Exploring the Synthesis, Structure, and Reactivity of Phosphorus- Chalcogen Heterocycles

Home , Phosphaalkyne, Phosphinidene, Sulfide

Western University Scholarship@Western

Electronic Thesis and Dissertation Repository

2-27-2018 10:30 AM

Cameron Graham The University of Western Ontario

Supervisor Ragogna, Paul J. The University of Western Ontario

Graduate Program in Chemistry A thesis submitted in partial fulfillment of the equirr ements for the degree in Doctor of Philosophy © Cameron Graham 2018

Follow this and additional works at: https://ir.lib.uwo.ca/etd

Part of the Inorganic Chemistry Commons

Recommended Citation Graham, Cameron, "Exploring the Synthesis, Structure, and Reactivity of Phosphorus-Chalcogen Heterocycles" (2018). Electronic Thesis and Dissertation Repository. 5258. https://ir.lib.uwo.ca/etd/5258

This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. Abstract

In recent years, low-coordinate main group chemistry has seen significant research interest due to the isolation of structures that demonstrate unique bonding and reactivity. Conversely, the area of phosphinidene chalcogenides, a low-coordinate phosphorus and chalcogen species, have yet to be thoroughly explored. In this context, this dissertation describes the synthesis of a number of phosphorus-chalcogen heterocycles that can be degraded to provide stoichiometric access to low-coordinate phosphorus species. The ability for successful P-Ch transfer relies on using a bulky m-terphenyl group at phosphorus that provides enough steric bulk to kinetically stabilize the phosphorus centre but is also accommodating enough to allow for further reactivity. Previous attempts at this chemistry have utilized more sterically accommodating ligands, however sterically demanding ligands have now been proven to be critical in controlling the fragmentation and transfer of these generated species. In Chapter 2, the synthesis of strained P-Ch heterocycles containing a 4- membered core will be discussed, as well as attempts to use these cyclic structures to gain access to low-coordinate phosphinidene chalcogenides. Chapter 3 continues from the success discussed in the previous chapter and uses these newly generated rings as P-Ch transfer reagents for reactions with alkynes. An alternative method of generating phosphinidene chalcogenides that mitigates the synthesis of P-Ch heterocycles will also be discussed. Chapter 4 explores the reactivity of these 4-membered rings using Lewis acids and bases, again linking these compounds to the monomeric phosphinidene chalcogenides. Chapter 5 introduces the idea of combining two different low-coordinate phosphorus compounds (both generated from their parent dimer heterocycles) to generate a new heterocycle containing elements from Group 13, 15 and 16. The highlight of this thesis is discovering new methods of generating and trapping phosphinidene chalcogenides. While the sulfur derivatives have been discussed in the literature, the chemistry surround the selenium compounds are unique and include some of the first structural confirmation of such species. All of the compounds discussed in this thesis were characterized to the fullest extent using a range of solution and solid-state techniques, with an emphasis on NMR spectroscopy and single crystal X-ray crystallography.

Keywords

Phosphorus • Chalcogen • Coordination Chemistry • Phosphinidene Chalcogenide • Structure and Bonding • Low-coordinate Main Group Chemistry • Heterocycles •

Co-Authorship Statement

This thesis includes work from four published manuscripts in chapters two, three, four, and five. The article presented in chapter two were co-authored by C. M. E. Graham, T. E. Pritchard, P. D. Boyle, J. Valjus, H. M. Tuononen, and P. J. Ragogna (Angew. Chem. Int. Ed. 2017, 56, 6236-6240). TEP was responsible for a portion of the cycloaddition chemistry, and this was conducted in her fourth-year thesis project under the direct supervision of CMEG. CMEG performed the majority of synthesis and comprehensive characterization of the compounds reported and collected and refined all X-ray diffraction data with some assistance from PDB. CMEG assembled the manuscript with some assistance from TEP. HMT and JV were responsible for the comprehensive DFT calculations for the manuscript, and responsible for the corresponding section in the manuscript. HMT and PJR edited the manuscript.

The work described in chapter three was co-authored by C. M. E. Graham, C. L. B. Macdonald, P. D. Boyle, J. A. Wisner, and P. J. Ragogna (Chem. – Eur. J. 2018, 24, 743- 749). CMEG was responsible for the synthesis and characterization of all compounds reported, collected and refined all X-ray diffraction data with some assistance from PDB, and assembled the manuscript. CLBM was responsible for the comprehensive computational experiments, and the corresponding section in the manuscript. JAW provided insight on the different mechanistic pathways reported in the manuscript. CLBM and PJR edited the manuscript.

The work described in chapter four was co-authored by C. M. E. Graham, J. Valjus, P. D. Boyle, T. E. Pritchard, H. M. Tuononen, and P. J. Ragogna (Inorg. Chem. 2017, 56, 13500-13509). TEP was responsible for a portion of the coinage-metal induced ring expansion chemistry, and this was conducted in her fourth-year thesis project – under the direct supervision of CMEG. CMEG conducted the synthesis and comprehensive characterization of the compounds reported and collected and refined all X-ray diffraction data with some assistance from PDB. CMEG assembled the manuscript with some assistance from TEP. HMT and JV were responsible for the comprehensive DFT calculations for the

iii manuscript, and responsible for the corresponding section in the manuscript. HMT and PJR edited the manuscripts.

The work described in chapter five was co-authored by C. M. E. Graham, C. R. P. Millet, A. N. Price, J. Valjus, M. J. Cowley, H. M. Tuononen, and P. J. Ragogna (Chem. – Eur. J. 2017, 24, 672-680). The synthesis, characterization and reactivity studies of 5.3Ch was a collaborative work between CRPM, ANP, and CMEG: the sulfur derivative by CRMP and ANP, and the selenium analogue by CMEG. CMEG collected and refined all X-ray diffraction data and assembled the manuscript. HMT and JV were responsible for the comprehensive DFT calculations for the manuscript, and responsible for the corresponding section in the manuscript. MJC, HMT, and PJR edited the manuscripts.

iv Acknowledgements

I would like to thank my supervisor Paul Ragogna for his continuous support throughout the duration of my Ph.D. Paul unquestionably improved my research and technical skills, pushed me to think outside the box, and enforced critical thinking – I certainly would not be the scientist I am today if it was not for his guidance. I appreciate Paul’s patience when it came to writing manuscripts and going through our editing process. At times, it was a daunting task to have a supervisor that was more excited about my research than I was, but I truly appreciate his enthusiasm in chemistry, and my scientific approach has been heavily influenced by his mentality. Paul’s intensity towards research is contagious, and I would not have been able to push myself in our projects if it wasn’t for his encouragement. I thank Paul for the countless thrilling conversations, life advice, strongly influencing my taste in beer, and allowing me to beat him at squash.

All of the graduate students, past and present, of the Ragogna group that I had the pleasure to work with: Jonathan, Ryan, Mahboubeh, Yuqinq, Tyler, Vanessa, Benjamin, Tristan, Soheil, Matt, and Taylor – thank you! We have all shared countless great memories, exciting conversations (some over a beer or two), and all of you helped create a group dynamic where it was enjoyable to come into the lab every day. It would have been a difficult task to manage graduate school without all of you. Thanks to Jonathan for showing me the ropes when I started in the group and instilling in me the Ragogna group demeanor – it’s a shame you weren’t around for longer! Thanks to Tyler for introducing me to the game of squash, and for the fun rounds of golf – you always helped give me something to think about other than chemistry. Thanks to Vanessa and Taylor, my main group partners in crime and lab mates over the years. Vanessa, thank you for broadening my taste in music, even though that meant going through a serious Abba phase. Vanessa’s enthusiasm towards chemistry is unparalleled, and you always made the lab an extremely fun place to work, and I hope you always keep the same frame of mind. Your mannerisms always helped to keep a calm vibe in the lab which was crucial when the results just weren’t there. Taylor, thank you for all of the good glovebox chats, and brainstorming ideas which generally resulted in me telling you to try some crazy idea that wouldn’t end up working. Thanks to Matt for all of our great office conversations, showing me how to make a delicious home brew, and to his v

appreciation for how difficult Microsoft Word can be at times. Thank you to the undergraduate students that I had the pleasure of mentoring: Chrissy, Taylor, and Deeksha. I appreciate all of your hard work and positive attitudes that made it a pleasure to mentor each of you, and you all helped add a number of pages to this document.

During my graduate school career, I had the pleasure of working with a number of collaborators from around the world including Charles Macdonald, Heikki Tuononen, Michael Cowley, and Phil Power. Thank you, Chuck and Heikki, for your timely calculations, and for helping us make sense of our results. Thank you, Mike and Phil, for sending us some of the compounds created in your lab and allowing us to explore some unique chemistry.

Western University has a talented and hardworking staff that made a large portion of this thesis possible. I thank Paul Boyle for his valuable training in X-ray crystallography, all of his help with my ongoing crystallography related questions, and for answering his phone on late evenings/weekends when I had diffractometer troubles. Thanks to Aneta Borecki for all of her hard work in the X-ray and NMR facilities. Mat Willans assisted me with all of my NMR related problems and worked tirelessly to keep the facility up and running when the spectrometers decided to misbehave. Doug Hairsine was extremely accommodating when it came to running air/moisture/temperature sensitive samples, and quick to help with vacuum pumps that just wouldn’t cooperate. I sincerely thank John and Jon in the machine shop for all of their timely help when dealing with glovebox or PH3 line issues. The Chembiostores staff were always there to help with any problems I had with ordering reagents, sending samples away, amongst many other things. A special thanks to Monica for not strangling me on numerous occasions when I came down with a Dewar order form 5 minutes after she had already placed the order with Praxair. The main office staff and secretaries were always very helpful and informative whenever I needed their assistance.

A big thank you to my friends and family for their unrelenting support since I started school. Thank you to my parents for encouraging me to follow what I am passionate about and being there for me in any way possible. Above all, I truly appreciate all of your attempts to understand what it is that I do. Thank you to all of my friends who have been by my side through this journey. To all of the members of the Strathroy Royals baseball team, thank you

vi for taking my mind off science periodically during the summer, and keeping my competitive spirit alive. A special thanks to Jeremy Bourque for everything we have been through during our tenure at Western. Our discussions about chemistry, baseball, and life will always be valued. It was a pleasure to work alongside you, and I’m looking forward to our lifelong friendship.

Finally, I need to thank my biggest supporter, my fiancée Jasmine. Jasmine has been by my side for almost my entire University career and has kept me grounded through all of the hills and valleys. I appreciate Jasmine putting parts of her life on hold while I finish school, and I could not have asked for any more support than what you have provided me with. I could not be more excited about our future.

vii

Table of Contents

Abstract ...... i

Co-Authorship Statement ...... iii

Acknowledgements ...... v

Table of Contents ...... viii

List of Tables ...... xiii

List of Figures ...... xiv

List of Schemes ...... xxv

List of Appendices ...... xxviii

List of Abbreviations...... xxix

List of Compounds Reported – The 22 Man Roster ...... xxxii

Chapter 1 ...... 1

1 Introduction ...... 1

1.1 A Brief History of Main Group Chemistry ...... 1

1.2 Low-Coordinate Main Group Chemistry ...... 3

1.3 Phosphinidenes – From Transient Intermediates to Isolable Compounds ...... 5

1.4 Phosphinidene Chalcogenides ...... 8

1.4.1 Generating RP=S in the Presence of Trapping Reagents ...... 11

1.4.2 Unique Ligand Design to Stabilize RP=S ...... 15

1.4.3 Transition Metal Stabilization of RP=S ...... 17

1.4.4 Synthesis of (c-RPCh)n Heterocycles ...... 19

1.5 Scope of Thesis ...... 20

1.6 References ...... 21

Chapter 2 ...... 28

2 Trapping Rare and Elusive Phosphinidene Chalcogenides (RP=Ch; Ch = S, Se) ...... 28 viii

2.1 Introduction ...... 28

2.2 Results and Discussion ...... 30

2.3 Conclusions ...... 42

2.4 Experimental Section ...... 43

2.4.1 Synthesis of 2.3S...... 43

2.4.2 Synthesis of 2.3Se ...... 44

2.4.3 Synthesis of 2.4SiPr ...... 44

2.4.4 Synthesis of 2.6S...... 45

2.4.5 Synthesis of 2.6Se ...... 46

2.4.6 Special Considerations for X-ray Crystallography ...... 48

2.4.7 Computational Details ...... 50

2.5 References ...... 50

Chapter 3 ...... 53

3 Addressing the Nature of Phosphinidene Sulfides via the Synthesis of P-S Heterocycles ...... 53

3.1 Introduction ...... 53

3.1 Results and Discussion ...... 55

3.2 Conclusion ...... 65

3.3 Experimental Section ...... 66

3.3.1 Synthesis of 3.1a ...... 66

3.3.2 Synthesis of 3.2a ...... 67

3.3.3 Synthesis of 3.2b...... 68

3.3.4 Special Considerations for X-ray Crystallography ...... 68

3.3.5 Computational Details ...... 70

3.4 References ...... 70

Chapter 4 ...... 74

4 Phosphorus-Chalcogen Ring Exansion and Metal Coordination ...... 74

4.1 Introduction ...... 74

4.2 Results and Discussion ...... 76

4.2.1 Formation of P/Ch Heterocycles...... 76

4.2.2 Reactivity of P/Ch Heterocycles with Coinage Metals ...... 82

4.2.3 X-ray Crystallography ...... 89

4.3 Conclusion ...... 93

4.4 Experimental ...... 94

4.4.1 General Experimental...... 94

4.4.2 Synthesis of 4.1S...... 94

4.4.3 Synthesis of 4.1Se ...... 95

4.4.4 General Methods for Coordination Chemistry with Coinage Metals ...... 96

4.4.5 Synthesis of 4.3SCu ...... 96

4.4.6 Synthesis of 4.3SAg ...... 97

4.4.7 Synthesis of 4.3SeAg ...... 98

4.4.8 Synthesis of 4.4S...... 98

4.4.9 Synthesis of 4.4Se ...... 99

4.4.10 Special Considerations for X-ray Crystallography ...... 100

4.4.11 Computational Details ...... 102

4.5 References ...... 102

Chapter 5 ...... 105

5 Preparation and Characterization of P2BCh Ring Systems (Ch = S, Se) and Their Reactivity with N-Heterocyclic Carbenes...... 105

5.1 Introduction ...... 105

5.2 Results and Discussion ...... 107

5.3 Conclusion ...... 119

5.4 Experimental Section ...... 120

5.4.1 General Experimental...... 120

5.4.2 General Method for the Synthesis of 5.3Ch ...... 120

5.4.3 Synthesis of 5.3S...... 120

5.4.4 Synthesis of 5.3Se ...... 121

5.4.5 Synthesis of 2.4SMe ...... 122

5.4.6 General Method for the Synthesis of 5.5R ...... 122

5.4.7 Synthesis of 5.5iPr ...... 123

5.4.8 Synthesis of 5.5Me ...... 123

5.4.9 Synthesis of 5.7Se ...... 124

5.4.10 Synthesis of 5.9 ...... 125

5.4.11 Synthesis of 5.10 ...... 126

5.4.12 Special Considerations for X-ray Crystallography ...... 127

5.4.13 Computational details...... 129

5.5 References ...... 129

Chapter 6 ...... 133

6 Summary, Conclusions, and Future Work ...... 133

6.1 Summary and Conclusions ...... 133

6.2 Future Work ...... 135

6.2.1 Bulky Ligands to Stabilize RP=Ch ...... 135

6.2.2 Electron-Withdrawing Ligands to Stabilize RP=Ch ...... 137

6.2.3 In situ Generation of Phosphinidene Chalcogenides ...... 138

6.2.4 Kinetic Studies to Probe the Presence of Phosphinidene Chalcogenides 139

6.2.5 Frustrated Lewis Pair Chemistry Based on NHC-Phosphinidenes ...... 139

6.3 References ...... 140

Chapter 7 ...... 142 xi

7 Appendices ...... 142

7.1 Synthesis of m-terphenyl phosphines ...... 142

7.1.1 Experimental ...... 144

7.1.2 Synthesis of 7.4 ...... 144

7.1.3 Synthesis of 7.3 ...... 145

7.2 Experimental Methods ...... 146

7.2.1 General Experimental Methods ...... 146

7.2.2 General Instrumentation ...... 146

7.2.3 General Crystallographic Methods ...... 147

7.3 Copyrights and Permissions ...... 147

7.3.1 John Wiley and Sons License Agreement ...... 147

7.3.2 American Chemical Society’s policy on theses and dissertations ...... 156

7.4 Supplementary Information for Chapter 2 ...... 158

7.5 Supplementary Information for Chapter 3 ...... 167

7.6 Supplementary Information for Chapter 4 ...... 175

7.7 Supplementary Information for Chapter 5 ...... 190

7.8 References ...... 203

Curriculum Vitae ...... 204

xii

List of Tables

Table 2-1: Selected Kohn-Sham orbitals (isovalue ± 0.04) of 2.3S and 2.3Se...... 41

Table 2-2: Selected Kohn-Sham orbitals (isovalue ± 0.04) of 2.2S; the shapes of orbitals for 2.2Se are similar...... 42

Table 2-3: Summary of X-ray diffraction collection and refinement details for the compounds reported in Chapter 2...... 49

Table 3-1: Summary of X-ray diffraction collection and refinement details for the compounds reported in Chapter 3...... 69

Table 4-1: Selected metrical parameters for compounds reported in Chapter 4...... 91

Table 4-2: Summary of X-ray diffraction collection and refinement details for the compounds reported in Chapter 4...... 101

Table 5-1: Summary of X-ray diffraction collection and refinement details for the compounds reported in Chapter 5...... 128

Table 7-1: Frontier orbital interactions (isovalue ± 0.05) relevant to the dimerization of 2.2S to 2.3S...... 166

Table 7-2: M06-2X/TZVP calculated energetic and thermochemical data for 3- and 4- membered ring isomers of Ar’PS(C2R2)...... 167

Table 7-3: (U)M06-2X/TZVP calculated energetic and thermochemical data for 3- and 4- membered ring isomers of HPS(C2R2)...... 168

xiii List of Figures

Figure 1-1: Early reported examples of low-coordination in the main group elements...... 3

Figure 1-2: Notable examples of multiple bonding within main group compounds...... 5

Figure 1-3: Top: General examples of phosphinidenes. Bottom: First example of spectroscopic detection of phosphinidenes...... 6

Figure 1-4: Sequence of energies (in eV) of the orbitals s and p, p* for HP=X, obtained from complete energy-optimized ab initio STO/3G calculations ...... 10

Figure 1-5: Top: Calculated molecular orbitals for MeP=S. Bottom: Different modes of reactivity for RP=Ch...... 11

Figure 1-6: Select examples of transition metal stabilized phosphinidene sulfides (1.28 – 1.34)...... 18

Figure 1-7: Reported (c-RPCh)n derivatives where the ligands are sterically demanding. .... 19

Figure 2-1: Top: General structures of phosphinidenes (2.1), phosphinidene chalcogenides

(2.2Ch), and P2Ch2 rings (2.3Ch). Previously reported ylid-stabilized "P=Ch" (2.A) and known phosphorus-chalcogen rings with a general formula (RPCh)n (1.35, n = 3; 1.36, n = 4). Bottom: General synthetic scheme for 2.3Ch and their potential equilibrium with 2.2Ch. ... 29

Figure 2-2: Reaction progression (31P{1H} NMR spectra) for synthesis of 2.3S showing crude reaction mixture (top, 16 hours) and purified material (bottom)...... 31

Figure 2-3: Reaction progression of (31P{1H} NMR spectra) for the synthesis of 2.3Se. Labels indicate the time at which the spectrum was collected, and the bottom spectrum shows the NMR spectrum of the isolated and purified material...... 32

Figure 2-4: Solid state structures for 2.3S (left) and 2.3Se (right) with thermal ellipsoids at

50% probability. Hydrogen atoms have been omitted for clarity, and side profile of the P2Ch2 core is shown below each structure. Selected bond lengths [Å] and bond angles [°]. 2.3S:

xiv

P(1)-S(1) 2.1489(2), P(1)-S(2) 2.1517(8), P(2)-S(1) 2.1359(8), P(2)-S(2) 2.1479(8), P(1)- C(1) 1.849(2), P(2)-C(25) 1.863(2), C(1)-P(1)-S(1) 105.11(7), C(1)-P(1)-S(2) 102.97(7), S(1)-P(1)-S(2) 88.74(3), C(25)-P(2)-S(1) 110.59(7), C(25)-P(2)-S(2) 101.17(7), S(1)-P(2)- S(2) 89.18(3), P(2)-S(1)-P(1) 86.14(3), P(2)-S(2)-P(1) 85.77(3), P(1)-S(1)-S(2)-P(2) 34.335(4). 2.3Se: P(1)-Se(1) 2.3113(14), P(1)-Se(2) 2.3060(16), P(2)-Se(1) 2.2931(16), P(2)- Se(2) 2.3033(16), P(1)-C(1) 1.851(5), P(2)-C(25) 1.853(5), C(1)-P(1)-Se(1) 103.74(15), C(1)-P(1)-Se(2) 103.72(16), Se(1)-P(1)-Se(2) 88.93(6), C(25)-P(2)-Se(1) 106.10(18), C(25)- P(2)-Se(2) 108.39(17), Se(1)-P(2)-Se(2) 89.45(6), P(2)-Se(1)-P(1) 82.17(6), P(2)-Se(2)-P(1) 82.06(5). P(1)-Se(1)-Se(2)-P(2) 45.442(8)...... 33

Figure 2-5: Solid state structures for compounds 2.4SiPr (a) 2.6S (b) and 2.6Se (c). Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms, and the mesityl groups from the m- terphenyl ligand for 2.6S have been omitted for clarity. Selected bond lengths [Å] and angles [°]. 2.4SiPr: P(1)-C(1) 1.869(4), P(1)-S(1) 2.0289(14), P(1)-C(25) 1.853(5), C(1)-P(1)-S(1) 113.02(13), C(2)-C(1)-P(1) 125.5(3), C(6)-C(1)-P(1) 115.6(3), C(1)-P(1)-C(25) 98.60(19), C(25)-P(1)-S(1) 98.91(13). 2.6S: P(1)-C(1) 1.832(3), P(1)-S(1) 2.0594(13), P(1)-C(25) 1.795(3), P(1)-C(26) 1.820(3)), C(27)-C(28) 1.331(4)), C(1)-P(1)-S(1) 109.62(9), C(2)-C(1)- P(1) 120.6(2), C(6)-C(1)-P(1) 120.6(2), C(1)-P(1)-C(25) 113.07(14), C(1)-P(1)-C(26) 115.45(13), C(25)-P(1)-S(1) 108.98(11), C(25)-P(1)-C(26) 104.33(15), P(1)-C(26)-C(27) 108.79(19), S(1)-C(29)-C(28) 114.7(2). 2.6Se: P(1)-C(1) 1.833(5), P(1)-Se(1) 2.2249(16), P(1)-C(25) 1.792(6), P(1)-C(26) 1.827(6), C(27)-C(28) 1.346(8), C(1)-P(1)-Se(1) 111.99(18), C(2)-C(1)-P(1) 119.9(4), C(6)-C(1)-P(1) 120.4(4), C(1)-P(1)-C(25) 114.5(3), C(1)-P(1)-C(26) 115.0(3), C(25)-P(1)-Se(1) 106.3(2), C(25)-P(1)-C(26) 102.1(3), P(1)- C(26)-C(27) 111.0(4), Se(1)-C(29)-C(28) 111.5(4)...... 35

Figure 2-6: Reaction coordinate diagrams for the conversion of 2.3S to 2.2S/2.4S (top) and 2.3Se to 2.2Se/2.5Se (bottom). Gibbs energies are reported in kJ mol-1 and relative to 2.3Ch. Phosphorus atoms are coloured orange, nitrogen blue, and the chalcogens (S and Se) are yellow...... 37

Figure 2-7: 31P{1H} NMR stacked plot showing cycloaddition product (2.5S, top) and quaternized product (2.6S, bottom)...... 39

Figure 2-8: 31P{1H} NMR stacked plot showing cycloaddition product (2.5Se, top) and isolated quaternized product (2.6Se, bottom)...... 40

