Hz, [CF3NH3]
+
).
19
F NMR: (HF, unlocked, -40˚C) δ = -
58.2 (t,
3
JFH(trans) = 33.3 Hz, [NH2CFNH2]
+
); -64.2 (s, [CF3NH3]
+
).
[NH2CFNH2][SbnF5n+1] (n = 1,2): In a FEP reactor at -196°C 1.00 mmol antimony pentafluoride
(SbF5; 217 mg) and hydrogen fluoride (HF; 3.00g) was condensed in excess. The mixture was
briefly warmed to 10 °C then cooled again to -196°C and 1.00 mmol of
bis(trimethylsilyl)carbodiimide (C7H18N2Si; 186 mg) was added under N2 flow. The reactor was
heated to 0°C for 15 min and then cooled to -78°C and volatile materials removed in vacuo.
Colorless, moisture-sensitive crystals were obtained in quantitative yield.
[ND2CFND2][AsF6]: AsF5 (255 mg, 1.50 mmol) and DF (3 g) were condensed into a Teflon-FEP
ampule at -196°C. The superacidic mixture was briefly warmed to 10°C. Then it was cooled back
to -196°C and bis(trimethylsilyl) carbodiimide was added under N2 (186 mg, 1.00 mmol). The
reaction mixture was warmed to 0°C for 15 min then cooled to -78°C and the volatile materials
removed in vacuo at -78°C resulting in a colorless crystalline solid in quantitative yield.
[NH2CNH][SbF6]: Method 1: NH2CN (60.0 mg, 1.43 mmol) was added to a Teflon-FEP ampule.
To a separate Teflon-FEP ampule a superacidic solution of SbF5 (934 mg, 4.31 mmol) and HF (2.0
mL) was prepared and mixed briefly at ambient temperature. The solution was then cooled to -
64˚C and transferred under N2 flow to the ampule containing NH2CN at -196˚C with Teflon septa
and cannula. When the transfer was complete, the ampule was warmed to -78˚C. As the mixture
began to melt, the volatile compounds were removed in vacuo at -78˚C, resulting in colorless
123
crystals. Method 2: SbF5 (217 mg, 1.00 mmol) and HF (3 g) were condensed into a Teflon-FEP
ampule at -196°C. The superacidic mixture was briefly warmed to 10°C. Then it was cooled back
to -196°C and bis(trimethylsilyl) carbodiimide was added under N2 (186 mg, 1.00 mmol). The
reaction mixture was warmed to -50°C for 10 min then cooled to -78°C and the volatile materials
removed in vacuo at -78°C resulting in colorless crystals.
14
N NMR: (SO2, -65˚C) δ = -262 (d, J = 78 Hz, Δυ1/2 = 195 Hz, [NH2CNH]
+
); -350 (s, Δυ1/2 = 700
Hz, [NH2CNH]
+
).
[NA2CNA][AsF6]: AsF5 (170 mg, 1.00 mmol) and DF or HF (3 g) were condensed into a Teflon-
FEP ampule at -196°C. The superacidic mixture was briefly warmed to 10°C. Then it was cooled
back to -196°C and bis(trimethylsilyl) carbodiimide was added under N2 (186 mg, 1.00 mmol).
The reaction mixture was warmed to -55°C for 10 min then cooled to -78°C and the volatile
materials removed in vacuo at -78°C resulting in a colorless crystalline solid in quantitative yield.
124
Vibrational Analysis
Table A2.1. Summary of the experimental and computational vibrational spectra and their assignments. (*) denotes
frequencies due to incompletely deuterated isotopomers.
1
indicates vibrational mode due to [NH2CNH]
+
due to
incomplete reaction.
125
Table A2.2. Summary of the experimental and computational vibrational spectra and their assignments. (*) denotes
frequencies due to incompletely deuterated isotopomers.
126
Crystallographic Details
Figure A2.1. Packing diagram of [NH2CFNH2][SbF6]. View normal to the 100 direction.
Figure A2.2. Packing diagram of [NH2CFNH2][SbF6]. View normal to the 010 direction.
127
Figure A2.3. Packing diagram of [NH2CFNH2][SbF6]. View normal to the 001 direction.
128
Table A2.3. Crystal data and structure refinement for [NH2CFNH2][SbF6].
Identification code NH2CFNH2
Empirical formula C H4 F7 N2 Sb
Formula weight 298.81 g/mol
Temperature 100(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P 1 21/c 1
Unit cell dimensions a = 5.0968(11) Å α = 90°
b = 17.882(4) Å β = 105.362(3)°
c = 7.8663(17) Å γ = 90°
Volume 691.3(3) Å
3
Z 4
Density (calculated) 2.871 g/cm
3
Absorption coefficient 4.070 mm
-1
F(000) 552
Crystal size 0.42 x 0.42 x 0.56 mm
3
Theta range for data collection 2.28 to 30.25°
Index ranges
-7<=h<=7, -25<=k<=25, -
11<=l<=11
Reflections collected 16296
Independent reflections 2063 [R(int) = 0.0472]
Completeness to theta = 30.25° 100.0%
Absorption correction Multiscan
Max. and min. transmission 0.7461 and 0.5106
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 2063 / 0 / 116
Goodness-of-fit on F
2
1.355
Final R indices [I>2sigma(I)] R1 = 0.0223, wR2 = 0.0555
R indices (all data) R1 = 0.0225, wR2 = 0.0556
Largest diff. peak and hole 0.485 and -1.555
129
Table A2.4. Atomic coordinates (x10
4
) and equivalent isotropic displacement parameters
(Å
2
x10
3
) for [NH2CFNH2][SbF6].
U(eq) is defined as one third of the trace of the orthogonalized U
ij
tensor.
x y z U(eq)
F2 3004(3) 2684(1) 3343(2) 17(1)
N2 9108(5) 1647(1) 4074(3) 13(1)
F3 8094(3) 3124(1) 4744(2) 17(1)
F4 6645(3) 4529(1) 3855(2) 16(1)
F7 4160(3) 3735(1) 5852(2) 15(1)
F6 5479(4) 3461(1) 1401(2) 19(1)
F5 1533(3) 4097(1) 2576(2) 16(1)
Sb1 4831(1) 3608(1) 3624(1) 8(1)
F1 7507(3) 503(1) 4180(2) 15(1)
N1 10535(5) 642(1) 2642(3) 15(1)
C1 9117(5) 952(1) 3603(3) 11(1)
130
Table A2.5. Bond lengths (Å) and angles (°) for [NH2CFNH2][SbF6].
F2-Sb1 1.8815(16)
N2-C1 1.296(3)
F3-Sb1 1.8750(16)
F4-Sb1 1.8735(16)
F7-Sb1 1.8864(16)
F6-Sb1 1.8813(16)
F5-Sb1 1.8802(16)
F1-C1 1.313(3)
N1-C1 1.301(3)
F4-Sb1-F3 90.36(7)
F4-Sb1-F5 89.69(7)
F3-Sb1-F5 178.01(7)
F4-Sb1-F6 90.54(8)
F3-Sb1-F6 91.17(8)
F5-Sb1-F6 90.82(8)
F4-Sb1-F2 178.88(7)
F3-Sb1-F2 89.98(8)
F5-Sb1-F2 90.01(7)
F6-Sb1-F2 88.38(8)
F4-Sb1-F7 90.57(7)
F3-Sb1-F7 88.58(8)
F5-Sb1-F7 89.44(7)
F6-Sb1-F7 178.86(8)
F2-Sb1-F7 90.51(7)
N2-C1-N1 128.3(2)
N2-C1-F1 116.0(2)
N1-C1-F1 115.8(2)
131
Table A2.6. Anisotropic displacement parameters (Å
2
x10
3
) for [NH2CFNH2][SbF6].
