Exploring New Synthetic Routes to Frustrated Lewis Pairs

Cheryl Anne Tanur

A thesis submitted in conformity with the requirements for the degree of Master of Science Department of Chemistry University of Toronto

Cheryl Anne Tanur

Master of Science

Department of Chemistry University of Toronto

2011 Abstract

Gold(I) and copper(I) imidazolium complexes were synthesized and probed for use as bulky

Lewis acids in frustrated Lewis pairs (FLPs) with bulky phosphines and amines. Their reactivity with small molecules was investigated and the compounds were fully characterized by multinuclear NMR spectroscopy, elemental analysis and X-ray crystallography. Secondly, a new methylene-linked boron sulfur Lewis acid was synthesized. Its thermodynamic properties were determined and its reactivity with terminal and internal alkynes was demonstrated. Adducts and heterocycles of this boron sulfur system were fully characterized by multinuclear NMR spectroscopy, elemental analysis and X-ray crystallography. The application of these new systems for the activation of small molecules is described in this thesis.

Acknowledgments

First and foremost I would like to thank my supervisor, Prof. Doug Stephan, for presenting me with this wonderful opportunity to perform research in his lab. I immensely enjoyed my time at the University of Toronto and learned a lot with the aid of his ideas and suggestions about my projects. I would also like to thank Gabriel Menard and Shokei Zhao for all of their help in the lab and their willingness to help me. Moreover, I would like to thank Dr. Sharonna Greenberg, Rebecca Neu and Dr. Clinton Lund for their chemistry knowledge, Christopher Brown and Michael Sgro for their endless help with X-ray crystallography, and Dr. Zachariah Heiden for his help with the Van’t Hoff calculations. The editing help of Dr. Renan Cariou, Dr. Sharonna Greenberg, Fatme Dahcheh, Stephanie Granville, and Christopher Cap uto is also greatly appreciated. In addition, thanks to Prof. Doug Stephan and Prof. Datong Song for their final edits of this thesis. I would also like to thank everyone in the Stephan Research Group for their moral support and all of the laughs. Lastly, I want to thank my parents, my older brother Luke and my older sister Adrienne for their unwavering support throughout my life. Without them, I would not be the person I am today.

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Table of Contents

Acknowledgments...... iii

Table of Contents ...... iv

List of Tables ...... vii

List of Figures ...... vii

List of Schemes ...... x

List of Abbreviations and Symbols...... xiii

1 Introduction ...... 1

1.1 Overview of Frustrated Lewis Pairs ...... 1

1.2 Frustrated Lewis Pairs: Hydrogenation ...... 3

1.3 Frustrated Lewis Pairs: Small Molecule Activation ...... 5

1.4 Frustrated Lewis Pairs: New Directions ...... 7

2 Gold(I) and Copper(I) Imidazolium Complexes ...... 10

2.1 Introduction ...... 10

2.2 Results and Discussion ...... 13

2.2.1 Gold(I) and Copper(I) Imidazolium Complexes...... 13

2.2.2 Reactions with Small Molecules...... 24

2.3 Conclusions ...... 27

2.4 Experimental ...... 27

2.4.1 General Considerations ...... 27

2.4.2 Synthesis and Characterization of Gold(I) Imidazolium Complexes ...... 28

2.4.3 Synthesis and Characterization of Copper(I) Imidazolium Complexes ...... 31

2.4.4 Experimental Considerations for Imidazolium Complexes ...... 35

2.4.5 X-ray Data Collection, Reduction, Solution and Refinement...... 35

3 Boron-Sulfur Linked Lewis Acid...... 40

3.1 Introduction ...... 40

3.2 Results and Discussion ...... 43

3.2.1 Synthetic Routes to Boron-Sulfur Linked Lewis Acid ...... 43

3.2.2 Thermodynamics of Boron-Sulfur Linked Lewis Acid ...... 47

3.2.3 FLP Reactivity ...... 49

3.2.4 Adduct Formations...... 50

3.2.5 Reactions of Internal and Terminal Alkynes ...... 52

3.3 Conclusions ...... 61

3.4 Experimental ...... 61

3.4.1 General Considerations ...... 61

3.4.2 Synthesis and Characterization of Boron-Sulfur Linked Lewis Acid ...... 62

3.4.3 Thermodynamic Calculations for (11) ...... 65

3.4.4 Synthesis and Characterization of Phosphine Adducts...... 66

3.4.5 Synthesis and Characterization of Five-membered Boron-Sulfur Heterocycles ...68

3.4.6 X-ray Data Collection, Reduction, Solution and Refinement...... 71

4 Summary and Conclusions...... 74

Appendix A: Thermodynamic studies of B(C6F5)3·SMe2 ...... 75

A.1 Introduction ...... 75

A.2 Experimental ...... 75

A.2.1 General Considerations ...... 75

A.2.2 Synthesis of B(C6F5)3·SMe2 ...... 76

A.3 Results and Discussion ...... 76

A.3.1 Reactions with Hydrogen...... 76

A.3.2 Thermodynamics of B(C6F5)3·SMe2 ...... 78

A.4 Conclusion ...... 82

References ...... 83

List of Tables

Table 2.1 Selected bond lengths (Å) and bond angles ( ) of (1)...... 17

Table 2.2 Selected bond lengths (Å) and bond angles ( ) of (2) and (3) ...... 18

Table 2.3 Bond lengths (Å) and bond angles ( ) involved in anagostic interactions in (2) and (7) ...... 19

Table 2.4 Selected bond lengths (Å) and bond angles ( ) of (7)...... 20

Table 2.5 Selected bond lengths (Å) and bond angles ( ) of (4) and (9) ...... 22

Table 2.6 Selected bond lengths (Å) and bond angles ( ) of (10)...... 23

Table 2.7 Crystallographic data for compounds (1)–(3)...... 37

Table 2.8 Crystallographic data for compounds (4), (7) and (9) ...... 38

Table 2.9 Crystallographic data for compound (10) ...... 39

Table 3.1 Selected bond lengths (Å) and bond angles ( ) of (11)...... 46

Table 3.2 Thermodynamic parameters (ΔH , ΔS , ΔG ) of related systems ...... 48

Table 3.3 Selected bond lengths (Å) and bond angles ( ) of (13)...... 51

Table 3.4 Selected bond lengths (Å) and bond angles ( ) of (17)...... 58

Table 3.5 Data used in Van’t Hoff plot for PhSCH2B(C6F5)2 ...... 65

Table 3.6 Crystallographic data for compounds (11), (13) and (17) ...... 73

Table A.1 Data used in Van’t Hoff plot for B(C6F5)3·SMe2 ...... 80

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List of Figures

Figure 2.1 Project proposal of developing a gold FLP ...... 13

1 Figure 2.2 H NMR of (3) at room temperature in CD2Cl2 ...... 15

1 Figure 2.3 H NMR of (10) at room temperature in CD2Cl2 ...... 16

Figure 2.4 POV-ray ball and stick representation of (1) with hydrogen atoms omitted...... 16

Figure 2.5 POV-ray ball and stick representation of (2) and (3) with omitted anion and hydrogen atoms except those involved in anagostic interactions ...... 17

Figure 2.6 POV-ray ball and stick representation of (7) with hydrogen atoms omitted except those involved in anagostic interactions ...... 20

Figure 2.7 POV-ray ball and stick representation of (4) and (9) with omitted anion and hydrogen atoms ...... 21

Figure 2.8 POV-ray ball and stick representation of (10) with hydrogen atoms omitted except those involved in agostic interactions ...... 23

Figure 3.1 Target aryl linked boron-sulfur Lewis acid ...... 43

1 Figure 3.2 H NMR of (11) at room temperature in d8-toluene ...... 44

19 1 Figure 3.3 F{ H} NMR of (11) at various temperatures in d8-toluene ...... 45

Figure 3.4 POV-ray ball and stick representation of (11) with hydrogen atoms omitted...... 46

Figure 3.5 Phosphine adducts (12), (14) and hydrolysis dimer (13) ...... 50

Figure 3.6 POV-ray ball and stick representation of the hydrolysis product (13) with hydrogen atoms omitted other than PH...... 51

1 Figure 3.7 H NMR of (16) at room temperature in d8-toluene ...... 54

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19 1 Figure 3.8 F{ H} NMR of (16) at room temperature in d8-toluene ...... 54

Figure 3.9 Close up of o-fluorine and overlapping m- and p-fluorine signals in the 19F{1H} NMR of (16) at room temperature in d8-toluene illustrating inequivalent C6F5 rings ...... 55

1 Figure 3.10 H NMR of (17) at room temperature in CD2Cl2 ...... 55

1 Figure 3.11 Aromatic region in H NMR of (17) at room temperature in CD2Cl2 ...... 56

19 1 Figure 3.12 F{ H} NMR of (17) at room temperature in CD2Cl2...... 56

Figure 3.13 Close up of o-, m- and p-fluorine signals in the 19F{1H} NMR of (17) at room temperature in CD2Cl2 illustrating inequivalent C6F5 rings ...... 57

Figure 3.14 POV-ray ball and stick representation of heterocycle (17) with hydrogen atoms omitted ...... 58

Figure 3.15 Van’t Hoff plot showing the relationship between the dimer and monomer of compound (11) ...... 66

Figure A.1 VT of 1H NMR tracking the methyl shift from adduct to free dimethylsulfide ...... 78

Figure A.2 Van’t Hoff plot of B(C6F5)3·SMe2 ...... 81

List of Schemes

Scheme 1.1 Formation of a classical Lewis acid-base adduct ...... 1

Scheme 1.2 Examples of unusual reactivity which contradicts Lewis’ postulation ...... 2

Scheme 1.3 A depiction of a frustrated Lewis pair...... 2

Scheme 1.4 First example of reversible metal-free hydrogenation activation by a sterically frustrated Lewis pair ...... 3

Scheme 1.5 Catalytic cycle for the reduction of imines (R = Mes, tBu) ...... 4

Scheme 1.6 Selected examples of using the bulky Lewis acid B(C6F5)3 with a variety of bulky Lewis bases to activate hydrogen...... 4

Scheme 1.7 Examples of linked FLPs and their reactivity towards dihydrogen ...... 5

t Scheme 1.8 Activation of CO2 and N2O by P Bu3/B(C6F5)3 and ethylene linked P B system ...... 6

t Scheme 1.9 Reactions of olefins, dienes and alkynes with P Bu3/B(C6F5)3 ...... 6

Scheme 1.10 Ring-opening of THF and cyclopropylbenzene with FLPs ...... 7

Scheme 1.11 FLPs of phosphinoferrocenes and hydrogen activation ...... 8

Scheme 1.12 Hydrogenation of a bis(arylimino-Cp)ZrCl2 complex and B(C6F5)3 ...... 8

Scheme 1.13 Methanol production from the CO2 complex of PMes3 and AlX3 ...... 9

Scheme 2.1 Demonstrated cleavage of hydrogen and ammonia by CAACs...... 10

t Scheme 2.2 FLP reactivity of I Bu and B(C6F5)3 ...... 11

t Scheme 2.3 Hydrogen and amine activation by I Bu and B(C6F5)3 and adduct formation of IDipp and B(C6F5)3...... 11

Scheme 2.4 Intramolecular addition of tertiary amines to internal alkynes using a gold(I) CAAC complexes...... 12

Scheme 2.5 Cyclization reactions using FLPs ...... 12

Scheme 2.6 Synthetic route to gold(I) and copper(I) imidazolium complexes ...... 14

Scheme 2.7 Attempted FLP chemistry with compounds (2) and (3)...... 24

Scheme 2.8 CO2 insertion and C H carboxylation using a gold(I) hydroxide imidazolium complex as reported by Nolan ...... 25

Scheme 2.9 CO2 insertion and N H carboxylation using a copper(I) hydroxide imidazolium complex as reported by Nolan ...... 26

Scheme 3.1 Gabbaï’s boron-sulfur aryl linked Lewis acids and their reactivity ...... 40

t Scheme 3.2 The heterolytic cleavage of diphenyl disulfide using the Bu2P(C6F4)B(C6F5)2 linked FLP...... 41

t Scheme 3.3 Heterolytic cleavage of disulfides from P Bu3 and B(C6F5)3 ...... 41

Scheme 3.4 Reactivity of the dimethylsulfide adduct of Piers’ borane with terminal alkynes and the consequent regeneration...... 42

Scheme 3.5 FLP reactivity of B(C6F5)3·SMe2 ...... 42

Scheme 3.6 Proposed mechanism of the synthesis of (11) ...... 44

Scheme 3.7 Postulated adduct formation at low temperatures of (11) ...... 45

Scheme 3.8 Dimerization of (11) at low temperatures ...... 45

Scheme 3.9 Thermodynamics of related systems ...... 48

Scheme 3.10 FLP reactivity of (11) ...... 49

Scheme 3.11 Attempted cyclizations of (11) through heating...... 50

Scheme 3.12 Reactions of (11) and terminal and internal alkynes ...... 53

Scheme 3.13 Proposed mechanism of the addition of alkynes to PhSCH2B(C6F5)2 ...... 59

Scheme 3.14 Cyclizations via FLPs...... 60

Scheme 3.15 Cyclizations with a geminal phosphorus/aluminum based FLP and phenylacetylene ...... 60

Scheme 3.16 Lack of reactivity between (15) and PR3 ...... 61

Scheme 3.17 Formation of lithiated precursor (11a) ...... 62

Scheme 3.18 Synthesis of compound (11)...... 63

Scheme A.1 Synthesis of B(C6F5)3·SMe2 ...... 76

Scheme A.2 Reactivity of B(C6F5)3·SMe2 with hydrogen ...... 76

Scheme A.3 Relationship studied of the adduct B(C6F5)3·SMe2 and free B(C6F5)3 and SMe2 .....78

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List of Abbreviations and Symbols

° degrees

Å Ångstrom, 10-10 m

δ chemical shift, ppm

Δ change

ΔG° change in Gibbs free energy (species in standard states)

ΔH° change in enthalpy (species in standard states)

ΔS° change in entropy (species in standard states)

p m change in between para-fluorine and meta-fluorine signals in 19F{1H} NMR

σ standard deviation

~ approximately

6-31G(d, p) a type of basis set

Abs coeff absorption coefficient, µ, mm-1

Anal Calcd calculated (elemental) analysis

Ar aryl

B3LYP a type of DFT exchange-correlational functional br broad

C Celsius cal calorie cc cubic centimeter, cm3

CCD charge-coupled device

5 ¯ Cp cyclopentadienyl ligand, η -C5H5 d doublet d (calc) density calculated, g·cm-3

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DCM dichloromethane, methylene chloride, CH2Cl2

EA elemental analysis eq. equivalents

Et ethyl, C2H5

Et2O diethyl ether, O(C2H5)2 et al. and others

Fc calculated structure factor

Fo observed structure factor

FLP frustrated Lewis pair

FT Fourier transform g gram h hour

HSQC heteronuclear single quantum correlation

Hz Hertz, s-1

i IDipp 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, C3H3N2(C6H2 Pr2)2 i Pr isopropyl, CH(CH3)2

J symbol for coupling constant, Hz kcal kilocalorie kJ kilojoule

K Kelvins

Keq equilibrium constant lut 2,6-lutidine, C7H9N m multiplet m meta

M molarity, mol/L

xiv

Me methyl, CH3

Mes mesityl, C6H2Me3 mg milligram

MHz megahertz, 106 s-1 min minute mL milliliter(s), 10-3 L mmol millimole(s), 10-3 mol

µmol micromole(s), 10-6 mol mol mole(s)

MW molecular weight, g/mol n Bu n-butyl, C4H9

NMR nuclear magnetic resonance

NR no reaction o ortho

ORTEP Oak Ridge thermal ellipsoid plot

¯ OTf trifluoromethanesulfonate, triflate, CF3SO3 p para

Ph phenyl, C6H5

POV-ray Persistence of Vision Raytracer pm picometer ppm parts per million, 10-6 py pyridine q quartet rt room temperature s singlet

t triplet t Bu tert-butyl, C(CH3)3

THF tetrahydrofuran, C4H8O

THT tetrahydrothiophene, C4H8S

¯ trityl triphenylmethyl, CPh3

TMP 2,2,6,6-tetramethylpiperidine, C9H19N

Tos tosyl, CH3C6H4SO2

V volume, Å3 vs. versus

VT variable temperature

Z formula units

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1 Introduction 1.1 Overview of Frustrated Lewis Pairs

Lewis acidity and basicity are fundamental concepts in chemistry which can be used to predict reactivity. In 1923, Lewis elucidated the ideas of a Lewis acid (A) acting as an electron pair acceptor and a Lewis base (B) acting as an electron pair donor.1 He formulated the axiom that the reaction of such a Lewis acid and a Lewis base would produce an inert adduct A-B (Scheme 1.1).1 However, over the years that followed this postulation, examples contradicting this theory began to surface. In 1942, H. C. Brown and coworkers discovered that the combination of 2,6- lutidine and trimethylborane resulted in no reaction, in contrast to the anticipated classical Lewis acid-base adduct (Scheme 1.2).2 Molecular modeling illustrated that the steric bulk of the trimethylborane and 2,6-lutidine precluded adduct formation, since the smaller bases trimethylamine and pyridine were able to form an adduct with trimethylborane due to the eliminated steric congestion.2 Eight years later, Wittig and Riickert noted that when trityl sodium was added to the THF adduct of triphenylborane, the Lewis acid-base adduct did not form and ring-opening of THF occurred instead (Scheme 1.2).3 Furthermore, Tochtermann in 1966 observed the 1,2-addition of trityl and triphenylborane to olefin when trityl sodium and triphenylborane were reacted with 1,3-butadiene (Scheme 1.2).4 Tochtermann coined this Lewis acid and Lewis base combination the German phrase “antagonistisches Paar”.4

H H B + N H B N H H H Lewis acid Lewis base Lewis acid-base adduct A B A-B

Scheme 1.1 Formation of a classical Lewis acid-base adduct 2

N + B NR

Ph B O + Ph CNa Ph C BPh Na 3 3 3 O 3

BPh3 Na Ph3CNa + BPh3 Ph3C

Scheme 1.2 Examples of unusual reactivity which contradicts Lewis’ postulation

In recent years, Stephan and coworkers decided to further probe this unusual reactivity. They also recognized that the novel reactivity results from steric hindrance from both the Lewis acid and Lewis base. Severe steric hindrance does not allow the Lewis acidity and basicity of these compounds to be quenched through formation of an adduct, hence Stephan and coworkers termed the Lewis acid-base pair a frustrated Lewis pair (FLP) (Scheme 1.3). Continued investigations have uncovered major discoveries in the field of FLPs in which they have been employed in applications such as hydrogenation, catalysis and small molecule activation.5-7 Since then, a plethora of researchers, most notably the groups of Stephan, Erker and Bertrand, have continued in the movement to broaden the scope of FLPs and their reactivity.