Figure 3-1: Top: Wittig olefination of a carbonyl with phosphonium ylides proceeding through a 1,2-oxaphosphetane intermediate. Bottom: Examples of 1,2-oxaphosphetanes (3.A & 3.B), literature reported 1,2-thiaphosphetanes (3.C & 3.D), the only known example of a PV 1,2-thiaphosphetene (3.E), and PIII 1,2-thiaphosphetene (3.F) and the phosphirene sulfide (3.G) discussed in this chapter...... 54

Figure 3-2: A 31P{1H} NMR stacked plot monitoring the conversion of 2.3S to yield a mixture of thiaphosphetene (3.1a) and phosphirene sulfide (3.2a). Labels indicate the time at which the spectrum was collected, and the bottom spectrum shows the isolated and purified material...... 56

Figure 3-3: Solid-state structure of 1,2-thiaphosphetene (3.1a). Thermal ellipsoids drawn at 50% probability, and hydrogen atoms have been omitted for clarity. Selected bond lengths [Å] and bond angles [°]: P(1)-S(1) 2.161(3), P(1)-C(1) 1.844(7), P(1)- C(25) 1.796(6), S(1)- C(26) 1.772(6), C(25)-C(26) 1.357(9), C(1)-P(1)-S(1) 106.1(2), P(1)-S(1)-C(26) 76.0(2), S(1)-C(26)-C(25) 105.3(5), C(26)-C(25)-P(1) 100.4(5), C(25)-P(1)-S(1)77.7(2), C(25)-P(1)- C(1) 109.2(3)...... 58

Figure 3-4: A 31P{1H} NMR stacked plot monitoring the reaction of 2.3S and diphenylacetylene to yield 3.2b. Labels indicate the time at which the spectrum was collected, and the bottom spectrum shows the isolated and purified material...... 60

Figure 3-5: Solid-state structures of phosphirene sulfides 3.2a (left) and 3.2b (right). Thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and bond angles [°] 3.2a: P(1)-S(1) 1.9390(13), P(1)-C(1) 1.819(3), P(1)-C(25) 1.757(3), P(1)-C(26) 1.746(3), C(25)-C(26) 1.328(4), C(1)-P(1)-S(1) 115.79(10), C(1)-P(1)-C(25) 115.57(13), C(1)-P(1)-C(26) 112.13(13), P(1)-C(25)-C(26) 67.30(18), P(1)-C(26)-C(25) 68.14(17), C(26)-P(1)-C(25) 44.56(13), S(1)-P(1)-C(25) 124.10(11), S(1)-P(1)-C(26) 125.87(11). 3.2b: P(1)-S(1) 1.9443(7), P(1)-C(1) 1.8176(14), P(1)-C(25) 1.7684(14), P(1)-C(26) 1.7561(14), C(25)-C(26) 1.3449(18), C(1)-P(1)-S(1) 113.74(5), C(1)-P(1)-C(25) 116.36(6), C(1)-P(1)-C(26) 116.19(6), P(1)-C(25)-C(26)

xvi

67.08(8), P(1)-C(26)-C(25) 68.05(8), C(26)-P(1)-C(25) 44.86(6), S(1)-P(1)-C(25) 125.14(5), S(1)-P(1)-C(26) 123.55(5)...... 61

Figure 3-6: A 31P{1H} NMR stacked plot monitoring the photolysis of phosphirene sulfide 3.2a. The parent dithiadiphosphetane (2.3S) was the major product, in addition to multiple other unknown phosphorus containing products...... 62

Figure 3-7: A 31P{1H} NMR stacked plot indicating the reaction progress yielding 3.2a from

Ar*PCl2...... 64

Figure 3-8: Reaction coordinate diagram for the formation of 3.1’e and 3.2’e...... 65

Figure 4-1: Top: Previously reported phosphorus-chalcogen rings, Woollins’ and V III Lawesson’s reagents with P (4.A), (c-RPCh)n with P (2.3Ch, 1.35, and 1.36), and polynuclear Ag sandwich complex (4.B). Bottom: i) Synthesis of 4.1S via base-induced ring expansion, ii) Synthesis of 4.1Se by cyclocondensation of Ar*PCl2 and Se(TMS)2, iii) Ring expansion and/or metal coordination to coinage metals...... 75

Figure 4-2: Solid-state structures of 4.1S (left) and 4.1Se (right). Thermal ellipsoids have been drawn at 50% probability, while hydrogen atoms and mesityl groups have been omitted for clarity. Key bond lengths and angles are listed in Table 4-1...... 78

Figure 4-3: A 31P{1H} NMR stacked plot showing ring expansion attempts on 2.3Se using nitrogen bases. Reactions were conducted over 16 hours at 50 °C in THF. Each reaction indicates evidence of ring expansion (4.1Se, dP = 87.8, shown in dotted lines) as well as multiple unknown phosphorus containing products...... 79

(chemical shift of 4.1Se is shown between dotted lines). Suggested SePR3 products are highlighted on their respective spectra...... 80

Figure 4-5: Reaction coordinate diagram for DMAP-induced (RPS)n ring expansion (phosphorus atoms are coloured orange, sulfur yellow, and nitrogen blue). For simplicity,

xvii interconversion of different conformers of 4.1S is omitted (dashed arrow). Gibbs free energies are reported in kJ mol-1 and relative to 2.3S + 4.2S...... 84

Figure 4-6: A stacked plot of 31P{1H} NMR spectra of different sulfur derivatives reported herein: parent 2.3S and ring expansion products 4.1S, 4.3SCu, 4.3SAg, and 4.4S...... 87

Figure 4-7: A stacked plot of 31P{1H} NMR spectra of different selenium derivatives reported herein: parent 2.3Se and ring expansion products 4.1Se, 4.3SeCu, 4.3SeAg, and 4.4Se...... 88

Figure 4-8: Solid-state structures of 4.3SCu (top left), 4.3SAg (top right), 4.4S (bottom left), and 4.4Se (bottom right). Thermal ellipsoids are drawn at 50% probability, and hydrogen atoms have been omitted for clarity. The terphenyl ligand in 4.3SAg, and the mesityl groups for 4.3SCu, 4.4S, and 4.4Se are omitted for clarity...... 89

Figure 5-1: Top: Examples of NHC-stabilized main group compounds: homodiatomic main group allotropes (5.A & 5.B), bent allenes (5.C), phosphinidenes (5.D), phosphaborenes (5.E), and phosphinidene sulfides (5.F). Bottom: Examples of base-/thermal-induced degradation of inorganic heterocycles yielding low-coordinate main group compounds (NR2 = TMP)...... 106

Figure 5-2: Left: Examples of small asymmetric P–Ch heterocycles (5.G-J). Right: Examples of small phosphorus heterocycles that contain an asymmetric core in the presence of a P–P bond (5.K-M) ([Fe] = Fe(Cp*)(CO)2)...... 107

Figure 5-3: Solid-state structures of 5.3S (left) and 5.3Se (right) with thermal ellipsoids at 50% probability. Hydrogen atoms and mesityl rings from terphenyl groups are omitted for clarity. Selected bond lengths [Å] and angles [°]. 5.3S: C(1)-P(1) 1.875(3), P(1)-P(2) 2.2371(9), P(1)-B(1) 1.955(2), P(2)-C(19) 1.862(2), P(2)-S(1) 2.1301(8), S(1)-B(1) 1.850(3), B(1)-N(1) 1.405(3), C(1)-P(1)-P(2) 118.15(8), C(1)-P(1)-B(1) 113.8(1), B(1)-P(1)-P(2) 83.50(8), P(1)-P(2)-S(1) 81.38(3), P(1)-P(2)-C(19) 110.69(8), P(2)-S(1)-B(1) 89.08(9), S(1)- B(1)-P(1) 96.9(1), S(1)-B(1)-N(1) 124.1(2), N(1)-B(1)-P(1) 138.7(2), C(19)-P(2)-S(1) 106.82(8). 5.3Se: C(1)-P(1) 1.885(2), P(1)-P(2) 2.243(1), P(1)-B(1) 1.957(2), P(2)-C(19) 1.861(2), P(2)-Se(1) 2.267(1), Se(1)-B(1) 1.985(2), B(1)-N(1) 1.414(2), C(1)-P(1)-P(2) 117.05(6), C(1)-P(1)-B(1) 113.03(9), P(1)-P(2)-C(19) 111.47(6), P(1)-P(2)-Se(1) 81.66(2), xviii

P(1)-B(1)-Se(1) 96.84(9), C(19)-P(2)-Se(1) 107.36(6), P(2)-Se(1)-B(1) 85.19(6), Se(1)-B(1)- P(1) 96.84(9), Se(1)-B(1)-N(1) 124.1(1), N(1)-B(1)-P(1) 138.6(2), B(1)-P(1)-P(2) 86.49(6)...... 109

31 1 Figure 5-4: A stacked plot of P{ H} NMR spectra of the P2BCh derivatives 5.3S, 5.3Se, and 5.7Se...... 110

Figure 5-5: Reaction coordinate diagram for the formation of 2,3 and 2,4 isomers of 5.3S. –1 Gibbs free energies are reported in kJ mol and relative to ArP=S + MesP=B-NMe2...... 112

Figure 5-6: 31P{1H} NMR spectra recorded from the crude reaction mixtures of the addition of NHCMe to 5.3S (top) and 5.3Se (bottom). Products of the reactions are labelled corresponding to their phosphorus NMR chemical shifts and leftover 5.3S is indicated by asterisks...... 113

Figure 5-7: Solid state structures of 5.5iPr (top left), 5.5Me (top right), 2.4SMe (bottom left), and 5.7Se (bottom right) with thermal ellipsoids drawn at 50% probability. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [°]. 5.5iPr: P(1)-C(1) 1.843(3), P(1)-C(25) 1.799(3), C(1)-P(1)-C(25) 101.53(11). 5.5Me: P(1)-C(1) 1.832(4), P(1)-C(25) 1.786(4), C(1)-P(1)-C(25) 99.10(17). 2.4SMe: P(1)-C(1) 1.867(3), P(1)-C(25) 1.852(3), P(1)- S(1) 2.0186(15), C(1)-P(1)-C(25) 97.01(14), C(1)-P(1)-S(1) 111.62(11), C(25)-P(1)-S(1) 100.48(12). 5.7Se: C(1)-P(2) 1.840(6), P(2)-P(1) 2.201(2), P(1)-C(25) 1.863(6), P(1)-B(1) 1.952(7), B(1)-N(1) 1.393(8), B(1)-Se(1) 2.007(7), P(2)-Se(1) 2.2492(18), P(2)-Au(1) 2.2344(17), Au(1)-Cl(1) 2.2978(17), C(1)-P(2)-Au(1)114.09(19), C(1)-P(2)-P(1)106.43(19), C(1)-P(2)-Se(1) 114.8(2), P(2)-P(1)-C(25) 112.66(18), P(2)-P(1)-B(1) 89.0(2), P(1)-B(1)- N(1) 137.1(5), P(1)-B(1)-Se(1) 96.7(3), B(1)-Se(1)-P(2) 86.3(2), Se(1)-P(2)-P(1) 83.33(7)...... 115

Figure 5-8: Solid state structures of 5.9 (left) and 5.10 (right) with thermal ellipsoids drawn at 50% probability. Mesityl groups and fluorine atoms from 5.9, and hydrogen atoms from both 5.9 and 5.10 have been omitted for clarity. Selected bond lengths [Å] and angles [°]: 5.9: P(1)-C(1) 1.843(4), P(1)-C(25) 1.839(4), P(1)-C(36), O(1)-B(1) 1.459(5), C(1)-P(1)- C(25) 100.59(16), C(1)-P(1)-C(36) 109.40(17), C(25)-P(1)-C(36) 99.36(17). 5.10: P(1)-C(1) 1.849(4), P(1)-C(25) 1.856(4), P(1)-Au(1) 2.2452(13), P(1)-Au(2) 2.2451(13), C(1)-P(1)-

xix

C(25) 102.64(18), C(1)-P(1)-Au(1) 115.96(14), C(1)-P(1)-Au(2) 111.54(13), C(25)-P(1)- Au(1) 103.71(14), C(15)-P(1)-Au(2) 111.54(13), Au(1)-P(1)-Au(2) 108.81(4)...... 119

Figure 7-1: A 31P{1H} NMR stacked plot displaying the spectra for each phosphorus starting material...... 144

1 Figure 7-2: H NMR spectrum of 2.3S in C6D6...... 158

13 1 Figure 7-3: C{ H} NMR spectrum of 2.3S in CDCl3...... 158

31 1 Figure 7-4: P{ H} NMR spectrum of 2.3S in C6D6...... 159

1 Figure 7-5: H NMR spectrum of 2.3Se in C6D6...... 159

13 1 Figure 7-6: C{ H} NMR spectrum of 2.3Se in C6D6...... 160

31 1 Figure 7-7: P{ H} NMR spectrum of 2.3Se in C6D6...... 160

77 1 Figure 7-8: Se{ H} NMR spectrum of 2.3Se in C6D6...... 161

1 Figure 7-9: H NMR spectrum of 2.4S in CDCl3...... 161

13 1 Figure 7-10: C{ H} NMR spectrum of 2.4S in CDCl3...... 162

31 1 Figure 7-11: P{ H} NMR spectrum of 2.4S in CDCl3...... 162

1 Figure 7-12: H NMR spectrum of 2.6S in CDCl3...... 163

13 1 Figure 7-13: C{ H} NMR spectrum of 2.6S in CDCl3...... 163

31 1 Figure 7-14: P{ H} NMR spectrum of 2.6S in CDCl3...... 164

1 Figure 7-15: H NMR spectrum of 2.6Se in CDCl3...... 164

13 1 Figure 7-16: C{ H} NMR spectrum of 2.6Se in CDCl3...... 165

31 1 Figure 7-17: P{ H} NMR spectrum of 2.6Se in CDCl3...... 165

Figure 7-18: 1H-31P HMBC spectrum of 3.2a. Cross peaks indicate P-H coupling...... 170

1 Figure 7-19: H NMR spectrum of 3.1a in C6D6...... 170

13 1 Figure 7-20: C{ H} NMR spectrum of 3.1a in C6D6...... 171

31 Figure 7-21: P NMR spectrum of 3.1a in C6D6...... 171

1 Figure 7-22: H NMR spectrum of 3.2a in C6D6...... 172

13 1 Figure 7-23: C{ H} NMR spectrum of 3.2a in C6D6...... 172

31 Figure 7-24: P NMR spectrum of 3.2a in C6D6...... 173

1 Figure 7-25: H NMR spectrum of 3.2b in C6D6...... 173

13 1 Figure 7-26: C{ H} NMR spectrum of 3.2b in C6D6...... 174

31 Figure 7-27: P NMR spectrum of 3.2b in C6D6...... 174

Figure 7-28: Reaction coordinate for the base-free ring expansion of 2.3S to 4.1S...... 175

31 1 Figure 7-29: P{ H} NMR stacked plot showing the synthesis of 4.3SeCu from 2.3Se. Top spectrum shows crude reaction mixture 15 minutes after addition of CuCl. More CuCl was added to the crude reaction mixture (bottom), which lead to the formation of multiple phosphorus containing products...... 175

Figure 7-30: Attempted synthesis of 4.3SAu. Major product at dP = 81 decomposed when left at -35 °C overnight. The chemistry of 4.3ChAu were no longer pursued...... 176

Figure 7-31: 31P{1H} NMR stacked plot showing the decomposition of 4.4S left in the solid state at room temperature for 2 days...... 176

31 1 Figure 7-32: P{ H} NMR stacked plot showing the decomposition of 4.3SCu left in the solid state at room temperature for 2 days...... 177

1 Figure 7-33: H NMR spectrum of purified 4.1S in C6D6...... 177

13 1 Figure 7-34: C{ H} NMR spectrum of purified 4.1S in C6D6...... 178

31 1 Figure 7-35: P{ H} NMR spectrum of purified 4.1S in C6D6...... 178 xxi

1 Figure 7-36: H NMR spectrum of purified 4.1Se in C6D6...... 179

13 1 Figure 7-37: C{ H} NMR spectrum of purified 4.1Se in C6D6...... 179

31 1 Figure 7-38: P{ H} NMR spectrum of purified 4.1Se in C6D6...... 180

77 1 Figure 7-39: Se{ H} NMR spectrum of purified 4.1Se in C6D6...... 180

1 Figure 7-40: H NMR spectrum of purified 4.3SCu in CDCl3...... 181

13 1 Figure 7-41: C{ H} NMR spectrum of 4.3SCu in CDCl3...... 181

31 1 Figure 7-42: P{ H} NMR spectrum of 4.3SCu in CDCl3...... 182

1 Figure 7-43: H NMR spectrum of 4.3SAg in CDCl3...... 182

13 1 Figure 7-44: C{ H} NMR spectrum of 4.3SAg in CDCl3...... 183

19 Figure 7-45: F NMR spectrum of 4.3SAg in CDCl3...... 183

31 1 Figure 7-46: P{ H} NMR spectrum of 4.3SAg in CDCl3...... 184

1 Figure 7-47: H NMR spectrum of 4.3SeAg in CDCl3...... 184

13 1 Figure 7-48: C{ H} NMR spectrum of 4.3SeAg in CDCl3...... 185

19 Figure 7-49: F NMR spectrum of 4.3SeAg in CDCl3...... 185

31 1 Figure 7-50: P{ H} NMR spectrum of 4.3SeAg in CDCl3...... 186

1 Figure 7-51: H NMR spectrum of 4.4S in CDCl3...... 186

13 1 Figure 7-52: C{ H} NMR spectrum of 4.4S in CDCl3...... 187

31 1 Figure 7-53: P{ H} NMR spectrum of 4.4S in CDCl3...... 187

1 Figure 7-54: H NMR spectrum of 4.4Se in CDCl3...... 188

13 1 Figure 7-55: C{ H} NMR spectrum of 4.4Se in CDCl3...... 188

xxii

31 1 Figure 7-56: P{ H} NMR spectrum of 4.4Se in CDCl3...... 189

Figure 7-57: Thermal ellipsoid plots for P3Ch3 cores of 4.1S (left) and 4.1Se (centre), with the minor component of the disorder indicated with a dashed line. Isotropic structure of

4.3SeAg (right). Thermal ellipsoids have been drawn at 50% probability...... 189

Figure 7-58: 1H NMR spectrum of 5.3S in THF-d8...... 190

Figure 7-59: 13C{1H} NMR spectrum of 5.3S in THF-d8...... 190

Figure 7-60: 11B NMR spectrum of 5.3S in THF-d8...... 191

Figure 7-61: 31P{1H} NMR spectrum of 5.3S in THF-d8...... 191

1 Figure 7-62: H NMR spectrum of 5.3Se in C6D6...... 192

13 1 Figure 7-63: C{ H} NMR spectrum of 5.3Se in C6D6...... 192

11 Figure 7-64: B NMR spectrum of 5.3Se in C6D6...... 193

31 1 Figure 7-65: P{ H} NMR spectrum of 5.3Se in C6D6...... 193

1 Me Figure 7-66: H NMR spectrum of 2.4S in C6D6...... 194

13 1 Me Figure 7-67: C{ H} NMR spectrum of 2.4S in C6D6...... 194

31 1 Me Figure 7-68: P{ H} NMR spectrum of 2.4S in C6D6...... 195

1 iPr Figure 7-69: H NMR spectrum of 5.5 in C6D6...... 195

13 1 iPr Figure 7-70: C{ H} NMR spectrum of 5.5 in C6D6...... 196

31 1 iPr Figure 7-71: P{ H} NMR spectrum of 5.5 in C6D6...... 196

1 Figure 7-72: H NMR spectrum of 5.7Se in CDCl3...... 197

13 1 Figure 7-73: C{ H} NMR spectrum of 5.7Se in CDCl3...... 197

11 Figure 7-74: B NMR of 5.7Se in CDCl3...... 198

xxiii

31 1 Figure 7-75: P{ H} NMR spectrum of 5.7Se in CDCl3...... 198

1 Figure 7-76: H NMR spectrum of 5.9 in CDCl3...... 199

13 1 Figure 7-77: C{ H} NMR spectrum of 5.9 in CDCl3...... 199

11 Figure 7-78: B NMR spectrum of 5.9 in CDCl3...... 200

19 Figure 7-79: F NMR spectrum of 5.9 in CDCl3...... 200

31 1 Figure 7-80: P{ H} NMR spectrum of 5.9 in CDCl3...... 201

1 Figure 7-81: H NMR spectrum of 5.10 in CDCl3...... 201

13 1 Figure 7-82: C{ H} NMR spectrum of 5.10 in CDCl3...... 202

31 1 Figure 7-83: P{ H} NMR spectrum of 5.10 in CDCl3...... 202

xxiv

List of Schemes

Scheme 1-1: Reactivity of electrophilic phosphinidene complexes...... 7

Scheme 1-2: Synthesis and reactivity of an isolable phosphinophosphinidene (1.12)...... 8

Scheme 1-3: Using 7-phosphanorbornadiene compounds as precursors to phosphinidene sulfides...... 12

Scheme 1-4: Reaction of in situ generated phosphinidene sulfides with alchols, diethyl sulfide, benzil, and 2,3-dimethylbutadiene...... 13

Scheme 1-5: Dechlorination of phenylthiophosphonoic dichloride using magnesium, and reactions of the generated PhP=S with trapping reagents...... 14

Scheme 1-6: Liberating phosphinidene sulfides from the PV heterocycles phosphirane sulfide (1.20) and phospholene sulfide (1.21)...... 15

Scheme 1-7: Synthesis of P=Ch units utilizing a octamethylxylidene ligand...... 16

Scheme 1-8: Synthesis of an ylidic stabilized P=Ch unit and its reactivity (Ch = S, Se)...... 17

Scheme 1-9: Synthetic methodology for generating P2Ch2 heterocycles...... 20

Scheme 2-1: Trapping of Ar*P=S and Ar*P=Se by treatment of 2.3Ch with NHCiPr and dmbd...... 34

Scheme 3-1: Generation of phosphinidene sulfide (2.2S) by thermolysis of 2.3S at elevated temperatures and subsequent trapping with alkynes yielding 1,2-thiaphosphetene (3.1a) and/or phosphirene sulfide (3.2a-b)...... 56

Scheme 3-2: Using phosphirene sulfides 3.2 as sources of phosphinidene sulfides...... 62

Scheme 3-3: Formation of 3.2a by addition of Ar*PCl2 and S(TMS)2. The reaction pathway has been hypothesized to proceed via “free” phosphinidene sulfide (left) or through a phosphenium intermediate (right). Reactions were performed either at room temperature or 80 °C, however phosphirene sulfides 3.2 were the only products generated...... 63

xxv

Scheme 4-1: Cyclocondensation of Ar*PCl2 with Ch(TMS)2 yielding 2.3S (right), 2.3Se, and 4.1Se (left). While base induced ring expansion yields 4.1S from 2.3S in high yield, the addition of a base to 2.3Se results in multiple products, including 4.1Se...... 77

Scheme 4-2: Top: Using 2.3Ch as sources of monomeric phosphinidene chalcogenides, trapping 2.2Ch with dmbd (2.5Ch) or by addition of an NHC (2.4SiPr). Bottom: Proposed reaction pathway for ring expansion of 2.3Ch induced by DMAP/heating and proceeding through the suggested intermediate 4.2Ch...... 79

Scheme 4-3: Ring expansion of 2.3Ch (Ch = S, Se) using coinage metals (MX = CuCl,

AgOTf) resulting in 4.3ChM. Similar products were obtained from the addition of 4.1Ch to MX. Addition of excess CuCl to either 2.3Ch or 4.1Ch resulted in the formation of 4.4Ch. 86

Scheme 5-1: Synthesis of mixed main group rings 5.3Ch by combining monomeric phosphinidene chalcogenides (2.2Ch) and phosphaborene (5.2) units (NR2 = TMP)...... 108

Scheme 5-2: Accessing low-coordinate phosphorus compounds from reacting 5.3S (top) and Me 5.3Se (bottom) with NHC (NR2 = TMP)...... 113

Scheme 5-3: Addition of Lewis acidic AuCl(THT) to 5.3Se, resulting in metal coordination...... 114

Scheme 5-4: Top: Reactivity of 2.3Ch with NHCR yields NHC-stabilized phosphinidene sulfides (left, 2.4SR) and phosphinidenes (right, 5.5R) as well as selenoureas (right, 5.6R). Bottom: Reactivity of 4.1Ch with NHCMe yields similar products as observed with 2.3Ch. Left: Structure of literature known methylenethioxophosphoranes (5.8)...... 117

iPr Scheme 5-5: Reactivity of NHC-stabilized phosphinidene 5.5 with B(C6F5)3 results in a controlled ring-opening of THF (left, 5.9), while reaction with two equivalents of Lewis acidic AuCl(THT) gives a coordination complex (right, 5.10)...... 118

Scheme 6-1: Using bulkier m-terphenyl ligands to stabilize phosphinidene chalcogenides 136

Scheme 6-2: Synthesis of phosphinidene chalcogenides stabilized by bulky amido ligands...... 137

xxvi

Scheme 6-3: Generation and trapping of phosphinidene selenides...... 139

Scheme 6-4: Using NHC-phosphinidenes for FLP chemistry...... 140

Scheme 7-1: Top: General procedure for generating terphenyl phosphines. Bottom: Stepwise approach for selective P-C bond formation...... 142

Scheme 7-2: Synthetic approach used in this thesis for generating 7.3...... 143

xxvii List of Appendices

Appendix 7.1: Synthesis of m-terphenyl phosphines ...... 142

Appendix 7.2: Experimental Methods ...... Error! Bookmark not defined.