The anisotropic displacement factor exponent takes the form:
-2π
2
[ h
2
a
*2
U
11
+ ... + 2 h k a
*
b
*
U
12
]
U
11
U
22
U
33
U
23
U
13
U
12
F2 19(1) 10(1) 23(1) -3(1) -3(1) -6(1)
N2 15(1) 10(1) 15(1) 0(1) 0(1) -1(1)
F3 13(1) 15(1) 22(1) -0(1) -0(1) 5(1)
F4 17(1) 10(1) 21(1) -0(1) -0(1) -4(1)
F7 17(1) 19(1) 11(1) -2(1) -2(1) 1(1)
F6 21(1) 27(1) 14(1) -5(1) -5(1) -6(1)
F5 13(1) 17(1) 17(1) 2(1) 2(1) 3(1)
Sb1 9(1) 7(1) 9(1) -0(1) -0(1) -0(1)
F1 19(1) 13(1) 17(1) 0(1) 0(1) -5(1)
N1 17(1) 14(1) 16(1) 0(1) 0(1) 1(1)
C1 11(1) 11(1) 10(1) 1(1) 1(1) -2(1)
Table A2.7. Hydrogen coordinates (x10
4
) and isotropic displacement parameters (Å
2
x10
3
) for
[NH2CFNH2][SbF6].
x y z U(eq)
H1 10250 160 2450 30
H2 11400 920 2210 35
H3 10090 1940 3740 28
H4 8140 1810 4750 16
132
Figure A2.4. Packing diagram of [NH2CNH][SbF6]. View normal to the 100 direction.
Figure A2.5. Packing diagram of [NH2CNH][SbF6]. View normal to the 010 direction.
133
Figure A2.6. Packing diagram of [NH2CNH][SbF6]. View normal to the 001 direction.
Table A2.8. Sample and crystal data for [NH2CNH][SbF6].
Identification code [NH2CNH][SbF6]
Chemical formula CH3F6N2Sb
Formula weight 278.80 g/mol
Temperature 100(2) K
Wavelength 0.71073 Å
Crystal size 0.126 x 0.270 x 0.291 mm
Crystal system triclinic
Space group P -1
Unit cell dimensions a = 5.1190(7) Å α = 82.148(2)°
b = 6.7214(9) Å β = 88.802(2)°
c = 9.4169(13) Å γ = 81.624(2)°
Volume 317.54(7) Å
3
Z 2
Density (calculated) 2.916 g/cm
3
Absorption coefficient 4.397 mm
-1
F(000) 256
134
Table A2.9. Data collection and structure refinement for [NH2CNH][SbF6].
Diffractometer Bruker APEX DUO
Radiation source fine-focus tube, MoKα
Theta range for data collection 2.18 to 30.50°
Index ranges -7<=h<=7, -9<=k<=9, -13<=l<=13
Reflections collected 7244
Independent reflections 1909 [R(int) = 0.0275]
Coverage of independent
reflections
97.9%
Absorption correction multi-scan
Max. and min. transmission 0.6070 and 0.3610
Structure solution technique direct methods
Structure solution program SHELXTL XT 2013/1 (Bruker AXS, 2014)
Refinement method Full-matrix least-squares on F
2
Refinement program SHELXTL XL 2014/7 (Bruker AXS, 2014)
Function minimized Σ w(Fo
2
- Fc
2
)
2
Data / restraints / parameters 1909 / 0 / 103
Goodness-of-fit on F
2
1.124
Δ/σmax 0.001
Final R indices 1844 data; I>2σ(I) R1 = 0.0182, wR2 = 0.0453
all data R1 = 0.0191, wR2 = 0.0458
Weighting scheme
w=1/[σ
2
(Fo
2
)+(0.0263P)
2
+0.0664P]
where P=(Fo
2
+2Fc
2
)/3
Largest diff. peak and hole 1.099 and -1.586 eÅ
-3
R.M.S. deviation from mean 0.158 eÅ
-3
135
Table A2.10. Atomic coordinates and equivalent isotropic atomic displacement parameters (Å
2
)
for [NH2CNH][SbF6].
U(eq) is defined as one third of the trace of the orthogonalized U ij tensor.
x/a y/b z/c U(eq)
C1 0.9251(4) 0.7870(3) 0.6840(2) 0.0135(4)
N1 0.8448(4) 0.7975(3) 0.5688(2) 0.0225(4)
N2 0.9996(3) 0.7954(3) 0.81110(19) 0.0133(3)
F1 0.7074(2) 0.5714(2) 0.36450(13) 0.0146(2)
F2 0.5973(3) 0.95328(19) 0.24794(14) 0.0149(2)
F3 0.2073(2) 0.7418(2) 0.32506(14) 0.0165(2)
F4 0.4170(3) 0.4553(2) 0.16919(15) 0.0165(2)
F5 0.8049(2) 0.6701(2) 0.08806(13) 0.0147(2)
F6 0.3054(3) 0.8457(2) 0.04647(14) 0.0159(2)
Sb1 0.50272(2) 0.70655(2) 0.20444(2) 0.00858(5)
Table A2.11. Bond lengths (Å) for [NH2CNH][SbF6].
C1-N1 1.158(3) C1-N2 1.275(3)
N1-H1 0.83(4) N2-H2 0.88(3)
N2-H3 0.83(3) F1-Sb1 1.8997(12)
F2-Sb1 1.8921(13) F3-Sb1 1.8790(12)
F4-Sb1 1.8790(13) F5-Sb1 1.8833(12)
F6-Sb1 1.8749(12)
Table A2.12. Bond angles (°) for [NH2CNH][SbF6].
N1-C1-N2 173.6(2) C1-N1-H1 136.(3)
C1-N2-H2 116.(2) C1-N2-H3 119.(2)
H2-N2-H3 124.(3) F6-Sb1-F4 92.15(6)
F6-Sb1-F3 91.01(6) F4-Sb1-F3 90.47(6)
F6-Sb1-F5 90.48(6) F4-Sb1-F5 90.05(6)
F3-Sb1-F5 178.41(5) F6-Sb1-F2 90.55(6)
F4-Sb1-F2 177.29(5) F3-Sb1-F2 89.25(6)
F5-Sb1-F2 90.15(6) F6-Sb1-F1 178.53(5)
F4-Sb1-F1 89.25(6) F3-Sb1-F1 89.45(6)
F5-Sb1-F1 89.05(6) F2-Sb1-F1 88.06(6)
136
Table A2.13. Anisotropic atomic displacement parameters (Å
2
) for [NH2CNH][SbF6].