A + B A B

frustrated Lewis pair FLP

Scheme 1.3 A depiction of a frustrated Lewis pair

1.2 Frustrated Lewis Pairs: Hydrogenation

In 2006, the first example of reversible metal-free hydrogenation activation was discovered in the Stephan group via a frustrated Lewis pair.8 Dimesitylphosphine was reacted with tris(pentafluorophenyl)borane in which the phosphine underwent p-attack on one of the C6F5 rings, leading to fluoride migration to the boron center. Further treatment of this zwitterionic phosphonium-borate (Mes)2PH(C6F4)BF(C6F5)2 with chlorodimethylsilane resulted in fluoride for hydride exchange. Upon heating (Mes)2PH(C6F4)BH(C6F5)2 above 100 C, stoichiometric loss of dihydrogen was observed to form the phosphinoborane (Mes)2P(C6F4)B(C6F5)2. When

(Mes)2P(C6F4)B(C6F5)2 was reacted with hydrogen at room temperature, the zwitterionic phosphonium-borate was reformed (Scheme 1.4).

F F F F F

PH + F B(C6F5)2 Mes2P B(C6F5)2 H 2 F F F F BrMgR R = alkyl Me2SiHCl

F F F F H o -H2, >100 C Mes2P B(C6F5)2 Mes2P B(C6F5)2 o H H2, 25 C F F F F

Scheme 1.4 First example of reversible metal-free hydrogenation activation by a sterically frustrated Lewis pair

Variations of this zwitterionic phosphonium-borate can also be synthesized,9 such as t ( Bu)2PH(C6F4)BH(C6F5)2. This reversible metal free hydrogen activation was applied to the catalytic hydrogenation of imines in which both the Mes- and tBu-phosphonium-borate species were employed as the catalysts (Scheme 1.5).10 It is noteworthy that only sterically bulky imines can be hydrogenated, illustrating the necessity of large steric hindrance in frustrated Lewis pairs.

R' R' N NH

H Ph imine H Ph H reduction

F F F F H

R2P B(C6F5)2 R2P B(C6F5)2 H F F F F

dihydrogen H activation 2

Scheme 1.5 Catalytic cycle for the reduction of imines (R = Mes, tBu)

Moreover, many other FLPs have been found to undergo hydrogen activation as well as catalytic hydrogenation. The reaction of tris(pentafluorophenyl)borane, B(C6F5)3, in combination with a variety of sterically hindered bases in the presence of hydrogen was found to heterolytically cleave dihydrogen (Scheme 1.6).11-14

1 atm H2 + - B(C6F5)3 + PR3 [R3PH] [HB(C6F5)3] Welch, Stephan 25oC (2007) R = Mes, tBu

R1 R1 N 5 mol% B(C6F5)3 NH 5 atm H , 120oC R2 R3 2 R2 R3 H Chase, Jurca, Stephan (2008) 1 5 mol% B(C6F5)3/PMes3 R N B(C6F5)3 H2N B(C6F5)3 5 atm H , 120oC 2 R1 H H

Tos Tos N NH 10 mol% B(C6F5)3 Chen, Klankermayer o 30 bar H2, 100 C (2008)

1 atm H 2 [HB(C F ) ]- Sumerin, Rieger et al. + B(C6F5)3 6 5 3 N 20oC N (2008) H H2

Scheme 1.6 Selected examples of using the bulky Lewis acid B(C6F5)3 with a variety of bulky Lewis bases to activate hydrogen

Linked FLPs containing a bulky Lewis acid and a bulky Lewis base within one molecule were also shown to heterolytically cleave dihydrogen. For example, Erker and coworkers reported H2 activation with an ethylene linked phosphine-borane (Scheme 1.7).15 Moreover, they were able to use this P B linked FLP to hydrogenate enamines, imines and conjugated phosphinoalkenylboranes.16 Similarly, Rieger and coworkers were able to reversibly activate hydrogen using a TMP aryl-linked FLP (Scheme 1.7).

1.5 bar H2 B(C6F5)2 Spies, Erker et al. (2008) Mes P B(C F ) 2 6 5 2 25oC Mes2P H

N H , 20oC N 2 H o Sumerin, Rieger et al. (2008) -H2, 110 C H B C6F5 B C6F5 C6F5 C6F5

Scheme 1.7 Examples of linked FLPs and their reactivity towards dihydrogen

These are some of the many examples of how FLPs can be used as hydrogenation catalysts. More recently, chiral FLPs have been developed and were found to perform enantioselective catalytic hydrogenation of imines.17 This discovery has extended the application of FLPs and continues to be a source of exploration.

1.3 Frustrated Lewis Pairs: Small Molecule Activation

In addition to hydrogenation, FLPs can undergo small molecule activation such as the insertion 18,19 20-22 of CO2 and N2O (Scheme 1.8), addition to alkenes and alkynes (Scheme 1.9), and ring- opening of THF and cyclopropanes (Scheme 1.10).23,24

o CO2, 25 C t t (C F ) B P Bu B(C6F5)3 + P Bu3 6 5 3 3 80oC, vacuum, -CO O 2 O

B(C6F5)2

Mes2P

o CO2, 25 C Mes2P B(C6F5)2 Mes2P B(C6F5)2 o CH2Cl2, > -20 C, -CO2 O O

o t N2O, 25 C t B(C6F5)3 + P Bu3 (C6F5)3B N P Bu3 O N

t Scheme 1.8 Activation of CO2 and N2O by P Bu3/B(C6F5)3 and ethylene linked P B system

Depending on the strength of the base, deprotonation or addition products can occur with reactions of terminal alkynes and tris(pentafluorophenyl)borane. This is illustrated in Scheme 1.8 in which the trans-addition product is formed when o-tolylphosphine is used in combination with B(C6F5)3. In contrast, the deprotonation product is formed when the stronger and bulkier base tri-tert-butylphosphine is used. Only the addition product is formed with olefins and dienes.

t P Bu3 t B(C6F5)3 + P Bu3 (C6F5)3B

(C6F5)3B t B(C6F5)3 + P Bu3 t P Bu3

Ph H B(C6F5)3

t P Bu3 P(o-tol)3

t [HP Bu3][Ph B(C6F5)3] (o-tol)3P H

Ph B(C6F5)3

t Scheme 1.9 Reactions of olefins, dienes and alkynes with P Bu3/B(C6F5)3

Smaller bases appeared to be required for the ring-opening of THF. Indeed, dimesityl phosphine and di-tert-butylphosphine were used in combination with tris(pentafluorophenyl)borane to ring- open THF. In the ring-opening of cyclopropanes, tri-tert-butylphosphine was used as the base (Scheme 1.9).

R2PH (C6F5)3B(THF) R2HP B(C6F5)3 R = Mes, tBu O

t P Bu3 Ph PtBu (C F ) B Ph B(C6F5)3 + 3 6 5 3

Scheme 1.10 Ring-opening of THF and cyclopropylbenzene with FLPs

The unquenched reactivity of FLPs can be employed in the activation of a variety of small molecules. The aforementioned schemes illustrate a few examples of this.

1.4 Frustrated Lewis Pairs: New Directions

While these early systems have been limited to phosphine/borane reagents, exploration in new FLP systems based on other main group elements and transition metals is currently being pursued. For example, phosphinoferrocenes in conjunction with tris(pentafluorophenyl)borane form a frustrated Lewis pair. Upon exposure to hydrogen these FLPs heterolytically cleave dihydrogen (Scheme 1.11).25,26 In the case of α-dimesitylphosphinoferrocene, the cleavage of dihydrogen is an intermediate step en route to a phosphine free ferrocene complex and

[Mes2PH·B(C6F5)3]. The cleavage of the Mes2PH moiety is predicted to be assisted by a

¯ 25 neighbouring iron group, which is followed by hydride attachment from [HB(C6F5)3] .

H2 + B(C F ) + HB(C6F5)3 + [Mes PH·B(C F Fe 6 5 3 o Fe Fe 2 6 25 C 5)3] H PMes2 PHMes2 H

t t P Bu2 PH Bu2

Fe B(C6F5)3 H2 Fe Ph NR Ph Ph Ph Ph Ph [HB(C6F5)3]

Ph Ph Ph Ph

Scheme 1.11 FLPs of phosphinoferrocenes and hydrogen activation

Another example is the FLP formation from a bis(arylimino-Cp)ZrCl2 complex with tris(pentafluorophenyl)borane illustrated in Scheme 1.12.27 This compound can undergo two sequential hydrogenations.

N Ar N Ar N Ar H H2 cat. B(C6F5)3 2 B(C6F5)3 ZrCl2 ZrCl2 ZrCl2 2 bar H , 25oC 2 bar H , 25oC N Ar 2 HN Ar 2 H2N Ar

2 [HB(C6F5)3]

Scheme 1.12 Hydrogenation of a bis(arylimino-Cp)ZrCl2 complex and B(C6F5)3

The above examples showcased bulky Lewis bases other than phosphines and amines, however the Lewis acid, B(C6F5)3, remained constant throughout the reactions. Recently it has been shown that aluminum can be substituted for boron in the Lewis acid.21,28 When two equivalents of aluminum trihalide were reacted with trimesitylphosphine under an atmosphere of CO 2, insertion of the gas occurred. The ensuing adduct was then reacted with ammonia borane followed by water to produce methanol in a stoichiometric amount (Scheme 1.13).28

X3Al AlX3 CO2 O O NH3BH3 [Mes3PH][(MeO)nAlX4-n] PMes3 + 2AlX3 15 min, 25oC P + (NHBH) Mes Mes n Mes

H2O

CH3OH

Scheme 1.13 Methanol production from the CO2 complex of PMes3 and AlX3

Frustrated Lewis pairs have been introduced as an alternative to transition metal catalysts. FLPs have been shown to be used as metal-free hydrogenation catalysts and for the activation of small molecules. Producing FLP systems containing Lewis acids other than tris(pentafluorophenyl)borane can be a challenge. Some synthetic routes to new b ulky Lewis acids are presented in this thesis. These Lewis acids contain a variety of different elements other than boron, carbon, and fluorine, such as gold, copper, and sulfur. The reactivity of these new Lewis acids with small molecules is reported in this thesis.

2 Gold(I) and Copper(I) Imidazolium Complexes 2.1 Introduction

In 2007, Bertrand and coworkers used his cyclic(alkyl)(amino)carbenes (CAACs) to split hydrogen and ammonia (Scheme 2.1).29 One can argue that the carbene center acts as a frustrated Lewis pair in itself, made possible by the bulkiness of the CAACs, the Lewis basic lone pair of electrons at carbon, and the vacant p-orbital also at carbon.

i i NH i N( Pr)2 H2 N( Pr)2 3 (l) N( Pr)2 -35oC -78oC to rt H H H2N H

R R R H2 NH3 (l) Dipp N o Dipp N o Dipp N R' -35 C R' -78 C to rt R' H H H NH2

Scheme 2.1 Demonstrated cleavage of hydrogen and ammonia by CAACs

One year later, the Tamm and Stephan research groups simultaneously discovered a new frustrated Lewis pair system based on N-heterocyclic carbenes (NHCs) as the Lewis base.30,31 Both groups discovered the heterolytic cleavage of dihydrogen with the bulky 1,3-di-tert-butyl- t 1,3-imidazol-2-ylidene (IBu) and B(C6F5)3 (Scheme 2.2 2.3). No reaction was observed in the absence of hydrogen at low temperature (-60 C). However at room temperature, a mixture of the two compounds in toluene afforded an abnormal imidazole in which migration of the hydrogen atom to the former carbene carbon atom occurred and the B(C6F5)3 moiety is apparent in the 4 position (Scheme 2.2 2.3), similar to the p-attack chemistry observed in R2PH(C6F4)BF(C6F5)2. t Tamm and coworkers also observed ring-opening of THF when both I Bu and B(C6F5)3 were placed in a solution of THF (Scheme 2.2). Moreover, Stephan and coworkers observed N H t 32 bond cleavage in amines using the I Bu and B(C6F5)3 pair. Conversely, if 1,3-bis(2,6- diisopropylphenyl)-1,3-imidazol-2-ylidene (IDipp) was used in place of ItBu, simple adduct formation occurs with B(C6F5)3 and no further reactivity with hydrogen was observed (Scheme

2.3).

tBu tBu tBu N N N 1 atm H2 H + B(C6F5)3 H HB(C6F5)3 N toluene, rt N rt N (C6F5)3B tBu tBu tBu

THF rt

B(C F ) t 6 5 3 Bu O N

N tBu

t Scheme 2.2 FLP reactivity of I Bu and B(C6F5)3

i t C6H2 Pr2 Bu N t N H2 IDipp I Bu H NR NR 2 B(C6F5)3 o B(C6F5)3 o o H HB(C6F5)3 N -78 C -60 C -60 C to rt N i t C6H2 Pr2 Bu HNRR'

tBu R R' R 2-3 mol% ItBu ItBu N C6F5H + N B(C6F5)2 H N B(C6F5)3 H N B(C6F5)3 R' R N R' t Bu

t Scheme 2.3 Hydrogen and amine activation by I Bu and B(C6F5)3 and adduct formation of IDipp and B(C6F5)3

Soon after, Bertrand and coworkers introduced the CAAC motifs as ligands on gold(I) complexes.33 They demonstrated that these complexes could homogeneously catalyze the hydroamination of alkynes and allenes in the presence of ammonia.34-36 In 2010, cyclizations via the intramolecular addition of N H from ammonium salts or N Me bonds from tertiary amines to alkynes was reported using these gold derivatives (Scheme 2.4).37

CAAC Au B(C6F5)4 OTf HOTf (1.0 eq.) Ph Ph N CDCl3, rt, 5 min N

B (1.0 eq.) A/AgOTf 5 mol% o CDCl3, rt, 5 min CDCl3, 70 C, 3h

Ph Ph HOTf (1.0 eq.)

CDCl3, rt, 5 min OTf N NH

CAAC CAAC

Au Au B(C6F5)4 Cl Dipp N

A B CAAC

Scheme 2.4 Intramolecular addition of tertiary amines to internal alkynes using a gold(I) CAAC complexes

This reactivity is analogous to the cyclizations that result from the intramolecular additions of amines to alkenes and alkynes via a frustrated Lewis pair as demonstrated by the Stephan and Erker groups (Scheme 2.5).38

B(C6F5)3

NMe2 Me2N B(C6F5)3

NMe2 Me2N B(C6F5)3 B(C6F5)3

Scheme 2.5 Cyclization reactions using FLPs

Bertrand initiated the idea of developing a gold imidazolium FLP (Figure 2.1). By having a sterically hindered group on the NHC, such as Dipp, the gold imidazolium would act as a bulky Lewis acid. In combination with a bulky base B, such as a phosphine or amine, there should be an equilibrium between the base and counterion X¯ to easily exchange on and off of the gold center, precluding adduct formation. Thus these gold(I) imidazolium complexes could act as FLPs and should therefore exhibit FLP reactivity.

R X- R N N Au B Au X + B R = Dipp N N R R

Figure 2.1 Project proposal of developing a gold FLP

2.2 Results and Discussion

2.2.1 Gold(I) and Copper(I) Imidazolium Complexes

Gold(I) and copper(I) imidazolium complexes were synthesized,39,40 and their reactivity towards Lewis bases was probed (Scheme 2.6). Attempts to abstract the chloride counterion from the

IDippAuCl and IDippCuCl starting materials with NaBF4, KBF4, AgBF4, CPh3B(C6F5)4, and

NaBPh4 proved to be inefficient, and best yields and fastest reaction times occurred with AgOTf. The triflate anion proved to be a useful NMR handle in which the shift of the fluorine signal could be easily monitored by 19F{1H} NMR.

OTf

N H M N M = Au (5) N M = Cu (10)

TMP CH2Cl2, 24 h

OTf OTf

N N N 2,6-lutidine PMes3 M N M O Cu P O CH Cl , 24 h N CH2Cl2, 24 h N S 2 2 N O F F F

M = Au (1) M = Au (4) M = Au (2) M = Cu (6) M = Cu (9) M = Cu (7)

t P Bu3 CH2Cl2, 24 h

OTf

N M P M = Au (3) N M = Cu (8)

Scheme 2.6 Synthetic route to gold(I) and copper(I) imidazolium complexes

Compounds (2) (5) and (7) (10) were anticipated to be weak adducts, however, all of the phosphine and amine adducts proved to be quite stable. Most of the gold(I) and copper(I) imidazolium complexes prepared were characterized by X-ray crystallography in addition to NMR and elemental analysis. Typical 1H NMR spectra of these complexes are illustrated in Figure 2.2 2.3. POV-ray depictions of these compounds are illustrated in Figure 2.4 2.8 and selected bond lengths and bond angles are listed in Table 2.1 2.6.