Appendix 7.3: Copyrights and Permissions ...... Error! Bookmark not defined.

Appendix 7.4: Supplementary Information for Chapter 2 Error! Bookmark not defined.

Appendix 7.5: Supplementary Information for Chapter 3 Error! Bookmark not defined.

Appendix 7.6: Supplementary Information for Chapter 4 Error! Bookmark not defined.

Appendix 7.7: Supplementary Information for Chapter 5 Error! Bookmark not defined.

Appendix 7.8: References ...... 203

xxviii

List of Abbreviations

Ad 1-Adamantyl (-C10H15) AIM Atoms In Molecules analysis Ar Aryl # Ar 2,6-(Trip)2C6H3 Ar* 2,6-(Mes)2C6H3 Avg. average BCF Tris(pentafluorophenyl)borane, B(C6F5)3 br broad Bu Butyl (-CH2CH2CH2CH3) CCDC Cambridge Crystallographic Data Centre cf. confer (compare) Ch Chalcogen; Group 16 element (O, S, Se, Te, Po) CH2Cl2 Methylene chloride, dichloromethane Cp* pentamethylcyclopentadienyl Cy Cyclohexyl group (-C6H11) d doublet dd doublet of doublets ddd doublet of doublet of doublets DFT Density Functional Theory Dipp 2,6-diisopropylphenyl, 2,6-(iPr)2C6H3 DMAP 4-dimethylaminopyridine dmbd 2,3-dimethyl-1,3-butadiene e.g. exempli gratia (for example) EA Elemental Analysis EPR Electron Paramagnetic Resonance eq. Equivalents ESI-MS Electro-spray Ionization Mass Spectrometry Et Ethyl (-CH2CH3) et al. et alii (and others) Et2O Diethylether Fe Ferrocenyl group F Ph Perfluorophenyl, (-C6F5) FT Fourier Transfer g gram GOF Goodness of Fit h Hour HMBC Heteronuclear Multiple Bond Correlation HOMO Highest Occupied Molecular Orbital hn UV-light Hz Hertz Im Imidazolium group iPr isopropyl (-CH(CH3)2)

xxix

IR Infrared J Coupling constant K Kelvin kJ Kilojoule LUMO Lowest Occupied Molecular Orbital m- meta m multiplet m/z mass:charge ratio m.p. Melting Point Me Methyl (-CH3) MeCN Acetonitrile (CH3CN) Mes Mesityl, 2,4,6-(CH3)3C6H2 Mes* Supermesityl, 2,4,6-(tBu)3C6H2 mg milligram MHz Megahertz min Minute(s) mL Millilitre mmHg Millimeter of mercury, 1 mmHg = 1 torr mmol millimole MO Molecular Orbital mol mole n- Normal NBO Natural Bond Order NHC N-Heterocyclic carbene NMR Nuclear Magnetic Resonance - OTf triflate, trifluoromethanesulfonate, CF3SO3 Ph Phenyl group (-C6H5) ppm Parts Per Million RT Room Temperature s singlet sept septet SHARCNET Shared Hierarchical Academic Research Computing Network STO Slater Type Orbitals t triplet tBu tertiary butyl (-C(CH3)3) td triplet of doublets THF Tetrahydrofuran (C4H8O) THT Tetrahydrothiophene (C4H8S) TMEDA N-N-N’-N’-tetramethylethylenediamine TMP 2,2,6,6-tetramethylpiperidine TMS Trimethylsilyl group (-Si(CH3)3) Trip Triisopropylphenyl, 2,4,6-(iPr)3C6H2 TS Transition State UV Ultra-violet XRD X-ray Diffraction Å Angstrom (10-10 metre)

xxx

D Delta (Heat) dH Hydrogen chemical shift (ppm) dB Boron chemical shift (ppm) dC Carbon chemical shift (ppm) dF Fluorine chemical shift (ppm) dP Phosphorus chemical shift (ppm) dSe Selenium chemical shift (ppm) {1H} Proton decoupled ° Degrees °C Degrees Celsius n Frequency l Wavelength

xxxi List of Compounds Reported – The 22 Man Roster

Synthetic Compound CCDC Structure Details Page Number Number Number

Mes Mes S P P 2.3S 43 1485220 S Mes Mes

Mes Mes Se P P 2.3Se 44 1485221 Se Mes Mes

Mes S P iPr Mes 2.4S 44 1485222 N N

Mes S

P N 2.4SMe 122 1573805

Mes N

Me Ar* P I 2.6S 45 1577309 S

xxxii

Me Ar* P I 2.6Se 46 1485223 Se

Mes

P S Mes 3.1a 66 1575227

Mes S P 3.2a 67 1575226

Mes

Mes S P 3.2b 68 1575225 Mes

Mes Mes P Mes S S Mes 4.1S 94 1569577 P P S

Mes Mes

xxxiii

Mes Mes P Mes Se Se Mes 4.1Se 95 1569578 P P Se

Mes Mes

Ar* S S P Ar* S P P Ar* 4.3SCu 96 1569579 Cu Cl

Ar* S S P Ar* S P P Ar* 4.3SAg 97 1569580 Ag OTf

Cu S Ar* Ar* P P S Cu S 4.4S 98 1569581 S Cu S P Cu P Ar* S Ar*

Cu Se Ar* Ar* P P Se Cu Se 4.4Se 99 1569582 Se Cu Se P P Cu Ar* Ar* Se

Mes

S P Mes 5.3S 120 1573801 B P tBu N tBu tBu

xxxiv

Mes

Se P Mes 5.3Se 121 1573802 B P tBu N tBu tBu

Mes

P N 5.5iPr 123 1573806 Mes N

Mes

P N 5.5Me 123 1573808 Mes N

NR2 B Mes* P Se 5.7Se 124 1573804 P AuCl Ar*

Mes O B(C6F5)3

P 5.10 125 1573807 Mes N N

xxxv

Mes AuCl AuCl P 5.11 126 1573803 Mes N N

xxxvi 1

Chapter 1 1 Introduction 1.1 A Brief History of Main Group Chemistry

The main group elements, those found in the s- and p-block on the periodic table, have been incorporated into numerous structures in a wide range of bonding motifs, with the chemistry of nearly every element being explored. The underlying theme of main group chemistry has focused on the bonding between these elements, comprehensive analysis of structures, and investigation into the influence of structure and bonding on reactivity. Although structure and bonding has been the focal point of main group chemistry, applications involving compounds composed of main group elements have seen significant developments over the last century, and a number of these advancements have been awarded Nobel Prizes in Chemistry. For example, the 1918 Nobel prize was awarded to Fritz Haber for his method of producing ammonia from the combination of its elements, nitrogen and hydrogen.1 The global output of ammonia is currently around 130 million tonnes per year, 80 % going to fertilizers,2 and the process developed by Haber is still the basis for its preparation today. Organotitanium/aluminum catalysts generated by Karl Ziegler and Giulio Natta towards the polymerization of terminal alkenes were recognized and received the Nobel Prize in 1963.3 The p-block elements have directly influenced the fields of organic chemistry, in particular with the development of Grignard reagents (Nobel Prize 1912).4 Herbert C. Brown and Georg Wittig shared the Nobel Prize in 1979 for their development of boron and phosphorus reagents in organic synthesis.5 Although not Nobel Prize worthy, but significant nonetheless, has been the development of polymers containing inorganic elements as repeatable units. The most notable examples being siloxane polymers, containing repeating (Si-O) linkages that are easily synthesized, contain a high degree of tenability, and possess applications ranging from heat transfer agents, high performance elastomers, waterproofing materials, biomedical materials, amongst many other applications.6 Other examples include polyphosphazenes which contain repeating (Cl2PN)n units, that are easily synthesized and have potential

1 2 applications as high-performance elastomers, polymer electrolytes, and biomedical membranes.7

The most recent developments in main group chemistry have been significantly aided by timely advancements in the fields of spectroscopic characterization, most notably in NMR spectroscopy (Nobel Prize 1991, Ernst)8 and X-ray crystallography (Nobel Prize in Physics 1915, Bragg and Bragg).9 The ability to probe various spin active nuclei via heteronuclear NMR spectroscopy, advancements in 1D and 2D acquisition and processing techniques, and the development of unique pulse sequences have all increased the applicability of this universal technique. The technology utilized in a data collection of standard single crystals have improved the process of X-ray diffraction experiments where data solutions can be obtained in a matter of hours, as compared to what used to take months. This significant enhancement has allowed for quicker results and absolute structure determination. The field of structural inorganic chemistry simply would not be significant without the ability for chemists to obtain a visual representation of targeted structures, and in-depth structure analysis.

In addition to the advancement in spectroscopic techniques, computational chemistry has seen significant improvements that have allowed for successful and accurate modelling of complex systems. These developments were recognized to both Walter Kohn and John A. Pople, who shared the Nobel Prize in 1998 for the development of density functional theory and computational methods in quantum chemistry.10 The advancements in computational chemistry has provided chemists the ultimate tools in both aiding in the explanation of their chemistry, but also for exploratory purposes in determining if target compounds are synthetically viable candidates.

These highlights were only intended to give a taste of the key developments in main group chemistry, and barely scratches the surface of the impact main group chemistry has had on other fields of research. It is imperative to understand that main group chemistry has seen significant changes in the last century and will continue to make an impact spanning from fundamental structure and bonding chemistry, to applied fields of research.

2 3

1.2 Low-Coordinate Main Group Chemistry

Over the last 30 years, the field of main group chemistry has progressed through a period of renaissance where the focus has shifted from developing systems that contain saturated main group element centres, to those that possess a low coordination number. One method of obtaining a low coordination number is to undergo multiple bonding, and the compounds found in Figure 1-1 represent early examples of main group element compounds that possess multiple bond character, and therefore defy the double bond rule.11–14 The double bond rule states that elements with principle quantum number ³ 3 will not participate in multiple bonding since they contain diffuse p-orbitals, therefore resulting in poor orbital overlap and possess lower p-bond energy in comparison to the lighter elements.15,16 These examples include the first isolated disilene (1.1), silene (1.2), phosphaalkyne (1.3), and diphosphene (1.4). Each of these compounds contain some degree of steric bulk surrounding the multiply bound main group elements in order to kinetically stabilize these reactive centres. These noted examples are not presented as the sole contributors to guiding the field of low-coordinate main group chemistry but have certainly influenced the current trend of isolating unique structures that challenge the traditional rules of structure and bonding.

Me3Si OSiMe3 Si Si Si C P P P Me3Si

1.1 1.2 1.3 1.4

Figure 1-1: Early reported examples of low-coordination in the main group elements.

Expanding from the work of the above-mentioned compounds, the Power research group have demonstrated that heavier main group elements can adopt bonding arrangements similar to alkenes and alkynes. A vast library of these compounds have been reported, which all contain m-terphenyl ligands positioned at the main group element.15–19 These compounds can often display unique reactivity, with one example

3 4 being the activation of dihydrogen using a digermyne (1.5, E = Ge) – the first reported 19 example of a non-transition metal species activating H2. The ability of main group compounds to mimic the reactivity of transition metal complexes has continued to drive much of the research in this field.

Neutral ligands have been used to stabilize main group elements in the zero oxidation state, resulting in main group allotropes (1.6).20–27 This field started from the discovery that carbodiphosphoranes can be represented as containing a central carbon atom with an oxidation state of zero, rather than containing a carbon centre multiply bound to two phosphorus atoms.28 This has led to the formation of diatomic main group elements that contain a formal oxidation state of zero, and mimic the structures of the natural occurring diatomic allotropes e.g. H2, N2, O2. These main group elements possess lone pairs, which have been demonstrated to act as donor atoms in simple Lewis acid- Lewis base interactions,25 and have the potential to be used as building blocks for more complex structures. This methodology of using strong donors, namely NHCs, to stabilize main group allotropes has been expanded to elements spanning across the p-block and provides a way to create soluble element (0) allotropes that could not be achieved otherwise.

The 2-phosphaethynolate anion (PºC–O-, 1.7) is the phosphorus analogue of the cyanate ion (NºC–O-) and is the simplest isolated stable compound that contains a P-C triple bond. Although this phosphorus anion was first reported in the 1990’s,29 substantial research in this area has been limited due to the technical challenges in its synthesis. Improved synthetic procedures have been recently developed by Grützmacher,30 Cummins,31 and Goicoechea,32 that have allowed for the safe and scalable synthesis of sodium phosphaethynolate, and resulting from these successful methodologies, the number of reports of using 2-phosphaethynolate have seen a dramatic increase in the last five years. This unique 3-atom building block has been used for the installation of [P]- or [PCO]- functionality,33–35 precursor for P-heterocycles,36–38 and also used in the development of phosphorus-containing small molecules including urea39 and cyanuric acid derivatives.40 This low-coordinate phosphorus derivative is a perfect example of how

4 5 a fundamental main group species can be utilized as a new reagent, and have a dramatic impact in numerous aspects of chemistry.

Ar Dipp N Dipp N E E Ar Ar E E Dipp N P C O Dipp N Ar E = Al, Ga, Ge, In, Sn, Pb E = Si, P, Ge, As 1.5 1.6 1.7

Figure 1-2: Notable examples of multiple bonding within main group compounds.

Compounds containing low-coordinate main group centres have been successful for elements spanning across the p-block, and this dissertation will focus on low- coordinate phosphorus species. Research into low-coordinate phosphorus is of interest to the main group community since they can display unusual structures, possess unique reactivity, and can be used as ligands to transition metals with numerous bonding modes.

1.3 Phosphinidenes – From Transient Intermediates to Isolable Compounds

Phosphinidenes (also known as phosphanylidenes; 1.8, Figure 1-3 top) are a low- coordinate phosphorus derivative that contain a formal mono-coordinate phosphorus centre, two lone pairs of electrons at phosphorus, and formal oxidation number of +1.41,42 These low-coordinate compounds are the phosphorus analogues of carbenes and nitrenes, and are incredibly reactive species. Phosphinidenes were first detected by Gaspar and coworkers by EPR spectroscopy, from trapping mesitylphosphinidene in a frozen matrix at 77 K, indicating that a triplet phosphinidene was present.43 Additionally, reactions using various trapping reagents also resulted in products indicative of in situ generated phosphinidenes (Figure 1-3, bottom). Common methods of generating intermediate phosphinidenes include the reduction of halophosphines, and the cycloreversion of phosphorus heterocycles (most notably the decomposition of 7-phosphanorborenes),44–50 however these methods generally use harsh conditions, and often result in uncontrolled reactivity, and therefore low isolated yields.

5 6

Cp*

OC M MLn P R P R P R P M(CO)5 OC i CO N Pr2 1.8 1.9 1.10 1.11

Et hν, 77 K 3-hexyne P P Mes P - C4H8 Et

Figure 1-3: Top: General examples of phosphinidenes. Bottom: First example of spectroscopic detection of phosphinidenes.

Similar to carbenes, phosphinidene-metal complexes can possess either nucleophilic (Schrock) or electrophilic (Fischer) character. In the simplest of explanations, the electrophilic phosphinidene complexes can be viewed as containing a dative interaction between a singlet phosphinidene and a singlet transition metal centre, and phosphorus being in the +1 oxidation state.51 These compounds were first discovered by Mathey ([RP-M(CO)5], where M = Cr, Mo, W; 1.9), and react similar to that of carbenes, undergoing [1+2] cycloadditions with alkenes and alkynes leading to phosphiranes,52 and phosphirenes,53–55 respectively (Scheme 1-1, top). Although the majority of electrophilic terminal phosphinidene complexes are identified from their reactions with various trapping reagents,47,50 a number of amino-substituted phosphinidene-metal complexes have been isolated and structurally characterized (1.10).56–60 Importantly, these isolated structures react similar to the transient electrophilic derivatives, indicating that the stabilizing amino group does not impede the reactivity of these compounds (i.e. [1+2] cycloaddition occuring at phosphorus with alkynes; Scheme 1-1, bottom).60

6 7

(OC)5M R P (OC)5M Ph R' Δ Ph Ph P R P M(CO)5 R R' Ph M = Cr, Mo, W Ph NiPr 2 i P N Pr2 CO Ph Ph Ph P OC Co CO CO OC Co CO Ph3P Ph3P

Scheme 1-1: Reactivity of electrophilic phosphinidene complexes.

Nucleophilic phosphinidene compounds can be envisioned as the combination of a triplet phosphinidene with a triplet transition metal complex, resulting in a P-M double bond (1.11).51 These compounds were first reported by Lappert in the late 1980’s, and their formation resulted from the addition of lithiated metal precursors with bulky dichlorophosphines, that resulted in the formation of a P-M double bond.61 Since their inception in the 1980’s, examples of nucleophilic phosphinidene complexes have been demonstrated with both early and late transition metals,45 and contrary to their electrophilic derivatives, the reactivity of these nucleophilic compounds stems from the P=M double bond – a clear indication of their nucleophilic behavior.

As alternatives to transition metal phosphinidene compounds, donor stabilization using NHCs25,27,62–64 and phosphine ligands65,66 have been used to stabilize the reactive phosphorus centre. Quite recently, the Bertrand group succeeded in isolating a phosphinophosphinidene (1.12), the first stable derivative of this kind, by the photolysis of a phosphaketene situated with extremely bulky groups on the nitrogen atoms of the backbone (2,6-bis[(4-tert-butylphenyl)methyl]-4-methylphenyl; Scheme 1-2).34 This unique structure was found to contain a terminal phosphinidene containing a P-P double bond, and reactions with CO, strong donors (NHCs, PR3) or trapping reagents (alkenes, nitriles) occurred solely at the terminal phosphorus atom, indicating electrophilic reactivity.34,67,68

7 8

Ar N P P PR3 N Ar

PR3

Ar Ar Ar O O O O N N N hν, C6D6 P P C O P P P P O Ar = N - CO N N Ar Ar Ar O 1.12

13CO

Ar N P P 13C O N Ar

Scheme 1-2: Synthesis and reactivity of an isolable phosphinophosphinidene (1.12).

The chemistry surrounding phosphinidenes has seen significant development in the last 30 years. Improvements in synthetic techniques, structural characterization methods, and construction of unique ligands will continue to have an impact on the chemistry of phosphinidenes, with the goal to develop reliable and reproducible synthetic schemes that correspond to low-coordinate phosphorus derivatives.

1.4 Phosphinidene Chalcogenides

Phosphinidene chalcogenides (RP=Ch; also known as phosphinochalcogoylidenes or chalcogophosphines) are reactive main group species that consist of a two-coordinate phosphorus centre, a lone pair of electrons at phosphorus, and a formal P=Ch double bond.42 “Free” phosphinidene chalcogenides fit the criteria as described above, and isolation of such a species still remains as a challenge for phosphorus chemists, although these elusive species have been identified in the gas phase by mass spectrometry and infrared spectroscopy.69–73 The clean synthesis of RP=Ch offers a potential method of introducing both phosphorus and chalcogen in a 1:1 stoichiometry, therefore one could envision these species as suitable P-Ch transfer species. In addition, the chemistry of PIII- Ch is underdeveloped in comparison to its PV counterparts, and exploring the

8 9 fundamental chemistry of these reactive units would be beneficial to fully understand their capabilities as inorganic synthons. The following sections will detail the chemistry of RP=Ch, but the focus will remain on the sulfur derivatives, with some commentary and comparisons being made that involve phosphinidene oxides and the heavier chalcogens.

Although phosphinidene sulfides have been synthetic targets since the early 1960’s, the thorough understanding of the electronic nature of RP=S is limited, and virtually unknown for the heavier chalcogens. In contrast to their parent phosphinidenes that contain a triplet ground state,74 phosphinidene chalcogenides have been calculated to possess a singlet ground state at phosphorus, which renders these reactive units isolobal to both singlet carbenes and silylenes.42,75 In a seminal report by Niecke and Schoeller, theoretical studies attempted to predict the reactivity for multiply bound P=X systems (X being a p-block element).76 They discovered that phosphaalkenes have a HOMO consisting of the P=C p-bond and LUMO being the p*-orbital of P=C, therefore predicting that these species react similar to olefins (Figure 1-4). As you move to more electronegative p-block elements bound to phosphorus (P=N, iminophosphines; P=O, phosphinidene oxides), the MO’s are reversed and now the HOMO is a s-orbital, namely the lone pair at phosphorus, and LUMO is still the p*-orbital of PX double bond. In addition to changing the electronegativity of X, modifying R to be either p-donating or p- accepting can inverse the energy of s and p, leading the chalcogophosphine to act as either a 1,1- or 1,2-dipole. In the case of HP=O, these theoretical findings indicate that the parent oxophosphine is assumed to have similar reactivity as singlet carbenes (i.e. 1,1-dipoles, s-HOMO). These theoretical findings were also confirmed experimentally, with numerous reports confirming the carbene-type reactivity of phosphinidene oxides.75,77,78

9 10

Figure 1-4: Sequence of energies (in eV) of the orbitals s and p, p* for HP=X, obtained from complete energy-optimized ab initio STO/3G calculations.76

While the reactivity of RP=O is solidified both experimentally and theoretically, the electronic nature of phosphinidene sulfides (and heavier chalcogens) are less developed in comparison. As Niecke and Schoeller discussed in their report, as X becomes more electronegative, carbene character dominates.76 Therefore, moving down Group 16 into the heavier chalcogens (Ch becoming less electronegative), the dominant carbene character will be lost and more alkene-type behaviour will be introduced. Mathey and coworkers addressed this issue and performed a series of frontier orbital calculations on the parent MeP=S that suggested that the computed bond order of P=S is 1.93 which is indicative of double bond character.79 The calculated HOMO is an in-plane orbital combining the s(P-C), the P-lone pair, and in-plane p orbital of sulfur, while the HOMO- 1 being the P=S p-orbital. In this scenario, both of the modes of reactivity, carbene or olefin type behaviour, are possible for MeP=S (Figure 1-5).

10 11

Figure 1-5: Top: Calculated molecular orbitals for MeP=S.79 Bottom: Different modes of reactivity for RP=Ch.

1.4.1 Generating RP=S in the Presence of Trapping Reagents

The production of phosphinidene sulfides can be accomplished in a number of ways, which will be described in detail in this section. These transient intermediates can be produced, and doing so in the presence of trapping reagents, hinders the self-reaction of RP=S or polymerization of this reactive group, and leads to products that can be isolated and characterized that hints towards the presence of RP=S. In the cases where “free” RP=S cannot be solely identified as its own molecular unit, the critical reader should keep in mind that other mechanisms that do not involve the production of RP=S should be considered.