The anisotropic atomic displacement factor exponent takes the form: -2π
2
[ h
2
a
*2
U11 + ... + 2 h k
a
*
b
*
U12 ]
U11 U22 U33 U23 U13 U12
C1 0.0141(8) 0.0101(9) 0.0158(9) -0.0020(7) 0.0009(7) -0.0001(7)
N1 0.0299(10) 0.0228(10) 0.0137(8) -0.0061(7) -0.0033(7) 0.0033(8)
N2 0.0134(8) 0.0152(9) 0.0121(8) -0.0026(7) -0.0018(6) -0.0041(7)
F1 0.0157(6) 0.0159(6) 0.0113(5) -0.0002(4) -0.0045(4) -0.0004(4)
F2 0.0175(6) 0.0121(6) 0.0167(6) -0.0043(5) -0.0018(5) -0.0051(4)
F3 0.0120(6) 0.0217(7) 0.0162(6) -0.0041(5) 0.0040(4) -0.0030(5)
F4 0.0190(6) 0.0127(6) 0.0201(6) -0.0052(5) -0.0005(5) -0.0075(5)
F5 0.0111(5) 0.0200(6) 0.0135(6) -0.0039(5) 0.0027(4) -0.0033(4)
F6 0.0155(6) 0.0187(6) 0.0129(6) 0.0005(5) -0.0054(4) -0.0024(5)
Sb1 0.00845(7) 0.00971(8) 0.00821(7) -0.00169(5) -0.00095(5) -0.00277(5)
Table A2.14. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
)
for [NH2CNH][SbF6].
x/a y/b z/c U(eq)
H1 0.865(8) 0.725(6) 0.504(4) 0.051(11)
H2 1.141(6) 0.853(5) 0.819(3) 0.026(8)
H3 0.919(6) 0.743(5) 0.880(3) 0.020(7)
References
(1) K. O. Christe, R. D. W., C. J. Schack, D. D. Desmarteau. In Inorganic Syntheses; Wiley:
New York, 1986; pp 3–6.
(2) SAINT +; Bruker AXS: Madison, WI, 2011.
(3) Mercier, H. P. A.; Sanders, J. C. P.; Schrobilgen, G. J.; Tsai, S. S. The
Oxotrifluoroxenon(VI) Cation: X-Ray Crystal Structure of XeOF3+SbF6- and a Solution Oxygen-
17 and Xenon-129 Nuclear Magnetic Resonance Study of the O-17, O-18-Enriched XeOF3+
Cation. Inorg Chem 1993, 32 (4), 386–393. https://doi.org/10.1021/ic00056a009.
(4) SADABS; Bruker AXS: Madison, WI, 2012.
137
(5) C. B. Hubschle, G. M. S., B. Dittrich. J. Appl. Crystallogr. 2011, No. 44, 1281–1284.
(6) Sheldrick, G. M. Acta Crystallogr. Sect. A 2008, No. 64, 112–122.
(7) Sheldrick, G. M. Acta Crystallogr. Sect. C 2015, No. 71, 3–8.
(8) Sheldrick, G. M. SHELXL; 2012.
(9) SHELXTL; Bruker AXS: Madison, WI, 2014.
(10) Farrugia, L. J. ORTEP-3 for Windows - a Version of ORTEP-III with a Graphical User
Interface (GUI). Journal of Applied Crystallography 1997, 30 (5–1), 565–565.
https://doi.org/10.1107/S0021889897003117.
138
APPENDIX 3: ADDITIONAL INFORMATION FOR THE
SYNTHESIS OF PRIMARY PERFLUORINATED
ALCOHOLS (CHAPTER 4)
Experimental Details
Materials and apparatus
All reactions were carried out in either Teflon-FEP ampules or NMR tubes that were closed by
stainless steel valves. Volatile materials were handled in a stainless steel/Teflon-FEP vacuum line.
1
Reaction vessels and the vacuum line were passivated with ClF3 then conditioned with HF prior to
use. Nonvolatile materials were handled in the dry nitrogen atmosphere of a glove box. HF (Galaxy
Chemicals) was dried by storage over BiF5.
2
The NMR spectra were recorded on Varian NMRS-
500 or Varian NMRS-600 spectrometers. Spectra were externally referenced to neat
tetramethylsilane for
1
H and
13
C NMR spectra, and to 80% CFCl3 in chloroform-d for
19
F NMR
spectra.
General Procedure 1 (GP1)
A 4mm. o.d. FEP tube was calibrated volumetrically. It was attached to a stainless-steel valve and
evacuated for 1 h prior to use. RfCOF (Rf = F, CF3, C2F5) was condensed into the tube at -196°C,
followed by anhydrous HF. The tube was heat sealed, and briefly warmed so that the volume of
liquid HF at room temperature could be determined. The tube was placed in a cryostat until a
sufficient equilibration time had been achieved after which the sample was placed into the
precooled NMR instrument. Each temperature point was approached from both a warmer and a
139
colder temperature.
19
F spectra were integrated to determine the relative equilibrium
concentrations of RfCF2OH and RfCOF. Using the known initial amount of RfCOF, the exact
equilibrium concentrations were calculated. The total volume of the solution was assumed to be
constant throughout the temperature window considered.
COF2 + HF CF3OH
(Higher Concentration): Sample was prepared according to GP1. Sample preparation details: 0.456
mmol of COF2, 0.70 mL HF.
Table A3.1. Summary of temperature-dependent equilibrium data for COF2 + HF CF3OH
(higher concentration).
Warming
Temp °C [CF₃OH]/[COF₂] Keq
-62 2.53 5.17E-02
-49 1.90 3.89E-02
-39 1.39 2.83E-02
-30 1.09 2.23E-02
-18 0.78 1.59E-02
-10 0.65 1.33E-02
2 0.48 9.76E-03
Cooling
Temp °C [CF₃OH]/[COF₂] Keq
-61 2.43 7.42E-02
-49 2.13 6.50E-02
-49 2.00 6.11E-02
-39 1.49 4.54E-02
-30 0.91 2.76E-02
-28 1.11 3.40E-02
-20 0.81 2.48E-02
-10 0.67 2.05E-02
0 0.48 1.46E-02
10 0.37 1.14E-02
140
COF2 + HF CF3OH
(Lower Concentration): Sample was prepared according to GP1. Sample preparation details: 0.260
mmol of COF2, 0.61 mL HF.
Table A3.2. Summary of temperature-dependent equilibrium data for COF2 + HF CF3OH
(lower concentration).
Warming
Temp °C [CF₃OH]/[COF₂] Keq
-57 2.41 4.89E-02
-49 2.05 4.16E-02
-48 2.05 4.17E-02
-39 1.52 3.09E-02
-30 1.16 2.35E-02
-23 0.77 1.57E-02
-9 0.59 1.19E-02
0 0.46 9.39E-03
10 0.38 7.73E-03
Cooling
Temp °C [CF₃OH]/[COF₂] Keq
-56 2.36 4.79E-02
-48 2.08 4.23E-02
-37 1.28 2.60E-02
-30 1.06 2.16E-02
-20 0.84 1.69E-02
-8 0.58 1.18E-02
0 0.46 9.28E-03
10 0.36 7.36E-03
141
CF3COF + HF C2F5OH
(Higher Concentration): Sample was prepared according to GP1. Sample preparation details: 1.00
mmol CF3COF, 0.49 mL HF.
Table A3.3. Summary of temperature-dependent equilibrium data for CF3COF + HF
CF3CF2OH (higher concentration).
Warming
Temp °C [C₂F₅OH]/[CF₃COF] Keq
-58 0.891 1.84E-02
-56 0.925 1.91E-02
-49 0.712 1.46E-02
-39 0.472 9.66E-03
-29 0.374 7.64E-03
-18 0.279 5.69E-03
-9 0.225 4.58E-03
0 0.186 3.78E-03
9 0.155 3.15E-03
Cooling
Temp °C [C₂F₅OH]/[CF₃COF] Keq
-59 0.961 1.98E-02
-49 0.629 1.29E-02
-38 0.525 1.08E-02
-30 0.419 8.57E-03
-21 0.310 6.32E-03
-8 0.229 4.66E-03
0 0.184 3.74E-03
10 0.151 3.07E-03
142
CF3COF + HF C2F5OH
(Lower Concentration): Sample was prepared according to GP1. Sample preparation details: 0.260
mmol CF3COF, 0.66 mL HF.