An example of a typical 1H NMR spectrum of a phosphine IDippM(I) adduct (M = Au, Cu) is illustrated with compound (3) in Figure 2.2. There are a variety of diagnostic signals in the proton NMR spectra that are present in compounds (1) (10). The downfield singlet, doublet and

15 triplet signals correspond to the NHC protons and Dipp aryl protons respectively. Furthermore, the septet and the two sets of doublets belong to the isopropyl groups. In the case of compound (3), the most upfield doublet is associated with the tBu groups of the phosphine (Figure 2.2). The 19F{1H} and 31P{1H} NMR show distinct singlets, at -78.9 and 92.0 respectively.

1 Figure 2.2 H NMR of (3) at room temperature in CD2Cl2

An example of a typical 1H NMR spectrum of an amine IDippM(I) adduct (M = Au, Cu) is illustrated with compound (10) in Figure 2.3. The 1H NMR of (10) shows the diagnostic peaks of the IDipp as well as the methylene peaks ( 1.53 1.38, 1.18 1.13) and methyl peaks ( 0.89, 0.63) of the TMP fragment (Figure 2.3). Also, at 2.60 there is an overlapping broad singlet with the septet at 2.57 which corresponds to the NH. Again the triflate counterion signal appears as a singlet at -78.9 in the 19F{1H} NMR.

1 Figure 2.3 H NMR of (10) at room temperature in CD2Cl2

Aside from characterizing these gold(I) and copper(I) imidazolium complexes by NMR spectroscopy, the majority of these compounds were also characterized by X-ray crystallography. Compound (1) is known,39 however it has not been characterized crystallographically previously. In Figure 2.4, the C1 Au1 O1 bond shows linearity at 177.6(3) , and the Au1 C1 bond length from the metal center to the NHC was determined to be 1.944(6) Å. The Au1 O1 bond length was slightly longer at 2.071(4) Å.

Figure 2.4 POV-ray ball and stick representation of (1) with hydrogen atoms omitted

Table 2.1 Selected bond lengths (Å) and bond angles ( ) of (1)

Bond Bond Length (Å)

Au1 C1 1.944(6)

Au1 O1 2.071(4)

C1 N1 1.362(8)

C1 N2 1.361(8)

Bond Bond Angle ( )

C1 Au1 O1 177.6(3)

In compounds (2) and (3) a lengthening of the gold carbon bond length is observed from that of

+ ¯ (1) by 0.093(9) Å and 0.087(8) Å respectively. In the [IDippAuPR3] [OTf] complexes the Au1 C1 and Au1 P1 bond lengths were comparable to each other, where the

t + ¯ [IDippAuP Bu3] [OTf] had marginally shorter bond lengths. Gold carbon bond lengths were 2.038(5) Å and 2.032(4) Å and gold phosphorus bond lengths were 2.3347(14) Å and 2.3109(12) Å, for compounds (2) and (3) respectively. These were both linear complexes in which the C1 Au1 P1 angles were 179.46(17) and was 177.43(11) for compounds (2) and (3) respectively (Figure 2.5).

Figure 2.5 POV-ray ball and stick representation of (2) and (3) with omitted anion and hydrogen atoms except those involved in anagostic interactions

Table 2.2 Selected bond lengths (Å) and bond angles ( ) of (2) and (3)

Compound (2) (3)

Bond Bond Length (Å) Bond Length (Å)

Au1 C1 2.038(5) 2.032(4)

Au1 P1 2.3347(14) 2.3109(12)

C1 N1 1.328(7) 1.339(5)

C1 N2 1.364(7) 1.367(5)

Bond Bond Angle ( ) Bond Angle ( )

C1 Au1 P1 179.46(17) 177.43(11)

During the course of this study, Nolan and coworkers published the structure of

t + ¯ 41 [IDippAuP Bu3] [BF4] . The bond lengths and bond angles of (2) and (3) are similar to that of

t + ¯ [IDippAuP Bu3] [BF4] (Table 2.2), in which the gold carbon bond was 2.044(7) Å, the gold phosphorus bond was 2.3145(18) Å and the C Au P angle was 176.23(19) for the latter compound. Interestingly, in compound (2) the methyl protons on the mesityl rings of the phosphine appear to have an anagostic interaction with the gold metal center.42 The three protons have distances ranging from 2.400 2.472 Å to the gold atom and display weak hydrogen bonding in Figure 2.5. Angles from C H Au1 ranged from 126.05 144.34 (Table 2.3).

Table 2.3 Bond lengths (Å) and bond angles ( ) involved in anagostic interactions in (2) and (7)

Compound (2) (7)

Bond Bond Length (Å) Bond Length (Å)

M H1a 2.472 2.397

M H2a 2.400 2.396

M H3a 2.457 2.359

Bond Bond Angle ( ) Bond Angle ( )

C1a M H1a 142.58 119.37

C2a M H2a 144.34 131.64

C2a M H2a 126.05 138.33

M = Au for (2), Cu for (7)

When comparing these gold(I) phosphine imidazolium complexes to the analogous copper(I) complex (7), a shortening of the copper carbon and copper phosphorus bond lengths is observed (1.914(4) Å and 2.2516(13) Å respectively) (Figure 2.6). Examples of crystallographically characterized NHC copper(I) phosphine complexes are rare,43 however the cyclopentadienyl triethylphosphine copper complex (CpCuPEt3) provides an example of a copper(I) phosphorus bond length of 2.1336(18).44 Again, the molecular structure of compound (7) displays anagostic interactions between the methyl protons of the mesityl rings on the phosphine and the copper center (Figure 2.6).42 These three protons range from 2.359 2.397 Å to the copper atom, a slightly stronger hydrogen bonding interaction to copper than the related gold complex (These three protons range from 2.359 2.397 Å to the copper atom, a slightly stronger hydrogen bonding interaction to copper than the related gold complex (Table 2.3). The C H Cu1 angles ranged from 119.37 138.33 (Table 2.3).

Figure 2.6 POV-ray ball and stick representation of (7) with hydrogen atoms omitted except those involved in anagostic interactions

Table 2.4 Selected bond lengths (Å) and bond angles ( ) of (7)

Bond Bond Length (Å)

Cu1 C1 1.914(4)

Cu1 P1 2.2516(13)

C1 N1 1.360(6)

C1 N2 1.358(5)

Bond Bond Angle ( )

C1 Cu1 P1 176.27(13)

Switching the base from a phosphine to an amine decreases the bond length between the metal to the NHC carbon, as illustrated in compounds (4), (9) and (10) (Figure 2.7 2.8, Table 2.5 2.6). The metal carbon bonds in these amine complexes are stronger than those in the phosphine complexes due to amines being less electron donating than phosphines. For compound (4), the

21 gold carbon bond length was found to be 1.974(3) Å and the gold nitrogen bond length was

+ ¯ 2.064(2) Å which is consistent to that of [IDippAupy] [PF6] , in which the gold carbon bond length was 1.961(7) Å and the gold nitrogen bond length was 2.049(6) Å.45

Similarly, compounds (9) and (10) had shorter bond lengths and smaller C Cu N bond angle. Both compounds had similar Cu1 C1 bond lengths of 1.877(3) Å and 1.875(3) Å for (9) and (10) respectively. These copper carbon bond lengths are consistent with the anilido adduct IDippCuNHPh which had a bond length of 1.875(3) Å.46 The TMP adduct had a slightly longer Cu N bond length of 1.945(3) Å compared to the lutidine adduct which had a Cu N bond length of 1.902(2) Å. The copper nitrogen bond length of IDippCuNHPh (1.841(2) Å) was shorter compared to compounds (9) and (10) which can be attributed to decreased steric bulk around the nitrogen center due to the lone pair of electrons present. Another example is the Cu N bond length of the cyanide 2-methylpyridine copper complex CNCu(2-Mepy), which had a slightly longer bond length of 2.044 Å.47 Both copper amine complexes diverged the most from linearity compared to the rest of the copper(I) and gold(I) imidazolium complexes in which (9) had a C Cu N bond angle of 175.29(11) and (10) had a C Cu N bond angle of 174.60(13) .

Figure 2.7 POV-ray ball and stick representation of (4) and (9) with omitted anion and hydrogen atoms

Table 2.5 Selected bond lengths (Å) and bond angles ( ) of (4) and (9)

Compound (4) (9)

Bond Bond Length (Å) Bond Length (Å)

M1 C1 1.974(3) 1.877(3)

M1 N3 2.064(2) 1.902(2)

C1 N1 1.352(3) 1.362(4)

C1 N2 1.354(3) 1.355(4)

Bond Bond Angle ( ) Bond Angle ( )

C1 M1 N3 176.66(9) 175.29(11)

M = Au for (4), Cu for (9)

The molecular structure of compound (10) was symmetric along the C1 Cu1 N2 axis (Figure 2.9). The NH proton was shown to have an agostic interaction with the copper center which had a Cu1 H2a bond distance of 1.364 Å and an N2 H2a bond distance of 0.880 Å. The N2 H2a Cu1 bond angle was determined to be 118.60 which is consistent with the 3-center-2- electron interaction of agostic compounds.42,48 An example of a copper hydride is the dimer

H2Cu2[CH3C(CH2PPh2)3]2 which has a Cu H bond distance that ranged from 1.66(8) 1.81(8) Å.49

Figure 2.8 POV-ray ball and stick representation of (10) with hydrogen atoms omitted except those involved in agostic interactions

Table 2.6 Selected bond lengths (Å) and bond angles ( ) of (10)

Bond Bond Length (Å)

Cu1 C1 1.875(3)

Cu1 N2 1.945(3)

C1 N1 1.359(2)

N1 C2 1.392(3)

C2 C2 1.344(5)

H2a Cu1 1.364

H2a N2 0.880

Bond Bond Angle ( )

C1 Cu1 N3 174.60(13)

N2 H2a Cu1 118.60

2.2.2 Reactions with Small Molecules

The reactivity of gold(I) phosphine imidazolium complexes (2) and (3) was probed with small molecules typical of FLP chemistry (Scheme 2.7). When either compound was put under 1 atm of CO2 or N2O or 4 atm of H2 gas no reaction occurred. Variable temperature NMR of (2) with 1 atm of CO2 from room temperature down to -85 C also showed no insertion reaction. VT NMR t was not carried out on (3) since the stronger donating effect of P Bu3 would result in a stronger adduct than the trimesitylphosphine complex, making it more difficult to participate in CO 2 insertion. Addition of (2) and (3) to phenylacetylene and 1-hexene did not afford any product, even when the latter reactions were heated to 90 C. Ring-opening of THF with (2) and (3) also did not occur.

NR NR

CO2 N2O

O OTf N HC CPh NR NR Au PR3 N

R = Mes, tBu

NR NR

Scheme 2.7 Attempted FLP chemistry with compounds (2) and (3)

The lack of reactivity could be attributed to the strong adduct formed between the phosphines and the gold metal center. Tri-tert-butylphosphine would produce a stronger adduct than trimesitylphosphine due to electronics, however in the molecular structure of

+ ¯ [IDippAuPMes3] [OTf] in Figure 2.7, there are anagostic interactions between the methyl protons of the mesityl groups which helps stabilize the gold center making a strong adduct interaction as well.

Moreover, since gold is a soft acid and phosphorus is a soft base the binding between the two atoms is highly favourable and perhaps the sterics of the Lewis acid was not enough to preclude adduct formation.50 In contrast, amines are harder bases than phosphines and therefore would form weaker adducts. Bulky amines such as 2,6-lutidine and 2,2,6,6-tetramethylpiperidine, which are known to react in FLP chemistry,14,51 should conceivably result in FLP reactivity with gold(I) imidazolium complexes. However, reactions of (4) or (5) with CO2 and H2 at 1 atm and 4 atm respectively still produced no reactivity. Before more reactivity could be tested with these two complexes, Nolan and coworkers demonstrated the ability to insert CO2 into the Au C bond of synthesized IDippAu(I) (substrate) complexes, and further experiments were halted (Scheme 2.8).52

HO O aq. HCl KO O O O N O N N H Au OH N N

KOH H2O

O N O N N Au Au O C N N N O

CO2

Scheme 2.8 CO2 insertion and C H carboxylation using a gold(I) hydroxide imidazolium complex as reported by Nolan

All the substrates used in these carboxylation reactions were hard nitrogen, sulfur or oxygen heterocycles such as oxazole illustrated in Scheme 2.8.52

The focus of the project was then moved onto copper(I) imidazolium complexes. Since copper is smaller than gold (128 pm vs. 144 pm atomic radius), the steric bulk of the IDipp could help prevent adduct formation, a problem that was persistent in the gold(I) imidazolium complexes.

Additionally, copper is a borderline hard/soft acid which would make it less donating to bases.50 Thus, the analogous copper complexes compounds (7) (10) were synthesized. However,

+ ¯ t + ¯ reactions with [IDippCuPMes3] [OTf] and [IDippCuP Bu3] [OTf] and H2 and CO2 under the same reaction conditions exhibited analogous non-reactivity. Again, the molecular structure of

+ ¯ [IDippCuPMes3] [OTf] (Figure 2.6) illustrated the same anagostic interactions as was seen in

+ ¯ [IDippAuPMes3] [OTf] , with even shorter H Cu distances by approximately 0.059 Å. Nevertheless, [IDippCulut]+[OTf]¯ and [IDippCuTMP]+[OTf]¯ were also tested under atmospheres of H2 and CO2, and all adducts remained intact. Soon after these reactions were performed, Nolan and coworkers reported carboxylation using an IDippCuOH precursor (Scheme 2.9).53

KO H N MeI N N N N O O N Cu OH N N

KOH H2O

N N N N N Cu N Cu O C N N O

CO2

Scheme 2.9 CO2 insertion and N H carboxylation using a copper(I) hydroxide imidazolium complex as reported by Nolan

Of the substrates they tried to perform N H carboxylation, they reported two N-heterocycles which did not complex CO2: 2,2,6,6-tetramethylpiperidine and aniline. Comparing the pKa values of those substrates which did undergo carboxylation (pKa = 15.0 19.8), to that of TMP

(pKa = 37.0) and aniline (pKa = 30.6) suggests that this property could be used to predict chemical reactivity.53 Furthermore, the molecular structure of [IDippCuTMP]+[OTf]¯ in Figure

2.8 illustrates an agostic interaction with the N H and copper center in which the Cu H bond length was determined to be 1.364 Å. This insight also attributes to the strong adduct of [IDippCuTMP]+[OTf]¯.

2.3 Conclusions

Novel gold(I) and copper(I) imidazolium complexes were synthesized and fully characterized. Reasons for strong adduct formations were determined to be from anagostic interactions with the

+ ¯ metal center as found in the molecular structures of [IDippAuPMes3] [OTf] and

+ ¯ + ¯ [IDippCuPMes3] [OTf] , agostic interaction between N2 H2a Cu1 in [IDippCuTMP] [OTf] , not enough steric hindrance from the Lewis acid, and from favourable soft acid/soft base attraction. A variety of small molecules were studied for their insertion or activation behavior, however no reactivity was observed for H2, CO2, N2O, ring-opening of THF or the addition to olefins or alkynes. This approach to a gold or copper FLP did not produce the expected results and a new strategy is needed in order to obtain these target molecules.

2.4 Experimental 2.4.1 General Considerations

All reactions were performed under a dry, oxygen-free atmosphere either in a nitrogen-filled Innovative Technologies glove box or on a Schlenk line under nitrogen. All solvents used were purchased from Caledon Laboratories and dried through a PureSolve solvent system. All deuterated solvents were purchased from Acros or Cambridge Isotope Laboratories. Deuterated solvents were dried overnight with the corresponding drying agent (CaH2 for CD2Cl2), were subsequently sonicated for half an hour, and were subsequently vacuum transferred into a dry 100 mL bomb charged with activated 4 Å molecular sieves. Molecular sieves were activated by storage overnight in an oven at 120 C. Reagents were purchased from Sigma Aldrich or Strem Chemicals and were stored in the glove box. All gas reactions were performed in a J. Young tube.

A 400 MHz Bruker UltraShield spectrometer, a 400 MHz Bruker Avance III Automatic Sample Changer or a 400 MHz Varian Mercury spectrometer were used to perform 1H, 13C , 11B, 19F and 31P NMR spectroscopy. 1H resonances were referenced internally to the residual protonated 13 solvent resonance (δ 5.32 ppm for CD2Cl2), C resonances were referenced internally to the 11 1 deuterated solvent resonance (δ 54.0 ppm for CD2Cl2), B{ H} resonances were referenced 19 1 externally to BF3∙Et2O, F{ H} resonances were referenced externally to 80% CFCl3 in CDCl3, 31 1 and P{ H} resonances were referenced externally to 85% H3PO4. To aid in the assignment of carbon atoms in the 13C{1H} NMR, 1H-13C HSQC experiments were carried out using conventional pulse sequences. Chemical shifts (δ) are expressed in ppm and coupling constants (J) in Hz. Elemental analysis was performed using a Perkin-Elmer CHN analyzer.

2.4.2 Synthesis and Characterization of Gold(I) Imidazolium Complexes

Experimental Procedure (1): Procedure followed as per Tsui, Müller, and Sadighi.39 IDippAuOTf was used as a starting material for the rest of the derived compounds. A 90% yield was obtained. NMR spectra correlated with literature values.

N O Au O N S O F F F

IDippAuOTf (1)

Experimental Procedure for compounds (2)–(3): In a 20 mL scintillation vial, 54.4 μmol of IDippAuOTf (40.0 mg) and 54.4 μmol of trimesitylphosphine (21.1 mg) or tri-tert- butylphosphine (11.0 mg) were weighed out and dissolved in ~4 mL of dichloromethane. The clear colourless solution was stirred overnight and volatiles were removed in vacuo. Subsequent washing of the white precipitate with pentanes, removal of volatiles and drying for at least 2 hours produced pure product.