One of the most commonly utilized methods of generating phosphinidene sulfides was adopted from phosphinidene chemistry, and relies on the degradation of 7- phosphanorbornadienes (or related bicycles – Scheme 1-3).53 Treating these compounds under thermal or photolytic conditions in the presence of a trapping reagent leads to extrusion, and trapping of the bridgehead RP=S fragment (Scheme 1-4).

11 12

R S P R' Δ or hν R' S + R P R' R'

Scheme 1-3: Using 7-phosphanorbornadiene compounds as precursors to phosphinidene sulfides.

Early reports indicated that extrusion of RP=S from norbornadiene precursors indicate 1,1-dipole reactivity undergoing insertion reactions with alcohols and disulfanes (Scheme 1-4, 1.13 and 1.14), and products resembling [1+4] cycloadditions with benzil (1.15) and 2,3-dimethylbutadiene (dmbd, 1.16). These results indicate that much like RP=O, the sulfides also react like carbenes.80–84 It wasn’t until recently that Mathey and coworkers reported alkene-type reactivity from the room temperature reaction of RP=S with dmbd leading to the [2+4] product (1.17) and no formation of 1.16.79 Compound 1.17 was identified in their crude reaction mixture (with 31P NMR resonances ranging from -9 to +26), however the authors were not able to isolate this product, but could isolate and characterize the W(CO)5 derivative. All prior reactions involving dmbd had been performed at elevated temperatures or under photolytic conditions, therefore there is the potential for 1.17 to decompose to its structural isomer, 1.16, although a direct mechanism has not been discussed in the literature. Regardless, these results indicate that 7-phosphanorbornadiene derivatives can be used as source of RPS, and reactivity of the ejected RP=S appears to follow multiple pathways and is not as straightforward as their oxide derivatives.

12 13

R S P SEt SEt 1.14

EtS SEt R Ph Ph O O S P OR' O O H R'-OH Ph Ph P 1.13 S R S 1.15 R P

S P P R R S 1.17 1.16

Scheme 1-4: Reaction of in situ generated phosphinidene sulfides with alchols, diethyl sulfide, benzil, and 2,3-dimethylbutadiene.

Another common method of producing RP=S is the dehalogenation of thiophosphonoic dihalides (1.18, Scheme 1-5) which was first discussed in the 1960’s by Harwood and Crofts,85,86 but was further developed by Inamoto and coworkers in the 1970’s.87,88 Performing these reactions in the presence of diethylsulfide and benzil yielded products consistent with the insertion of RP=S into the trapping reagent, and consistent with the results obtained using norbornadiene precursors (yielding 1.14 and 1.15). The addition of dienes during the dechlorination step resulted in products consistent with [2+4] cycloaddition, and resembles the same structures observed recently by Mathey (1.17). The ambiguity of this result stems from the inability to isolate 1.17, however the corresponding oxide or sulfide (1.19) could be isolated and characterized, in which the authors suggested the product either oxidized or decomposed upon workup. The dehalogenation of thiophosphonoic dihalides has now become a standard approach for the in situ formation of RP=S and used on a number of separate occasions.88–93 Although some concern has been raised in the literature whether “free” RP=S is formed

13 14 through this method based on the inconsistent results by Inamoto,94 the production of similar products via the norbornadiene or dehalogenation methods indicates that RP=S is a factor in each of these processes.

1.15

(PhCO)2 X = O, S S Mg S S P Cl S dmbd X - MgCl Ph P P P Cl 2 Ph Ph 1.18 1.17 1.19 (EtS)2

1.14

Scheme 1-5: Dechlorination of phenylthiophosphonoic dichloride using magnesium, and reactions of the generated PhP=S with trapping reagents.

A less common, but successful route for liberating RP=S has been accomplished from thermolysis/photolysis of P-S heterocycles, primarily phosphirane sulfides (Scheme 1-6, 1.20) and phospholene sulfides (1.21).75,95,96 Either thermolysis or photolysis of 2,6- dimethoxyphenylphosphirane sulfide (1.20) in the presence of alcohols, diethylsulfide, or dmbd produced products consistent with previous reports (compounds 1.13-1.17). Gaspar and coworkers revealed that the consumption of 1.20 was a clean first order process, and the rate of disappearance of phosphirane sulfide does not change with increased concentration of EtS-SEt, indicating that the formation of 1.14 is from the reaction of free RP=S and diethylsulfide.75 Interestingly, the thermolysis/photolysis of 1.20 in the presence of dmbd yielded products 1.16 and 1.17, indicating both carbene and olefin type reactivity by the intermediate RP=S. These products likely arise from competing reactions of the generated phosphinidene sulfide, that occurs from performing these reactions at elevated temperatures or under photolytic conditions.

14 15

OMe S hν or Δ S hν P R P - C2H4 - P OMe Ph S 1.20 1.21

Scheme 1-6: Liberating phosphinidene sulfides from the PV heterocycles phosphirane sulfide (1.20) and phospholene sulfide (1.21).

1.4.2 Unique Ligand Design to Stabilize RP=S

Up until this point, analysis of products obtained from reactions with trapping reagents and in situ generated phosphinidene sulfides assumes that “free” RP=S is an accessible intermediate. Instead of trapping RP=S, strategically designed ligands have been made in attempt to isolate/stabilize the reactive P=S unit. The first successful attempt at isolating RP=Ch was performed in the early 1990’s using the octamethylxylidene ligand (abbreviated to Mx).97–99 This ligand draws similar comparisons to the bulky supermesityl group, however in this case one of the ortho t- butyl groups is replaced by a dimethylamino substituent, giving the ligand the ability to afford both steric protection and stabilization through donor participation. The addition of

P(NMe2)3 to diselenoxophosphorane (1.22Se) resulted in the ligand stabilized phosphinidene selenide and the concomitantly formed phosphine selenide (Scheme 1-7, 1.23). MxP=Se was found to be metastable in solution, and the authors were able to obtain solution NMR data on their hypothesized product that included a very downfield

31 1 1 shifted P{ H} NMR signal (dP = 399.0) that also contained selenium coupling ( JSe-P = 708 Hz). Unfortunately, this compound readily disproportionated to the diphosphene (1.23a) and diselenoxophosphorane (1.22Se) and precluded structural characterization.

15 16

Ch Ch P 4 P(NMe2)3 P Me N P P + 2 1.22Ch 4 Se 4 2 NMe2 - 4 SeP(NMe2)3 NMe2 NMe2 Ch = S, Se 1.22Ch 1.23 1.23a

Scheme 1-7: Synthesis of P=Ch units utilizing a octamethylxylidene ligand.

The same approach was utilized to generate the ligand stabilized phosphinidene sulfide, however their precursor being selenoxothioxophosphorane (1.22S).98 Treating this with P(NMe2)3 yielded the ligand stabilized MxP=S (1.23). This compound was thoroughly characterized by multinuclear NMR studies that included a similar downfield phosphorus chemical shift as found with the selenium derivative (dP = 382.0) and also characterized by mass spectrometry and elemental analysis. While the authors mentioned the long-standing stability of the product, the characterization data excluded structural confirmation of the ligand-stabilized phosphinidene sulfide, which would truly confirm the connectivity of the product, as well as observing any interaction with the neighbouring NMe2 moiety. Unfortunately, no further work on this ligand framework has been reported since.

A different approach by Schmidpeter and coworkers utilized ylidic stabilization to yield a terminal P=Ch unit (Scheme 1-8).100,101 The argument lies in whether the terminal RP=Ch contains a phosphorus-chalcogen double bond (1.25) or the charge-separated resonance form being dominant (1.26). The 31P{1H} NMR resonances for 1.25 were found between dP = 485 – 495, resembling chemical shifts similar to those reported by Yoshifuji, and indicating an electron poor phosphorus centre. The P=S bond length was 1.981(2) Å, slightly longer than the expected P=S bond distance (Pyykko and Atsumi 102,103 calculated bond length for P=S is 1.96 Å). The Ph3P-C bond length (1.759(4) Å) was significantly longer than C-PS bond length (1.704(5) Å), leading to believe that resonance form 1.26 is likely the dominant structure. Reacting the ylid-stabilized P=S with an electrophile yielded nucleophilic addition to benzylbromide stemming from the chalcogen atom (1.27), again supporting the notion that the charge-separated species 1.26

16 17 is the likely dominant resonance form. Although this is elegant work, the ylidic stabilization deters from the P=S character, and for this reason, the quest for a truly free phosphinidene chalcogenide remains.

R R R Na2Ch Ch Ch Ph3P PCl2 Ph3P P Ph3P P 1.24 1.25 1.26

PhCH2Br

R Br Ch CH Ph Ph3P P 2 1.27

Scheme 1-8: Synthesis of an ylidic stabilized P=Ch unit and its reactivity (Ch = S, Se).

1.4.3 Transition Metal Stabilization of RP=S

Another approach to the stabilization of phosphinidene sulfides has been accomplished using transition metal complexes. With the presence of more than one heteroatom in RP=S, one can easily envision numerous bonding modes for these reactive units towards one, or multiple, transition metal centres. The two primary methods of transition metal stabilized phosphinidene sulfides is by generation of “free” RP=S (by the methods discussed previously) in the presence of a transition metal complex, or by generating the RP=S framework while the phosphorus unit is bound to the transition metal complex.

The first example of the reaction of “free” RP=S with transition metals was conducted by Seyferth and Withers, in which they generated PhP=S from the dehalogenation of thiophosphonoic dihalides. Doing so in the presence of Fe3(CO)12 unfortunately did not produce transition metal stabilized phosphinidene sulfide, however it was suggested that the P=S bond was broken, and the in situ generated phosphinidene sulfide was degraded and led to the formation of a trinuclear iron complex (Figure 1-6, 1.28).104

17 18

The first successful example of transition-metal stabilized RP=S involved the generation of MeP=S by the dehalogenation of dichloromethylthioxophosphorane, and doing so in the presence of Mn2(CO)10 resulted in 1.29 containing side-on P-S bound to

91 Mn(CO)4 and an end on coordination of phosphorus to Mn(CO)5. Fragmentation of a 7-

5 phosphanonorbornadiene precursor in the presence of (h -C5H5)2Mo2(CO)6 resulted in multiple products: the binuclear metal complex that retained a M-M bond (1.30), and the binuclear metal complex where RP=S inserts between the M-M bond (1.31).105 The same products (1.30 and 1.31) were also generated upon reacting the same metal complex with Lawesson’s reagent.106,107

Ph R P R Cp Mes C H S P CO Fe(CO)3 5 5 CO (OC)3Fe (OC) Mn P Mo Mo C H OC M P CO 4 Mn(CO) 5 5 5 OC OC S M CO Fe(CO)3 S C CO S O Cp 1.28 1.29 1.30 1.31 PPh3 TMP TMP OC Cy S S Os Cp P Cp P P Fe Fe OC PH OC C CO (OC)3Mn S PPh3 O S Mn(CO)3 1.32 1.33 1.34

Figure 1-6: Select examples of transition metal stabilized phosphinidene sulfides (1.28 – 1.34).

The majority of examples of transition-metal stabilized phosphinidene sulfides stems from the generation of the RPS unit within the coordination sphere of a transition metal complex. Although these examples do not contain a source of free RP=S, they still possess the ability to use these newly formed complexes to transfer a stoichiometric amount of P-S. The parent phosphinidene sulfide, HP=S, was generated in the coordination sphere of an osmium complex leading to 1.32, by the addition of base to its secondary phosphine precursor.108 The Ruiz group has demonstrated the ability to generate RPS units in the coordination sphere of a transition metal on a number of occasions, where the metal compounds contain nucleophilic character stemming from the phosphorus site have been reacted with elemental sulfur. This leads to the RPS

18 19 framework being associated to transition metal coordination spheres (notable examples being 1.33 and 1.34).109–114

1.4.4 Synthesis of (c-RPCh)n Heterocycles

The final discussion regarding the reactivity of phosphinidene chalcogenides involves the synthesis of P-Ch heterocycles, and primarily those that contain the general formula (c-RPCh)n. In the previous sections, the discussion was focused on the formation of RP=S that contained sterically accommodating ligands (e.g. phenyl) in the presence of a variety of trapping reagents. However, when the steric demand of the ligand is increased and without any trapping reagent, the formation of cyclic oligomers with the general formula (c-RPCh)n are favoured. For the sulfur derivatives, the dehalogenation route has been applied with R = Mes or Mes* that results in the 6-membered (RPS)3 ring (Figure 1-7, 1.35). Alternatively, a different approach using a PIII precursor was utilized 115 116 by Sheldrick and later Weigand which generated the cyclic tetramer ((RPS)4, 1.36) from the addition of RPCl2 and either S(TMS)2 or Na2S. Identical compounds as those in Figure 1-7 have been reported from a variety of different reactions, but stem from the formation of intermediate RP=S.92,93,99,117 Selenium derivatives (n = 3, 4) have been

118,119 reported, however lack sufficient characterization data. Phosphorus-tellurium heterocycles have been reported using supermesityl or trityl groups at phosphorus leading to 6-membered P3Te3 rings (1.35), and represent the only reported examples of (RPTe)n 120 heterocycles.

R R Ch R P P P Ch Ch Ch Ch P P P P R Ch R R Ch R Ch = S, Se; R = Mes, Mes* Ch = S; R = Mes, Im Ch = Te; R = Mes*, CPh3 Ch = Se; R = tBu, Mes 1.35 1.36

Figure 1-7: Reported (c-RPCh)n derivatives where the ligands are sterically demanding.

19 20

1.5 Scope of Thesis

This dissertation focuses on the synthesis of main group heterocycles, primarily those containing phosphorus and chalcogen elements. As per the discussion above, significant advancements have been made using large bulky ligands to kinetically stabilize reactive centres. For this study, all examples involve the use of a bulky ligand situated at phosphorus, specifically m-terphenyl, that appears to be an ideal candidate for stabilizing reactive phosphorus centres, but not so much to halt reactivity. The goal was to create phosphorus-chalcogen ring systems containing a dimeric structure (i.e. (c-

RPCh)2) and use these strained precursors to access monomeric phosphinidene chalcogenides. Low-coordinate phosphorus-sulfur examples are significantly underdeveloped in comparison to phosphorus-oxygen, or other main group elements, and the heavier chalcogens are virtually unknown (e.g. phosphinidene selenide, telluride). Investigation into the sulfur chemistry would allow to further develop this field of work and add to an already vast library of phosphorus-sulfur compounds. Research into the heavier chalcogen derivatives would aid in the development of a nonexistent realm of chemistry. Taken together, we have developed new main group element heterocycles that can act as a storage form for highly reactive monomers, which can be used for more significant applications rather than the simple synthesis of new heterocycles.

The parent phosphorus-chalcogen rings, that are the starting point for all of the chemistry reported in this dissertation, were generated by the room temperature transformation involving m-terphenyl dichlorophosphine and bis(trimethylsilyl)chalcogenide (Scheme 1-9). Upon the elimination of two equivalents of

TMSCl, the parent 4-membered P2Ch2 rings can be generated in high yields, and scalable to multiple grams.

PCl Mes Mes 2 THF, 25 °C Ch Mes Mes Ch 4 - 24 h + Me Si SiMe P P 3 3 - 2 TMSCl Ch Mes Mes Yields > 60%

Scheme 1-9: Synthetic methodology for generating P2Ch2 heterocycles.

20 21

Chapter 2 focuses on the synthetic methodology and the formation of these P2Ch2 rings, as well as our initial attempts to utilize these strained 4-membered rings as sources of low-coordinate phosphinidene chalcogenides. Heating samples of these rings in the presence of a diene resulted in cycloaddition of the generated RP=Ch, indicating that at elevated temperature these rings could be utilized as a source of monomeric phosphinidene chalcogenide. The addition of strong donors (e.g. NHC) to the sulfur derivative resulted in controlled degradation of the dimer into a base-stabilized monomer.

Chapter 3 focuses on further developing the cycloaddition chemistry involving the P-S ring, specifically with alkynes, that resulted in the formation of new strained P-S heterocycles. We also developed an alternative, room temperature method of generating [RP=S]. This new method allowed us to analyze the true electronic character of phosphinidene sulfides.

Chapter 4 focuses on the reactivity of the parent 4-membered rings, primarily with Lewis acids (coinage metals) and Lewis bases (nitrogen and phosphorus bases). Ring expansion occurred with both chalcogens by the addition of acid or base, resulting in a 6-membered P3Ch3 ring. In the case of Lewis acids, the coinage metals were bound to each of the three phosphorus atoms, leading to unique coordination complexes. The addition of excess coinage metal resulted in the formation of unexpected structures consisting of a P4Ch6Cu4 core.

Finally, Chapter 5 involves a comprehensive study on the synthesis of new P-Ch heterocycles that were generated by the reaction of monomeric phosphinidene chalcogenides and phosphaborenes (RP=B-NR2). Reactivity studies involving these new rings was performed with coinage metals resulting in simple phosphorus-metal coordination, and NHCs were found to degrade these rings into low-coordinate phosphorus compounds. Additionally, the parent 4- and 6-membered rings were also subjected to reactions with NHCs, that also resulted in the degradation and formation of new low-coordinate phosphorus compounds.

1.6 References (1) Nobel Prize Media AB. Press Release: The 1918 Nobel Prize in Chemistry

21 22

https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1918/ (accessed Dec 2, 2017). (2) Smil, V. Nature 1999, 400, 415. (3) Nobel Prize Media AB. Press Release: The 1963 Nobel Prize in Chemistry https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1963/ (accessed Dec 2, 2017). (4) Nobel Prize Media AB. Press Release: The 1912 Nobel Prize in Chemistry https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1912/ (accessed Dec 2, 2017). (5) Nobel Prize Media AB. Press Release: The 1979 Nobel Prize in Chemistry https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1979/ (accessed Dec 2, 2017). (6) Mark, J. E.; Allcock, H. R.; West, R. Inorganic Polymers, Second Edition; 2005. (7) Chivers, T.; Konu, J. Comments Inorg. Chem. 2009, 30, 131–176. (8) Nobel Prize Media AB. Press Release: The 1991 Nobel Prize in Chemistry https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1991/ (accessed Dec 2, 2017). (9) Nobel Prize Media AB. Press Release: The 1915 Nobel Prize in Physics https://www.nobelprize.org/nobel_prizes/physics/laureates/1915/ (accessed Dec 2, 2017). (10) Nobel Prize Media AB. Press Release: The 1998 Nobel Prize in Chemistry https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1998/ (accessed Dec 2, 2017). (11) West, R.; Fink, M. J.; Michl, J. Science 1981, 214, 1343–1344. (12) Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi, T. J. Am. Chem. Soc. 1981, 103, 4587–4589. (13) Brook, A. G.; Abdesaken, F.; Gutekunst, B.; Gutekunst, G.; Kallury, R. K. Chem. Comm. 1981, 191–192. (14) Becker, G.; Gresser, G.; Uhl, W. Z. Naturforsch. 1981, 36, 16–19. (15) Power, P. P. Chem. Rev. 1999, 99, 3463–3504. (16) Fischer, R. C.; Power, P. P. Chem. Rev. 2010, 110, 3877–3923. (17) Twamley, B.; Sofield, C. D.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1999, 121, 3357–3367. (18) Rivard, E.; Power, P. P. Inorg. Chem. 2007, 46, 10047–10064. (19) Power, P. P. Nature 2010, 463, 171–177. (20) Wang, Y.; Xie, Y.; Wei, P.; King, B.; Schaefer, H.; Schleyer, P. V. R.; Robinson, G. H. Science 2008, 321, 1069–1071. (21) Sidiropoulos, A.; Jones, C.; Stasch, A.; Klein, S.; Frenking, G. Angew. Chem., Int.

22 23

Ed. 2009, 48, 9701–9704. (22) Wang, Y.; Xie, Y.; Wei, P.; King, R. B.; Schaefer, H. F.; Schleyer, P. V. R.; Robinson, G. H. J. Am. Chem. Soc. 2008, 130, 14970–14971. (23) Abraham, M. Y.; Wang, Y.; Xie, Y.; Wei, P.; Schaefer, H. F.; Von Schleyer, P. R.; Robinson, G. H. Chem. - Eur. J. 2010, 16, 432–435. (24) Wilson, D. J. D.; Dutton, J. L. Chem. - Eur. J. 2013, 19, 13626–13637. (25) Wang, Y.; Robinson, G. H. Inorg. Chem. 2014, 53, 11815–11832. (26) Wang, Y.; Robinson, G. H. Dalton Trans. 2012, 337–345. (27) Wang, Y.; Robinson, G. H. Inorg. Chem. 2011, 50, 12326–12327. (28) Tonner, R.; Öxler, F.; Neumüller, B.; Petz, W.; Frenking, G. Angew. Chem., Int. Ed. 2006, 45, 8038–8042. (29) Becker, G.; Schwarz, W.; Seidler, N.; Westerhausen, M. Z. Anorg. Allg. Chem. 1992, 612, 72–82. (30) Puschmann, F. F.; Stein, D.; Heift, D.; Hendriksen, C.; Gal, Z. A.; Grützmacher, H. F.; Grützmacher, H. Angew. Chem., Int. Ed. 2011, 50, 8420–8423. (31) Krummenacher, I.; Cummins, C. C. Polyhedron 2012, 32, 10–13. (32) Jupp, A. R.; Goicoechea, J. M. Angew. Chem., Int. Ed. 2013, 52, 10064–10067. (33) Tondreau, A. M.; Benkö, Z.; Harmer, J. R.; Grützmacher, H. Chem. Sci. 2014, 1545–1554. (34) Liu, L.; Ruiz, D. A.; Bertrand, G.; Liu, L.; Ruiz, D. A.; Munz, D.; Bertrand, G. Chem 2016, 1, 147–153. (35) Robinson, T. P.; Cowley, M. J.; Scheschkewitz, D.; Goicoechea, J. M. Angew. Chem., Int. Ed. 2015, 54, 683–686. (36) Chen, X.; Alidori, S.; Puschmann, F. F.; Santiso-Quinones, G.; Benko, Z.; Li, Z.; Becker, G.; Grützmacher, H. F.; Grützmacher, H. Angew. Chem., Int. Ed. 2014, 53, 1641–1645. (37) Heift, D.; Benḱ, Z.; Grützmacher, H. Chem. - Eur. J. 2014, 20, 11326–11330. (38) Robinson, T. P.; Goicoechea, J. M. Chem. - Eur. J. 2015, 21, 5727–5731. (39) Jupp, A. R.; Goicoechea, J. M. J. Am. Chem. Soc. 2013, 135, 19131–19134. (40) Suter, R.; Mei, Y.; Baker, M.; Benkő, Z.; Li, Z.; Grützmacher, H. Angew. Chem., Int. Ed. 2017, 56, 1356–1360. (41) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy; Wiley, 1998. (42) Regitz, M.; Scherer, O. J.; Appel, R. Multiple bonds and low coordination in phosphorus chemistry; G. Thieme Verlag: New York, 1990. (43) Li, X.; Weissman, S. I.; Lin, T.; Gaspar, P. P. J. Am. Chem. Soc. 1994, 116, 7899– 7900.