Table A3.4. Summary of temperature-dependent equilibrium data for CF3COF + HF
CF3CF2OH (lower concentration).
Warming
Temp °C [C₂F₅OH]/[CF₃COF] Keq
-56.3 0.993 2.01E-02
-48.8 0.745 1.51E-02
-38.6 0.507 1.03E-02
-29 0.408 8.26E-03
-18.3 0.277 5.61E-03
-8.7 0.240 4.86E-03
-0.3 0.194 3.92E-03
8.5 0.162 3.28E-03
Cooling
Temp °C [C₂F₅OH]/[CF₃COF] Keq
-58.8 0.908 1.84E-02
-49.1 0.671 1.36E-02
-38.1 0.554 1.12E-02
-29.5 0.420 8.50E-03
-21 0.332 6.72E-03
-8.3 0.236 4.77E-03
-0.3 0.192 3.88E-03
9.5 0.158 3.20E-03
143
C2F5COF + HF C3F7OH
(Higher Concentration): Sample was prepared according to GP1. Sample preparation details: 1.00
mmol C2F5COF, 0.50 mL HF.
Table A3.5. Summary of temperature-dependent equilibrium data for CF3CF2COF + HF
CF3CF2CF2OH (higher concentration).
Warming
Temp °C [C₃F₇OH]/[C₂F₅COF] Keq
-57 7.09E-02 1.44E-03
-49 5.37E-02 1.09E-03
-39 4.89E-02 9.89E-04
-30 4.50E-02 9.11E-04
-18 4.05E-02 8.20E-04
-9 2.92E-02 5.90E-04
0 2.89E-02 5.85E-04
9 2.35E-02 4.74E-04
25 2.01E-02 4.07E-04
Cooling
Temp °C [C₃F₇OH]/[C₂F₅COF] Keq
-58 7.33E-02 1.48E-03
-48 5.83E-02 1.18E-03
-37 4.24E-02 8.58E-04
-30 4.21E-02 8.52E-04
-20 3.77E-02 7.63E-04
-8 2.89E-02 5.84E-04
0 2.70E-02 5.46E-04
10 2.33E-02 4.71E-04
144
C2F5COF + HF C3F7OH
(Lower Concentration): Sample was prepared according to GP1. Sample preparation details: 0.250
mmol C2F5COF, 0.63 mL HF.
Table A3.6. Summary of temperature-dependent equilibrium data for CF3CF2COF + HF
CF3CF2CF2OH (lower concentration).
Warming
Temp °C [C₃F₇OH]/[C₂F₅COF] Keq
-59 8.02E-02 1.62E-03
-48 6.60E-02 1.33E-03
-39 4.89E-02 9.88E-04
-30 4.59E-02 9.28E-04
-18 3.83E-02 7.74E-04
-9 3.12E-02 6.31E-04
0 2.80E-02 5.65E-04
9 2.40E-02 4.84E-04
Cooling
Temp °C [C₃F₇OH]/[C₂F₅COF] Keq
-58 8.10E-02 1.64E-03
-49 6.73E-02 1.36E-03
-37 4.82E-02 9.75E-04
-30 4.78E-02 9.65E-04
-20 4.00E-02 8.08E-04
-8 3.00E-02 6.07E-04
0 2.60E-02 5.26E-04
145
NMR Results
Preparation of CF3OH, CF3CF2OH and CF3CF2CF2OH NMR samples
Anhydrous HF (~ 0.5 mL) was condensed on a vacuum line at −196°C into a passivated and tared
4 mm Teflon-FEP ampule, which was closed by a stainless steel valve. The HF in the ampule was
allowed to warm to ambient temperature and the exact amount of HF was determined by weight.
The ampule was connected to the vacuum line, cooled to –196°C and RfCOF (Rf = F, CF3, CF3CF2)
(~ 1–2 mmol) was condensed. The Teflon-FEP ampule containing a frozen mixture of HF and
RfCOF was heat-sealed, warmed to ambient temperature and once again weight to determine the
exact amount of RfCOF. The sealed tube was placed in a cooling bath at –65°C for 2 days for
COF2, 14 days for CF3COF and 16 days for CF3CF2COF. CF3OH: HF (31.4 mmol); COF2 (2.76
mmol); CF3CF2OH: HF (29.0 mmol); CF3COF (1.41 mmol); CF3CF2CF2OH: HF (30.1 mmol);
CF3CF2COF (2.65 mmol).
Preparation of CF3OH2
+
, CF3CF2OH2
+
and CF3CF2CF2OH2
+
NMR samples
Anhydrous HF (~ 0.75 mL) was condensed into a tared 9 mm Teflon-FEP ampule containing a
frozen sample of SbF5 (~ 1–2 mmol) at -196˚C. The mixture was allowed to warm to ambient
temperature to form a clear colourless solution and the exact amount of HF added was determined
by weight. The solution was cooled to -64˚C and, under a stream of dry nitrogen using an 18 gauge
FEP tubing, transferred into a passivated 4 mm Teflon-FEP ampule cooled to -78 ˚C. RfCOF (Rf
= F, CF3, CF3CF2) (~ 1 mmol) were condensed on a vacuum line at −196 °C into the 4 mm Teflon-
FEP ampule containing the cooled HF/SbF5 mixture. The Teflon-FEP ampule was heat-sealed,
warmed to room-temperature and once again weight to determine the exact amount of RfCOF (Rf
= F, CF3, CF3CF2). The sealed tube was placed in a cooling bath at –65 °C for 2 days for COF2,3
146
days for CF3COF and 5 days for CF3CF2COF. CF3OH2
+
: HF (43.2 mmol); SbF5 (1.61 mmol);
COF2 (0.29 mmol); CF3OH/CF3OH2
+
: HF (25.3 mmol); SbF5 (0.55 mmol); COF2 (1.08 mmol);
CF3CF2OH2
+
: HF (44.1 mmol); SbF5 (1.90 mmol) CF3COF (0.72 mmol); CF3CF2CF2OH2
+
: HF
(40.8 mmol); SbF5 (2.33 mmol); CF3CF2COF (0.71 mmol).
CF3OH
Figure A3.1.
1
H NMR spectrum COF2 + HF CF3OH.
147
Figure A3.2.
13
C NMR spectrum COF2 + HF CF3OH.
Figure A3.3.
19
F NMR spectrum COF2 + HF CF3OH.
148
Figure A3.4.
19
F-
13
C HSQC spectrum COF2 + HF CF3OH.
CF3OH/CF3OH2
+
Figure A3.5.
1
H NMR spectrum 2COF2 + 3HF + SbF5 CF3OH + [CF3OH2][SbF6].
149
Figure A3.6.
13
C NMR spectrum 2COF2 + 3HF + SbF5 CF3OH + [CF3OH2][SbF6].
Figure A3.7.
19
F NMR spectrum 2COF2 + 3HF + SbF5 CF3OH + [CF3OH2][SbF6].
150
CF3OH2
+
Figure A3.8.
1
H NMR spectrum COF2 + 2HF + SbF5 [CF3OH2][SbF6].
Figure A3.9.
13
C NMR spectrum COF2 + 2HF + SbF5 [CF3OH2][SbF6].
151
Figure A3.10.
19
F NMR spectrum COF2 + 2HF + SbF5 [CF3OH2][SbF6].