4 O 3 F 2 O S F 1 6 F 13 O 5 10 8 N 7 11 14 Au P 9 12 N

+ - [IDippAuPMes3] [OTf] (2)

[1,3-bis(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene]gold(I)trimesitylphosphine triflate

1 3 H NMR (CD2Cl2, 400 MHz): δ 7.59 (t, 2H, JH-H = 7.8 Hz, H-4), 7.34 (s, 2H, H-8), 7.30 (d, 4H, 3 4 3 JH-H = 7.8 Hz, H-3), 6.73 ( d, 6H, JH-H = 3.9 Hz, H-11), 2.50 (septet, 4H, JH-H = 6.8 Hz, H-5), 3 3 2.26 ( s, 9H, H-14), 1.83 (s, 18H, H-13), 1.17 (d, 12H, JH-H = 6.8 Hz, H-7), 0.99 ( d, 12H, JH-H 19 1 31 1 = 6.8 Hz, H-6); F{ H} NMR (CD2Cl2, 377 MHz): δ -79.0 (s); P{ H} NMR (CD2Cl2, 162 13 1 2 MHz): δ 7.3 (s); C{ H} NMR partial (CD2Cl2, 100 MHz): δ 146.2 (s, C-1), 143.0 (d, JP-C = 1 3 10.8 Hz, C-10), 142.2 (d, JP-C = 2.5 Hz, C-9), 132.2 (d, JP-C = 9.6 Hz, C-11), 131.7 (s, C-4), 4 3 125.5 (d, JP-C = 4.1 Hz, C-12), 125.1 (s, C-3 & C-8), 29.4 (s, C-5), 25.1 (s, C-7), 24.2 (d, JP-C =

9.4 Hz, C-13), 23.8 (s, C-6), 21.1 (s, C-14); Yield: 78%; Anal Calcd for C55H69AuF3N2O3PS: C 58.82, H 6.19, N 2.49; Found: C 58.76, H 6.50, N 2.05. X-ray quality crystals were grown from a diffusion of pentane into a solution of the product in bromobenzene at rt.

4 O 3 F 2 10 O S F 1 6 O F 5 9 8 N 7 Au P N

t + - [IDippAuP Bu3] [OTf] (3)

[1,3-bis(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene]gold(I)tri-tert-butylphosphine triflate

1 3 H NMR (CD2Cl2, 400 MHz): δ 7.54 (t, 2H, JH-H = 7.8 Hz, H-4), 7.44 (s, 2H, H-8), 7.34 (d, 4H, 3 3 3 JH-H = 7.8 Hz, H-3), 2.57 (septet, 4H, JH-H = 6.9 Hz, H-5), 1.30 (d, 12H, JH-H = 6.9 Hz, H-7), 3 4 19 1 1.24 (d, 12H, JH-H = 6.9 Hz, H-6), 1.13 (d, 27H, JH-H = 13.4 Hz, H-10); F{ H} NMR (CD2Cl2, 31 1 13 1 377 MHz): δ -78.9 (s); P{ H} NMR (CD2Cl2, 162 MHz): δ 92.0 (s); C{ H} NMR partial 4 (CD2Cl2, 100 MHz): δ 146.1 (s, C-1), 134.3 (s, C-2), 131.5 (s, C-4), 125.1 (d, JP-C = 4.1 Hz, C- 1 2 8), 124.8 (s, C-3), 39.7 (d, JP-C = 18.1Hz, C-9), 32.4 (d, JP-C = 4.0 Hz, C-10), 29.4 (s, C-5), 24.8

(s, C-7), 24.4 (s, C-6); Yield: 90%; Anal Calcd for C40H63AuF3N2O3PS: C 51.28, H 6.78, N 2.99; Found: C 50.93, H 6.64, N 3.00. X-ray quality crystals were grown from a diffusion of pentane into a solution of the product in bromobenzene at rt.

Experimental Procedure for compounds (4)–(5): In a 20 mL scintillation vial, 55.7 μmol of IDippAuOTf (41.0 mg) was weighed out and dissolved in ~4 mL of dichloromethane. Next, 55.7 μmol of 2,6-lutidine (5.97 mg) or 2,2,6,6-tetramethylpiperidene (7.87 mg) was added into the stirring IDippAuOTf solution. The clear colourless solution was stirred overnight and volatiles were removed in vacuo affording pure product.

3 O F 2 O S F 12 1 6 O F 5 9 10 8 N 7 Au N 11 N

[IDippAulut]+[OTf]- (4)

[1,3-bis(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene]gold(I)2,6-lutidine triflate

1 3 3 H NMR (CD2Cl2, 400 MHz): δ 7.72 (t, 1H, JH-H = 7.8 Hz, H-11), 7.60 (t, 2H, JH-H = 7.8 Hz, 3 3 H-4), 7.50 (s, 2H, H-8), 7.39 (d, 4H, JH-H = 7.8 Hz, H-3), 7.18 ( d, 2H, JH-H = 7.8 Hz, H-10), 3 3 2.56 (septet, 4H, JH-H = 6.8 Hz, H-5), 1.97 (s, 6H, H-12), 1.30 (d, 12H, JH-H = 6.8 Hz, H-7), 3 19 1 13 1 1.28 (d, 12H, JH-H = 6.8 Hz, H-6); F{ H} NMR (CD2Cl2, 377 MHz): δ -78.9 (s); C{ H}

NMR partial (CD2Cl2, 100 MHz): δ 159.6 (s, C-9), 146.5 (s, C-1), 141.5 (s, C-11), 134.2 (s, C- 2), 131.8 (s, C-4), 125.0 (s, C-8), 124.9 (s, C-3), 124.5 (s, C-10), 29.5 (s, C-5), 24.8 (s, C-12),

24.7 (s, C-7), 24.5 (s, C-6); Yield: 75%; Anal Calcd for C35H45AuF3N3O3S: C 49.94, H 5.39, N

4.99; Found: C 48.24, H 4.51, N 4.53. X-ray quality crystals were grown from a diffusion of pentane into a solution of the product in dichloromethane at rt. Low carbon and hydrogen content due to light sensitivity and consequent degradation of compound. Closest agreement obtained after repeated elemental analysis.

3 O F 2 O S F 13 1 6 12 O F 5 9 10 8 N 7 H 11 14 Au N N

[IDippAuTMP]+[OTf]- (5)

[1,3-bis(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene]gold(I)-2,2,6,6-tetramethylpiperidine triflate

1 3 H NMR (CD2Cl2, 400 MHz): δ 7.54 (t, 2H, JH-H = 7.8 Hz, H-4), 7.40 (s, 2H, H-8), 7.35 (d, 4H, 3 3 JH-H = 7.8 Hz, H-3), 3.43 (s, 1H, NH), 2.54 (septet, 4H, JH-H = 6.9 Hz, H-5), 1.55–1.52 (m, 4H, 3 3 H-10), 1.31 (d, 12H, JH-H = 6.9 Hz, H-7), 1.23 (d, 12H, JH-H = 6.9 Hz, H-6), 1.14–1.12 (m, 2H, 19 1 H-11), 0.98 (s, 6H, H-12), 0.80 (s, 6H, H-13); F{ H} NMR (CD2Cl2, 377 MHz): δ -78.9 (s); 13 1 C{ H} NMR (CD2Cl2, 100 MHz): δ 173.4 (s, C-14), 146.2 (s, C-1), 134.4 (s, C-2), 131.5 (s, C- 4), 124.9 (s, C-3), 124.6 (s, C-8), 58.5 (s, C-9), 37.8 (s, C-10), 34.0 (s, C-13), 29.5 (s, C-5), 28.2 (s, C-12), 24.8 (s, C-6), 24.3 (s, C-7), 17.4 (s, C-11); Yield: 84%; Anal Calcd for

C37H55AuF3N3O3S: C 50.74, H 6.33, N 4.80; Found: C 50.53, H 5.80, N 4.59.

2.4.3 Synthesis and Characterization of Copper(I) Imidazolium Complexes

Experimental Procedure (6): Procedure followed as per Munro-Leighton, Blue and Gunnoe with the alteration of using dichloromethane as the solvent and no hexanes was used to precipitate the product.40 IDippCuOTf was used as a starting material for the rest of the derived compounds. A 93% yield was obtained. NMR spectra correlated with literature values.

N Cu O O N S O F F F

IDippCuOTf (6)

Experimental Procedure for compounds (7)–(8): In a 20 mL scintillation vial, 54.8 μmol of IDippCuOTf (33.0 mg) and 54.8 μmol of trimesitylphosphine (21.3 mg) or tri-tert- butylphosphine (11.1 mg) were weighed out and dissolved in ~4 mL of dichloromethane. The clear colourless solution was stirred overnight and volatiles were removed in vacuo. Subsequent washing of the white precipitate with pentanes, removal of volatiles and drying for at least 2 hours produced pure product.

4 O 3 F 2 O S F 1 6 F 13 O 5 10 8 N 7 11 14 Cu P 9 12 N

+ - [IDippCuPMes3] [OTf] (7)

[1,3-bis(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene]copper(I)trimesitylphosphine triflate

1 3 H NMR (CD2Cl2, 400 MHz): δ 7.60 (t, 2H, JH-H = 7.8 Hz, H-4), 7.31 (s, 2H, H-8), 7.30 (d, 4H, 3 4 3 JH-H = 7.8 Hz, H-3), 6.72 ( d, 6H, JH-H = 3.3 Hz, H-11), 2.49 (septet, 4H, JH-H = 6.9 Hz, H-5), 3 3 2.26 ( s, 9H, H-14), 1.75 (s, 18H, H-13), 1.16 (d, 12H, JH-H = 6.9 Hz, H-7), 0.97 ( d, 12H, JH-H 19 1 31 1 = 6.9 Hz, H-6); F{ H} NMR (CD2Cl2, 377 MHz): δ -78.9 (s); P{ H} NMR (CD2Cl2, 162 13 1 2 MHz): δ -28.8 (s); C{ H} NMR partial (CD2Cl2, 100 MHz): δ 146.2 (s, C-1), 142.4 (d, JP-C = 1 3 11.6 Hz, C-10), 141.8 (d, JP-C = 1.8 Hz, C-9), 135.0 (s, C-2), 132.1 (d, JP-C = 8.1 Hz, C-11), 3 131.7 (s, C-4), 125.2 (s, C-3 & C-8), 29.4 (s, C-5), 25.4 (s, C-7), 23.8 (s, C-6), 23.7 (d, JP-C =

12.4 Hz, C-13), 21.2 (s, C-14); Yield: 92%; Anal Calcd for C55H69CuF3N2O3PS: C 66.74, H 7.03, N 2.83; Found: C 64.86, H 7.03, N 3.18. X-ray quality crystals were grown from a diffusion of pentane into a solution of the product in dichloromethane at -38 C. Low carbon content due to copper carbide formation.54 Closest agreement obtained after repeated elemental analysis.

4 O 3 F 2 10 O S F 1 6 O F 5 9 8 N 7 Cu P N

t + - [IDippCuP Bu3] [OTf] (8)

[1,3-bis(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene]copper(I)tri-tert-butylphosphine triflate

1 3 H NMR (CD2Cl2, 400 MHz): δ 7.54 (t, 2H, JH-H = 7.7 Hz, H-4), 7.38 (s, 2H, H-8), 7.36 (d, 4H, 3 3 3 JH-H = 7.7 Hz, H-3), 2.61 (septet, 4H, JH-H = 6.6 Hz, H-5), 1.28 (d, 12H, JH-H = 6.6 Hz, H-7), 3 4 19 1 1.23 (d, 12H, JH-H = 6.6 Hz, H-6), 1.07 (d, 27H, JH-H = 13.9 Hz, H-10); F{ H} NMR (CD2Cl2, 31 1 13 1 377 MHz): δ -78.0 (s); P{ H} NMR (CD2Cl2, 162 MHz): δ 67.2 (s); C{ H} NMR partial 1 (CD2Cl2, 100 MHz): δ 146.1 (s, C-1), 131.6 (s, C-4), 124.9 (s, C-3, C-8), 37.6 (d, JP-C = 12.6 Hz, 2 C-9), 32.4 (d, JP-C = 5.4 Hz, C-10), 29.5 (s, C-5), 25.0 (s, C-6), 24.5 (s, C-7); Yield: 70%; Anal

Calcd for C40H63CuF3N2O3PS: C 59.79, H 7.90, N 3.49; Found: C 60.02, H 8.61, N 3.60. Closest agreement obtained after repeated elemental analysis (H is 0.71% off).

Experimental Procedure for compounds (9)–(10): In a 20 mL scintillation vial, 49.8 μmol of IDippCuOTf (30.0 mg) was weighed out and dissolved in ~4 mL of dichloromethane. Next, 49.8 μmol of 2,6-lutidine (5.34 mg) or 2,2,6,6-tetramethylpiperidene (7.04 mg) was added into the stirring IDippCuOTf solution. The clear colourless solution was stirred overnight and volatiles were removed in vacuo affording pure product.

3 O F 2 O S F 12 1 6 O F 5 9 10 8 N 7 Cu N 11 N

[IDippCulut]+[OTf]- (9)

[1,3-bis(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene]copper(I)2,6-lutidine triflate

1 3 3 H NMR (CD2Cl2, 400 MHz): δ 7.66 (t, 1H, JH-H = 7.7 Hz, H-11), 7.59 (br t, 2H, JH-H = 7.2 3 3 Hz, H-4), 7.44 (br s, 2H, H-8), 7.40 (d, 4H, JH-H = 7.2 Hz, H-3), 7.06 ( d, 2H, JH-H = 7.7 Hz, H- 3 3 10), 2.58 (septet, 4H, JH-H = 6.8 Hz, H-5), 1.82 (s, 6H, H-12), 1.28 (d, 12H, JH-H = 6.8 Hz, H-7), 3 19 1 13 1 1.24 (d, 12H, JH-H = 6.8 Hz, H-6); F{ H} NMR (CD2Cl2, 377 MHz): δ -78.9 (s); C{ H}

NMR partial (CD2Cl2, 100 MHz): δ 158.8 (s, C-9), 146.5 (s, C-1), 141.4 (s, C-11), 134.8 (s, C- 2), 131.7 (s, C-4), 125.1 (s, C-3), 125.0 (s, C-8), 123.5 (s, C-10), 29.4 (s, C-5), 25.3 (s, C-6), 24.3

(s, C-12), 24.2 (s, C-7); Yield: 96%; Anal Calcd for C35H45CuF3N3O3S: C 59.35, H 6.40, N 5.93; Found: C 59.31, H 6.58, N 5.73. X-ray quality crystals were grown from layering cyclohexane on top of a solution of the product in dichloromethane at rt.

3 O F 2 O S F 13 1 6 12 O F 5 9 10 8 N 7 H Cu N 11 N

[IDippCuTMP]+[OTf]- (10)

[1,3-bis(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene]copper(I)2,2,6,6- tetramethylpiperidene triflate

1 3 3 H NMR (CD2Cl2, 400 MHz): δ 7.54 (t, 2H, JH-H = 7.8 Hz, H-4), 7.36 (d, 4H, JH-H = 7.8 Hz, 3 H-3), 7.35 (s, 2H, H-8), 2.60 (s, 1H, NH), 2.57 (septet, 4H, JH-H = 6.9 Hz, H-5), 1.53–1.38 (m,

3 3 4H, H-10), 1.28 (d, 12H, JH-H = 6.9 Hz, H-7), 1.23 (d, 12H, JH-H = 6.9 Hz, H-6), 1.18–1.13 (m, 19 1 2H, H-11), 0.89 (s, 6H, H-12), 0.63 (s, 6H, H-13); F{ H} NMR (CD2Cl2, 377 MHz): δ -78.9 13 1 (s); C{ H} NMR partial (CD2Cl2, 100 MHz): δ 146.2 (s, C-1), 135.0 (s, C-2), 131.5 (s, C-4), 125.0 (s, C-3), 124.8 (s, C-8), 55.8 (s, C-9), 37.0 (s, C-10), 34.3 (s, C-13), 29.5 (s, C-12), 29.4 (s,

C-5), 25.0 (s, C-6), 24.5 (s, C-7), 17.5 (s, C-11); Yield: 94%; Anal Calcd for C37H55CuF3N3O3S: C 59.85, H 7.47, N 5.66; Found: C 60.20, H 7.47, N 5.89. X-ray quality crystals were grown from layering cyclohexane on top of a solution of the product in dichloromethane at rt.

2.4.4 Experimental Considerations for Imidazolium Complexes

The synthesis of these compounds proved to be somewhat difficult in that decomposition was observed after prolonged reaction time in dichloromethane. Therefore reactions were carried out for no more than 24 hours. Additionally, compounds (3) and (6) discoloured from a pure white to a pale yellow or brown over time. Although NMR analysis showed the desired spectrum for the complexes, subsequent reactions with discoloured starting material resulted in unclean products most likely due to unidentified inorganic impurities. In order to prevent decomposition, these complexes were stored in the dark and in the glovebox freezer (-38 C).

2.4.5 X-ray Data Collection, Reduction, Solution and Refinement

Each single crystal was placed in paratone-N oil and put under an N2 atmosphere before bringing outside of the glovebox and mounted onto a MiTegen Micromount. X-ray data for all single crystals was collected at 150(2)K on a Bruker SMART Apex II System CCD diffractometer using a graphite monochromator with a Mo Kα radiation (λ = 0.71073 Å) using the SMART software package. Data frames were integrated with the Bruker SAINT software package using a narrow-frame algorithm and the data was corrected for absorption effects using the empirical multi-scan method (SADABS). The structures were solved by direct methods using XS and refined by full-matrix least-squares on F2 using XL as implemented in the SHELXTL solution package.