23 24

(44) Lammertsma, K. In Topics in Current Chemistry; Majoral, J.-P., Ed.; Topics in Current Chemistry; Springer Berlin Heidelberg: Berlin, Heidelberg, 2003; pp 95– 119. (45) Aktaş, H.; Slootweg, J. C.; Lammertsma, K. Angew. Chem., Int. Ed. 2010, 49, 2102–2113. (46) Weber, L. Eur. J. Inorg. Chem. 2007, 2, 4095–4117. (47) Mathey, F. Dalton Trans. 2007, 1861–1868. (48) Lammertsma, K.; Vlaar, M. J. M. Eur. J. Org. Chem. 2002, 1127–1138. (49) Cowley, A. H. Acc. Chem. Res. 1997, 30, 445–451. (50) Mathey, F. Angew. Chem., Int. Ed. 1987, 26, 275–370. (51) Mathey, F. Dalton Trans. 2007, No. 19, 1861–1868. (52) Marinetti, A.; Mathey, F. F. Organometallics 1984, 3, 456–461. (53) Marinetti, A.; Mathey, F. J. Am. Chem. Soc. 1982, 104, 4484–4485. (54) Marinetti, A.; Mathey, F. J. Am. Chem. Soc. 1985, 107, 4700–4706. (55) Marinetti, A.; Fischer, J.; Mathey, F. J. Am. Chem. Soc. 1985, 107, 5001–5002. (56) Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Organometallics 2001, 20, 2657– 2659. (57) Sterenberg, B. T.; Carty, A. J. J. Organomet. Chem. 2001, 617–618, 696–701. (58) Graham, T. W.; Cariou, R. P. Y.; Sánchez-Nieves, J.; Allen, A. E.; Udachin, K. A.; Regragui, R.; Carty, A. J. Organometallics 2005, 24, 2023–2026. (59) Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Organometallics 2003, 22, 3927– 3932. (60) Sánchez-Nieves, J.; Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. J. Am. Chem. Soc. 2003, 125, 2404–2405. (61) Hitchcock, P. B.; Lappert, M. F.; Leung, W. J. Chem. Soc., Chem. Commun. 1987, 1282–1283. (62) Lemp, O.; Balmer, M.; Reiter, K.; Weigend, F.; H, C. Von. Chem. Commun. 2017, 7620–7623. (63) Pal, K.; Hemming, O. B.; Day, B. M.; Pugh, T.; Evans, D. J.; Layfield, R. A. Angew. Chem., Int. Ed. 2016, 55, 1690–1693. (64) Bispinghoff, M.; Tondreau, A. M.; Grützmacher, H.; Faradji, C. A.; Pringle, P. G. Dalton Trans. 2016, 5999–6003. (65) Ellis, B. D.; Macdonald, C. L. B. Coord. Chem. Rev. 2007, 251, 936–973. (66) Protasiewicz, J. D. Eur. J. Inorg. Chem. 2012, 4539–4549. (67) Hansmann, M. M.; Jazzar, R.; Bertrand, G. J. Am. Chem. Soc. 2016, 138, 8356– 8359.

24 25

(68) Hansmann, M. M.; Bertrand, G. J. Am. Chem. Soc 2016, 138, 15885–15888. (69) Schnockel, H.; Schunck, S. Z. Anorg. Allg. Chem. 1987, 552, 155. (70) Schnockel, H.; Lakenbrink, M. Z. Anorg. Allg. Chem. 1983, 507, 70. (71) Binnewies, M. Z. Anorg. Allg. Chem. 1983, 507, 66. (72) Schnockel, H.; Schunck, S. Z. Anorg. Allg. Chem. 1987, 552, 163. (73) Binnewies, M.; Borrmann, H. Z. Anorg. Allg. Chem. 1987, 552, 147. (74) Nixon, J. F. Chem. Rev. 1988, 88, 1327–1362. (75) Gaspar, P. P.; Qian, H.; Beatty, A. M.; d’Avignon, D. A.; Kao, J. L. F.; Watt, J. C.; Rath, N. P. Tetrahedron 2000, 56, 105–119. (76) Schoeller, W. W.; Niecke, E. J. Chem. Soc., Chem. Commun. 1982, 569–570. (77) Soc, J. A. C.; Yamamoto, Y.; Soc, J. A. C.; Robinson, S. D.; Acta, I. C.; Joshi, K. K.; Mills, S.; Pauson, P. L. Angew. Chem., Int. Ed. 1978, 17, 867–868. (78) Cowley, A. H.; Gabbaï, F. P.; Corbelin, S.; Decken, A. Inorg. Chem. 1995, 34, 5931–5932. (79) Wang, L.; Ganguly, R.; Mathey, F. Organometallics 2014, 33, 5614–5617. (80) Santini, C. C.; Fischer, J.; Mathey, F.; Mitschler, A. J. Am. Chem. Soc. 1980, 102, 5809–5815. (81) Hussong, R.; Heydt, H.; Regitz, M. Z. Naturforsch 1986, 41b, 915–921. (82) Compain, C.; Donnadieu, B.; Mathey, F. Organometallics 2005, 24, 1762. (83) Kashman, Y.; Wagenstein, I.; Rudi, A. Tetrahedron 1976, 32, 2427–2431. (84) Quin, L. D.; Szewczyk, J. J. Chem. Soc., Chem. Commun. 1986, 844–846. (85) Crofts, P. C.; Fox, I. S. J. Chem. Soc. B. 1968, 1416–1420. (86) Harwood, H. J.; Pollart, K. A. J. Org. Chem. 1963, 28, 3430–3433. (87) Nakayama, S.; Yoshifuji, M.; Okazaki, R.; Inamoto, N. Chem. Commun. 1971, 1186–1187. (88) Nakayama, S.; Yoshijiuji, M.; Okazaki, R.; Inamoto, N. J. Chem. Soc., Perkin I 1973, 2069–2071. (89) Nakayama, S.; Yoshifuji, M.; Okazaki, R.; Inamoto, N. Bull. Chem. Soc. Jpn. 1975, 48, 546–548. (90) Nakayama, S.; Yoshijiuji, M.; Okazaki, R.; Inamoto, N. Bull. Chem. Soc. Jpn. 1975, 48, 3733–3737. (91) Lindner, E.; Auch, K.; Hiller, W.; Fawzi, R. Angew. Chem., Int. Ed. 1984, 23, 320–320. (92) Yoshifuji, M.; Toyota, K.; Ando, K.; Inamoto, N. Chem. Lett. 1984, 317–318. (93) Yoshijiuji, M.; Ando, K.; Shibayama, K.; Inamoto, N.; Hiroisu, K.; Higuchi, T. Angew. Chem., Int. Ed. 1983, 22, 418–419.

25 26

(94) Schmidt, U. Angew. Chem., Int. Ed. 1975, 14, 523–528. (95) Tomioka, H.; Takata, S.; Kato, Y.; Izawa, Y. J. Chem. Soc., Perkin II 1980, 1017– 1021. (96) Holand, S.; Mathey, F. J. Org. Chem. 1981, 46, 4386–4389. (97) Yoshifuji, M.; Hirano, M.; Toyota, K. Tetrahedron Lett. 1993, 34, 1043–1046. (98) Yoshifuji, M.; Sangu, S.; Hirano, M.; Toyota, K. Chem. Lett. 1993, 1715–1718. (99) Kamijo, K.; Toyota, K.; Yoshifuji, M. Chem. Lett. 1999, 567–568. (100) Jochem, G.; Nöth, H.; Schmidpeter, A. Angew. Chem., Int. Ed. 1993, 32, 1089– 1091. (101) Jochem, G.; Karaghiosoff, K.; Plank, S.; Dick, S.; Schmidpeter, A. Chem. Ber. 1995, 128, 1207–1219. (102) Pyykkö, P.; Atsumi, M. Chem. - Eur. J. 2009, 15, 12770–12779. (103) Pyykkö, P.; Atsumi, M. Chem. - Eur. J. 2009, 15, 186–197. (104) Seyferth, D.; Withers, H. P. Organometallics 1982, 1, 1294–1299. (105) Hussong, R.; Heydt, H.; Maas, G.; Regitz, M. Chem. Ber. 1987, 120, 1263. (106) Alper, H.; Einstein, F. W. B.; Petrignani, J. F.; Willis, A. C. Organometallics 1983, 2, 1422–1426. (107) Weng, Z.; Leong, W. K.; Vittal, J. J.; Goh, L. Y. Organometallics 2003, 22, 1645– 1656. (108) Bohle, S.; Rickard, C. E. F.; Roper, W. R. Angew. Chem., Int. Ed. 1988, 27, 302– 304. (109) Alvarez, C. M.; Alvarez, M. A.; Garcia, M. E.; Gonzalez, R.; Ruiz, M. A.; Hamidov, H.; Jeffery, J. C. Organometallics 2005, 24, 5503–5505. (110) Graham, T. W.; Udachin, K. A.; Carty, A. J. Inorg. Chim. Acta 2007, 360, 1376– 1379. (111) Hirth, U.-A.; Malisch, W.; Kab, H. J. Organomet. Chem. 1992, 439, 20–24. (112) Alvarez, B.; Alvarez, M. A.; Amor, I.; García, M. E.; García-Vivó, D.; Suárez, J.; Ruiz, M. A. Inorg. Chem. 2012, 51, 7810–7824. (113) Alvarez, B.; Angeles Alvarez, M.; Amor, I.; García, M. E.; Ruiz, M. A. Inorg. Chem. 2011, 50, 10561–10563. (114) Albuerne, I. G.; Alvarez, M. A.; García, M. E.; García-Vivó, D.; Ruiz, M. A. Inorg. Chem. 2015, 54, 9810–9820. (115) Lensch, C.; Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1984, 2855–2857. (116) Henne, F. D.; Watt, F. A.; Schwedtmann, K.; Hennersdorf, F.; Kokoschka, M.; Weigand, J. J. Chem. Commun. 2016, 2023–2026. (117) Cetinkaya, B.; Hitchcock, P. B.; Lappert, M. F.; Thorne, A. J.; Goldwhite, H. J.

26 27

Chem. Soc., Chem. Commun. 1982, 691–693. (118) Karaghiosoff, K.; Eckstein; Motzer, K. Phosphorus. Sulfur. Silicon Relat. Elem. 1994, 93/94, 185–188. (119) An, D.-L.; Toyota, K.; Yasunami, M.; Yoshifuji, M. Chem. Lett. 1994, 24, 199– 200. (120) Nordheider, A.; Chivers, T.; Schon, O.; Karaghiosoff, K.; Athukorala Arachchige, K. S.; Slawin, A. M. Z.; Woollins, J. D. Chem. - Eur. J. 2014, 20, 704–712.

27 28

Chapter 2 2 Trapping Rare and Elusive Phosphinidene Chalcogenides (RP=Ch; Ch = S, Se) 2.1 Introduction

Phosphinidenes (R-P, 2.1, Figure 2-1) are often considered the phosphorus analogues of carbenes based on their electronic structure that contains a monocoordinate, neutral PI centre.1–9 Phosphinidene chalcogenides (RP=Ch, 2.2Ch) are oxidized versions of phosphinidenes (PI®PIII). The presence of phosphinidene sulfides (RP=S) in solution has been verified using a variety of trapping reagents leading to either carbene-like or olefin-type reactivity from RP=S.10–17 Although this is elegant work demonstrating the resilience of RP=S, the outcome of the reaction precludes a close examination of the P=S functional group with phosphorus in the +3 oxidation state. Alternatively to cycloaddition chemistry, transition metal complexes18–23 and unique ligand design24,25 have been used to stabilize RP=Ch. With the exception of single examples demonstrating zwitterionic stabilization of RP=Ch (Ch = S, Se; 2.A, Figure 2-1), the quest to isolate “free” phosphinidene chalcogenides remains a challenge in phosphorus-chalcogen chemistry.26,27 Moreover, these reports chronicle nucleophilic behaviour that stemmed from the terminal chalcogenide,26,27 the prevalent resonance form, rather than olefinic as one might expect for a P=Ch functionality.

28 29

Figure 2-1: Top: General structures of phosphinidenes (2.1), phosphinidene chalcogenides (2.2Ch), and P2Ch2 rings (2.3Ch). Previously reported ylid-stabilized

"P=Ch" (2.A) and known phosphorus-chalcogen rings with a general formula (RPCh)n (1.35, n = 3; 1.36, n = 4). Bottom: General synthetic scheme for 2.3Ch and their potential equilibrium with 2.2Ch.

The RP=Ch unit is speculated as a key species in the formation of larger (c-

28–35 RPCh)n rings (1.35 and 1.36, Figure 2-1), and the smallest member of the series III V (RPCh)2 (2.3S) has yet to be identified for P as compared to P , where numerous examples are known (e.g. Woollin’s and Lawesson’s Reagents).29,36–42 Nevertheless, breaking apart the cyclic structures (c-RPCh)n into their monomeric units (n[RP=Ch]) is one strategy envisioned to establish systematic and stoichiometric access to a low- III coordinate P centre. In this context, we report the synthesis of (c-RPCh)2 heterocycles (2.3S, 2.3Se) which represent the first four-membered organophosphorus-chalcogen rings with phosphorus in the +3 oxidation state, a species absent in the well-established chemistry of P and S/Se. The success in preparing the (RPS)2 ring provided means to the isolation of an NHC-stabilized phosphinidene sulfide. The monomeric sulfide and

29 30

selenide unit were also ascertained by a reaction of the (c-RPCh)2 ring with dmbd, giving a six-membered Diels-Alder product. A mechanistic investigation using density functional theory revealed that the PIII centres in 2.3Ch can display Lewis acidic behaviour and react with strong nucleophiles such as NHCs, and controllably degrade the four-membered ring. The results of computational investigations also supported the notion that the reactivity of 2.3Ch with dmbd likely involves monomeric phosphinidene chalcogenides as intermediates, consistent with the elevated temperatures required to induce reactivity.

2.2 Results and Discussion

The 1:1 stoichiometric addition of S(TMS)2 to Ar*PCl2 (Figure 2-1) at 25 °C

31 1 resulted in the gradual appearance of a new singlet in P{ H} NMR (dP = 126.6 ppm,

Figure 2-2). After 16 hours, the starting material Ar*PCl2 (dP = 160.6 ppm) was consumed and the volatiles were removed in vacuo to give a yellow powder. Adding a small amount of n-pentane and placing the resulting solution at -35 °C for overnight gave single crystals of X-ray diffraction quality that were confirmed to be 2.3S by a subsequent structure analysis (64% total yield). NMR spectroscopy data recorded on

31 1 crystalline 2.3S redissolved in benzene-d6 showed the same P{ H} NMR signal as the reaction mixture along with a single set or Ar* resonances in the 1H NMR spectrum, which confirmed the equivalence of Ar*PS fragments on the NMR time scale. In the solid state, 2.3S was found have a high melting point (204 °C), and the compound proved to be resistant to oxidation upon short exposure to the ambient environment.

30 31

Figure 2-2: Reaction progression (31P{1H} NMR spectra) for synthesis of 2.3S showing crude reaction mixture (top, 16 hours) and purified material (bottom).

An analogous synthetic procedure was used to make 2.3Se. In this instance, a sample of the crude reaction mixture displayed multiple phosphorus containing products as determined by 31P{1H} NMR spectroscopy (Figure 2-3). However, the minor products could be removed by washing the crude product with n-pentane, yielding a single major

1 product as evidenced by the NMR data (dP = 24.0 ppm, JSe-P = 46.0 Hz). The isolated material (86% yield) was redissolved in CH2Cl2, and a sample was used in a

CH2Cl2/toluene vapour diffusion to yield single crystals suitable for X-ray diffraction. The signal in the 31P{1H} NMR data of redissolved crystalline 2.3Se was identical to that observed in the reaction mixture; a corresponding broad triplet was also observed in the

77 1 1 Se{ H} NMR spectrum (dSe = 484.6 ppm, JSe-P = 46.0 Hz). Relative to 2.3S, 2.3Se is far less stable. For example, solution 31P{1H} NMR spectroscopic studies demonstrate that 2.3Se decomposes when left at room temperature in solution over an extended period of time, while 2.3S does not show any noticeable decomposition under similar conditions.

31 32

X-ray crystallographic analysis of 2.3S showed that, in the solid state, the P2S2 core adopts a butterfly conformation (Figure 2-4) with narrow bond angles (P-S-Pavg =

85.96(3)°, S-P-Savg = 88.96(3)°) and P-S bond lengths suggestive of single bonds (P-Savg = 2.1461(8) Å; sum of Pyykkö & Atsumi single bond covalent radii for P and S is 2.14 43,44 Å). The solid-state structure of 2.3Se is similar to 2.3S (Figure 2-4) in that the P2Se2 core is folded with acute bond angles (P-Se-Pavg = 85.96(3)°, Se-P-Seavg = 89.20(3)°) and

P-Se bond lengths slightly longer than that expected for single bonds (P-Seavg = 2.3033(16) Å; the sum of Pyykkö & Atsumi single bond covalent radii for P and Se is 2.27 Å). The two structures, however, differ in the relative orientation of the terphenyl ligands e.g. anti for 2.3S and syn for 2.3Se (as visualized in Figure 2-4). The syn- conformation of 2.3Se appears to cause some ring strain and steric repulsion of the Ar* groups, leading to elongation of P-Se bonds – a likely reason for the instability of 2.3Se.

32 33

Figure 2-4: Solid state structures for 2.3S (left) and 2.3Se (right) with thermal ellipsoids at 50% probability. Hydrogen atoms have been omitted for clarity, and side profile of the

P2Ch2 core is shown below each structure. Selected bond lengths [Å] and bond angles [°]. 2.3S: P(1)-S(1) 2.1489(2), P(1)-S(2) 2.1517(8), P(2)-S(1) 2.1359(8), P(2)-S(2) 2.1479(8), P(1)-C(1) 1.849(2), P(2)-C(25) 1.863(2), C(1)-P(1)-S(1) 105.11(7), C(1)-P(1)-S(2) 102.97(7), S(1)-P(1)-S(2) 88.74(3), C(25)-P(2)-S(1) 110.59(7), C(25)-P(2)-S(2) 101.17(7), S(1)-P(2)-S(2) 89.18(3), P(2)-S(1)-P(1) 86.14(3), P(2)-S(2)-P(1) 85.77(3), P(1)-S(1)-S(2)-P(2) 34.335(4). 2.3Se: P(1)-Se(1) 2.3113(14), P(1)-Se(2) 2.3060(16), P(2)-Se(1) 2.2931(16), P(2)-Se(2) 2.3033(16), P(1)-C(1) 1.851(5), P(2)-C(25) 1.853(5), C(1)-P(1)-Se(1) 103.74(15), C(1)-P(1)-Se(2) 103.72(16), Se(1)-P(1)-Se(2) 88.93(6), C(25)-P(2)-Se(1) 106.10(18), C(25)-P(2)-Se(2) 108.39(17), Se(1)-P(2)-Se(2) 89.45(6), P(2)-Se(1)-P(1) 82.17(6), P(2)-Se(2)-P(1) 82.06(5). P(1)-Se(1)-Se(2)-P(2) 45.442(8).

33 34

Given the acute bond angles in 2.3Ch, we hypothesised that the structures might be amenable to liberating 2.2Ch. To test this hypothesis, trapping reactions were carried out by dropwise addition of a THF solution of two stoichiometric equivalents of NHCiPr to a THF solution of 2.3S at 25 °C over 15 min (Scheme 2-1). A 31P{1H} NMR spectrum of the reaction mixture revealed complete consumption of 2.3S and the formation of a new product (dP = 28.9 ppm). The volatiles were removed in vacuo and the crude material rinsed with n-pentane to give an insoluble yellow powder (73% yield; dP = 28.9 ppm). X-ray diffraction studies performed on single crystals grown by CH2Cl2/Et2O vapour diffusion confirmed that the product is a base-stabilized phosphinidene sulfide (2.4SiPr, Figure 2-5). The metrical parameters of 2.4SiPr show that the phosphorus atom is significantly pyramidal (Σ 310.5°) with two essentially equal P-C bonds (1.869(4) and 1.853(5) Å). The most notable feature in the structure is, however, the P-S bond (2.029(14) Å) that is more than 0.1 Å shorter than that in 2.3S, suggestive of some multiple bond character, however is still longer than the calculated P-S double bond length (the sum of Pyykkö & Atsumi double bond covalent radii for P and S is 1.96 Å).43,44

Scheme 2-1: Trapping of Ar*P=S and Ar*P=Se by treatment of 2.3Ch with NHCiPr and dmbd.

34 35

Figure 2-5: Solid state structures for compounds 2.4SiPr (a) 2.6S (b) and 2.6Se (c). Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms, and the mesityl groups from the m-terphenyl ligand for 2.6S have been omitted for clarity. Selected bond lengths [Å] and angles [°]. 2.4SiPr: P(1)-C(1) 1.869(4), P(1)-S(1) 2.0289(14), P(1)-C(25) 1.853(5), C(1)-P(1)-S(1) 113.02(13), C(2)-C(1)-P(1) 125.5(3), C(6)-C(1)-P(1) 115.6(3), C(1)-P(1)-C(25) 98.60(19), C(25)-P(1)-S(1) 98.91(13). 2.6S: P(1)-C(1) 1.832(3), P(1)- S(1) 2.0594(13), P(1)-C(25) 1.795(3), P(1)-C(26) 1.820(3)), C(27)-C(28) 1.331(4)), C(1)- P(1)-S(1) 109.62(9), C(2)-C(1)-P(1) 120.6(2), C(6)-C(1)-P(1) 120.6(2), C(1)-P(1)-C(25) 113.07(14), C(1)-P(1)-C(26) 115.45(13), C(25)-P(1)-S(1) 108.98(11), C(25)-P(1)-C(26) 104.33(15), P(1)-C(26)-C(27) 108.79(19), S(1)-C(29)-C(28) 114.7(2). 2.6Se: P(1)-C(1) 1.833(5), P(1)-Se(1) 2.2249(16), P(1)-C(25) 1.792(6), P(1)-C(26) 1.827(6), C(27)-C(28) 1.346(8), C(1)-P(1)-Se(1) 111.99(18), C(2)-C(1)-P(1) 119.9(4), C(6)-C(1)-P(1) 120.4(4), C(1)-P(1)-C(25) 114.5(3), C(1)-P(1)-C(26) 115.0(3), C(25)-P(1)-Se(1) 106.3(2), C(25)- P(1)-C(26) 102.1(3), P(1)-C(26)-C(27) 111.0(4), Se(1)-C(29)-C(28) 111.5(4).

A similar base stabilization approach was undertaken to obtain 2.4Se. This chemistry proved to be less straightforward than for sulfur, and the NHC-stabilized phosphinidene selenide could not be isolated (details regarding the reactivity of NHC and 2.3Se will be addressed in Chapter 5). Nevertheless, the hypothesis for accessing an as yet unknown RP=Se fragment in solution remained, so we opted to explore the Diels- Alder chemistry known for trapping compound 2.2S. The addition of dmbd to 2.3Se in a

35 36

2:1 stoichiometric ratio at 25 °C showed no consumption of the starting material in 31P{1H} NMR spectroscopy even after two days. We therefore examined the chemistry of 2.3Ch and the possible dimer ⇌ monomer equilibrium with computational methods using density functional theory at the PBE1PBE/TZVP level (see Section 2.4.7 for computational details). For simplicity, the Ar* groups were replaced by the parent terphenyl ligand in all calculations.

The frontier orbitals of 2.3Ch revealed that the compounds are amphoteric and capable of reacting not only with Lewis acids but also with Lewis bases as the p-type atomic orbitals of phosphorus make a large contribution on both the HOMO and LUMO of 2.3Ch. Thus, NHCs were found to add to the PIII centres in 2.3S, leading to a stepwise breakup of the P2S2 ring and the formation of 2.4S via 2.3S-NHC (Figure 2-6). The reaction is exergonic by 106 kJ mol-1 and has an activation energy of 42 kJ mol-1 for the second addition step. This indicates that the formation of 2.4S is spontaneous and fast even at room temperature, in agreement with experimental observations. Another possible pathway for the formation of 2.4S is the reaction between 2.2S and NHC, provided that 2.3Ch dissociates to 2.2Ch in solution. For this reason, the possible dimer ⇌ monomer equilibrium was put to the fore (Figure 2-6). Potential energy scans revealed that the dissociation of 2.3S and 2.3Se is endergonic by 67 and 82 kJ mol-1, respectively. Furthermore, the reaction was found to proceed through a high-energy transition state with activation barriers of 113 and 147 kJ mol-1 for 2.3S and 2.3Se, respectively. This immediately suggests that the monomer 2.2S is an unlikely intermediate en route to 2.4S, especially since the reactions were conducted at room temperature and appear to react with NHC spontaneously. As a corollary of the above, the dimers 2.3Ch are the preferred end products from the reaction between Ch(TMS)2 and Ar*PCl2 even though the monomers 2.2Ch are most likely the species initially formed in the process (more insight on this mechanism will be addressed in Chapter 3).