CF3CF2OH
Figure A3.11.
1
H NMR spectrum CF3COF + HF CF3CF2OH.
152
Figure A3.12.
13
C NMR spectrum CF3COF + HF CF3CF2OH.
Figure A3.13.
19
F NMR spectrum CF3COF + HF CF3CF2OH.
153
Figure A3.14.
19
F-
19
F COSY spectrum CF3COF + HF CF3CF2OH.
CF3CF2OH2
+
Figure A3.15.
1
H NMR spectrum CF3COF + 2HF + SbF5 [CF3CF2OH2][SbF6].
154
Figure A3.16.
13
C NMR spectrum CF3COF + 2HF + SbF5 [CF3CF2OH2][SbF6].
Figure A3.17.
19
F NMR spectrum CF3COF + 2HF + SbF5 [CF3CF2OH2][SbF6].
155
CF3CF2CF2OH
Figure A3.18.
1
H NMR spectrum CF3CF2COF + HF CF3CF2CF2OH.
Figure A3.19.
13
C NMR spectrum CF3CF2COF + HF CF3CF2CF2OH.
156
Figure A3.20.
13
C NMR spectrum CF3CF2COF + HF CF3CF2CF2OH.
Figure A3.21.
19
F NMR spectrum CF3CF2COF + HF CF3CF2CF2OH.
157
Figure A3.22.
19
F-
13
C HSQC spectrum CF3CF2COF + HF CF3CF2CF2OH.
CF3CF2CF2OH2
+
Figure A3.23.
1
H NMR spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6].
158
Figure A3.24.
13
C NMR spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6].
Figure A3.25.
13
C NMR spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6].
159
Figure A3.26.
19
F NMR spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6].
Figure A3.27.
19
F-
13
C HSQC spectrum CF3CF2COF + 2HF + SbF5 [CF3CF2CF2OH2][SbF6].
160
HF
Figure A3.28.
1
H NMR spectrum of HF at -60°C.
Figure A3.29.
19
F NMR spectrum of HF at -60°C.
161
HF/SbF5
Figure A3.30.
19
F NMR spectrum of HF (33.3 mmol) and SbF5 (1.5 mmol) at -60°C.
Figure A3.31.
1
H NMR spectrum of HF (33.3 mmol) and SbF5 (1.5 mmol) at -60°C.
162
References
(1) K. O. Christe, R. D. W., C. J. Schack, D. D. Desmarteau. In Inorganic Syntheses; Wiley:
New York, 1986; pp 3–6.
(2) Christe, K. O.; Wilson, W. W.; Schack, C. J. On the Syntheses and Properties of Some
Hexafluorobismuthate (V) Salts and Their in the Metathetical Synthesis of NF+4 Salts. Journal of
Fluorine Chemistry 1978, 11 (1), 71–85. https://doi.org/10.1016/S0022-1139(00)81599-7.
163
APPENDIX 4: ADDITIONAL INFORMATION FOR THE
CRYSTAL STRUCTURES OF
HEPTAFLUOROCYCLOBUTANOL AND
HEXAFLUOROCYCLOBUTANE-1,1-DIOL (CHAPTER 5)
Experimental Details
Caution! Anhydrous HF can cause severe burns. Contact with the skin must be avoided.
Materials and apparatus: All reactions were carried out in either teflon-FEP ampules or NMR
tubes that were closed by stainless steel valves. Volatile materials were handled in a stainless
steel/teflon-FEP vacuum line.(1) Reaction vessels and the vacuum line were passivated with ClF3
and then conditioned with anhydrous HF prior to use.(2) HF (Galaxy Chemicals) was dried by
storage over BiF5.(3). The NMR spectra were recorded at 258 K on a Bruker AMX-500 or a Varian
NMRS-500. Spectra were externally referenced to neat neat tetramethylsilane for
1
H and
13
C NMR
spectra, and to 80% Freon-11 in chloroform-d for
19
F NMR spectra. Raman spectra were recorded
directly in the Teflon reactors in the range 4000–80 cm
-1
on a Bruker Equinox 55 FT-RA
spectrophotometer, using a Nd-YAG laser at 1064 nm. Infrared spectra were recorded in the range
4000-400 cm
-1
on a Bruker Vertex 70 FT-IR spectrometer using a Teflon gas cell with AgCl
windows.
Crystal Structure determinations: Diffraction-quality single crystals were grown from aHF
solution by slow evaporation of the solid at -78°C under a dynamic vacuum in 9 mm o.d. thin-
walled Teflon-FEP reactors. The Teflon-FEP reactor was opened under a stream of cold N2 gas at
164
approximately -80 °C, and the crystalline contents were dropped into the lip of a low-temperature
crystal-mounting apparatus. A glass fiber, attached to a magnetic base, was used to trap a crystal
using PFPE (perfluoropolyether) oil, and to mount it on the magnetic goniometer. The single-
crystal X-ray diffraction data were collected on a Bruker SMART APEX DUO 3-circle platform
diffractometer, equipped with an APEX II CCD, using Mo Kα radiation (TRIUMPH curved-
crystal monochromator) from a fine-focus tube. The diffractometer was equipped with an Oxford
Cryosystems Cryostream 700 apparatus for low-temperature data collection. The frames were
integrated using the SAINT algorithm to give the hkl files corrected for Lp/decay.(4) The
absorption correction was performed using the SADABS program.(5) The structures were solved
by the direct method and refined on F
2
using the Bruker SHELXTL Software Package and
ShelXle.(6) All non-hydrogen atoms were refined anisotropically. ORTEP drawings were
prepared using the ORTEP-3 for Windows V2.02 program.(7)
C4F7OH: Hexafluorocyclobutanone (1.00 mmol) and HF (2.0 mL) were added in vacuo at -196˚C
into a Teflon-FEP ampule. The colorless solution was allowed to warm to ambient temperature
and stirred for 15 min. Then the reactor was cooled to -78˚C and left under dynamic vacuum until
the volatile materials were removed, and colorless crystals remained.
1
H NMR (500 MHz, HF, unlocked) OH proton not observed
13
C NMR (151 MHz, HF, unlocked) δ = 112.25 (t of m
1
JCF = 294 Hz), 104.87 (d of m,
1
JCF = 281
Hz).
19
F NMR (470 MHz, HF, unlocked) δ = -134.91 (s), -135.20-137.67 (m).
Raman (200 mW): 1012 (0.4), 702 (100.0), 443 (2.8).
165
IR (AgCl, 22 torr): 3634 (vw), 3616 (s), 1852 (m), 1426 (w), 1392 (vw), 1370 (m), 1326 (m), 1266
(vw), 1028 (s), 1008 (m), 956 (vs), 933 (w), 856 (m), 742 (w), 702 (w), 659 (m), 569 (vs).
C4F6(OH)2: When hexafluorocyclobutanol was allowed to stand in the thin-walled FEP reactor in
which it was prepared for several days, a colorless solid, rather than a liquid, was observed at 25˚C.
The water vapor that diffused through the FEP over time caused this hydrolysis reaction. The solid
was recrystallized in HF solution, which was in turn removed under dynamic vacuum at -78˚C
affording colorless crystals suitable for X-ray diffraction.
1
H NMR (500 MHz, HF, unlocked) OH protons not observed
13
C NMR (126 MHz, HF, unlocked) δ = 110.59 (t of m,
1
JCF = 299 Hz), 101.14 (m).
19
F NMR (470 MHz, HF, unlocked) δ = -133.01 – -133.28 (m), -134.15 – -134.39 (m).