Non-hydrogen atomic scattering factors were taken from literature tabulations.55 The heavy atom positions were determined using direct methods via the SHELXTL direct methods routine. The remaining non-hydrogen atoms were located from successive difference Fourier map calculations. The refinements were carried out by using full-matrix least squares techniques on 2 2 2 F, minimizing the function ω( Fo - Fc ) where the weight ω is defined as 4Fo /2σ(Fo ) and Fo and Fc are the observed and calculated structure factor amplitudes respectively. In the final cycle of each refinement, all non-hydrogen atoms were assigned anisotropic temperature factors except in the presence of disorder or insufficient data in which case the atoms were treated as isotropic. Carbon-bound hydrogen atom positions were calculated and were allowed to ride on the carbon to which they are bonded, assuming a C H bond length of 0.95 Å. Hydrogen atom temperature factors were fixed at 1.10 times the isotropic temperature factor of the carbon atom to which they are bonded. The hydrogen atom parameters were calculated, but not refined. The locations of the largest peaks in the final difference Fourier map calculation as well as the magnitude of the residual electron densities in each case were of no chemical significance.

In the crystallographic model of (3), there is disorder in the tBu groups. In the crystallographic model of (10), the hydrogen atom on nitrogen was located and refined. The thermal parameters of the H atom were fixed, but the positions were allowed to vary. All other H atoms were calculated and allowed to ride on the carbon to which they are bonded assuming a C–H bond length of 0.95 Å.

Table 2.7 Crystallographic data for compounds (1)–(3)

Crystal (1) (2)·C6H5Br (3)

Formula C28H36AuF3N2O3S C61H74AuBrF3N2O3PS C40H63AuF3N2O3PS

Formula weight 734.61 1280.13 936.92

Crystal system Orthorhombic Orthorhombic Monoclinic

Space group P212121 P212121 P21/n a (Å) 10.5050(11) 11.8959(4) 10.9225(3) b (Å) 14.1020(14) 21.6324(9) 20.8373(6) c (Å) 20.632(2) 22.5758(9) 19.5125(6)

α (o) 90.00 90.00 90.00

β (o) 90.00 90.00 92.511(1)

γ (o) 90.00 90.00 90.00

V (Å3) 3056.4(5) 5809.6(4) 4436.7(2)

Z 4 4 4 d (calc) g·cm-3 1.596 1.464 1.403

Abs coeff, µ, mm-1 4.930 3.338 3.447

Data collected 6528 13327 10199

2 2 Data Fo >2σ(Fo ) 5399 10568 7676

Variables 351 658 460

R1 0.0418 0.0446 0.0350 wR2 0.0728 0.0872 0.1191

Goodness of Fit 0.888 1.014 0.829

2 2 2 2 2 1/2 R1 = ∑||Fo|-|Fc||/∑|Fo|; wR2 = [∑w(Fo – Fc ) /∑w(Fo ) ]

Table 2.8 Crystallographic data for compounds (4), (7) and (9)

Crystal (4) (7)·CH2Cl2 (9)

Formula C35H45AuF3N3O3S C56H71Cl2CuF3N2O3PS C35H45CuF3N3O3S

Formula weight 841.77 1074.62 708.34

Crystal system Monoclinic Monoclinic Monoclinic

Space group P21/c P21/c P21/c a (Å) 12.5137(5) 12.9010(8) 12.3702(7) b (Å) 19.3925(8) 14.9816(9) 19.0368(9) c (Å) 14.9497(6) 28.7762(15) 15.0392(8)

α (o) 90.00 90.00 90.00

β (o) 94.343(2) 96.510(2) 97.977(2)

γ (o) 90.00 90.00 90.00

V (Å3) 3617.5(3) 5525.9(6) 3507.3(3)

Z 4 4 4 d (calc) g·cm-3 1.546 1.292 1.341

Abs coeff, µ, mm-1 4.177 0.612 0.736

Data collected 13770 9723 6173

2 2 Data Fo >2σ(Fo ) 10057 6943 4651

Variables 425 639 415

R1 0.0308 0.0687 0.0443 wR2 0.0689 0.2056 0.1185

Goodness of Fit 1.025 1.023 1.022

2 2 2 2 2 1/2 R1 = ∑||Fo|-|Fc||/∑|Fo|; wR2 = [∑w(Fo – Fc ) /∑w(Fo ) ]

Table 2.9 Crystallographic data for compound (10)

Crystal (10)

Formula C37H55CuF3N3O3S

Formula weight 742.44

Crystal system Orthorhombic

Space group Pnma a (Å) 20.533(3) b (Å) 17.138(2) c (Å) 11.6225(15)

α (o) 90.00

β (o) 90.00

γ (o) 90.00

V (Å3) 4089.9(9)

Z 4 d (calc) g·cm-3 1.206

Abs coeff, µ, mm-1 0.634

Data collected 4839

2 2 Data Fo >2σ(Fo ) 3830

Variables 237

R1 0.0435 wR2 0.1227

Goodness of Fit 1.035

2 2 2 2 2 1/2 R1 = ∑||Fo|-|Fc||/∑|Fo|; wR2 = [∑w(Fo – Fc ) /∑w(Fo ) ]

3 Boron-Sulfur Linked Lewis Acid 3.1 Introduction

The reactivity of frustrated Lewis pairs has been extended vastly in the recent years;24,56-58 however the greatest detriment to these systems is their sensitivity towards air and moisture. In 2009, Gabbaï and coworkers reported boron-sulfur aryl linked Lewis acids that were water stable.59-61 These Lewis acids were methylated using methyltriflate and were used to trap cyanide and fluoride ions in water (Scheme 3.1).59-61 These systems spurred the idea that perhaps a similar design with a more bulky Lewis acidic boron center could act as an FLP in combination with a bulky Lewis base.

Mes Mes Mes F B SMe B SMe2 B SMe Mes MeOTf Mes KF Mes

CH2Cl2, rt -MeOTf

Mes N Mes Mes Mes Mes B B Mes B MeOTf CN- (0.1 ppm) SMe SMe2 SMe2 CH2Cl2, rt H2O, 40 min, pH 7

Scheme 3.1 Gabbaï’s boron-sulfur aryl linked Lewis acids and their reactivity

FLPs have been shown to heterolytically cleave disulfides.62 This reactivity was illustrated with the P-B linked system as well as the combination of tri-tert-butylphosphine and tris(pentafluorophenyl)borane (Scheme 3.2 3.3). This further posed the question of how having sulfur incorporated in the Lewis acid would affect the boron center. Moreover, such a Lewis acid could have a hemilabile interaction between the boron and sulfur atoms. This relationship could potentially be used to stabilize the compound in the presence of air and moisture, while possessing the ability to selectively bind substrates.

F F F F PhS t PhSSPh t (C6F5)2B P Bu2 (C6F5)2B P Bu2 SPh F F F F

S8 -PhSSPh donor

F F F F S (donor) t t (C6F5)2B P Bu2 (C6F5)2B P Bu2

F F F F

t Scheme 3.2 The heterolytic cleavage of diphenyl disulfide using the Bu2P(C6F4)B(C6F5)2 linked FLP

R (C6F5)3B S PtBu S S 3 R = H, Me B(C6F5)3 S PtBu R 3 R

PtBu (C F ) B S S S 3 6 5 3 t B(C6F5)3 S P Bu3

t P Bu3 t S t S P Bu3 S B(C6F5)3 + S=P Bu3 S B(C6F5)3 S

B(C6F5)3

t Scheme 3.3 Heterolytic cleavage of disulfides from P Bu3 and B(C6F5)3

In 2007, Hoshi, Shirakawa and Okimoto discovered that the reaction of B(C6F5)3 with BH3·SMe2 63 produced the adduct of Piers’ borane (HB(C6F5)2), and dimethylsulfide, HB(C6F5)2·SMe2, in

42 low yields.64 The addition of a terminal alkyne to the adduct yielded the addition product and subsequent addition of pinacolborane regenerated HB(C6F5)2·SMe2 (Scheme 3.4).

B(C6F5)3 + BH3 SMe2

O HB(C6F5)2 SMe2 O B H C C H R HC CR

O SMe2 BH (C6F5)2B H O H R

Scheme 3.4 Reactivity of the dimethylsulfide adduct of Piers’ borane with terminal alkynes and the consequent regeneration

Likewise, the adduct B(C6F5)3·SMe2 can be synthesized by reacting B(C6F5)3 with a slight excess 65,66 of SMe2 in toluene at 60 C for three days. Unsurprisingly, B(C6F5)3·SMe2 in conjunction with a bulky phosphine heterolytically cleaves hydrogen, and can add across phenylacetylene (Scheme 3.5, Appendix A).67

1) B(C6F5)3 SMe2 + PR3 NR C6D5Br, rt

H , 4 atm 2 - + 2) B(C6F5)3 SMe2 + PR3 [HB(C6F5)3] [HPR3] + SMe2 C6D5Br, rt

R = Mes, tBu

Me S H PhCCH 2 3) B(C6F5)3 • SMe2 Ph B(C6F5)3 CD2Cl2, rt

Scheme 3.5 FLP reactivity of B(C6F5)3·SMe2

These examples show promise that a bulky Lewis acid incorporating both boron and sulfur could work well in FLP systems. Furthermore, in reaction 3), Stephan and coworkers noted a slight reverse reaction that occurred in DCM at room temperature.67

With this evidence in hand, we formulated our target molecule with the objective of developing an air and moisture stable sulfur protected Lewis acid (Figure 3.1). The Lewis acidity and the steric bulk of the boron center could be tuned by changing the substituents R and R’ on the sulfur and boron atoms, respectively. With all of the above properties, this compound could theoretically serve as a hydrogenation catalyst and activator for small molecules.

BR' 2 R' = Cl, C6F5 R = Me, Ph SR

Figure 3.1 Target aryl linked boron-sulfur Lewis acid

3.2 Results and Discussion

3.2.1 Synthetic Routes to Boron-Sulfur Linked Lewis Acid

The target compound depicted in Figure 3.1 (R = Me, R’ = C6F5) was not obtained; instead (11) was isolated (Scheme 3.6). It is likely that the lithiation initially occurs at the ortho position on the phenyl ring in thioanisole or 2-bromothioanisole, and a rearrangement occurs in which the α- lithio derivative is produced.68 A proposed mechanism on the synthesis of (11) from 2- bromothioanisole or thioanisole is illustrated in Scheme 3.6. Synthetic routes to targeted compounds R = Me, R’ = Cl, and R = Ph, R’ = Cl or C6F5 resulted in multiple products.

X 1. nBuLi (1 eq.), -78oC, Et O 2 C F o 6 5 2. ClB(C6F5)2, -38 C, hexanes or pentane S B S C6F5 (11) X = H, Br PhSCH2B(C6F5)2

1. 2.

H H Li H H (11a) S H S H

Scheme 3.6 Proposed mechanism of the synthesis of (11)

The broad signal at 5.1 in the 11B{1H} NMR indicates a tricoordinate boron species. In the 19F{1H} NMR, a major set of signals is present as well as a significantly smaller second set of signals. Variable temperature NMR showed multiple o-, m- and p-fluorine signals at -60 C 1 indicating inequivalent C6F5 rings and one set of o-, m- and p-fluorine signals at 55 C. The H NMR at room temperature and 19F{1H} NMR at 55 C, room temperature and -60 C are displayed in Figure 3.2 3.3 respectively.

1 Figure 3.2 H NMR of (11) at room temperature in d8-toluene

19 1 Figure 3.3 F{ H} NMR of (11) at various temperatures in d8-toluene

Initially, (11) was thought to form an adduct based on an intramolecular boron sulfur interaction (Scheme 3.7). However, single crystals grown at low temperatures indicated a different formulation involving intermolecular boron sulfur dimer formation (Scheme 3.8, Figure 3.4).

- 60oC C F C F 6 5 o 6 5 S B C F 55 C S B 6 5 C6F5

Scheme 3.7 Postulated adduct formation at low temperatures of (11)

Ph C6F5 o C6F5 - 60 C S B S B C6F5 Ph C6F5 o 55 C B S PhSCH2B(C6F5)2 C6F5 C6F5 (11)

Scheme 3.8 Dimerization of (11) at low temperatures

Figure 3.4 POV-ray ball and stick representation of (11) with hydrogen atoms omitted

This dimer preferentially adopts a boat conformation rather than a chair conformation due to - stacking between the S-Ph and B-C6F5 groups. The phenyl groups and one set of C6F5 rings are equatorial whereas the other set of C6F5 rings point downwards in the axial position. Selected bond lengths and bond angles of compound (11) are tabulated in Table 3.1.

Table 3.1 Selected bond lengths (Å) and bond angles ( ) of (11)

Bond Bond Length (Å) Bond Bond Angle ( )

S1 C1 1.814(4) B1 C1 S1 112.5(3)

S1 B2 2.054(4) B2 C2 S2 113.4(3)

S2 B1 2.071(5) C1 B1 S2 105.8(3)

S2 C2 1.815(4) C1 S1 B2 104.60(17)

C1 B1 1.623(6) C2 B2 S1 104.6(3)

C2 B2 1.619(6) C2 S2 B1 102.91(19)

The boron sulfur bond lengths and sulfur carbon bond lengths of the dimer are comparable to 66 those of the adduct B(C6F5)3·SMe2. Denis et al. reported a boron sulfur bond length of 2.091(5) Å for the dimethylsulfide adduct of tris(pentafluorophenyl)borane which is commensurate to the boron sulfur bond lengths found in (11): S1 B2 = 2.054(4) Å and S2 B1 = 2.071(5) Å. Moreover, the sulfur carbon bond lengths of the dimethyl sulfide adduct were reported to be 1.794(5) Å and 1.810(5) Å which is similar to that of the sulfur carbon bond lengths of the methylene linker of the dimer which was 1.814(4) Å and 1.815(4) Å.66 The boron carbon bond lengths of the methylene linker in the dimer can also be compared to that of

¯ a methyl borate anion of tris(pentafluorophenyl)borane, [MeB(C6F5)3] . Rogers and coworkers reported a boron carbon bond length of 1.631(5) Å in the borate which is slightly longer than the boron methylene bond lengths of 1.623(6) Å and 1.619(6) Å in (11).69 The bond angles of the boat conformation of the dimer are consistent with that of the theoretically calculated cyclohexane model which had angles of 111.5 (B3LYP/6-31G(d, p)).70

3.2.2 Thermodynamics of Boron-Sulfur Linked Lewis Acid

From the VT NMR of (11), a Van’t Hoff plot was constructed by plotting the natural logarithm of Keq against the inversion of the temperature (Table 3.5, Figure 3.15). The change in enthalpy, entropy and Gibbs free energy of the cleavage of the dimer (11) were determined to be: ΔH = 34.3 kJ/mol, ΔS = 119.5 J/(mol·K) and ΔG = -1.28 kJ/mol. These thermodynamic parameters are comparable to other related systems: the ethylene linked P B FLP system,71 and the dimethylsulfide adduct of tris(pentafluorophenyl)borane (Scheme 3.9). The standard changes in enthalpy, entropy and Gibbs free energy of the three systems are listed in Table 3.2.

B(C6F5)2

Mes2P B(C6F5)2 Mes2P

B(C6F5)3 SMe2 B(C6F5)3 + SMe2

Ph C6F5 S B C6F5 Ph C6F5 S B B S C6F5 C6F5 C6F5

Scheme 3.9 Thermodynamics of related systems

Table 3.2 Thermodynamic parameters (ΔH , ΔS , ΔG ) of related systems

ΔH ΔS ΔG System (kJ/mol) J/(mol·K) (kJ/mol)

Mes2P B(C6F5)2 66.5 62.8 47.8

B(C F ) SMe 6 5 3 2 76.1 168.1 26.0

Ph C6F5 S B C F Ph 6 5 34.3 119.5 -1.28 B S C6F5 C6F5

The B(C6F5)3·SMe2 system has the highest standard change in entropy of 168.1 J/mol·K which is consistent with the breakage of the adduct to borane and dimethylsulfide as the temperature increases. In contrast, the ethylene-linked P B system shows the lowest standard change in standard entropy of 62.8 J/mol·K consistent with minimal interaction between P and B in the open form of the molecule. The B S linked system has a change in standard entropy intermediate between the two other systems (119.5 J/mol·K). The ethylene-linked P B system has the largest positive standard Gibbs free energy change of 47.8 kJ/mol in agreement with the unfavourable breaking of the P B intereaction. The B(C6F5)3·SMe2 system also has a positive standard Gibbs free energy of 26.0 kJ/mol in agreement with the unfavourable breaking of the B S adduct. The B S linked system has a negative standard Gibbs free energy of -1.28 kJ/mol

49 indicating that the B S monomer is favourable at room temperature, which is confirmed by NMR (Figure 3.3).

3.2.3 FLP Reactivity

The use of (11) in FLP chemistry was investigated (Scheme 3.10). Addition of one equivalent of N-benzylidene-tert-butylamine to (11) resulted in no reaction suggesting FLP formation occurred due to the bulkiness of the aldimine and the C6F5 rings of the Lewis acid. Subsequent addition of 4 atm of hydrogen gas in order to hydrogenate the aldimine led to no reaction. Since N- benzylidene-tert-butylamine is a common substrate used in FLP reactions,10,12,16,31,72 the reaction was gently heated overnight at 60 C to see if the hydrogenation would proceed. However, most of the mixture remained the unreacted Lewis acid and Lewis base and a small amount of HC6F5 could be seen as a distinctive multiplet at 5.83 in the 1H NMR as well as the set of fluorine signals -139.2 (o-F), -154.2 (p-F), -162.4 (m-F) in the 19F{1H} NMR. Furthermore, no reaction occurred when (11) was mixed together with PMes3. Attempts to heterolytically cleave dihydrogen or insert carbon dioxide using this reaction mixture resulted in no reaction as well, and subsequent hydrolysis could be observed by NMR when the reactions were left for several days.

C6F5 S B C6F5

toluene, rt toluene, rt PMes3

CO2, 1 atm NR NR NR CD2Cl2 H2, 4 atm H2, 4 atm d8-toluene d8-toluene

o Lose HC F 60 C 6 5 NR NR

Scheme 3.10 FLP reactivity of (11)

Adding 4 atm of dihydrogen to (11) in d8-toluene also led to no reaction and as time progressed some degradation byproduct could be observed by NMR. Heating (11) in C6D5Br in order to observe o-attack of one of the C6F5 rings, in which fluoride would migrate to the boron center and cyclization would occur, as seen in previous works,73 resulted in no reaction and only degradation of the compound was observed at high temperatures (150 C) (Scheme 3.11).