36 37

37 38

The tendency of 2.2Ch to dimerize follows directly from their electronic structure. As discussed in the literature,17 the HOMO and LUMO of 2.2Ch are both P-S π*-orbitals. Thus, the interaction of two molecules of 2.2Ch allows for two pairwise donor-acceptor interactions, leading to the formation of two new P-S bonds and, consequently, 2.3Ch (Table 2-1, Table 2-2). As this process involves the occupation of the initially empty P-S antibonding LUMOs of 2.2Ch, all P-S bonds in 2.3Ch are single bonds. This is clearly seen in the calculated P-S Wiberg bond indices that are close to unity for 2.3S (0.95) and 2.3Se (0.96), while those of 2.2S (1.89) and 2.2Se (1.91) are significantly higher; a similar trend is also seen in the delocalization indices calculated for 2.2Ch and 2.3Ch. For comparison, the Wiberg bond index for the P-S bond in 2.4SiPr is 1.22, which, together with the calculated natural atomic charges, indicates that the ylidic (P+-S-) resonance structure makes a high contribution to bonding in 2.4SiPr.

Although the calculations indicated that a dimer ⇌ monomer equilibrium is unlikely at room temperature, it is plausible that some 2.2Ch could be liberated by heating 2.3Ch. It is also expected that the steric bulk of the Ar* substituent will destabilize the dimer more than the monomer, potentially lowering the barrier for the dissociation of 2.3Ch below of that predicted by our calculations. Consequently, the trapping reaction between 2.3Ch and dmbd was repeated at 50 °C, which resulted in complete consumption of the starting materials after 16 hours and the appearance of a

31 1 1 singlet in the P{ H} spectrum (Ch = S: dP = 6.2, Figure 2-7; Ch = Se: dP = 11.7, JSe-P = 184.1 Hz, Figure 2-8). The resulting compounds (2.5Ch, Scheme 2-1) were colourless oils, which prevented straightforward structural characterization by X-ray crystallography. For this reason, the products were derivatized using a stoichiometric amount of iodomethane, targeting the quaternization of phosphorus and the formation of

2.6Ch (Scheme 2-1). After 16 hours of stirring with iodomethane in Et2O at 25 °C, the starting material was fully consumed, and a new singlet appeared in the 31P{1H}

1 spectrum (Ch = S: dP = 52.0; Ch = Se: dP = 44.5, JSe-P = 212.3 Hz), both phosphorus chemical shifts downfield from the precursor 2.5Ch. The crude white powder was washed with n-pentane, and the precipitate was redissolved in CH2Cl2 and layered with

Et2O to give single crystals suitable for X-ray diffraction (Ch = S: 91% yield; Ch = Se:

38 39

64% yield). The structures (Figure 2-5) confirmed the product to be the salt 2.6Ch with a six-membered ring and tetrahedral geometry around the phosphorus atom, indicating a Diels-Alder type initial reaction of Ar*P=S and dmbd. It is notable that the P-Se bond is significantly shorter in 2.6Se (2.3113(15) Å) than in 2.3Se (2.225(2) Å), indicating relief of strain upon dissociation of the dimeric structure.

Figure 2-7: 31P{1H} NMR stacked plot showing cycloaddition product (2.5S, top) and quaternized product (2.6S, bottom).

39 40

Figure 2-8: 31P{1H} NMR stacked plot showing cycloaddition product (2.5Se, top) and isolated quaternized product (2.6Se, bottom).

The reaction between 2.3Se and dmbd was also examined computationally (Figure 2-6). Despite numerous attempts, we were not able to identify a Diels-Alder-type transition state (concerted or stepwise) that would connect 2.3Se and dmbd directly to 2.5Se. The lack of reactivity is not surprising considering that bonding analyses indicated that the P-Ch bonds in 2.3Ch are single bonds. In contrast, 2.2Se has a P=Se double bond and it was found to be a probable intermediate leading to 2.5Se. Specifically, the Diels- Alder reaction between two equivalents of 2.2Se and dmbd is exergonic by 104 kJ mol-1 with an activation barrier of only 66 kJ mol-1 (concerted mechanism). Thus, even though the conversion of 2.3Se to 2.2Se is endergonic, the facile reactivity of 2.2Se with dmbd more than compensates this and transforms the overall reaction exergonic by 22 kJ mol-1.

40 41

Table 2-1: Selected Kohn-Sham orbitals (isovalue ± 0.04) of 2.3S and 2.3Se.

2.3S LUMO 2.3S HOMO

2.3Se LUMO+1 2.3Se HOMO

41 42

Table 2-2: Selected Kohn-Sham orbitals (isovalue ± 0.04) of 2.2S; the shapes of orbitals for 2.2Se are similar.

2.2S LUMO 2.2S HOMO

2.2S HOMO-7 2.2S HOMO-8

2.3 Conclusions

We have detailed the synthesis of four-membered phosphorus-chalcogen rings (2.3Ch) that are the first representatives of such cyclic inorganic systems with phosphorus in the +3 oxidation state. We have also demonstrated access to monomeric phosphinidene-chalcogenides; the sulfur derivative being stabilized with an N- heterocyclic carbene (2.4SiPr) and trapped with dmbd (2.6S), while the selenium congener was trapped with 2,3-dimethylbutadiene (2.6Se). Computational work has showed that 2.4S forms from 2.3S via base-assisted cleavage of the P2S2 ring. In contrast,

42 43 the formation of 2.5Ch from 2.3Ch and dmbd most likely proceeds via monomeric phosphinidene chalcogenide (2.2Ch), with the selenium derivate being a previously unknown member of the phosphinidene chalcogenide family.

2.4 Experimental Section

See Section 7.2 for general experimental and crystallographic procedures. For experimental details regarding Ar*PCl2, refer to Section 7.1.

2.4.1 Synthesis of 2.3S

A solution of S(TMS)2 (1.933 g, 10.8 mmol, 10 mL THF) was added to a vigorously stirred solution of Ar*PCl2 (900 mg, 2.17 mmol, 15 mL THF) at 25 °C. Monitoring by 31P{1H} NMR showed complete consumption of the starting material after 16 h, at which time the volatiles were removed in vacuo. The resulting yellow oil was taken up in 10 mL of n-pentane and let sit overnight at -35 °C to yield single crystals of 2.3S. The volume of the supernatant was reduced by half and the solution let sit overnight at -35 °C to precipitate the remaining product (520 mg, 64% combined yield) m.p. (nitrogen sealed capillary): 204.0-205.0 °C.

FT-IR (KBr, cm-1 (ranked relative intensity)): 747 (6), 803 (5), 847 (3), 1030 (8), 1109 (10), 1180 (9), 1262 (14), 1374 (7), 1443 (2), 1558 (11), 1610 (4), 1723 (12), 2442 (15), 2727 (13), 2914 (1).

+ ESI-MS: 752.4 m/z C48H50P2S2 [M] .

Elemental Analysis: Calculated: 76.56% C, 6.69% H, 8.52% S; Found: 75.57% C, 6.75% H, 7.79% S.

1 H NMR (C6D6, 400 MHz, δ): 2.09 (s, 24H; Mes o-CH3), 2.28 (s, 12H; Mes para-CH3),

3 3 6.73 (s, 8H; Mes CH), 6.79 (d, JH-H = 7.6 Hz, 4H; Ar meta-CH), 7.08 (t, JH-H = 7.4 Hz, 2H; Ar para-CH).

13 1 C{ H} NMR (CDCl3, 150 MHz, δ): 21.1, 21.3, 128.0, 128.6, 129.2, 129.9, 136.2, 1 136.5, 136.6, 136.8, 139.2, 139.5, 139.8, 143.3 (d, JP-C = 7.1 Hz).

43 44

31 1 P{ H} NMR (C6D6, 161.8 MHz, δ): 126.6 (s).

2.4.2 Synthesis of 2.3Se

A solution of Se(TMS)2 (421 mg, 1.87 mmol) was added in 4 portions (each in 1 mL of

THF) at one hour intervals to a solution of Ar*PCl2 (780 mg, 1.87 mmol, 7 mL THF) at 25 °C. Monitoring by 31P{1H} NMR showed complete consumption of the starting material after 4 h. At this time, volatiles were removed in vacuo. The resulting orange oil was taken up in 10 mL of n-pentane and centrifuged. The orange insoluble powder was rinsed with 3 x 10 mL n-pentane and put under vacuum to remove all residual solvent

(630 mg, 86% yield). Single crystals of 2.3Se were grown by CH2Cl2/pentane vapour diffusion. m.p. (nitrogen sealed capillary): 250 °C (decomposes, turned yellow).

FT-IR (KBr, cm-1 (ranked relative intensity)): 746 (7), 771 (13), 804 (3), 846 (1), 1031 (5), 1107 (9), 1178 (12), 1260 (10), 1375 (8), 1439 (2), 1560 (11), 1608 (6), 2852 (14), 2915 (4), 2947 (15).

+ ESI-MS: 846.7 m/z C48H50P2Se2 [M] .

1 H NMR (C6D6, 600 MHz, δ): 2.16 (s, 24H; Mes ortho-CH3), 2.28 (s, 12H; Mes para- 3 3 CH3), 6.69 (d, JH-H = 7.6 Hz, 4H; Ar meta-CH), 6.75 (s, 4H, Mes CH), 7.04 (t, JH-H = 7.6 Hz, 2H, Ar para-CH).

13 1 C{ H} NMR (C6D6, 151.0 MHz, δ): 21.4, 21.5, 128.4, 128.4, 128.7, 128.8, 129.3, 1 130.1, 130.5, 136.6, 136.7, 136.8, 136.8, 137.0, 137.4, 137.5, 143.8 (d, JP-C = 6.2 Hz).

31 1 1 P{ H} NMR (C6D6, 161.8 MHz, δ): 24.0 (s, JSe-P = 46.0 Hz).

77 1 1 Se{ H} NMR (C6D6, 114.4 MHz, δ): 484.6 (br t, JSe-P = 46.0 Hz).

2.4.3 Synthesis of 2.4SiPr

A solution of 1,3-isopropyl-4,5-dimethylimidazol-2-ylidene (12 mg, 0.070 mmol, 2 mL THF) was added to a solution of 2.3S (25 mg, 0.033 mmol, 2 mL THF). The combined

44 45 solution was stirred at 25 °C for 15 min and monitored by 31P{1H} NMR, which showed a complete consumption of 2.3S after 20 min. At this time, the volatiles were removed in vacuo, the powder was washed with 2 x 5 mL of n-pentane and the insoluble part collected as a bright yellow powder (27 mg, 73% yield). Single crystals of 2.4SiPr·THF were grown by slowly concentrating a THF solution of 2.4SiPr. m.p. (nitrogen sealed capillary): 209.3-210.0 °C.

+ + ESI-MS: 557.3 m/z C35H45N2PS [M + H] , 524.7 m/z C35H45N2P [M + H – S] .

FT-IR (KBr, cm-1 (ranked relative intensity)): 654 (15), 751(9), 814 (5), 847 (4), 904 (10), 1065 (3), 1111(11), 1131 (12), 1179 (13), 1212 (7), 1394 (2), 1439 (8), 1566 (14), 1624 (6), 2974 (1).

1 3 3 H NMR (CDCl3, 600 MHz, δ): 0.93 (d, JH-H = 7.2 Hz, 3H; iPr CH3), 0.99 (d, JH-H = 3 3 7.2 Hz, 3H; iPr CH3), 1.30 (d, JH-H = 6.6 Hz, 3H; iPr CH3), 1.45 (d, JH-H = 6.6 Hz, 3H; iPr CH3), 1.84 (br s, 6H; Mes CH3), 2.08 (s, 3H; NHC CH3), 2.17 (s, 3H; NHC CH3), 3 3 2.27 (br s, 12H; Mes CH3), 4.63 (sept, JH-H = 7.2 Hz, 1H; iPr CH), 5.79 (sept, 1H; JH-H = 7.2 Hz; iPr CH), 6.72 (br s, 2H; Mes CH), 6.86 (br m, 4H; Mes CH & Ar meta-CH),

3 7.21 (br t, 1H; JH-H = 7.5 Hz, Ar para-CH).

13 1 C{ H} NMR (C6D6, 151.0 MHz, δ): 10.2 (NHC CH3), 10.7 (NHC CH3), 19.8 (iPr

CH3), 21.0 (iPr CH3) 21.1 (MesCH3), 21.2 (Mes CH3), 21.3 (Mes CH3), 21.9 (iPr CH3),

23.3 (iPr CH3), 51.6 (iPr CH), 52.2 (iPr CH), 125.2, 126.6, 126.6 (para-CH), 127.9 (meta-CH), 136.1, 136.4, 139.3, 143.3, 143.6, 144.2, 156.8, 157.5.

31 1 P{ H} NMR (C6D6, 161.8 MHz, δ): 28.9 (s).

2.4.4 Synthesis of 2.6S

A mixture of 2.3S (130 mg, 0.173 mmol) and 2,3-dimethylbutadiene (141 mg, 1.73 mmol) were heated at 50 °C for 24 hours. At this time, the volatiles were removed in vacuo and the residual oil was taken up in minimal amount of n-pentane and filtered 31 1 through Celite to yield 2.5S. P{ H} (C6D6, 161.8 MHz, δ): 6.2 (s).

45 46

2.5S was taken up in 7 mL of diethyl ether and neat iodomethane (246 mg, 1.73 mmol) was added to the flask. After stirring at 25 °C for 16 hours, copious amounts of white precipitate formed. After centrifuging the solution and washing the insoluble white powder with 3 x 10 mL Et2O, the product was isolated (190 mg, 91% yield). Single crystals suitable for X-ray diffraction were grown via CH2Cl2/Et2O vapour diffusion that confirmed the product to be 2.6S. m.p. (nitrogen sealed capillary): 215.4-216.1 °C

+ + ESI-MS: 1072.3 m/z C62H76P2S2I [2 x M – I] , 473.2 m/z C31H38PS [M – I] , 391.2 m/z + C25H28PS [M – I – dmbd] .

FT-IR (KBr, cm-1 (ranked relative intensity)): 677 (2), 733 (13), 816 (5), 855 (7), 900 (6), 917 (11), 1037 (12), 1076 (1), 1262 (9), 1299 (15), 1405 (14), 1448 (4), 1564 (8), 1609 (10), 2917 (3).

1 2 4 H NMR (C6D6, 400 MHz, δ): 1.45 (d, JP-H = 12.6 Hz, 3H; P-CH3), 1.65 (d, JP-H = 6.6

Hz, 3H; Cy CH3), 1.68 (br m, 1H; CH2), 1.87 (br s, 3H; Cy CH3), 2.07 (s, 6H; Mes 2 ortho-CH3), 2.08 (s, 6H; Mes ortho-CH3), 2.23 (s, 6H; Mes para-CH3), 2.80 (br t, JH-H = 2 2 2 14.7 Hz, 1H; CH2), 3.09 (dd, JP-H = 26.4 Hz, JH-H = 13.2 Hz, 1H; CH2), 3.93 (dd, JH-H 2 = 14.4 Hz, JH-H = 8.4 Hz, 1H; CH2), 6.88 (br s, 2H; Mes CH), 6.90 (br s, 2H; Mes CH), 3 4 3 5 7.17 (dd, JH-H = 7.8 Hz, JP-H = 4.8 Hz, 1H; Ar meta-CH), 7.68 (td, JH-H = 7.8 Hz, JP-H = 2.4 Hz, 1H; Ar para-CH).

13 1 C{ H} NMR (C6D6, 150.8 MHz, δ): 17.4, 17.7, 19.3, 21.1, 21.4, 21.5, 21.9, 22.1, 29.6, 1 29.9 (d, JP-C = 31.8 Hz; P-CH3), 35.2, 35.3, 119.4, 126.5, 126.6, 128.9, 129.0, 132.1, 1 132.2, 133.2, 133.4, 134.7, 136.0, 136.8, 137.0, 139.6, 147.5 (d, JP-C = 11.3 Hz; Ar PC).

31 P NMR (C6D6, 161.8 MHz, δ): 52.0 (br s).

2.4.5 Synthesis of 2.6Se

Neat 2,3-dimethylbutadiene (22 mg, 0.28 mmol) was added to a solution of 2.3Se (120 mg, 0.14 mmol, 10 mL benzene) and heated at 50 °C in a pressure tube for 16 hours. At this time, the volatiles were removed in vacuo and the residual oil was taken up in

46 47

31 1 minimal amount of n-pentane and filtered through Celite to yield 2.5Se. P{ H} (C6D6, 1 161.8 MHz, δ): 11.7 (s, JSe-P = 184.1 Hz).

2.5Se was taken up in 7 mL of diethyl ether and neat iodomethane (42 mg, 0.29 mmol) was added to the flask. After stirring at 25 °C for 16 hours, copious amounts of white precipitate formed. After centrifuging the solution and washing the insoluble white powder with 3 x 10 mL Et2O, the product was isolated (118 mg, 64% yield). Single crystals of 2.6Se were grown from the product redissolved in CH2Cl2 and layered with

Et2O. m.p. (nitrogen sealed capillary): 230.4 °C (decomposed, turned grey).

+ + ESI-MS: 521.2 m/z C31H38PSe [M - I] , 439.1 m/z C25H28PSe [M – I – C6H10] .

FT-IR (KBr, cm-1 (ranked relative intensity)): 731 (1), 810 (7), 832 (15), 856 (4), 902 (2), 918 (9), 1038 (6), 1117 (13), 1183 (8), 1265 (10), 1296 (14), 1440 (3), 1562 (12), 1607 (11), 2901 (5).

Elemental Analysis: Calculated 57.51% C, 5.92% H; Found: 57.17% C, 6.04% H.

1 2 4 H NMR (CDCl3, 600 MHz, δ): 1.51 (d, JP-H = 12.6 Hz, 3H; P-CH3), 1.76 (d, JP-H = 7.2 2 2 Hz, 3H; Cy CH3), 1.88 (br s, 3H; Cy CH3), 1.94 (br dd, JP-H = 16.5 Hz, JH-H = 10.0 Hz,

1H; Cy CH), 2.13 (s, 6H; Mes CH3), 2.14 (s, 6H; Mes CH3), 2.32 (s, 6H; Mes CH3), 3.00 3 2 2 2 (dd, JP-H = 13.8 Hz, JH-H = 13.8 Hz, 1H; Cy CH), 3.41 (dd, JP-H = 14.4 Hz, JH-H = 10.0 3 2 Hz, 1H; Cy CH), 3.51 (dd, JP-H = 22.2 Hz, JH-H = 12.0 Hz, 1H; Cy CH), 6.97 (br s, 2H,

3 4 Mes CH), 7.00 (br s, 2H; Mes CH), 7.26 (dd, JH-H = 7.8 Hz, JP-H = 4.2 Hz, 2H; Ar meta- 3 5 CH), 7.77 (td, JH-H = 7.8 Hz, JP-H = 2.4 Hz, 1H; Ar para-CH).

13 1 C{ H} NMR (CDCl3, 151.0 MHz, δ): 16.8, 17.3, 19.1 (d, JP-C = 4.4 Hz), 21.1, 21.6 (d, 1 3 JP-C = 4.2 Hz), 21.9, 22.1, 31.1 (d, JP-C = 26.0 Hz), 31.4 (d, JP-C = 6.9 Hz), 119.9, 120.4,

125.3, 125.4, 128.3, 129.0, 129.1, 132.1, 132.2, 134.5 (d, JP-C = 3.2 Hz), 135.8, 135.8, 135.9, 136.0, 136.7, 136.8, 139.8, 147.1, 147.2.

31 1 1 P{ H} NMR (C6D6, 161.8 MHz, δ): 44.5 (s, JSe-P = 212.3 Hz).

47 48

2.4.6 Special Considerations for X-ray Crystallography

For 2.3Se and 2.4SiPr all of the non-hydrogen atoms were well ordered and refined with anisotropic thermal parameters. For 2.3S and 2.6Se the solvent molecules were severely disordered and could not be successfully modelled to give a chemically sensible solution. The solvates was treated as a diffuse contribution to the overall scattering by SQUEEZE/Platon.45 For 2.3Se, some residual electron density was found in the difference map. Several attempts were made to model this density; however, a chemically sensible solution could not be obtained

48 49

Table 2-3: Summary of X-ray diffraction collection and refinement details for the compounds reported in Chapter 2. 2.3S 2.3Se 2.4SiPr 2.6S 2.6Se CCDC Ref # 1485220 1485221 1485222 1577309 1485223

Formula C48H50P2S2 C48H50P2Se2 C35H45N2PS-C4H8O C31H38PSI CH2Cl2 C31H38IPSe Formula weight 752.94 846.74 628.86 671.44 647.44 Crystal system monoclinic monoclinic monoclinic triclinic monoclinic

Space group C 2/c C 2/c Pn P -1 P 21/n T (K) 110 110 110 110 110 a (Å) 47.209(6) 28.758(11) 9.0360(12) 10.160(4) 10.557(5) b (Å) 12.0860(14) 16.854(6) 13.0239(13) 12.283(7) 23.540(12) c (Å) 15.3160(19) 19.604(7) 15.335(2) 13.604(8) 13.099(5) α (°) 90 90 90 75.858(13) 90 β (°) 96.299(4) 120.260(7) 97.034(10) 86.296(7) 95.751(17) γ (°) 90 90 90 85.598(7) 90 V (Å3) 8686.1(18) 8208(5) 1791.1(4) 1639.8(15) 3239(3) Z 8 8 2 2 4 F(000) 3200 3488 680 700 1304 ρ (g cm-1) 1.152 1.370 1.166 1.388 1.328 λ (Å) 1.54178 0.71073 1.54178 0.71073 0.71073 µ (cm-1) 2.031 1.913 1.456 1.271 2.177 Measured 0.989 0.998 0.994 0.998 0.998 fraction of data

Rmerge 0.0353 0.1007 0.0402 0.0520 0.0473

R1, wR2 0.0445, 0.1232 0.0675, 0.1811 0.0408, 0.1081 0.0480, 0.1127 0.0659, 0.1564 R (all data), 1 0.0463, 0.1246 0.1147, 0.2036 0.0437, 0.1121 0.0726, 0.1259 0.0782, 0.1636 wR2 (all data) GOF 1.029 1.045 1.045 1.045 1.126

2 2 2 4 ½ 2 2 2 ½ Where: R1 = Σ( |Fo| - |Fc| ) / Σ Fo, wR2 = [ Σ(w(Fo - Fc ) ) / Σ(w Fo )] GOF = [Σ( w( Fo - Fc ) ) / (No. of reflns. - No. of params.)]

49 50

2.4.7 Computational Details

Geometry optimizations were performed with the Gaussian09 (D.01) program46 using the PBE1PBE hybrid functional47–49 and Ahlrichs’ TZVP basis sets.50 The nature of all stationary points found (minimum or transition state) was confirmed with a frequency calculation. Wiberg bond51 and delocalization52 indices were calculated on the optimized geometries with the NBO 3.153 and AIMAll54 programs, respectively.

2.5 References (1) Fritz, G.; Vaahs, T.; Fleischer, H.; Matern, E. Angew. Chem., Int. Ed. 1989, 28, 315–316. (2) Mathey, F. Angew. Chem., Int. Ed. 1987, 26, 275–370. (3) Li, X.; Weissman, S. I.; Lin, T.; Gaspar, P. P. J. Am. Chem. Soc. 1994, 116, 7899– 7900. (4) Cowley, A. H. Acc. Chem. Res. 1997, 30, 445–451. (5) Shah, S.; Simpson, M. C.; Smith, R. C.; Protasiewicz, J. D. J. Am. Chem. Soc. 2001, 123, 6925–6926. (6) Lammertsma, K.; Vlaar, M. J. M. Eur. J. Org. Chem. 2002, 1127–1138. (7) Lammertsma, K. In Topics in Current Chemistry; Majoral, J.-P., Ed.; Topics in Current Chemistry; Springer Berlin Heidelberg: Berlin, Heidelberg, 2003; pp 95– 119. (8) Mathey, F. Dalton Trans. 2007, 1861–1868. (9) Aktaş, H.; Slootweg, J. C.; Lammertsma, K. Angew. Chem., Int. Ed. 2010, 49, 2102–2113. (10) Nakayama, S.; Yoshifuji, M.; Okazaki, R.; Inamoto, N. Chem. Commun. 1971, 1186–1187. (11) Gaspar, P. P.; Qian, H.; Beatty, A. M.; d’Avignon, D. A.; Kao, J. L. F.; Watt, J. C.; Rath, N. P. Tetrahedron 2000, 56, 105–119. (12) Yoshifuji, M.; Nakayama, S.; Okazaki, R.; Inamoto, N. J. Chem. Soc., Perkin I 1973, 2065–2068. (13) Hussong, R.; Heydt, H.; Regitz, M. Z. Naturforsch 1986, 41b, 915–921. (14) Santini, C. C.; Fischer, J.; Mathey, F.; Mitschler, A. J. Am. Chem. Soc. 1980, 102, 5809–5815. (15) Nakayama, S.; Yoshijiuji, M.; Okazaki, R.; Inamoto, N. J. Chem. Soc., Perkin I 1973, 2069–2071.