166
Crystallographic Details
Figure A4.1. Packing diagram of C4F7OH. View along the 001 direction.
Figure A4.2. Packing diagram of C4F7OH. View along the 010 direction.
167
Figure A4.3. Packing diagram of C4F7OH. View along the 100 direction.
Table A4.1. Sample and crystal data for C4F7OH.
Chemical formula C4HF7O
Formula weight 198.05 g/mol
Temperature 100(2) K
Wavelength 0.71073 Å
Crystal size 0.120 x 0.210 x 0.230 mm
Crystal habit clear colourless prism
Crystal system monoclinic
Space group P 1 21/c 1
Unit cell dimensions a = 7.458(2) Å
b = 7.798(2) Å α = 90°
c = 20.307(4) Å β = 97.95(3)°
γ = 90°
Volume 1169.7(5) Å
3
Z 8
Density (calculated) 2.249 g/cm
3
Absorption coefficient 0.301 mm
-1
F(000) 768
F(000) 768
Table A4.2. Data Collection and Structure Refinement for C4F7OH.
168
Diffractometer Bruker APEX DUO
Radiation source fine-focus tube, MoKα
Theta range for data
collection
2.02 to 27.48°
Index ranges -9<=h<=9, -10<=k<=10, -26<=l<=26
Reflections collected 17718
Independent reflections 2664 [R(int) = 0.0411]
Coverage of independent
reflections
99.6%
Absorption correction multi-scan
Max. and min. transmission 0.9650 and 0.9340
Structure solution technique direct methods
Structure solution program
SHELXTL XT 2014/5 (Bruker AXS,
2014)
Refinement method Full-matrix least-squares on F
2
Refinement program SHELXL-2014/7 (Sheldrick, 2014)
Function minimized Σ w(Fo
2
- Fc
2
)
2
Data / restraints / parameters 2664 / 2 / 223
Goodness-of-fit on F
2
1.153
Final R indices 2313 data; I>2σ(I)
R1 = 0.0629, wR2 =
0.1666
all data
R1 = 0.0702, wR2 =
0.1709
Weighting scheme
w=1/[σ
2
(Fo
2
)+(0.0480P)
2
+6.0668P]
where P=(Fo
2
+2Fc
2
)/3
Largest diff. peak and hole 0.731 and -0.410 eÅ
-3
R.M.S. deviation from mean 0.111 eÅ
-3
169
Table A4.3. Atomic coordinates and equivalent isotropic atomic displacement parameters (Å
2
)
for C4F7OH.
U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
x/a y/b z/c U(eq)
C1 0.5709(5) 0.8510(5) 0.33432(17) 0.0153(7)
C2 0.7563(5) 0.9472(5) 0.34572(18) 0.0175(7)
C3 0.7761(5) 0.9063(5) 0.42126(18) 0.0185(7)
C4 0.5858(5) 0.8190(5) 0.41063(17) 0.0163(7)
F1 0.7422(3) 0.1157(3) 0.33186(12) 0.0261(5)
F2 0.4312(3) 0.9572(3) 0.31144(12) 0.0238(5)
F3 0.8839(3) 0.8786(3) 0.31423(11) 0.0256(5)
F4 0.9104(3) 0.7964(3) 0.44100(12) 0.0287(6)
F5 0.7877(3) 0.0426(3) 0.46079(11) 0.0276(6)
F6 0.5867(3) 0.6526(3) 0.42765(11) 0.0222(5)
F7 0.4622(3) 0.9022(3) 0.43974(11) 0.0244(5)
O1 0.5672(4) 0.7023(4) 0.29912(13) 0.0207(6)
C5 0.3203(5) 0.3656(5) 0.37408(17) 0.0160(7)
C6 0.1462(5) 0.2516(5) 0.36111(17) 0.0172(7)
C7 0.0265(5) 0.4119(5) 0.36971(19) 0.0191(7)
C8 0.2002(5) 0.5170(5) 0.39423(18) 0.0168(7)
F8 0.4430(3) 0.3081(3) 0.42451(11) 0.0236(5)
F9 0.1372(3) 0.1346(3) 0.40853(12) 0.0249(5)
F10 0.1185(3) 0.1761(3) 0.30185(11) 0.0226(5)
F11 0.9114(3) 0.3956(3) 0.41368(13) 0.0309(6)
F12 0.9381(3) 0.4673(3) 0.31201(13) 0.0297(6)
F13 0.2209(3) 0.5472(3) 0.45898(11) 0.0260(5)
F14 0.2173(3) 0.6636(3) 0.36115(12) 0.0237(5)
O2 0.3934(4) 0.3897(4) 0.31695(13) 0.0192(6)
Table A4.4. Bond lengths (Å) for C4F7OH.
170
C1-O1 1.361(4) C1-F2 1.362(4)
C1-C4 1.558(5) C1-C2 1.562(5)
C2-F3 1.330(4) C2-F1 1.345(4)
C2-C3 1.554(5) C3-F5 1.328(4)
C3-F4 1.337(4) C3-C4 1.562(5)
C4-F7 1.331(4) C4-F6 1.342(4)
O1-H1 0.928(19) C5-F8 1.352(4)
C5-O2 1.361(4) C5-C6 1.566(5)
C5-C8 1.570(5) C6-F10 1.330(4)
C6-F9 1.335(4) C6-C7 1.559(5)
C7-F11 1.328(4) C7-F12 1.335(4)
C7-C8 1.555(5) C8-F13 1.324(4)
C8-F14 1.341(4) O2-H2 0.930(19)
171
Table A4.5. Bond angles (°) for C4F7OH.
O1-C1-F2 112.4(3) O1-C1-C4 112.3(3)
F2-C1-C4 112.5(3) O1-C1-C2 116.1(3)
F2-C1-C2 112.2(3) C4-C1-C2 89.4(3)
F3-C2-F1 109.5(3) F3-C2-C3 114.6(3)
F1-C2-C3 113.7(3) F3-C2-C1 114.4(3)
F1-C2-C1 113.3(3) C3-C2-C1 90.5(3)
F5-C3-F4 110.4(3) F5-C3-C2 114.9(3)
F4-C3-C2 113.1(3) F5-C3-C4 114.5(3)
F4-C3-C4 113.0(3) C2-C3-C4 89.6(3)
F7-C4-F6 109.7(3) F7-C4-C1 113.9(3)
F6-C4-C1 114.1(3) F7-C4-C3 113.4(3)
F6-C4-C3 114.4(3) C1-C4-C3 90.3(3)
C1-O1-H1 110.(3) F8-C5-O2 112.5(3)
F8-C5-C6 113.4(3) O2-C5-C6 110.8(3)
F8-C5-C8 113.8(3) O2-C5-C8 115.4(3)
C6-C5-C8 88.9(3) F10-C6-F9 109.5(3)
F10-C6-C7 115.9(3) F9-C6-C7 112.4(3)
F10-C6-C5 115.1(3) F9-C6-C5 112.9(3)
C7-C6-C5 90.0(3) F11-C7-F12 109.5(3)
F11-C7-C8 115.0(3) F12-C7-C8 113.5(3)
F11-C7-C6 115.6(3) F12-C7-C6 112.5(3)
C8-C7-C6 89.7(3) F13-C8-F14 109.9(3)
F13-C8-C7 112.9(3) F14-C8-C7 115.0(3)
F13-C8-C5 113.6(3) F14-C8-C5 114.4(3)
C7-C8-C5 90.0(3) C5-O2-H2 109.(3)
172
Table A4.6. Torsion angles (°) for C4F7OH.