F F F F C6F5 S B F S B C6F5 F 25oC to 150oC F F

F F

Scheme 3.11 Attempted cyclizations of (11) through heating

3.2.4 Adduct Formations

t PhSCH2B(C6F5)2 formed an adduct with P Bu3 (compound (12), 85% yield) as indicated by the strong sharp borate signal at -7.2 and the small para-meta gap in the 19F{1H} NMR ( p m = 4.3) (Figure 3.5). The phosphorus signal also shifted from 62.4 in free tri-tert-butylphosphine to bound adduct at 68.4. An attempt to heterolytically cleave dihydrogen with compound (12) was unsuccessful. While trying to grow X-ray quality crystals of this adduct, the hydrolysis dimer crystallized, indicating the air- and water-sensitivity of PhSCH2B(C6F5)2 and its derivatives (compound (13), Figure 3.6).

C6F5 C6F5 C6F5 S B S B C F S B C6F5 6 5 C6F5 P O O B S P C6F5 C6F5 PH

(12) (13) (14)

Figure 3.5 Phosphine adducts (12), (14) and hydrolysis dimer (13)

Figure 3.6 POV-ray ball and stick representation of the hydrolysis product (13) with hydrogen atoms omitted other than PH

Table 3.3 Selected bond lengths (Å) and bond angles ( ) of (13)

Bond Bond Length (Å)

S1 C1 1.815(4)

B1 C1 1.620(6)

B1 O1 1.558(5)

B2 O1 1.574(5)

B2 C2 1.621(6)

S2 C2 1.814(4)

S3 C3 1.799(4)

B3 C3 1.628(6)

B3 O2 1.563(5)

B4 O2 1.568(5)

B4 C4 1.612(6)

S4 C4 1.803(4)

Bond Bond Angle ( )

B1 C1 S1 108.7(3)

B1 O1 B2 129.2(3)

B2 C2 S2 108.1(3)

B3 C3 S3 110.5(3)

B3 O2 B4 131.4(3)

B4 C4 S4 110.9(3)

The sulfur carbon bond lengths of (13) (1.799(4) 1.815(4) Å) were consistent with the sulfur carbon bond lengths of dimer (11) (1.814(4) 1.815(4) Å). The boron carbon bond lengths were also similar, which ranged from 1.612(6) 1.628(6) Å and 1.619(6) 1.623(6) Å for compounds (13) and (11) respectively. Comparing the B C S bond angles between (13) and (11), the angle is slightly smaller for the hydrolysis compound (108.1(3) 110.9(3) vs.

¯ 112.5(3) 113.4(3) ). Another four coordinate dimer, [HO(B(C6F5)3)2] , has similar boron oxygen bond lengths compared to compound (13), 1.558(4) 1.563(4) Å and 1.558(5) 1.574(4) Å respectively.74 The B1 O1 B2 bond angle is smaller for (13) which ranged from

¯ 74 129.2(3) 131.4(3) compared to that of [HO(B(C6F5)3)2] which was 140.8(2) .

Similarly, the adduct of PhSCH2B(C6F5)2 with triethylphosphine oxide (14) was prepared in 87% yield. The phosphorus signal shifted from 50.7 in free triethylphosphine oxide to bound adduct at 76.9. The boron signal of PhSCH2B(C6F5)2 shifted from 5.1 upfield to 0.61 and the para-meta gap in the 19F{1H} NMR was also quite small ( p m = 5.1) (Figure 3.5).

3.2.5 Reactions of Internal and Terminal Alkynes

Reaction of PhSCH2B(C6F5)2 with 2,3-dimethylbuta-1,3-diene or 1-hexene showed no addition 6,7,22 products, in contrast to that reported for FLP systems. Interestingly, when PhSCH2B(C6F5)2 is reacted with internal or terminal alkynes, addition across the triple bond occurs and a new heterocycle is produced (Scheme 3.12). This can be attributed to the higher reactivity of alkynes

53 compared to alkenes, due to the greater electron density available in alkynes. In FLP chemistry, this increased reactivity of alkynes manifests itself in the formation of different products: reactions of FLPs with alkynes results in addition or deprotonation whereas reactions of FLPs with alkenes results only in addition.21,67

C6F5 Ph S B C6F5 (18)

C6F5 C6F5 Ph S B Ph C6F5 Ph Ph Ph S B C6F5 C6F5 S B Ph C6F5 Ph Ph (19) (17) H Ph H

C6F5 C6F5 Ph Ph S B C6F5 S B C6F5

Ph H H (15) (16)

Scheme 3.12 Reactions of (11) and terminal and internal alkynes

Compounds (15) (19) were synthesized in moderately high yields (70 92%). Compound (17) required a prolonged reaction time compared to all other heterocycles. NMR after 1 day showed incomplete conversion with some unreacted starting material, (11). This could be due to the bulkiness of the phenyl substituents. This is supported by the faster reaction times of compound (11) with less bulky internal alkynes, 3-hexyne and 1-phenyl-1-hexyne, resulting in compounds (18) and (19) respectively. Reaction times were found to be shorter for the smaller internal alkynes and terminal alkynes (reaction is complete after 1 day instead of 3 days). Reactions with the terminal alkynes phenylacetylene and 1-hexyne were the most facile (compounds (15) and (16)) and the alkynyl proton served the purpose as an NMR handle. In compound (15) the alkenyl proton appeared at 8.33 as a broad singlet whereas the alkenyl proton in compound

(16) was more shielded and appeared at 7.61 in the 1H NMR. All 19F{1H} NMR spectra for compounds (15) (19) depicted two sets of ortho-, meta- and para-fluorine signals corresponding to two inequivalent C6F5 rings. Sharp borate signals ranging from -8.3 to -6.1 were observed for each compound. All compounds were clean by NMR, and typical 1H and 19F{1H} spectra for compounds (16) and (17) are exhibited in Figure 3.7 3.13.

1 Figure 3.7 H NMR of (16) at room temperature in d8-toluene

19 1 Figure 3.8 F{ H} NMR of (16) at room temperature in d8-toluene

Figure 3.9 Close up of o-fluorine and overlapping m- and p-fluorine signals in the 19F{1H} NMR of (16) at room temperature in d8-toluene illustrating inequivalent C6F5 rings

In each of the heterocyclic compounds (15) (19), there are two distinctive doublets present 1 ranging from 2.39 3.73 in the H NMR, corresponding to the inequivalent protons in the CH2 19 1 moiety (Figure 3.7, Figure 3.10). The F{ H} NMR spectra also illustrate inequivalent C6F5 environments in which there are two sets of fluorine signals: two doublets (o-F), two triplets (p- F), and two multiplets (m-F). Sometimes these peaks overlap with each other and are present in these distinctive patterns (Figure 3.8 3.9, Figure 3.12 3.13).

1 Figure 3.10 H NMR of (17) at room temperature in CD2Cl2

1 Figure 3.11 Aromatic region in H NMR of (17) at room temperature in CD2Cl2

19 1 Figure 3.12 F{ H} NMR of (17) at room temperature in CD2Cl2

Figure 3.13 Close up of o-, m- and p-fluorine signals in the 19F{1H} NMR of (17) at room temperature in CD2Cl2 illustrating inequivalent C6F5 rings

Heterocycle formation was confirmed when a single crystal of compound (17) was obtained (Figure 3.14). Selected bond lengths and bond angles of compound (17) are listed in Table 3.4.

Figure 3.14 POV-ray ball and stick representation of heterocycle (17) with hydrogen atoms omitted

Table 3.4 Selected bond lengths (Å) and bond angles ( ) of (17)

Bond Bond Length (Å)

S1 C1 1.8059(14)

S1 C3 1.7887(14)

B1 C1 1.666(2)

B1 C2 1.634(2)

C2 C3 1.3462(19)

Bond Bond Angle ( )

B1 C1 S1 107.44(9)

C2 B1 C1 103.38(11)

C2 C3 S1 113.62(10)

C3 C2 B1 116.53(12)

C3 S1 C1 96.11(7)

Sulfur carbon bond lengths of heterocycle (17) (1.7887(14) 1.8059(14) Å) are slightly shorter than that of the hydrolysis compound (13) (1.799(4) 1.915(4) Å) and shorter still than that of dimer (11) (1.814(4) 1.815(4) Å). Boron carbon bond lengths are the longest for compound (17), which ranges from 1.634(2) 1.666(2) Å, when compared to the hydrolysis compound (1.612(6) 1.628(6) Å) and the dimer (1.619(6) 1.623(6) Å). The five-membered ring contained angles ranging from 96.11(7) 116.53(12) to accommodate for all heteroatoms, which is similar to theoretically calculated cyclopentene (108 for C C C, 120 for C=C C).75 The carbon carbon bond in compound (17) is unusually short for a double bond 1.3462(19) Å, which is shorter than that calculated in cyclopentene (1.44 Å),75 and longer than that of free diphenylacetylene (1.198(3) Å),76 indicating some triple bond character within the carbon carbon double bond.

A proposed mechanism for the addition of alkynes to the boron sulfur linked compound (11) is illustrated in Scheme 3.13. Initial coordination of the least sterically hindered carbon to the boron center is thought to occur first while the sulfur atom stabilizes the multiple bond, similar to Gabbaï’s system shown previously in Scheme 3.1.59 Next, bond formation between the sulfur and terminal carbon ensues, forming the heterocycle.

C F C F C6F5 R R' 6 5 6 5 S B S B C F S B C6F5 C6F5 6 5 R = alkyl, Ph R' = H, alkyl, Ph R R' R' R

Scheme 3.13 Proposed mechanism of the addition of alkynes to PhSCH2B(C6F5)2

This mechanism is speculative, however it may be related to the FLP induced cyclizations resulting from the intramolecular addition of amines to alkenes and alkynes (Scheme 3.14).38 Recently phosphorus/aluminum based FLPs have been reported to form heterocycles upon addition of terminal alkynes (Scheme 3.15).77

B(C6F5)3 NMe2 Me2N B(C6F5)3

NMe2 Me2N B(C6F5)3 B(C6F5)3

Scheme 3.14 Cyclizations via FLPs

Ph t HAl Bu2 H Ph Mes2P Ph t Mes2P Al Bu2 Ph Ph

t t Mes2P Al Bu2 + Mes2P Al Bu2 H Ph H Ph

Scheme 3.15 Cyclizations with a geminal phosphorus/aluminum based FLP and phenylacetylene

Moreover, to test the thermostability of these heterocycles, ~10 mg of compound (15) was dissolved in ~1 mL of d8-toluene, transferred into a J. Young tube and heated overnight. No decomposition occurred when the compound was heated overnight to 60 C or 90 C. Upon further heating to 120 C, only 4% of decomposition was observed in NMR. There was no evidence of a new borane or borate in the 11B{1H} NMR. This indicates that these heterocycles are quite stable and remain intact up to 120 C, negating decomposition. This is also evident when the heterocyclic compounds are reacted with phosphines. Phenylacetylene was added to (11) at room temperature and after stirring for a few minutes, phosphine was subsequently added at -38 C (trimesitylphosphine or tri-tert-butylphosphine). After stirring overnight, the solvent was removed in vacuo and only heterocycle (15) was formed and free phosphine was observed in NMR (Scheme 3.16).

C6F5 C6F5 1. HC CPh, rt, toluene S B C F + PR S B C F o 6 5 3 6 5 2. PR3, -38 C, toluene

R = Mes, tBu

Scheme 3.16 Lack of reactivity between (15) and PR3

3.3 Conclusions

A new boron sulfur linked Lewis acid, PhSCH2B(C6F5)2, was synthesized and characterized crystallographically and by multinuclear NMR spectroscopy. VT NMR allowed the determination of the thermodynamic parameters of the system and could be compared to similar systems (Appendix A). The standard change in enthalpy was determined to be 34.3 kJ/mol, the standard change in entropy was 119.5 J/mol·K and the standard change in Gibbs free energy was found to be -1.28 kJ/mol. Despite the air/moisture sensitivity and unreactive FLP nature of

PhSCH2B(C6F5)2, it was proven to show interesting reactivity with alkynes forming novel boron- and sulfur-containing heterocycles.

3.4 Experimental 3.4.1 General Considerations

C6D5Br, Na/Ph2CO for d8-toluene), were subsequently sonicated for half an hour, and were subsequently vacuum transferred into a dry 100 mL bomb charged with activated 4 Å molecular sieves. Molecular sieves were activated by storage overnight in an oven at 120 C. Reagents were purchased from Sigma Aldrich (thioanisole, 2-bromothioanisole), Strem Chemicals or

Acros and were stored in the glove box except for the sulfur precursors which were stored over 4 Å molecular sieves and kept inside the fumehood. nBuLi was stored in the freezer at -38 C. All gas reactions were performed in a J. Young tube.

A 400 MHz Bruker UltraShield spectrometer, a 400 MHz Bruker Avance III Automatic Sample Changer or a 400 MHz Varian Mercury spectrometer were used to perform 1H, 13C , 11B, 19F and 31P NMR spectroscopy. 1H resonances were referenced internally to the residual protonated 13 solvent resonance (δ 5.32 ppm for CD2Cl2, δ 2.09 for d8-toluene, δ 6.94 for C6D5Br), C resonances were referenced internally to the deuterated solvent resonance (δ 54.0 ppm for 11 1 19 1 CD2Cl2), B{ H} resonances were referenced externally to BF3∙Et2O, F{ H} resonances were 31 1 referenced externally to 80% CFCl3 in CDCl3, and P{ H} resonances were referenced 13 1 1 externally to 85% H3PO4. To aid in the assignment of carbon atoms in the C{ H} NMR, H- 13C HSQC experiments were carried out using conventional pulse sequences. Chemical shifts (δ) are expressed in ppm and coupling constants (J) in Hz. Elemental analysis was performed using a Perkin-Elmer CHN analyzer.

3.4.2 Synthesis and Characterization of Boron-Sulfur Linked Lewis Acid

Experimental Procedure for compound (11): First the lithiation of compound (11) was carried out by either reacting 2-bromothioanisole with 1.1eq. nBuLi (route A) or thioanisole with 1.1eq. nBuLi in diethylether (route B, Scheme 3.17).

Route A

Br nBuLi (1.1 eq.) o S -78 C, Et2O

Route B S Li

nBuLi (1.1 eq.) (11a) -78oC, Et O S 2

Scheme 3.17 Formation of lithiated precursor (11a)

Route A: In a pre-weighed 50 mL Schlenk flask with a stirbar, ~25 mL of Et2O was added via cannula or syringe. To the reaction vessel 0.30 mL of 2-bromothioanisole (2.25 mmol) was added via a needle under a constant flow of N2 gas. The flask was then submerged in an acetone/dry ice bath and the contents were stirred for a few minutes to allow for the temperature to equilibrate to -78 C. Next, 1.55 mL of 1.6 M nBuLi in hexanes (2.47 mmol) was added dropwise to the cold solution using a needle and syringe. The reaction was allowed to stir for at least 2 hours at -78 C in which the clear colourless solution turned milky (colours varied from pale yellow to white). The solution was allowed to warm up to room temperature to evacuate the volatiles and the contents were dried for at least 2 hours. An off-white to pale yellow precipitate resulted and yields were over 100% due to impurities and brominated side products.

Route B: In a pre-weighed 50 mL Schlenk flask with a stirbar, ~25 mL of Et2O was added via cannula or syringe. To the reaction vessel 0.38 mL of thioanisole (3.23 mmol) was added via a needle under a constant flow of N2 gas. The flask was then submerged in an acetone/dry ice bath and the contents were stirred for a few minutes to allow for the temperature to equilibrate to -78 C. Next, 2.22 mL of 1.6 M nBuLi in hexanes (3.56 mmol) was added dropwise to the cold solution using a needle and syringe. The reaction was allowed to stir for at least 2 hours at -78 C in which the clear colourless solution turned slightly milky pale yellow. The solution was allowed to warm up to room temperature to evacuate the volatiles and the contents were dried for at least 2 hours. A pale yellow precipitate resulted and yields were over 100% due to impurities and side products.

+ ClB(C6F5)2 C6F5 -38oC, hexanes or pentane S B S Li C6F5 (11a) (11)

Scheme 3.18 Synthesis of compound (11)

The lithiated compound (11a) was then reacted with ClB(C6F5)2, the latter of which was prepared previously (Scheme 3.18).63 In a 20 mL scintillation vial with stir bar, 0.241 g of (11a) (1.85 mmol) was weighed out and put in a cold brass ring from the glovebox freezer (-38 C). To (11a), ~2 mL of cold pentane was added and the mixture was stirred. In a separate scintillation vial, 0.704 g of ClB(C6F5)2 (1.85 mmol) was weighed out and dissolved in ~10 mL of cold

64 pentane (-38 C). The chloroborane solution was transferred to the vial with the lithiated compound while vigorously stirring cold. The vial was capped tightly and kept stirring overnight while the reaction mixture slowly warmed to room temperature. If the (11a) used was produced from thioanisole, the reaction mixture turned milky white and if the (11a) used was produced from 2-bromothioanisole, the reaction mixture turned milky bright yellow. Upon filtration of the reaction mixture and discarding the solute, the product (11) can be extracted from dissolving the resulting precipitate in toluene in low yields (32%). Repeated extractions from the precipitate led to slightly higher yields. The final product (11) is a fine white powder.