50 51

(16) Nakayama, S.; Yoshifuji, M.; Okazaki, R.; Inamoto, N. Bull. Chem. Soc. Jpn. 1975, 48, 546–548. (17) Wang, L.; Ganguly, R.; Mathey, F. Organometallics 2014, 33, 5614–5617. (18) Albuerne, I. G.; Alvarez, M. A.; García, M. E.; García-Vivó, D.; Ruiz, M. A. Inorg. Chem. 2015, 54, 9810–9820. (19) Alvarez, B.; Alvarez, M. A.; Amor, I.; García, M. E.; García-Vivõ, D.; Suárez, J.; Ruiz, M. A. Eur. J. Inorg. Chem. 2014, 1706–1718. (20) Alvarez, B.; Alvarez, M. A.; Amor, I.; García, M. E.; García-Vivó, D.; Suárez, J.; Ruiz, M. A. Inorg. Chem. 2012, 51, 7810–7824. (21) Alvarez, M. A.; García, M. E.; González, R.; Ramos, A.; Ruiz, M. A. Organometallics 2010, 29, 1875–1878. (22) Alonso, M.; Alvarez, M. A.; García, M. E.; Ruiz, M. A.; Hamidov, H.; Jeffery, J. C. Inorg. Chem. 2010, 49, 11595–11605. (23) Alonso, M.; Alvarez, M. A.; García, M. E.; García-Vivó, D.; Ruiz, M. A. Inorg. Chem. 2010, 49, 8962–8976. (24) Yoshifuji, M.; Hirano, M.; Toyota, K. Tetrahedron Lett. 1993, 34, 1043–1046. (25) Yoshifuji, M.; Sangu, S.; Hirano, M.; Toyota, K. Chem. Lett. 1993, 1715–1718. (26) Jochem, G.; Karaghiosoff, K.; Plank, S.; Dick, S.; Schmidpeter, A. Chem. Ber. 1995, 128, 1207–1219. (27) Jochem, G.; Nöth, H.; Schmidpeter, A. Angew. Chem., Int. Ed. 1993, 32, 1089– 1091. (28) Baudler, V. M.; Koch, D.; Vakratsas, T.; Tollis, E.; Kipker, K. Z. Anorg. Allg. Chem. 1975, 413, 239–251. (29) Cetinkaya, B.; Hitchcock, P. B.; Lappert, M. F.; Thorne, A. J.; Goldwhite, H. J. Chem. Soc., Chem. Commun. 1982, 691–693. (30) Lensch, C.; Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1984, 2855–2857. (31) Lensch, C.; Clegg, W.; Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1984, 723– 725. (32) Yoshifuji, M.; Toyota, K.; Ando, K.; Inamoto, N. Chem. Lett. 1984, 317–318. (33) Karaghiosoff, K.; Eckstein, K. Phosphorus. Sulfur. Silicon Relat. Elem. 1993, 75, 257–260. (34) Kamijo, K.; Toyota, K.; Yoshifuji, M. Chem. Lett. 1999, 567–568. (35) Henne, F. D.; Watt, F. A.; Schwedtmann, K.; Hennersdorf, F.; Kokoschka, M.; Weigand, J. J. Chem. Commun. 2016, 2023–2026. (36) He, G.; Shynkaruk, O.; Lui, M. W.; Rivard, E. Chem. Rev. 2014, 114, 7815–7880. (37) Gray, I. P.; Bhattacharyya, P.; Slawin, A. M. Z.; Woollins, J. D. Chem. - Eur. J. 2005, 11, 6221–6227.

51 52

(38) Groûmann, G.; Ohms, G.; Karaghiosoff, K. Z. Anorg. Allg. Chem. 2001, 627, 1269–1278. (39) Van Zyl, W. E.; Fackler, J. P. Phosphorus. Sulfur. Silicon Relat. Elem. 2000, 167, 117–132. (40) Foreman, M. R. S.; Novosad, J.; Slawin, A. M. Z.; Woollins, J. D. J. Chem. Soc., Dalton Trans. 1997, 6, 1347–1350. (41) Foreman, M. R. S. J.; Slawin, A. M. .; Woollins, J. D. J. Chem. Soc., Dalton Trans. 1996, 3653–3657. (42) Fitzmaurice, J. C.; Williams, D. J.; Wood, P. T.; Woollins, J. D. J. Chem. Soc., Chem. Commun. 1988, 741–743. (43) Pyykkö, P.; Atsumi, M. Chem. - Eur. J. 2009, 15, 12770–12779. (44) Pyykkö, P.; Atsumi, M. Chem. - Eur. J. 2009, 15, 186–197. (45) Spek, A. L. ACTA Crystallogr. 2009, D65, 148. (46) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Marenichm, A. V.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakaji; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A. J.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 09, Revision D.01; Wallingford, CT, USA, 2009. (47) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997, 78, 1396. (48) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865–3868. (49) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158–6170. (50) Schäfer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829-5835. (51) Wiberg, K. B. Tetrahedron 1968, 24, 1083-1096. (52) Wang, Y.; Werstiuk, N. H. J. Comput. Chem. 2003, 24, 379–385. (53) Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F. NBO version 3.1, 1990. (54) Keith, T. A. AIMAll version 16.05.18, 2016.

52 53

Chapter 3 3 Addressing the Nature of Phosphinidene Sulfides via the Synthesis of P-S Heterocycles 3.1 Introduction

Strained inorganic heterocycles have captured the interest of chemists for decades and despite the inorganic elemental composition, their chemistry is typically reported in the context of organic chemistry. Nevertheless, these ring systems offer unique insights into structure, bonding and reactivity for the inorganic elements and thus remain key synthetic targets. Aside from fundamental structure and bonding interests, strained heterocycles play a critical role in organic chemistry as they can act as reactive intermediates in important chemical transformations. The isolation of such intermediates (and derivatives thereof) are of particular interest since they provide insight into reaction pathways and aids in solidifying our understanding of fundamental and important chemical transformations.

One of the more noteworthy examples of inorganic heterocycles as important reaction intermediates is in the Wittig olefination (Figure 3-1, top). The mechanism was unclear for some time as to whether it proceeded through a charge-separated betaine or 1,2-oxaphosphetane intermediate. In this particular case, structural characterization of the first 1,2-oxaphosphetane1 and NMR spectroscopic data2 favoured the formation of the strained 4-membered P-O heterophosphete.3–9 Although chemistry of the 1,2- oxaphosphetanes, either containing transition-metal stabilized PIII (3.A)10–13 or pentavalent phosphorus (3.B)14–17 have been studied, the heavier chalcogen derivatives are considerably underdeveloped in comparison. The most common examples of heterophosphetes containing heavier chalcogens are 1,2-thiaphosphetanes, which contain a saturated 4-membered PSC2 ring and a pentavalent phosphorus atom (3.C & 3.D). These P-S heterocycles have either been isolated18,19 or observed as intermediates20,21 during transformations. It is surprising that the chemistry of the PIII derivatives of these rings have yet to be explored, and the unsaturated species (e.g. 1,2-thiaphosphetenes, 3.F)

53 54 are unknown for PIII, and their existence in the literature is limited to a single report of a ring system containing a PV centre stabilized by the Martin ligand (3.E).22

The dearth of heterophosphetes containing heavier chalcogen atoms is a direct consequence of the inability to control the transfer of P and Ch, especially when phosphorus is in the +3 oxidation state. A potential synthetic route is using phosphinidene chalcogenides (RP=Ch) as a source of both phosphorus and chalcogen in ring formation. Although these species are an elusive member of the P-Ch family of compounds, their presence in solution has been rationalized through the assessment of products prepared from trapping experiments indicating either carbene-like23–28 or olefin- like reactivity.23,24,29,30 We have recently reported a method that provides a stoichiometric source of RP=Ch via the strained (c-RPCh)2 rings (Ch = S, Se), where upon gentle heating of these heterocycles in the presence of 2,3-dimethylbutadiene, yielded [2+4] cycloaddition products of the in situ generated RP=Ch and diene in moderate yields.31 Although reactions of intermediate RP=S have been successful with dienes, benzil, diethylsulfide, methanol, and cyclic ethers, there have been no reports of trapping the intermediate phosphinidene sulfides to yield strained cyclic P-S containing products. In this context, we report the synthesis and characterization of unsaturated, strained

54 55 phosphorus-sulfur heterocycles, namely derivatives of 1,2-thiaphosphetenes (3.F) and the structural isomers phosphirene sulfide (3.G) derivatives. These unprecedented structures were prepared by either [1+2] or [2+2] cycloaddition of phosphinidene sulfide (Ar*P=S, generated from 2.3S) with alkynes under mild heating. These P-S heterocycles represent the first structurally characterized examples of two unique classes of rings, which are isomers of each other and surprisingly, absent from the well-developed phosphorus and sulfur literature. Modifying the steric demand of the alkyne imposes a preference of a 3- or 4- membered ring system containing exo- or endocyclic sulfur atoms, respectively. In addition, DFT calculations on model compounds indicate that the 3-membered phosphirene sulfides are considerably less stable than the isomeric 4-membered thiaphosphetene.

3.1 Results and Discussion

Heating a mixture of 2.3S and excess phenylacetylene at 80 °C over 5 hours (Scheme 3-1) resulted in consumption of the starting material and appearance of two

31 2 singlets in the P NMR spectra: dP = 38.1 ( JP-H = 31.6 Hz) and dP = -83.3, both of which are shifted significantly upfield from the starting material (dP = 126.6; Figure 3-2). Removing the volatiles of the crude reaction mixture in vacuo and washing with n- pentane resulted in an off-white precipitate. Slowly concentrating an Et2O solution of this precipitate resulted in single crystals suitable for X-ray diffraction, and structural analysis identified the compound to be 3.1a, the first structurally characterized 1,2- thiaphosphetene (yield = 66%). Multinuclear NMR spectroscopic data on the redissolved

2 crystals of 3.1a were obtained, which featured the doublet at dP = 38.1 ( JP-H = 31.6 Hz) that was observed in the crude 31P NMR spectrum, while the 1H NMR spectrum displayed a doublet for the olefinic C-H resonance with identical P-H coupling noted 31 2 from the P NMR spectrum ( JP-H = 31.6 Hz). The presence of three separate singlets in the aliphatic region, corresponding to each of the CH3 environments of the m-terphenyl ligand provided strong evidence for the asymmetric nature of the compound. The composition of 3.1a was also confirmed by elemental analysis, and ESI-MS revealed a + molecular ion peak corresponding to 3.1a (479.2 m/z C32H31PS [M] ).

55 56

The structure 3.1a was confirmed via single crystal X-ray diffraction, and revealed the first structural characterized 1,2-thiaphosphetene (Figure 3-3). The solid- state structure of 3.1a indicates the presence of a planar, 4-membered PSC2 ring

56 57

(0.135(9)° out of plane) that contains a C=C double bond (1.348(9) Å) and a P-S single bond (2.165(2) Å). The phosphorus atom exhibited the expected P-C bond distances (P- C(1) 1.843(7) and P-C(25) 1.787(7) Å) and a distorted trigonal pyramidal geometry (å of angles at phosphorus = 289.36°).

Leaving the n-pentane soluble portion of the crude reaction mixture at -35 °C for one week resulted in a second set of single crystals suitable for X-ray analysis and confirmed the formation of a phosphirene sulfide, 3.2a (21% yield; Scheme 3-1).

Redissolving the single crystals in benzene-d6 displayed a peak consistent with the most upfield signal observed from the original reaction mixture (dP = -83.3), which was a multiplet in the 31P NMR spectrum. The P-H coupling was evident in the 1H NMR

2 spectrum with the olefinic C-H signal appearing furthest downfield at d = 7.40, with JP-H = 10.3 Hz. The long-range P-H coupling that gave rise to the multiplet in the 31P NMR spectra was confirmed through 1H-31P HMBC analysis (Figure 7-18) and clearly showed a correlation between the broad aromatic proton environment (d = 6.82), the olefinic C-H resonance (d = 7.40) and phosphorus. Whereas the aromatic region was dominated by overlapping multiplets, the aliphatic region, similarly to 3.1a, displayed three resonances for each of the methyl groups present on the m-terphenyl ligand. The ESI-MS of 3.2a displayed a similar fragmentation pattern as its structural isomer 3.1a, with the molecular

+ ion peak present (501.2 m/z C32H31PSNa [M + Na] ). The formation of both 3.1a and 3.2a indicates that the initial reaction of 2.2S with phenylacetylene yields both the [1+2] and [2+2] cycloaddition products, indicating that the phosphinidene sulfide generated from the thermolysis of 2.3S reacted in a similar fashion to both a carbene and an olefin (see computational work below).27,30

57 58

Figure 3-3: Solid-state structure of 1,2-thiaphosphetene (3.1a). Thermal ellipsoids drawn at 50% probability, and hydrogen atoms have been omitted for clarity. Selected bond lengths [Å] and bond angles [°]: P(1)-S(1) 2.161(3), P(1)-C(1) 1.844(7), P(1)- C(25) 1.796(6), S(1)-C(26) 1.772(6), C(25)-C(26) 1.357(9), C(1)-P(1)-S(1) 106.1(2), P(1)-S(1)- C(26) 76.0(2), S(1)-C(26)-C(25) 105.3(5), C(26)-C(25)-P(1) 100.4(5), C(25)-P(1)- S(1)77.7(2), C(25)-P(1)-C(1) 109.2(3).

Compound 3.1a was derived from a terminal alkyne and it raised the question as to whether the same chemistry could be achieved using a 1,2-disubstituted alkyne. Heating a mixture of 2.3S with an excess of diphenylacetylene (2.7 molar eq.) at 80 °C for 4 days resulted in the consumption of starting material and the formation of one

31 1 product in the P{ H} NMR spectrum (dP = -81.1; Figure 3-4). Removing the volatiles in vacuo, and slowly concentrating a CH2Cl2 solution of the crude reaction mixture resulted in single crystals suitable for X-ray diffraction, that upon a structure analysis revealed the formation of 3.2b, a phosphirene sulfide generated via [1+2] cycloaddition of 2.2S and diphenylacetylene (Figure 3-5). Redissolving the single crystals in benzene-d6 gave rise to the same singlet observed in the crude 31P NMR spectrum, which unlike 3.2a did not contain P-H coupling. The 1H NMR spectrum of 3.2b displays two singlets in the aliphatic region, corresponding to the ortho- and para- methyl groups from m-terphenyl, indicative of a symmetrical product. The preparation of 3.2b was also supported by

58 59 elemental analysis, and ESI-MS revealed a molecular ion peak corresponding to the + 31 sodium salt of 3.2b (577.2 m/z, C38H35PSNa [M + Na] ). From the P NMR spectra, there was no indication that the 1,2-thiaphosphetene (3.1b) was formed in this reaction, leading us to believe that the steric imposition of an internal alkyne and our terphenyl substituted phosphinidene sulfide was too large to allow for a [2+2] cycloaddition to occur. While the chemistry of phosphiranes and phosphirenes are known and can be formed by the [1+2] cycloaddition of in situ generated phosphinidenes with alkynes or alkenes,32–38 literature reported examples of phosphirane/ene sulfides are scarce. Phosphirane24,39 and phosphirene32,40 sulfides combined are limited to one structurally characterized example of a phosphirane sulfide supported by a 2,6-dimethoxyphenyl ligand.24

Compounds 3.2a and 3.2b (Figure 3-5) contain a strained three membered planar

PC2 ring with P-Cavg bond distances of 1.752(3) and 1.7623(14) Å for 3.2a and 3.2b, respectively, a C=C double bond (1.328(3) and 1.349(2) Å for 3.2a and 3.2b) and an exocyclic P=S double bond (1.939(1) and 1.9453(7) Å for 3.2a and 3.2b).

In order to ascertain the relative stabilities of the isomers 3.1 and 3.2, we performed a series of DFT calculations using the M06-2X/TZVP method. Preliminary calculations revealed that attempts to model the bulky aromatic substituent on P with either a phenyl group or an unsubstituted terphenyl group did not adequately reproduce the experimental geometrical features, therefore we employed models featuring the 2,6- bis(2,6-dimethylphenyl)phenyl substituent (Ar’). The model compounds 3.1’a-d and 3.2’a-d (a: R = Ph, R’ = H; b; R = R’= Ph; c: R = R’= H; d: R = R’= Me) were fully optimized in the absence of symmetry constraints (see Section 3.3.5 for full details). The geometrical features of the optimized structures with the Ar’ substituent reproduced all of the structural features observed in the experimental structures and justify the choice of method and model.

59 60

For each of the pairs of isomeric model alkyne cycloaddition products investigated, we find that the 4-membered ring isomer is significantly more stable than the 3-membered ring isomer with free energy differences ranging from 35 to 72 kJ mol-1. Interestingly, the largest difference (72 kJ mol-1) is found for the phenylacetylene adduct (a) and the smallest difference (35 kJ mol-1) is exhibited in the diphenylacetylene adduct (b); the parent acetylene adduct isomers feature a difference of 70 kJ mol-1 while the dimethylacetylene adduct isomers have a much smaller difference of 47 kJ mol-1. Thus, it is clear that although the steric and electronic differences of the substituents alter the relative stabilities of the adducts, the formation of the 4 membered ring variants 3.1’a-d, are always more favored thermodynamically (Table 7-2, Table 7-3).

60 61

Figure 3-5: Solid-state structures of phosphirene sulfides 3.2a (left) and 3.2b (right). Thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and bond angles [°] 3.2a: P(1)-S(1) 1.9390(13), P(1)- C(1) 1.819(3), P(1)-C(25) 1.757(3), P(1)-C(26) 1.746(3), C(25)-C(26) 1.328(4), C(1)- P(1)-S(1) 115.79(10), C(1)-P(1)-C(25) 115.57(13), C(1)-P(1)-C(26) 112.13(13), P(1)- C(25)-C(26) 67.30(18), P(1)-C(26)-C(25) 68.14(17), C(26)-P(1)-C(25) 44.56(13), S(1)- P(1)-C(25) 124.10(11), S(1)-P(1)-C(26) 125.87(11). 3.2b: P(1)-S(1) 1.9443(7), P(1)-C(1) 1.8176(14), P(1)-C(25) 1.7684(14), P(1)-C(26) 1.7561(14), C(25)-C(26) 1.3449(18), C(1)-P(1)-S(1) 113.74(5), C(1)-P(1)-C(25) 116.36(6), C(1)-P(1)-C(26) 116.19(6), P(1)- C(25)-C(26) 67.08(8), P(1)-C(26)-C(25) 68.05(8), C(26)-P(1)-C(25) 44.86(6), S(1)-P(1)- C(25) 125.14(5), S(1)-P(1)-C(26) 123.55(5).

Knowing now that the 4-membered 1,2-thiaphosphetene derivatives were more stable based on the computations (as compared to the corresponding phosphirene sulfides) we tested compounds 3.2 to see if it could convert to the thermodynamically favoured isomer. Heating a sample of 3.2a over 5 days at 80 °C resulted in no change in the 31P NMR spectrum and revealed that the strained 3-membered phosphirene sulfides are thermally stable. Alternatively, irradiating 3.2a with UV light led to multiple phosphorus containing products (Figure 3-6), and although the 1,2-thiaphosphetene products (3.1) were not formed, the major product was the parent dithiadiphosphetane (2.3S, Scheme 3-2). The photolysis of 3.2 appears to be a unique method of utilizing an indefinitely stable PV-centered compound as a stoichiometric source of PIII-S, by leveraging to the extrusion of the monomeric Ar*P=S, which is consistent with what has been reported for the fully saturated phosphirane sulfide derivatives.24

61 62

Scheme 3-2: Using phosphirene sulfides 3.2 as sources of phosphinidene sulfides.

As an alternative to thermolysis of dithiadiphosphetane (2.3S) as a precursor to

Ar*P=S and ultimately compounds 3.1 or 3.2, the direct 1:1 addition of Ar*PCl2 and

S(TMS)2 (Scheme 3-3) in the presence of excess phenylacetylene at room temperature resulted in 3.2a being the only P-S heterocycle formed as indicated by 31P{1H} NMR spectroscopy (Figure 3-7). This route also leads to an improved overall yield in comparison to thermolysis (44% yield).41 Scheme 3-3 proposes two potential pathways for the generation of 3.2, and the difference in reactivity between the two synthetic routes. Method (i) (Scheme 3-3, left) details that the condensation of Ar*PCl2 and

S(TMS)2 proceeds via the elimination of 2 stoichiometric equivalents of TMSCl to give the phosphinidene sulfide 2.2S, which in the presence of phenylacetylene forms 3.2a as

62 63 the [1+2] cycloaddition product. This result is indicative of carbene-like reactivity only, which is contrary to the recent results from Mathey,30 and our group.31 Therefore we propose that using method (ii) (Scheme 3-3, right) proceeds via the stepwise elimination of TMSCl, giving rise to a phosphenium-like intermediate (3.3). In the presence of phenylacetylene, compound 3.3 can undergo a [1+2] cycloaddition followed by a second TMSCl elimination to yield the cycloadduct 3.2a. The [1+2] cycloaddition of phosphenium cations and alkynes is well established,43 and provides a solid grounding as to why phosphirene sulfide (3.2) is the only product formed.

63 64

Figure 3-7: A 31P{1H} NMR stacked plot indicating the reaction progress yielding 3.2a from Ar*PCl2.

We probed this concept computationally and examined the frontier orbitals on the monomeric phosphinidene sulfide (for computational efficiency, the terphenyl group was replaced by the m-xylyl ligand). The calculations revealed that the HOMO is consistent with a phosphenium-like P-lone pair whereas the P=S π-bond is mostly attributable to HOMO-3, which allow the ArP=S at least two potential reactivity pathways (Table 7-2, Table 7-3).

Potential energy scans revealed possible reaction pathways in the formation of 3.1 and 3.2 stemming from RP=S (for computational efficiency, the parent phosphinidene sulfide, HP=S, and acetylene were used, leading to 3.1’e and 3.2’e, Figure 3-8). In the case of forming 3.1’e, a transition state is endergonic by 131 kJ mol-1 that reveals the P=S unit interacting with the alkyne with sulfur being in close proximity (S···C: 2.50 Å;

CCPS dihedral angle: 29°). This then cyclizes to form the 4-membered PSC2 ring which is significantly lower in energy, and overall exergonic by 117 kJ mol-1. The transition state in forming 3.2’e is only endergonic by 68 kJ mol-1, which shows exclusively P- alkyne interaction with sulfur facing away from the alkyne (S···C: 3.38 Å; CCPS

64 65 dihedral angle: 82°), which proceeds to cyclize in [1+2] fashion leading to 3.2’e and an overall exergonic process (29 kJ mol-1). Our experimental results are in direct agreement with our theoretical findings. Thermolysis of 2.3S in the presence of phenylacetylene yielded a mixture of 3.1 and 3.2, and since both pathways have energetically accessible activation barriers, this leads to competing reactions and a mixture of products. The competition of reactions to form multiple products is consistent with reports by Gaspar et al. for other cycloaddition reactions.24

Figure 3-8: Reaction coordinate diagram for the formation of 3.1’e and 3.2’e.