O1-C1-C2-F3 5.7(4) F2-C1-C2-F3 -125.5(3)
C4-C1-C2-F3 120.4(3) O1-C1-C2-F1 132.1(3)
F2-C1-C2-F1 1.0(4) C4-C1-C2-F1 -113.2(3)
O1-C1-C2-C3 -111.7(3) F2-C1-C2-C3 117.1(3)
C4-C1-C2-C3 3.0(3) F3-C2-C3-F5 122.8(3)
F1-C2-C3-F5 -4.1(4) C1-C2-C3-F5 -120.0(3)
F3-C2-C3-F4 -5.2(4) F1-C2-C3-F4 -132.1(3)
C1-C2-C3-F4 112.0(3) F3-C2-C3-C4 -120.2(3)
F1-C2-C3-C4 112.9(3) C1-C2-C3-C4 -3.0(3)
O1-C1-C4-F7 -128.8(3) F2-C1-C4-F7 -0.9(4)
C2-C1-C4-F7 113.0(3) O1-C1-C4-F6 -1.9(4)
F2-C1-C4-F6 126.0(3) C2-C1-C4-F6 -120.1(3)
O1-C1-C4-C3 115.2(3) F2-C1-C4-C3 -116.9(3)
C2-C1-C4-C3 -3.0(3) F5-C3-C4-F7 4.0(5)
F4-C3-C4-F7 131.5(3) C2-C3-C4-F7 -113.4(3)
F5-C3-C4-F6 -122.8(3) F4-C3-C4-F6 4.7(4)
C2-C3-C4-F6 119.8(3) F5-C3-C4-C1 120.4(3)
F4-C3-C4-C1 -112.1(3) C2-C3-C4-C1 3.0(3)
F8-C5-C6-F10 -116.7(3) O2-C5-C6-F10 10.9(4)
C8-C5-C6-F10 127.8(3) F8-C5-C6-F9 10.0(4)
O2-C5-C6-F9 137.7(3) C8-C5-C6-F9 -105.5(3)
F8-C5-C6-C7 124.4(3) O2-C5-C6-C7 -107.9(3)
C8-C5-C6-C7 8.9(3) F10-C6-C7-F11 115.1(4)
F9-C6-C7-F11 -11.8(5) C5-C6-C7-F11 -126.8(3)
F10-C6-C7-F12 -11.7(4) F9-C6-C7-F12 -138.6(3)
C5-C6-C7-F12 106.4(3) F10-C6-C7-C8 -127.2(3)
F9-C6-C7-C8 105.9(3) C5-C6-C7-C8 -9.0(3)
F11-C7-C8-F13 11.5(5) F12-C7-C8-F13 138.7(3)
C6-C7-C8-F13 -106.8(3) F11-C7-C8-F14 -115.6(4)
F12-C7-C8-F14 11.6(4) C6-C7-C8-F14 126.1(3)
F11-C7-C8-C5 127.3(3) F12-C7-C8-C5 -105.5(3)
C6-C7-C8-C5 9.0(3) F8-C5-C8-F13 -9.0(4)
O2-C5-C8-F13 -141.2(3) C6-C5-C8-F13 106.2(3)
F8-C5-C8-F14 118.2(3) O2-C5-C8-F14 -13.9(4)
C6-C5-C8-F14 -126.5(3) F8-C5-C8-C7 -124.2(3)
O2-C5-C8-C7 103.7(3) C6-C5-C8-C7 -8.9(3)
173
Table A4.7. Anisotropic atomic displacement parameters (Å
2
) for C4F7OH.
The anisotropic atomic displacement factor exponent takes the form:
-2π
2
[ h
2
a
*2
U11 + ... + 2 h k a
*
b
*
U12 ]
U11 U22 U33 U23 U13 U12
C1 0.0151(16) 0.0126(17) 0.0178(16) 0.0012(12) 0.0014(12) -0.0013(13)
C2 0.0161(16) 0.0175(18) 0.0193(17) -0.0007(13) 0.0039(13) -0.0034(14)
C3 0.0152(16) 0.0198(18) 0.0200(17) -0.0026(14) 0.0011(13) -0.0026(14)
C4 0.0159(16) 0.0151(17) 0.0185(17) -0.0011(13) 0.0045(13) -0.0009(13)
F1 0.0305(13) 0.0150(11) 0.0318(12) 0.0037(9) 0.0007(10) -0.0056(10)
F2 0.0146(10) 0.0246(12) 0.0316(12) 0.0094(10) 0.0011(9) 0.0045(9)
F3 0.0169(11) 0.0367(14) 0.0244(11) -0.0085(10) 0.0078(9) -0.0040(10)
F4 0.0175(11) 0.0335(14) 0.0336(13) 0.0074(11) -0.0019(9) 0.0034(10)
F5 0.0324(13) 0.0286(13) 0.0224(11) -0.0098(10) 0.0059(9) -0.0117(11)
F6 0.0255(12) 0.0176(11) 0.0230(11) 0.0052(9) 0.0013(9) -0.0036(9)
F7 0.0194(11) 0.0309(13) 0.0245(11) -0.0075(10) 0.0086(9) 0.0009(10)
O1 0.0268(14) 0.0208(14) 0.0156(12) -0.0035(10) 0.0070(10) -0.0069(11)
C5 0.0166(16) 0.0145(17) 0.0168(16) -0.0005(13) 0.0022(13) 0.0015(14)
C6 0.0170(16) 0.0171(18) 0.0183(17) 0.0022(13) 0.0052(13) 0.0016(14)
C7 0.0160(16) 0.0192(18) 0.0229(18) 0.0002(14) 0.0051(13) -0.0002(14)
C8 0.0161(16) 0.0138(17) 0.0217(17) 0.0011(13) 0.0061(13) 0.0022(13)
F8 0.0214(11) 0.0229(12) 0.0247(11) 0.0018(9) -0.0032(9) 0.0022(9)
F9 0.0239(12) 0.0217(12) 0.0306(12) 0.0102(9) 0.0090(9) 0.0008(9)
F10 0.0210(11) 0.0235(12) 0.0241(11) -0.0059(9) 0.0066(8) -0.0050(9)
F11 0.0247(12) 0.0272(13) 0.0456(15) -0.0070(11) 0.0216(11) -0.0032(10)
F12 0.0231(12) 0.0260(13) 0.0365(13) 0.0037(10) -0.0080(10) 0.0042(10)
F13 0.0266(12) 0.0308(13) 0.0211(11) -0.0068(10) 0.0056(9) 0.0011(10)
F14 0.0192(11) 0.0165(11) 0.0365(13) 0.0059(9) 0.0070(9) 0.0013(9)
O2 0.0195(13) 0.0198(14) 0.0200(13) -0.0039(10) 0.0085(10) -0.0046(11)
174
Table A4.8. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
) for
C4F7OH.
x/a y/b z/c U(eq)
H1 0.591(6) 0.724(6) 0.2563(12) 0.025
H2 0.448(6) 0.497(3) 0.318(2) 0.023
Figure A4.4. Packing diagram of C4F6(OH)2. View along the 001 direction.
175
Figure A4.5. Packing diagram of C4F6(OH)2. View along the 010 direction.
Figure A4.6. Packing diagram of C4F6(OH)2. View along the 100 direction.
Table A4.15. Anisotropic atomic displacement parameters (Å
2
) for C4F6(OH)2.