The reaction of the lithiated compound (11a) with ClB(C6F5)2 to produce compound (11) proved to be somewhat difficult in the second step where the chloroborane is added. Addition of reagents must be carried out at low temperature since a vigorous reaction producing brown unidentified products occurred at room temperature. In addition, extraction of compound (11) in toluene sometimes results in a clear colourless oil which does not produce a precipitate as expected. Furthermore, the corresponding NMR shows multiple side products. This behavior is believed to be resulting from contamination of compound (11a). Moreover, hydrolysis of the chloroborane to (C6F5)2B-O-B(C6F5)2 could occur if one is not careful making compound (11a).58 This compound is most stable in toluene and bromobenzene and some solvent interaction can be observed in chlorinated solvents such as dichloromethane in which multiple signals are observed in the 1H NMR spectrum.

6 7 F F Ph C6F5 2 5 1 F F S B 3 4 C6F5 Ph S B F B S C6F5 C6F5 C6F5 PhSCH2B(C6F5)2 (11)

1 H NMR (d8-toluene, 400 MHz): δ 6.72 (d, 2H, H-1), 6.59–6.55 (m, 3H, H-2, H-3), 2.82 (s, 2H, 1 H-4); H NMR (d8-toluene, 400 MHz, -60 C): δ 6.74 (d, 2H, H-1), 6.45 (t, 1H, H-3), 6.32 (t, 19 1 2H, H-2), 3.39 (s, 2H, H-4); F{ H} NMR (d8-toluene, 377 MHz): δ -130.7 (m, 4F, F-5), -153.6 3 19 1 (t, 2H, JF-F = 20.4 Hz, F-7), -163.0 (m, 4F, F-6); F{ H} NMR (d8-toluene, 377 MHz, -60 C): δ 3 3 -126.3 (m, 1F, o-F), -128.7 (m, 1F, o-F), -132.1 (d, 1F, JF-F = 24.3 Hz, o-F), -132.4 (d, 1F, JF-F

3 3 = 24.3 Hz, o-F), -153.7 (t, 1F, JF-F = 21.7 Hz, p-F), -153.8 (t, 1F, JF-F = 21.7 Hz, p-F), -161.8 11 1 (m, 1F, m-F), -162.2 (m, 1F, m-F), -162.5 (m, 1F, m-F), -162.6 (m, 1F, m-F); B{ H} NMR (d8- 13 1 toluene, 128 MHz): δ 5.1 (s); C{ H} NMR partial (CD2Cl2, 100 MHz): δ 130.7 (s, C-3), 129.9

(s, C-1), 129.8 (s, C-2), 33.3 (s, C-4); Yield: 32%; Anal Calcd for C19H7BF10S: C 48.75, H 1.51; Found: C 49.22, H 1.65. X-ray quality crystals of the dimer were obtained from a concentrated solution of product in toluene and bromobenzene at -38 C.

3.4.3 Thermodynamic Calculations for (11)

From the VT NMR of compound (11), one can calculate the change in enthalpy ( H), change in entropy ( S), and change in Gibbs free energy ( G) of the system. By measuring the integral of the peak corresponding to the CH2 protons of the monomer of (11) as well as the integral of the peak corresponding to the CH2 protons of the dimer that appears at lower temperatures, one can obtain a monomer to dimer ratio and calculate the equilibrium constant Keq. At room temperature the 1H resonances were referenced internally to the residual protonated solvent 1 resonance (δ 2.09 for d8-toluene) and at every other temperature the H resonances were referenced externally to the aryl protons of trimethoxyborane (δ 6.14). A Van’t Hoff plot was then constructed by plotting the natural logarithm of Keq against the inversion of the temperature (Figure 3.15). The data used to construct the Van’t Hoff plot are tabulated in Table 3.5.

Table 3.5 Data used in Van’t Hoff plot for PhSCH2B(C6F5)2

-1 Keq = ∫ monomer/ T ( C) T (K) 1/T (K ) ∫ monomer ∫ dimer ln(Keq) ∫ dimer

15 288 0.00347 10000.00 8084.02 1.237 0.213

5 278 0.00360 10000.00 13271.53 0.753 -0.283

-5 268 0.00373 10000.00 43961.46 0.227 -1.481

-15 258 0.00388 10000.00 57090.23 0.175 -1.742

-25 248 0.00403 10000.00 110865.80 0.090 -2.406

-35 238 0.00420 10000.00 151386.89 0.066 -2.717

Figure 3.15 Van’t Hoff plot showing the relationship between the dimer and monomer of compound (11)

3.4.4 Synthesis and Characterization of Phosphine Adducts

Experimental Procedure for compounds (12) and (14): In a 20 mL scintillation vial with a stirbar in a cold brass ring (-38 C), 49.1 µmol of compound (11) (23.0 mg) and 49.1 µmol of phosphine (9.94 mg tri-tert-butylphosphine, 6.59 mg triethylphosphine oxide) were weighed out. These compounds were dissolved in ~4 mL of cold toluene (-38 C) and stirred overnight (-38 C to 25 C). Subsequent evacuation of solvent resulted in clear colourless oils. Addition of cold pentane and placement of the vial in the glovebox freezer overnight resulted in a white precipitate.

8 9 F F

2 7 1 F F 3 4 S B F P C6F5 6

(12)

1 3 H NMR (d8-toluene, 400 MHz): δ 7.37 (d, 2H, JH-H = 7.4 Hz, H-1), 6.89–6.85 (m, 2H, H-2), 1 3 6.83–6.81 (m, 1H, H-3), 2.38 (d, 2H, JH-H = 16.4 Hz, H-4), 0.93 (d, JH-H = 13.3 Hz, 27Hz, H-5); 19 1 3 F{ H} NMR (d8-toluene, 377 MHz): δ -129.6 (br m, 4F, F-7), -160.6 (t, 2F, JF-F = 20.6 Hz, F- 11 1 31 1 9), -164.9 (m, 4F, F-8); B{ H} NMR (d8-toluene, 128 MHz): δ -7.2 (s); P{ H} NMR (d8- 13 1 toluene, 162 MHz): δ 68.4 (s); C{ H} NMR partial (CD2Cl2, 100 MHz): δ 134.2 (s, C-2), 2 128.2 (s, C-1), 125.4 (s, C-3), 40.0 (d, JP-C = 31.2 Hz, C-6), 30.9 (br s, C-4, C-5); Yield: 85%;

Anal Calcd for C31H34BF10PS: C 55.54, H 5.11; Found: C 54.92, H 5.70. Closest agreement obtained after repeated elemental analysis (H is 0.59% off). Low carbon content due to boron carbide formation.78-80 Closest agreement obtained after repeated elemental analysis.

8 9 F F

2 7 1 F F 3 4 S B F C F 5 O 6 5 6 P

(14)

1 H NMR (CD2Cl2, 400 MHz): δ 7.28–7.25 (m, 2H, H-1), 7.25–7.21 (m, 2H, H-2), 7.07–7.03 (m, 1H, H-3), 2.74 (s, 2H, H-4), 2.07–1.98 (m, 6H, H-5), 1.21–1.08 (m, 9H, H-6); 19F{1H} NMR 3 (CD2Cl2, 377 MHz): δ -134.7 (m, 4F, F-7), -160.1 (t, 2F, JF-F = 20.1 Hz, F-9), -165.2 (m, 4F, F- 11 1 31 1 8); B{ H} NMR (CD2Cl2, 128 MHz): δ 0.61 (s); P{ H} NMR (CD2Cl2, 162 MHz): δ 76.9 (s); 13 1 C{ H} NMR partial (CD2Cl2, 100 MHz): δ 141.9 (s, ipso C), 129.1 (s, C-2), 126.4 (s, C-1), 1 2 124.5 (s, C-3), 28.2 (s, C-4), 18.3 (d, JP-C = 65.7 Hz, C-5), 5.8 (d, JP-C = 4.7 Hz, C-6); Yield:

87%; Anal Calcd for C25H22BF10OPS: C 49.86, H 3.68; Found: C 51.01, H 4.14. Closest agreement obtained after repeated elemental analysis (C is 1.15% off).

3.4.5 Synthesis and Characterization of Five-membered Boron-Sulfur Heterocycles

Experimental Procedure for compounds (15)–(16), (18)–(19): In a 20 mL scintillation vial with a stirbar in a cold brass ring (-38 C), 64.1 µmol of compound (11) (30.0 mg) was weighed out and dissolved in ~4 mL of cold toluene (-38 C). Next, 64.1 µmol of terminal or internal alkyne (6.55 mg phenylacetylene, 5.26 mg 1-hexyne, 5.26 mg 3-hexyne and 10.1 mg 1-pheynyl- 1-hexyne respectively) was added to the vial via a 0.50 cc syringe. The solution was stirred overnight (-38 C to 25 C) and subsequent evacuation of solvent resulted in clear colourless oils. Addition of cold pentane and placement of the vial in the glovebox freezer overnight resulted in a white to off-white precipitate.

Experimental Procedure for compound (17): In a 20 mL scintillation vial with a stirbar in a cold brass ring (-38 C), 29.0 mg of compound (11) (61.9 µmol) and 11.0 mg of diphenylacetylene (61.9 µmol) were weighed out. These compounds were dissolved in ~4 mL of cold toluene (-38 C) and stirred for 3 days (-38 C to 25 C). Subsequent evacuation of solvent resulted in a light brown oil. Addition of cold pentane and placement of the vial in the glovebox freezer overnight and evacuation of volatiles resulted in clear colourless cubic crystals.

10 11 F F

2 9 F 1 F 3 4 F F S B F 6 5 F F14 12 F 13 7

8 (15)

1 3 H NMR (d8-toluene, 400 MHz): δ 8.33 (s, 1H, H-5), 7.08–7.06 (m, 2H, H-6), 6.88 (d, 2H, JH-H = 7.5 Hz, H-1), 6.84–6.79 (m, 3H, H-2, H-3), 6.64–6.60 (m, 1H, H-8), 6.56–6.52 (m, 2H, H-7), 1 1 19 1 3.46 (d, 1H, JH-H = 13.6 Hz, H-4a), 2.60 (d, 1H, JH-H = 13.6 Hz, H-4b); F{ H} NMR (d8- 3 3 toluene, 377 MHz): δ -132.6 (d, 2F, JF-F = 24.2 Hz, F-9), -133.5 (d, 2F, JF-F = 24.2 Hz, F-12), 3 3 -159.3 (t, 1F, JF-F = 20.2 Hz, F-11), -159.5 (t, 1F, JF-F = 20.2 Hz, F-14), -163.7 (m, 2F, F-10), 11 1 13 1 -164.0 (m, 2F, F-13); B{ H} NMR (d8-toluene, 128 MHz): δ -7.8 (s); C{ H} NMR partial

(CD2Cl2, 100 MHz): δ 133.7 (s, C-8), 131.5 (s, ipso C), 131.2 (s, C-7), 129.9 (s, C-6), 129.5 (s,

C-2, C-3), 129.3 (s, ipso C), 127.2 (s, C-1), 39.4 (s, C-4); Yield: 88%; Anal Calcd for

C27H13BF10S: C 56.87, H 2.30; Found: C 56.03, H 2.71. Low carbon content due to boron carbide formation.78-80 Closest agreement obtained after repeated elemental analysis.

12 11 F F

2 10 F 1 F 3 4 F S B F F 7 5 F13 F15 F 9 6 14 8 (16)

1 3 H NMR (d8-toluene, 400 MHz): δ 7.61 (s, 1H, H-5), 6.96 (d, 2H, JH-H = 7.6 Hz, H-1), 6.85 (t, 3 3 1 1H, JH-H = 7.6 Hz, H-3), 6.76 (t, 2H, JH-H = 7.6 Hz, H-2), 3.57 (d, 1H, JH-H = 11.8 Hz, H-4a), 1 2.49 (d, 1H, JH-H = 11.8 Hz, H-4b), 1.87–1.79 (m, 1H, H-6a), 1.63–1.55 (m, 1H, H-6b), 1.24– 3 19 1 1.16 (m, 2H, H-7), 1.06–0.89 (m, 2H, H-8), 0.65 (t, 3H, JH-H = 7.2 Hz, H-9); F{ H} NMR (d8- 3 3 toluene, 377 MHz): δ -132.9 (d, 2F, JF-F = 19.3 Hz, F-10), -133.6 (d, 2F, JF-F = 19.3 Hz, F-13), 3 3 -159.6 (t, 1F, JF-F = 20.4 Hz, F-12), -159.7 (t, 1F, JF-F = 20.4 Hz, F-15), -163.9 (m, 2F, F-11), 11 1 13 1 -164.0 (m, 2F, F-14); B{ H} NMR (d8-toluene, 128 MHz): δ -8.3 (s); C{ H} NMR partial

(CD2Cl2, 100 MHz): δ 135.6 (s, ipso C), 134.0 (s, C-3), 131.3 (s, C-2), 130.4 (s, C-1), 129.9 (s, ipso C), 42.9 (s, C-4), 30.8 (s, C-6), 30.7 (s, C-7), 22.4 (s, C-8), 14.0 (s, C-9); Yield: 91%; Anal

Calcd for C25H17BF10S: C 54.57, H 3.11; Found: C 52.79, H 3.37. Low carbon content due to boron carbide formation.78-80 Closest agreement obtained after repeated elemental analysis.

12 13 F F

2 11 F 1 F 3 4 F B F S F F14 F 16 5 F 15 6 8

7 9 10 (17)

1 H NMR (CD2Cl2, 400 MHz): δ 7.75–7.73 (m, 2H, Ar-H), 7.57–7.52 (m, 1H, Ar-H), 7.52–7.48 (m, 2H, Ar-H), 7.39–7.36 (m, 1H, Ar-H), 7.15–7.12 (m, 2H, Ar-H), 7.12–7.09 (m, 3H, Ar-H),

1 7.06–7.00 (m, 2H, Ar-H), 6.89–6.87 (m, 2H, Ar-H), 3.81 (d, 1H, JH-H = 12.2 Hz, H-4a), 2.76 (d, 1 19 1 3 1H, JH-H = 12.2 Hz, H-4b); F{ H} NMR (CD2Cl2, 377 MHz): δ -131.9 (d, 2F, JF-F = 24.2 Hz, 3 3 F-11), -133.1 (d, 2F, JF-F = 24.2 Hz, F-14), -160.9 (t, 1F, JF-F = 20.0 Hz, F-13), -161.3 (t, 1F, 3 11 1 JF-F = 20.0 Hz, F-16), -165.3 (m, 2F, F-12), -165.8 (m, 2F, F-15); B{ H} NMR (CD2Cl2, 128 13 1 MHz): δ -6.3 (s); C{ H} NMR partial (CD2Cl2, 100 MHz): δ 133.8 (s, Ar-C), 133.4 (s, ipso C), 132.1 (s, Ar-C), 131.2 (s, Ar-C), 130.7 (s, ipso C), 130.6 (s, Ar-C), 130.2 (s, Ar-C), 129.1 (s, Ar-C), 129.0 (s, Ar-C), 128.9 (s, Ar-C), 128.1 (s, Ar-C), 127.3 (s, Ar-C), 43.0 (s, C-4); Note: all Ar-H and Ar-C are associated with protons and carbons 1–3, 5–10; Yield: 70%; Anal Calcd for

C33H17BF10S: C 61.32, H 2.65; Found: C 60.95, H 3.10. Due to the multiple aryl signals in compound (17), aryl protons and carbons could not be assigned in the NMR spectra. X-ray quality crystals were grown from submerging the product in a solution of pentane at -38 C overnight, and the consequent evacuation of solvent resulted in clear colourless cubic crystals.

11 10F F

2 9 F 1 F 3 4 F B F S F F F14 5 7 12 6 F13 8

(18)

1 H NMR (CD2Cl2, 400 MHz): δ 7.67–7.64 (m, 2H, H-1), 7.64–7.62 (m, 1H, H-3), 7.60–7.55 1 3 (m, 2H, H-2), 3.55 (d, 1H, JH-H = 12.9 Hz, H-4a), 2.62 (sextet, 1H, JH-H = 7.7 Hz, H-7a), 2.52– 1 3 2.47 (m, 2H, H-6), 2.39 (d, 1H, JH-H = 12.9 Hz, H-4b), 1.83 (sextet, 1H, JH-H = 7.7 Hz, H-7b), 3 3 19 1 1.03 (t, 3H, JH-H = 7.7 Hz, H-5), 0.64 (t, 3H, JH-H = 7.7 Hz, H-8); F{ H} NMR (CD2Cl2, 377 3 MHz): δ -132.6 (m, 2F, F-9), -133.2 (m, 2F, F-12), -159.7 (t, 1F, JF-F = 20.2 Hz, F-11), -159.8 (t, 3 11 1 1F, JF-F = 20.2 Hz, F-14), -164.0 (m, 2F, F-10), -164.1 (m, 2F, F-13); B{ H} NMR (CD2Cl2, 13 1 128 MHz): δ -7.0 (s); C{ H} NMR partial (CD2Cl2, 100 MHz): δ 133.8 (s, C-3), 131.3 (s, C- 2), 130.4 (s, C-1), 43.3 (s, C-4), 25.5 (s, C-6), 21.3 (s, C-7), 14.5 (s, C-8), 13.1 (s, C-5); Yield:

80%; Anal Calcd for C25H17BF10S: C 54.57, H 3.11; Found: C 53.28, H 3.28. Low carbon content due to boron carbide formation.78-80 Closest agreement obtained after repeated elemental analysis.

13 14 F F

12 2 F 1 F 3 4 F B F S F 9 F F17 8 15 F16 10 7 11 6 5 (19)

1 H NMR (CD2Cl2, 400 MHz): δ 7.63–7.61 (m, 2H, H-9), 7.53–7.49 (m, 1H, H-11), 7.48–7.44 (m, 2H, H-10), 7.31–7.28 (m, 2H, H-1), 7.28–7.26 (m, 2H, H-2), 7.24–7.20 (m, 1H, H-3), 3.73 1 1 (d, 1H, JH-H = 13.2 Hz, H-4a), 2.68–2.62 (m, 1H, H-8a), 2.45 (d, 1H, JH-H = 13.2 Hz, H-4b), 2.41–2.34 (m, 1H, H-8b), 0.92–0.86 (m, 2H, H-7), 0.84–0.74 (m, 1H, H-6a), 0.51 (t, 3H, H-5), 19 1 0.41–0.40 (m, 1H, H-6b); F{ H} NMR (d8-toluene, 377 MHz): δ -132.6 (m, 2F, F-12), -133.0 3 3 (m, 2F, F-15), -159.5 (t, 1F, JF-F = 20.3 Hz, F-14), -159.6 (t, 1F, JF-F = 20.3 Hz, F-17), -163.8 11 1 13 1 (m, 2F, F-13), -163.9 (m, 2F, F-16); B{ H} NMR (d8-toluene, 128 MHz): δ -6.1 (s); C{ H}

NMR partial (CD2Cl2, 100 MHz): δ 133.6 (s, C-6), 133.5 (s, ipso C), 132.0 (s, ipso C), 131.6 (s, ipso C), 131.1 (s, C-10), 130.3 (s, C-9), 129.7 (s, C-1), 129.4 (s, C-3), 129.0 (s, C-2), 128.8 (s, ipso C), 127.1 (s, ipso C), 43.6 (s, C-4), 32.3 (s, C-8), 31.3 (s, C-6), 23.5 (s, C-7), 13.6 (s, C-5);

Yield: 92%; Anal Calcd for C31H21BF10S: C 59.44, H 3.38; Found: C 57.72, H 3.65. Low carbon content due to boron carbide formation.78-80 Closest agreement obtained after repeated elemental analysis.

3.4.6 X-ray Data Collection, Reduction, Solution and Refinement

72 refined by full-matrix least-squares on F2 using XL as implemented in the SHELXTL solution package.

Table 3.6 Crystallographic data for compounds (11), (13) and (17)

Crystal (11) (13) (17)

Formula C38H14B2F20S2 C100H84B4F40O2P2S4 C33H17BF10S

Formula weight 936.23 2311.09 647.34

Crystal system Monoclinic Orthorhombic Monoclinic

Space group P21/n P212121 C2/c a (Å) 8.1411(7) 15.7991(12) 31.0478(12) b (Å) 18.587(2) 19.3599(14) 11.4951(4) c (Å) 23.881(3) 32.888(3) 18.9964(7)

α (o) 90.00 90.00 90.00

β (o) 96.257(4) 90.00 122.759(2)

γ (o) 90.00 90.00 90.00

V (Å3) 3594.0(6) 10059.3(13) 5701.5(4)

Z 4 4 8 d (calc) g·cm-3 1.730 1.526 1.508

Abs coeff, µ, mm-1 0.284 0.251 0.203

Data collected 6329 17712 8625

2 2 Data Fo >2σ(Fo ) 4011 12804 6376

Variables 559 1377 406

R1 0.0546 0.0464 0.0436 wR2 0.1373 0.1041 0.1200

Goodness of Fit 1.015 0.994 1.030

2 2 2 2 2 1/2 R1 = ∑||Fo|-|Fc||/∑|Fo|; wR2 = [∑w(Fo – Fc ) /∑w(Fo ) ]

4 Summary and Conclusions

Frustrated Lewis pairs are a growing field in inorganic chemistry. Veering away from the “classical FLP systems” which contain phosphine/borane entities has led to many other combinations of bulky Lewis acids and Lewis bases. Regrettably, gold(I) and copper(I) imidazolium complexes do not form FLPs with the ordinary bulky phosphines and amines which are known to undergo FLP reactivity.5 These compounds form very stable adducts and do not react with H2, CO2, N2O, ring-open THF or add to alkenes or alkynes, even upon heating or cooling. However, a substantial number of new compounds were characterized crystallographically and the molecular structures led insight as to why the activation of s mall molecules was unsuccessful. Anagostic interactions were present in compounds

+ ¯ + ¯ [IDippAuPMes3] [OTf] and [IDippCuPMes3] [OTf] , and agostic interactions were displayed in [IDippCuTMP]+[OTf]¯ helping to stabilize the metal center and making it even harder to break the adduct. Soft and hard acid/base theory also explains that both the Lewis acid and Lewis base were more likely to make classical Lewis acid-base adducts and thus remained inert.

The moisture sensitivity of FLPs has always been an issue, and FLP systems which can withstand the presence of trace water are constantly being sought after. Protecting the Lewis acid with group(s) involved in hemilabile interactions, which can exclude molecules such as water but include substrates would be ideal in overcoming this obstacle. The boron sulfur methylene-linked Lewis acid, PhSCH2B(C6F5)2, was an attempt to solve this problem, however hydrolysis products confirmed that this is still a challenge. Nevertheless, this new Lewis acid demonstrated interesting reactivity with terminal and internal alkynes in which 5-membered boron sulfur heterocycles were produced. However, this work is still preliminary and the reactivity with many substrates remains to be explored. Incorporating different main group elements into the Lewis acid of an FLP system is perhaps a step in the right direction in developing an ultimately water-stable molecule. Routes to synthesize such FLPs are being explored.

Appendix A: Thermodynamic studies of B(C6F5)3·SMe2 A.1 Introduction

Prior to commencing the development of boron sulfur linked Lewis acids, a simpler model was examined to determine the feasibility of this project. The dimethylsulfide adduct of tris(pentafluorophenyl)borane has previously been reported by Lancaster and Hughes as well as Denis and coworkers in 2003.65,66 This is possibly the simplest boron sulfur adduct reported in the literature and by probing its thermodynamics as well as reactivity in FLP chemistry, one can determine the relationship between boron and sulfur and whether there exists a hemilabile interaction between the two atoms.

A.2 Experimental A.2.1 General Considerations

All reactions were performed under dry, oxygen-free atmospheres either in a nitrogen-filled Innovative Technologies glove box or on a Schlenk line under nitrogen. All solvents used were purchased from Caledon Laboratories and dried through a PureSolve solvent system. All deuterated solvents were purchased from Acros or Cambridge Isotope Laboratories. Deuterated solvents were dried overnight with the corresponding drying agent (CaH2 for C6D5Br), were subsequently sonicated for half an hour, and were subsequently vacuum transferred into a dry 100 mL bomb charged with activated 4 Å molecular sieves. Molecular sieves were activated by storage overnight in an oven at 120 C. Tris(pentafluorophenyl)borane was purchased from Boulder Scientific and was stored in the glovebox. Dimethylsulfide was purchased from Sigma Aldrich and was degassed and stored in a bomb with 4 Å molecular sieves. All gas reactions were performed in a J. Young tube.

A 400 MHz Bruker UltraShield spectrometer was used to perform 1H, 11B, 19F and 31P NMR spectroscopy. 1H resonances were referenced internally to the residual protonated solvent 11 1 resonance (δ 6.94 for C6D5Br), B{ H} resonances were referenced externally to BF3∙Et2O, 19 1 31 1 F{ H} resonances were referenced externally to 80% CFCl3 in CDCl3, and P{ H} resonances

were referenced externally to 85% H3PO4. Chemical shifts (δ) are expressed in ppm and coupling constants (J) in Hz.

A.2.2 Synthesis of B(C6F5)3·SMe2

Experimental procedure was followed as per Lancaster and Hughes and B(C6F5)3·SMe2 was obtained in 82% yield (Scheme A.1).65 NMR spectra correlated with literature values.

B(C F ) + 3 SMe2 B(C F ) SMe2 6 5 3 toluene, 60oC 6 5 3 3 hrs

Scheme A.1 Synthesis of B(C6F5)3·SMe2

A.3 Results and Discussion A.3.1 Reactions with Hydrogen

t The combination of B(C6F5)3 and bulky phosphines (P Bu3, PMes3) can heterolytically split 11 hydrogen. When the dimethylsulfide adduct of B(C6F5)3 is used and reacted with the same bulky phosphines, the identical outcome is observed (Scheme A.2).

1) B(C6F5)3 SMe2 + PR3 NR C6D5Br, rt

H , 4 atm 2 - + 2) B(C6F5)3 SMe2 + PR3 [HB(C6F5)3] [HPR3] + SMe2 C6D5Br, rt

t R = Mes, Bu

Scheme A.2 Reactivity of B(C6F5)3·SMe2 with hydrogen

t When P Bu3 or PMes3 is combined with B(C6F5)3·SMe2 in solution at room temperature, no reaction occurs, analogous to previous observations with B(C6F5)3. However, upon pressurizing the J. Young tube with 4 atm of hydrogen gas, cleavage of dihydrogen occurred. P H coupling 1 31 1 could be seen in the H NMR as well as the P NMR ( JP-H = 433 or 480 Hz). Although the

B H coupling could not be seen in the 1H NMR, the sharp signal in the 11B NMR confirmed a four-coordinate boron species. Moreover, the NMR data for these two reactions correlated 11 closely with that of the literature, with slight variations due to the trapped SMe2 in solution. These reactions were only performed on a small scale (mg) in a J. Young tube to confirm reactivity and were not isolable since the products without SMe2 have been fully characterized previously,11 thus no 13C{1H} NMR were obtained.

+ ¯ [HPMes3] [HB(C6F5)3] + SMe2

1 1 4 H NMR (C6D5Br, 400 MHz): δ 8.06 (d, 1H, JP-H = 480 Hz, P-H), 6.72 (d, JP-H = 3.0 Hz, 6H,

P(C6H2Me)3), 2.09 (s, 9H, P(C6H2Me-4)3), 2.01 (br s, 9H, P(C6H2Me-2)3), 1.86 (s, 6H, SMe2), 11 1 19 1 1.75 (br s, 9H, P(C6H2Me-6)3; B{ H} NMR (C6D5Br, 128 MHz): δ -24.8 (s); F{ H} NMR 3 3 (C6D5Br, 377 MHz): δ -132.1 (d, 6F, JF-F = 19.1 Hz, o-F), -163.4 (t, 3F, JF-F = 21.0 Hz, p-F), 31 1 -166.2 (m, 6F, m-F); P{ H} NMR (C6D5Br, 162 MHz): δ -26.7 (s).

t + ¯ [HP Bu3] [HB(C6F5)3] + SMe2

1 1 H NMR (C6D5Br, 400 MHz): δ 4.57 (d, 1H, JP-H = 433 Hz, P-H), 1.86 (s, 6H, SMe2), 1.00 (d, 4 t 11 1 19 1 27H, JH-H = 15.7 Hz, P( Bu)3); B{ H} NMR (C6D5Br, 128 MHz): δ -24.7 (s); F{ H} NMR 3 3 (C6D5Br, 377 MHz): δ -132.1 (d, 6F, JF-F = 19.2 Hz, o-F), -162.8 (t, 3F, JF-F = 20.8 Hz, p-F), 31 1 -165.8 (m, 6F, m-F); P{ H} NMR (C6D5Br, 162 MHz): δ 59.4 (s).

Care should be taken when doing these reactions even when synthesizing B(C6F5)3·SMe2 since hydrolysis can easily occur to form the hydroxide or water adduct of - tris(pentafluorophenyl)borane: [HOB(C6F5)3] or H2O·B(C6F5)3. It is notable that the reaction times for the hydrogenation of B(C6F5)3·SMe2 with phosphine is much slower than that of

B(C6F5)3. While the latter reactions occurred in 12 hours, the former reactions did not go to completion even after 2 weeks and when heated to 60 C overnight for a few days. This is due to the strong adduct of the dimethylsulfide and the inability to mix the contents of the J. Young tube.

A.3.2 Thermodynamics of B(C6F5)3·SMe2

VT NMR was performed in order to determine the change in enthalpy ( H), change in entropy ( S), and change in Gibbs free energy ( G) of the system described in Scheme A.3. At room temperature the 1H resonances were referenced internally to the residual protonated solvent 1 resonance (δ 6.94 for C6D5Br) and at every other temperature the H resonances were referenced externally to the methyl protons of trimethoxyborane (δ 3.51). The adduct B(C6F5)3·SMe2 and 1 free B(C6F5)3 and SMe2 were monitored by the two peaks in the H NMR corresponding to the methyl protons. At room temperature there is only one peak occurring at 1.60 for the dimethylsulfide adduct ( adduct). At 140 C there is no more adduct and there is only free

B(C6F5)3 and SMe2 species in which the methyl protons occur at 1.84 ( free). At temperatures between 25 140 C, this peak shift ( peak) was monitored, as displayed in Figure A.1.

140oC B(C6F5)3 SMe2 B(C6F5)3 + SMe2 rt

Scheme A.3 Relationship studied of the adduct B(C6F5)3·SMe2 and free B(C6F5)3 and SMe2

Figure A.1 VT of 1H NMR tracking the methyl shift from adduct to free dimethylsulfide

Using these chemical shifts, the ratio of adduct converted to free species can be calculated by the expression:

Ratio converted = | peak - adduct| / | adduct - free|

From this ratio, the concentrations of the adduct [B(C6F5)3·SMe2], and free species [B(C6F5)3],

[SMe2], can be calculated by knowing the initial concentration of [B(C6F5)3·SMe2]i from the beginning.

The initial concentration of [B(C6F5)3·SMe2]i is calculated from the initial number of moles of adduct NB(C6F5)3·SMe2 and the volume of the sample V. The number of moles of adduct can be calculated from the number of moles of trimethoxyborane (NTMB), the integration of the methoxy protons of TMB (∫TMB), the integration of the methyl protons of B(C6F5)3·SMe2 (∫B(C6F5)3 ·SMe2 ) and the number of protons associated with each integration. The expression is shown below:

NB(C6F5)3·SMe2 = NTMB (9H / ∫TMB) (∫B(C6F5)3 ·SMe2 / 6H)

There were 6 mg of TMB added to the sample (mTMB) and the molecular mass of TMB is 168.19 g/mol (MTMB). Thus the number of moles of TMB is:

-3 -5 NTMB = mTMB/MTMB = (6.0 10 g)/(168.19 g/mol) = 3.57 10 mol

Solving for NB(C6F5)3·SMe2 :

-5 -6 NB(C6F5)3·SMe2 = 3.57 10 mol (9H/10000) (1546.5/6H) = 8.28 10 mol

The volume of the sample can be calculated by the following formula:81

V = (0.1435 solution height) – 0.0249 = (0.1435 6.8 mL) – 0.0249 = 0.951 mL

= 9.51 10-3 L

The initial concentration [B(C6F5)3·SMe2]i is:

-6 -3 [B(C6F5)3·SMe2]i = NB(C6F5)3·SMe2/V = 8.28 10 mo l/9.51 10 L = 0.00870 mol/L

This concentration was then multiplied by the ratio converted to determine the concentrations of

[B(C6F5)3] = [SMe2]. The remaining concentrations of [B(C6F5)3·SMe2]r were simply the subtraction of [B(C6F5)3·SMe2]i - [B(C6F5)3] or [B(C6F5)3·SMe2]i - [SMe2], since B(C6F5)3 and

SMe2 were present in a 1:1 ratio. The equilibrium constant Keq was determined by:

Keq = [B(C6F5)3] [SMe2]/[B(C6F5)3·SMe2]

A Van’t Hoff plot was then constructed by plotting the natural logarithm of K eq against the inverse of the temperature (Figure A.2). The data used to construct the Van’t Hoff plot are tabulated in Table A.1.

Table A.1 Data used in Van’t Hoff plot for B(C6F5)3·SMe2

Keq = -1 [B(C6F5)3·SMe2] [B(C6F5)3] = [SMe2] T (K) 1/T (K ) [B(C6F5)3][SMe2] ln(K ) (mol/L) (mol/L) eq [B(C6F5)3·SMe2]

308 0.00325 0.00546 0.00325 5.46 10-3 -5.21

318 0.00314 0.00556 0.00314 5.56 10-3 -5.19

328 0.00305 0.00565 0.00305 5.65 10-3 -5.18

338 0.00296 0.00574 0.00296 5.74 10-3 -5.16

348 0.00287 0.00583 0.00287 5.83 10-3 -5.14

358 0.00279 0.00591 0.00279 5.91 10-3 -5.13

Figure A.2 Van’t Hoff plot of B(C6F5)3·SMe2

The change in enthalpy ( H), change in entropy ( S), and change in Gibbs free energy ( G) of the system can be expressed in the following two equations:

ΔG = ΔH - TΔS = -RTln(Keq)

ln(Keq) = -ΔH/(RT) + ΔS/R (y = mx + b) where R is the rate constant (8.314 J/(mol·K)), T is the temperature in Kelvins, y is the equation of the linear relationship of the Van’t Hoff plot (y-axis corresponds to ln(Keq), m is the slope of the line, x corresponds to the inverse temperature values (K-1) and b is the intercept). The standard change in enthalpy (ΔH ) and standard change in entropy (ΔS ) can be determined by these following relationships:

ΔH = -mR = -(-9148.5 K)(8.314 J/(mol·K)) = 76.1 kJ/mol

ΔS = bR = (20.215)(8.314 J/(mol·K))= 168.1 J/(mol·K)

Substituting into the previous equation the standard change in Gibbs free energy could be determined at room temperature:

ΔG = ΔH - TΔS = (76.1 kJ/mol) - (298.15 K)(168.1 J/(mol·K)) = 26.0 kJ/mol

The positive standard change in Gibbs free energy indicates an uphill reaction which correlates to the large amount of energy needed to break the B S bond in the adduct (140 C). The standard change in enthalpy is also positive due to this endothermic reaction.

A.4 Conclusion

The dimethylsulfide adduct of tris(pentafluorophenyl)borane heterolytically splits hydrogen in the presence of bulky phosphines such as tri-tert-butylphosphine or trimesitylphosphine, however no reaction occurs between B(C6F5)3·SMe2 and phosphine alone. Thermodynamic studies were performed to probe the cleavage of the boron sulfur bond and the standard change in enthalpy was determined to be 76.1 kJ/mol, the standard change in entropy was 168.1 J/mol·K and the standard change in Gibbs free energy was found to be 26.0 kJ/mol.

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