176
The anisotropic atomic displacement factor exponent takes the form: -2π
2
[ h
2
a
*2
U11 + ... + 2 h k
a
*
b
*
U12 ]
U11 U22 U33 U23 U13 U12
F1 0.0151(7) 0.0388(11) 0.0301(9) -0.0007(8) -0.0050(6) 0.0096(7)
O1 0.0132(9) 0.0213(11) 0.0226(10) -0.0033(8) 0.0011(7) -0.0014(8)
C1 0.0099(10) 0.0245(15) 0.0147(13) 0.0000(11) 0.0010(9) 0.0005(10)
C2 0.0122(11) 0.0240(15) 0.0190(13) 0.0002(11) 0.0000(10) -0.0009(10)
O2 0.0123(8) 0.0286(11) 0.0184(10) 0.0045(8) 0.0041(7) 0.0016(8)
F2 0.0222(8) 0.0360(11) 0.0283(9) -0.0012(8) 0.0000(7) -0.0146(7)
F3 0.0255(9) 0.0558(14) 0.0304(10) 0.0231(10) 0.0037(7) 0.0021(8)
C3 0.0170(12) 0.0292(15) 0.0134(13) -0.0017(12) -0.0007(10) -0.0012(11)
F4 0.0273(9) 0.0503(13) 0.0303(10) -0.0217(9) 0.0027(7) -0.0033(8)
C4 0.0119(11) 0.0265(15) 0.0154(13) -0.0008(11) 0.0020(9) 0.0000(10)
F6 0.0253(8) 0.0381(11) 0.0241(9) 0.0042(8) 0.0071(7) 0.0159(7)
F5 0.0186(8) 0.0437(11) 0.0280(9) -0.0086(8) 0.0108(7) -0.0134(7)
F7 0.0299(9) 0.0250(10) 0.0580(13) -0.0019(9) 0.0266(9) 0.0010(7)
Table A4.16. Hydrogen atomic coordinates and isotropic atomic displacement parameters (Å
2
) for
C4F6(OH)2.
x/a y/b z/c U(eq)
H1 0.770(6) 0.933(7) 0.258(2) 0.041(11)
H2 0.583(6) 0.496(7) 0.2891(19) 0.035(10)
H3 0.887(9) 0.413(12) 0.281(3) 0.11(2)
177
APPENDIX 5: ADDITIONAL INFORMATION FOR
PARTIALLY FLUORINATED GRAPHENE AS A
CATHODE CATALYST SUPPORT IN PROTON
EXCHANGE MEMBRANE FUEL CELLS (CHAPTER 6)
XRD
Figure A5.1. XRD pattern of heat treated graphene.
178
XPS
Figure A5.2. XPS survey spectra.
179
Figure A5.3. Deconvoluted C1s XPS spectrum of Pt/FG1.
Figure A5.4. Deconvoluted C1s XPS spectrum of Pt/FG2.
180
Figure A5.5. Deconvoluted C1s XPS spectrum of G.
Figure A5.6. Deconvoluted C1s XPS spectrum of Pt/G.
181
Figure A5.7. Deconvoluted Pt4f XPS spectrum of Pt/FG1.
Figure A5.8. Deconvoluted Pt4f XPS spectrum of Pt/FG2.
182
Figure A5.9. Deconvoluted Pt4f XPS spectrum of Pt/G.
183
SEM-EDS
Figure A5.10. SEM-EDS spectrum and maps FG1. Red C, Blue F, Green O.
184
Figure A5.11. SEM-EDS spectrum of FG2.
185
Figure A5.12. SEM-EDS spectrum and maps PtFG1. Red C, Blue F, Yellow Na, Green O, Pink
Pt.
186
Figure A5.13. SEM-EDS spectrum PtFG2.
187
Figure A5.14. SEM-EDS spectrum and maps of Pt/G; Red C, Green O, Blue Pt.
188
Half-Cell Data
Figure A5.15. Effect of rotation rate Pt/G under O2 10 mV/s, positive going direction.
Figure A5.16. Effect of rotation rate Pt/FG1 under O2 10 mV/s, positive going direction.
189
Figure A5.17. Kinetic current vs. Potential
Figure A5.18. Mass activity v. Potential.
190
Electrochemical Impedance Spectroscopy
Table A5.1. EIS fitting details for Pt/FG1 in 0.5M H2SO4 under O2 at 0.7 V v. RHE.
Table A5.2. EIS fitting details for Pt/FG2 in 0.5M H2SO4 under O2 at 0.7 V v. RHE.
191
Table A5.3. EIS fitting details for Pt/G in 0.5M H2SO 4 under O2 at 0.7 V v. RHE.
Table A5.4. EIS Fitting details for Pt/G fuel cell, 70°C at OCV.
192
Table A5.5. EIS fitting details for Pt/FG2 fuel cell, 70°C at OCV.
Abstract (if available)
Abstract
Broadly, this dissertation explores fluorination reactions. Chapters 2-5 involve the synthesis of fluorinated molecules, specifically exploring hydrogen fluoride addition reactions. The inspiration for this work came from the knowledge that α-fluoroalcohols and α-fluoroalkylamines are thermally unstable due to facile HF elimination and the question of whether the reverse reaction could be performed to prepare these compounds under certain conditions. Chapters 2 and 3 study HF addition reactions across the C≡N bond of cyanides and nitriles to synthesize α-fluoroalkylammonium and -iminium salts. In this case, addition of a strong Lewis acid allowed for the isolation of thermally stable ammonium or iminium salts. Chapters 4 and 5 study HF addition reactions across the C=O bond of carbonyl fluorides to synthesize perfluorinated alcohols. In Chapter 4, primary perfluorinated alcohols were synthesized at low temperature. While in Chapter 5, heptafluorocyclobutanol (hfcb) was isolated. Hfcb is the exception to the rule of thermally unstable α-fluoroalcohols as it is stabilized by its substantial ring strain. This molecule was characterized by its single crystal X-ray structure and is the first example of a crystallographically characterized α-fluoroalcohol. Chapter 6 investigates the synthesis of partially fluorinated graphene by reaction with xenon difluoride. This fluorinated material was investigated as a catalyst support for the oxygen reduction reaction in proton exchange membrane fuel cells and compared to a non-fluorinated analogue.
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University of Southern California Dissertations and Theses
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Asset Metadata
Creator
Baxter, Amanda F.
(author)
Core Title
Hydrogen fluoride addition reactions and a fluorinated cathode catalyst support material for fuel cells
School
College of Letters, Arts and Sciences
Degree
Doctor of Philosophy
Degree Program
Chemistry
Publication Date
05/18/2020
Defense Date
02/27/2020
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
catalyst support,fluorinated graphene,fuel cell,HF addition reaction,OAI-PMH Harvest,perfluorinated alcohols
Language
English
Contributor
Electronically uploaded by the author
(provenance)
Advisor
Prakash, G. K. Surya (
committee chair
), Christe, Karl O. (
committee member
), Egolfopoulos, Fokion N. (
committee member
)
Creator Email
afbaxter@usc.edu,amanda.f.baxter@gmail.com
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c89-312532
Unique identifier
UC11663614
Identifier
etd-BaxterAman-8545.pdf (filename),usctheses-c89-312532 (legacy record id)
Legacy Identifier
etd-BaxterAman-8545.pdf
Dmrecord
312532
Document Type
Dissertation
Rights
Baxter, Amanda F.
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Access Conditions
The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...
Repository Name
University of Southern California Digital Library
Repository Location
USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA
Tags
catalyst support
fluorinated graphene
fuel cell
HF addition reaction
perfluorinated alcohols