3.2 Conclusion

In conclusion, we have detailed the synthesis, and first structural characterization of 1,2-thiaphosphetenes (3.1) and phosphirene sulfides (3.2). Upon photolysis of phosphirene sulfides (3.2), the strained 3-membered rings liberate free phosphinidene sulfide, and in the absence of a trapping reagent readily reforms the parent 4-membered dithiadiphosphetane (2.3), indicating that these strained PV rings are likely stoichiometric sources of PIII-S, much like compound 2.3 itself. Computational analysis revealed that the 4-membered 1,2-thiaphosphetenes (3.1) are considerably more stable than the isomeric 3- membered phosphirene sulfides (3.2). At this time, it is an open question as to whether

65 66 phosphinidene sulfides are generated by either thermolysis of 2.3 or condensation of

Ar*PCl2 and S(TMS)2 however mechanistic pathways have been found stemming from RP=S to form both 3.1 and 3.2. It is clear that both of the methods described here

(thermolysis of 2.3S and condensation of Ar*PCl2 and S(TMS)2) can be used to access a molecular unit formally derived from Ar*PS.

3.3 Experimental Section

See Section 7.2 for general experimental and crystallographic procedures.

3.3.1 Synthesis of 3.1a

A solution of 2.3S (60 mg, 0.080 mmol) and phenylacetylene (16 mg, 0.16 mmol) in 1 mL of toluene were heated in an NMR tube at 80 °C. Monitoring the reaction by 31P NMR spectroscopy revealed that the starting material (2.3S) was consumed after 5 hours. The volatiles were removed in vacuo and washed with 5 mL n-pentane. The resulting off- white precipitate was collected. Yield: 25 mg (66%). Slowly concentrating an ether solution of 3.1a resulted in X-ray quality single crystals. m.p. (nitrogen sealed capillary): 189.3-190.2 °C.

+ + ESI-MS: 501.2 m/z C32H31PSNa [M + Na] , 479.2 m/z C32H31PS [M] .

FT-IR (KBr, cm-1 (ranked relative intensity)): 687 (4), 745 (1), 784 (11), 805 (5), 851 (2), 914 (7), 1027 (6), 1106 (13), 1156 (10), 1377 (12), 1445 (3), 1483 (15), 1559 (14), 1609 (9), 2914 (8).

Elemental Analysis: Calculated 80.30% C, 6.53% H, 6.70% S; Found 81.00% C, 6.76% H, 7.28% S.

1 H NMR (C6D6, 400 MHz, δ): 2.19 (s, 6 H; Mes CH3), 2.20 (s, 6 H; Mes CH3), 2.23 (s, 6

2 H; Mes CH3), 4.89 (d, JP-H = 31.6 Hz, 1 H; P-CH), 6.85 (br s, 2 H; Mes CH), 6.92 (m, 6 H), 7.17 (m, 4 H).

13 1 1 C{ H} NMR (C6D6, 150.8 MHz, δ): 21.0, 21.1, 21.2, 21.3, 21.4, 117.8 (d, JP-C = 13.6 2 Hz), 123.7 (d, JP-C = 2.0 Hz), 128.4, 128.7, 128.8, 129.0, 129.1, 130.0, 136.0, 136.5,

66 67

2 1 136.8, 137.6, 137.9, 138.4, 138.6 (d, JP-C = 2.1 Hz), 144.5 (d, JP-C = 19.3 Hz), 145.8 (d, 1 JP-C = 32.6 Hz).

31 2 P NMR (C6D6, 161.8 MHz, δ): 38.1 (d, JP-H = 31.6 Hz).

3.3.2 Synthesis of 3.2a

Leaving the pentane soluble portion of the crude reaction mixture used to yield 3.1a at - 35 °C for one week resulted in single crystals of 3.2a. Yield: 8 mg (21%). Alternatively, an improved synthesis was used that included heating Ar*PCl2 (200 mg, 0.482 mmol),

S(TMS)2 (146 mg, 0.819 mmol) and phenylacetylene (492 mg, 4.82 mmol) in 6 mL toluene in a pressure tube at 80 °C for 16 h. The volatiles were removed in vacuo, and the resulting yellow oil was triturated with 3 mL n-pentane for 1 hour. The off-white precipitate was filtered and collected yielding 3.2a. Yield: 100 mg (44%). Single crystals were grown by layering an Et2O solution with n-pentane at -35 °C for 3 days. m.p. (nitrogen sealed capillary): 194.1-194.5 °C.

+ + ESI-MS: 501.2 m/z C32H31PSNa [M + Na] , 399.1 m/z C24H25PSNa [M – C8H6 + Na] .

FT-IR (KBr, cm-1, (ranked relative intensity)): 535 (1), 550 (13), 559 (6), 591 (9), 668 (11), 672 (14), 1073 (3), 1506 (12), 1520 (8), 1539 (10), 1652 (5), 1683 (7), 1699 (4), 1733 (2), 2912 (15).

Elemental Analysis: Calculated 80.30% C, 6.53% H, 6.70% S; Found 78.75% C, 6.68% H, 7.13% S.

1 H NMR (C6D6, 400 MHz, δ): 2.04 (s, 6 H; Mes CH3), 2.22 (s, 6 H; Mes CH3), 2.25 (s, 6

H; Mes CH3), 6.67 (br s, 2 H; Mes CH), 6.82 (m, 4 H), 6.93 (m, 4 H), 7.01 (m, 1 H), 7.10 3 5 2 (td, JH-H = 7.6, JP-H = 1.9 Hz, 1 H; Ar para-CH), 7.41 (d, JP-H = 10.3 Hz, 1 H; P-CH).

13 1 C{ H} NMR (C6D6, 150.8 MHz, δ): 21.3, 21.6, 21.7, 34.5, 128.6, 128.9, 129.0, 129.4, 2 129.5, 129.6, 130.4, 131.4 (d, JP-C = 2.9 Hz), 135.5, 136.5, 136.8, 136.9, 137.0, 137.3,

2 2 137.5, 137.7, 137.7, 143.3 (d, JP-C = 12.1 Hz), 156.8 (d, JP-C = 6.4 Hz).

31 P NMR (C6D6, 161.8 MHz, δ): -83.3 (m).

67 68

3.3.3 Synthesis of 3.2b

A solution of 2.3S (75 mg, 0.099 mmol) and diphenylacetylene (40 mg, 0.23 mmol) in 3 mL toluene were heated at 80 °C in a pressure tube for 4 days. The volatiles were removed in vacuo, and the crude white powder was washed 3 x 5 mL with n-pentane, and the pentane insoluble portion was collected. The crude powder was then dissolved in diethyl ether, and passed through a Celite filter pipette. The ether soluble portion was collected, the solvent was removed in vacuo that yielded 3.2b (Yield: 67 mg, 61%).

Single crystals were grown by slowly concentrating a CH2Cl2 solution of 3.2b. m.p. (nitrogen sealed capillary): 161.0-161.4 °C (decomposes, turns yellow).

+ + ESI-MS: 1131.4 m/z C76H70P2S2Na [2 x M + Na] , 577.2 m/z C38H35PSNa [M + Na] , + + 399.2 m/z C24H25PSNa [M - C14H10 + Na] , 343.2 m/z C24H24P [M - C14H11] .

FT-IR (KBr, cm-1 (ranked relative intensity)): 516 (1), 550 (4), 590 (9), 614 (14), 1030 (12), 1074 (2), 1119 (7), 1181 (6), 1298 (3), 1377 (13), 1443 (15), 1481 (10), 1559 (5), 1610 (11), 2911 (8).

Elemental Analysis: Calculated 82.28% C, 6.36% H, 5.78% S; Found 81.19% C, 6.52% H, 6.54% S.

1 H NMR (C6D6, 400 MHz, δ): 2.12 (s, 6 H; Mes CH3), 2.17 (br s, 12 H; Mes CH3), 6.58 (br s, 4 H; Mes CH), 6.82 (m, 2 H), 6.89-6.98 (m, 6 H), 7.05-7.11 (m, 5 H).

13 1 C{ H} NMR (C6D6, 150.8 MHz, δ): 21.3, 21.8, 128.7, 128.8, 128.9, 129.2, 129.3, 1 129.3, 129.7, 129.9, 131.3, 131.4, 132.0, 135.7, 136.7, 137.1, 137.2, 138.0 (d, JP-C = 5.2

1 1 Hz), 143.4 (d, JP-C = 12.3 Hz), 148.0 (d, JP-C = 8.2 Hz).

31 1 P{ H} NMR (C6D6, 161.8 MHz, δ): -81.1 (s).

3.3.4 Special Considerations for X-ray Crystallography

For compound 3.2a, severely disordered n-pentane solvates were present. Several attempts were made to model this disorder, however, we were unable to obtain a

68 69 chemically sensible solution. For this reason, the solvates were treated as a diffuse contribution to the overall scattering by SQUEEZE/PLATON.44

Table 3-1: Summary of X-ray diffraction collection and refinement details for the compounds reported in Chapter 3.

3.1a 3.2a 3.2b Formula C32H31PS C32H31PS C38H35PS CCDC Ref. # 1575227 1575226 1575225 Formula Weight (g/mol) 478.60 478.60 554.69 Crystal System monoclinic monoclinic triclinic Space Group P 21 C 2/c P -1 Temp, K 110 110 110 a, Å 12.741(3) 46.42(3) 13.435(4) b, Å 7.9021(12) 8.738(5) 14.476(4) c, Å 26.032(4) 15.226(8) 16.611(5) α, deg 90 90 72.145(8) β, deg 92.115(11) 107.859(14) 80.495(14) γ, deg 90 90 89.783(8) V, Å3 2619.0(8) 5878(5) 3028.8(15) Z 4 8 4 F(000) 1016 2032 1176 ρ (g/cm) 1.214 1.082 1.216 λ, Å, (MoKα or CuKα) 1.54178 0.71073 0.71073 µ, (cm-1) 1.794 0.181 0.185 Measured fraction of 0.991 0.997 0.999 data Rmerge 0.0584 0.0561 0.0270 R1, wR2 0.0557, 0.1438 0.0816, 0.2079 0.0508, 0.1513 R (all data), wR (all 1 2 0.0688, 0.1536 0.0996, 0.2164 0.0642, 0.1613 data) GOF 1.028 1.106 1.027

2 2 2 4 ½ 2 Where: R1 = Σ( |Fo| - |Fc| ) / Σ Fo, wR2 = [ Σ(w(Fo - Fc ) ) / Σ(w Fo )] GOF = [Σ( w( Fo - 2 2 ½ Fc ) ) / (No. of reflns. - No. of params.)]

69 70

3.3.5 Computational Details

Calculations were performed with the Gaussian 09 suite of programs45 using Compute Canada's SHARCNET. Model complexes featuring the 2,6-bis(2,6- dimethylphenyl)phenyl substituent (Ar’) (Table 7-2) were fully optimized using the M06- 2X DFT method46 in conjunction with the TZVP basis sets for all atoms.47 Frequency calculations were also performed at that level of theory in order to confirm that the optimized structures were minima on the potential energy hypersurface and to determine thermochemical information. Population analyses were conducted using the Natural Bond Orbital 6.0 (NBO)48 implementation included with the Gaussian package. Mechanistic insights were obtained using the model complexes HP=S and HC≡CH calculated using the M06-2X/TZVP or UM06-2X/TZVP methods (Table 7-3); IRC calculations were employed to confirm that the transition states identified linked reactants and products (or intermediates). The molecular orbital depictions were generated using ADF2016.10649 using a single-point M06-2X/TZVP calculation using the G09 optimized geometry. Summaries of the optimized structures, including electronic energies and Cartesian coordinates for each of the atoms, are detailed in the ESI of the manuscript that can be accessed free of charge from DOI: 10.1002/chem.201705198.

3.4 References (1) Ul-Haque, M.; Caughlan, C. N.; Ramirez, F.; Pilot, J. F.; Smith, C. P. J. Am. Chem. Soc. 1971, 93, 5229–5235. (2) Vedejs, E.; Snoble, K. A. J. J. Am. Chem. Soc. 1973, 95, 5778–5780. (3) Wittig, G.; Geissler, G. Justus Liebigs Ann. Chem. 1953, 580, 44–57. (4) Wittig, G.; Schollkopf, U. Chem. Ber. 1954, 87, 1318–1330. (5) Maryanoff, B. E.; Reitz, A. B. Chem. Rev. 1989, 89, 863–927. (6) Kolodiazhnyi, O. I. Phosphorus Ylides: chemistry and application in organic synthesis, Wiley-VCH: Weinheim, 1999. (7) Byrne, P. A.; Gilheany, D. G. Chem. Soc. Rev. 2013, 42, 6670–6696. (8) Vedejs, E. Phosphorus. Sulfur. Silicon Relat. Elem. 2015, 190, 612–618. (9) Robiette, R.; Richardson, J.; Aggarwal, V. K.; Harvey, J. N. J. Am. Chem. Soc. 2006, 128, 2394–2409. (10) Kyri, A. W.; Nesterov, V.; Schnakenburg, G.; Streubel, R. Angew. Chem., Int. Ed.

70 71

2014, 53, 10809–10812. (11) Kyri, A. W.; Schnakenburg, G.; Streubel, R. Chem. Commun. 2016, 8593–8595. (12) Kyri, A. W.; Schnakenburg, G.; Streubel, R. Organometallics 2016, 35, 563–568. (13) Kyri, A. W.; Brehm, P.; Schnakenburg, G.; Streubel, R. Dalton Trans. 2017, 2904–2909. (14) Kawashima, T.; Kato, K.; Okazaki, R. J. Am. Chem. Soc. 1992, 114, 4008–4010. (15) Kawashima, T.; Okazaki, R.; Okazaki, R. Angew. Chem., Int. Ed. 1997, 36, 2500– 2502. (16) Kawashima, T.; Takami, H.; Okazaki, R. J. Am. Chem. Soc. 1994, 116, 4509– 4510. (17) Kawashima, T.; Kato, K. Angew. Chem., Int. Ed. 1993, 32, 869–870. (18) Foreman, M. R. S. J.; Slawin, A. M. Z.; Woollins, J. D. J. Chem. Soc., Dalton Trans. 1999, 1175–1184. (19) Foreman, M. R. S. J.; Slawin, A. M. Z.; Woollins, J. D. Chem. Commun. 1997, 855–856. (20) Puke, C.; Erker, G.; Aust, N. C.; Wurthwein, E. U.; Frohlich, R. J. Am. Chem. Soc. 1998, 120, 4863–4864. (21) Wilker, S.; Laurent, C.; Sarter, C.; Puke, C.; Erker, G. J. Am. Chem. Soc. 1995, 117, 7293–7294. (22) Kawashima, T.; Iijima, T.; Kikushi, H.; Okazaki, R. Phosphorus. Sulfur. Silicon Relat. Elem. 1999, 144, 149–152. (23) Nakayama, S.; Yoshifuji, M.; Okazaki, R.; Inamoto, N. Chem. Commun. 1971, 1186–1187. (24) Gaspar, P. P.; Qian, H.; Beatty, A. M.; d’Avignon, D. A.; Kao, J. L. F.; Watt, J. C.; Rath, N. P. Tetrahedron 2000, 56, 105–119. (25) Yoshifuji, M.; Nakayama, S.; Okazaki, R.; Inamoto, N. J. Chem. Soc., Perkin I 1973, 2065–2068. (26) Hussong, R.; Heydt, H.; Regitz, M. Z. Naturforsch 1986, 41b, 915–921. (27) Santini, C. C.; Fischer, J.; Mathey, F.; Mitschler, A. J. Am. Chem. Soc. 1980, 102, 5809–5815. (28) Nakayama, S.; Yoshijiuji, M.; Okazaki, R.; Inamoto, N. J. Chem. Soc., Perkin I 1973, 2069–2071. (29) Nakayama, S.; Yoshifuji, M.; Okazaki, R.; Inamoto, N. Bull. Chem. Soc. Jpn. 1975, 48, 546–548. (30) Wang, L.; Ganguly, R.; Mathey, F. Organometallics 2014, 33, 5614–5617. (31) Graham, C. M. E.; Pritchard, T. E.; Boyle, P. D.; Valjus, J.; Tuononen, H. M.; Ragogna, P. J. Angew. Chem., Int. Ed. 2017, 56, 6236–6240.

71 72

(32) Marinetti, A.; Mathey, F.; Fischer, J.; Mitschler, A. J. Chem. Soc., Chem. Commun. 1984, 45–46. (33) Ostrowski, A.; Jeske, J.; Jones, P. G.; Streubel, R. J. Chem. Soc., Chem. Commun. 1995, 2507–2508. (34) Huy, N. H. T.; Ricard, L.; Mathey, F. J. Chem. Soc., Dalton Trans. 1999, 2409– 2410. (35) Jayaraman, A.; Sterenberg, B. T. Organometallics 2014, 33, 522–530. (36) Wong, J.; Li, Y.; Hao, Y.; Tian, R.; Mathey, F. Angew. Chem., Int. Ed. 2015, 54, 12891–12893. (37) Wit, J. B. M.; de Jong, G. B.; Schakel, M.; Lutz, M.; Ehlers, A. W.; Slootweg, J. C.; Lammertsma, K. Organometallics 2016, 35, 1170–1176. (38) Transue, W. J.; Velian, A.; Nava, M.; García-Iriepa, C.; Temprado, M.; Cummins, C. C. J. Am. Chem. Soc. 2017, 139, 10822–10831. (39) Gaspar, P. P.; Beatty, A. M.; Li, X.; Qian, H.; Rath, N. P.; Watt, J. C. Phosphorus. Sulfur. Silicon Relat. Elem. 1999, 144, 277–280. (40) Marinetti, A.; Mathey, F. J. Am. Chem. Soc. 1985, 107, 4700–4706. (41) Reaction proceeds at room temperature and full conversion was reached after 36 h. Gentle heating at 80 °C leads to full conversion after 16 h. (42) Schoeller, W. W.; Niecke, E. J. Chem. Soc., Chem. Commun. 1982, 569–570. (43) Fongers, K. S.; Hogeveen, H.; Kingma, R. F. Tetrahedron Lett. 1983, 24, 643–646. (44) Spek, A. L. ACTA Crystallogr. 2009, D65, 148. (45) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Marenichm, A. V.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakaji; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A. J.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 09, Revision D.01; Wallingford, CT, USA, 2009. (46) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215–241. (47) Schäfer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829–5835. (48) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.; Bohnmann, J.

72 73

A.; Morales, C. M.; Landis, C. R.; Weinhold, F. Theoretical Chemistry Institute, University of Wisconsin, 6th ed.; Madison, WI, 2013. (49) SCM, Theoretical Chemistry, Vrije Universiteit, Amsterdam, The Netherlands, 2016.

73 74

Chapter 4 4 Phosphorus-Chalcogen Ring Exansion and Metal Coordination 4.1 Introduction

Small inorganic ring systems have been of interest to chemists for decades as they normally offer a window into unique structure, bonding, and reactivity,1–4 and a comprehensive review regarding the breadth of these compounds was recently published by Rivard and coworkers.5 Inorganic rings containing phosphorus-p-block element cores have been extensively explored and reported in the literature. Of this large collection of phosphorus-containing main group rings, phosphorus-chalcogen (P-Ch) heterocycles have been a particular focus area because of their widespread application as ligands for transition metals,6,7 and “P” or “Ch” transfer reagents.8 Major developments in P-Ch heterocyclic chemistry feature PV compounds, with noteworthy examples being Lawesson’s (Ch = S)9 and Woollins’ (Ch = Se)10 reagents (Figure 4-1, 4.A) that contain

P2Ch2 cores with each phosphorus further oxidized by an additional sulfur or selenium atom, respectively.11–13 These compounds have proven to be indispensable reagents in a variety of synthetic transformations14–18 and material applications.19,20 While there have been extensive studies on PV-Ch derivatives, examples of PIII within the ring core are more uncommon, especially in regards to cyclic structures with a general formula (c-

RPCh)n. Examples of (c-RPCh)n have been reported for n = 2, 3, and 4, where bulky R groups are required to kinetically stabilize the PIII centre (Figure 4-1, 2.3Ch, 1.35, 1.36).21–26 In particular, our group has recently reported the syntheses of strained (c-

RPCh)2 rings 2.3Ch (Ch = S, Se) with P in the +3 oxidation state, the first representatives of these strained compounds, by installing m-terphenyl substituents at phosphorus.24

74 75

Although select examples of (c-RPCh)n have been reported since the early 1980’s, a thorough examination of their chemistry has not been discussed, though related P(III)- Ch-N macrocycles have recently been reported to form polynuclear AgI sandwich complexes upon reaction with various amounts of AgOTf (Figure 4-1, 4.B).7 In this context, we report herein on the chemistry of 2.3Ch and the possibility to use them to access larger (c-RPCh)3 rings (4.1Ch, Ch = S, Se). Although consistent reactivity

75 76 between 2.3S and 2.3Se is not observed, identical derivatives can still be prepared using different synthetic approaches. In particular, the reaction of 2.3S with Lewis bases gives 4.1S, whereas the selenium analogue 4.1Se can be synthesised and isolated via cyclocondensation of Ar*PCl2 and Se(TMS)2. We have also discovered that introducing coinage-metals Cu and Ag to 2.3Ch results in ring expansion products (c-RPCh)3 for both chalcogens. The rings were found to be further bound to the employed metal cation in a tripodal fashion through phosphorus, giving coordination complexes 4.3ChM (Ch = S, Se; M = Cu, Ag); the same coordination complexes can also be prepared directly from 4.1Ch.

4.2 Results and Discussion

4.2.1 Formation of P/Ch Heterocycles

The synthesis of 2.3Ch resulted from the cyclocondensation of Ar*PCl2 with

Ch(TMS)2 (Scheme 4-1). Although the sulfur chemistry proceeds cleanly, multiple products are present in the crude reaction mixture for Ch = Se. The major product 2.3Se

(dP = 24.0) could be isolated by washing the crude reaction mixture with n-pentane, yielding an orange powder. A minor product from this reaction was isolated by precipitating out a yellow powder from a CH2Cl2 solution at -35 °C (dP = 87.8). Slowly concentrating a CH2Cl2 solution resulted in single crystals suitable for X-ray diffraction that confirmed the preparation of 4.1Se (Figure 4-2). Although numerous examples of

(RPS)3 are known, 4.1Se represents the first structurally characterized selenium derivative, and is one of the few known examples of heavier chalcogens in such a ring system.23

76 77

After successfully isolating 2.3Ch, we endeavored to utilize these strained compounds as precursors to the monomeric RP=Ch, which have been elusive intermediates in low-coordinate phosphorus-chalcogen chemistry. In our initial work (Scheme 4-2, top), 2.3Ch could be monomerized by gentle heating, giving solution accessible RP=Ch that could be trapped using dmbd to give 2.5Ch. Alternatively, monomerization of 2.3S could be induced through the addition of NHCiPr, which resulted in the formation of the adduct 2.4SiPr even without heating.24 Taking our lead from these results, the reaction of a weaker base (e.g. DMAP) with 2.3S in 2:1 stoichiometry yielded

31 1 one major product in the P{ H} NMR spectrum at dP = 96.7, an upfield shift from the

iPr parent 2.3S (dP = 126.6), and significantly downfield shifted from 2.4S (dP = 28.9).

Slowly concentrating a CH2Cl2 solution at -35 °C resulted in pale-yellow single crystals. Single crystal X-ray diffraction experiments revealed that the product is not a simple DMAP adduct of 2.3S but instead the 6-membered ring expansion species 4.1S, analogous to 4.1Se (Figure 4-2). 31P{1H} NMR spectra obtained from solutions containing redissolved crystals of 4.1S showed the same distinct singlet (dP = 96.7) observed in the crude reaction mixture, while the 1H NMR spectra showed a single set of terphenyl protons, indicating equivalence of aromatic substituents on the NMR timescale.

77 78

Although the ring expansion product was the only species obtained from the reaction between 2.3S and DMAP, the analogous reaction using 2.3Se gave numerous products, as determined by 31P{1H} NMR spectroscopy (Figure 4-3). Even though none of these products could be isolated and characterized, the NMR spectroscopic data clearly indicated that ring expansion to 4.1Se did occur (dP = 87.8) when using nitrogen bases. Other structurally related Lewis bases such as pyridine and 2,6-lutidene also generated 4.1Se, but again with multiple other side products (Figure 4-3). Alternatively, phosphine- based donors (PEt3, PCy3, and PPh3) produced multiple products as determined by 31P{1H} NMR spectroscopy (Figure 4-4), and there was no evidence for a ring expansion product 4.1Se. The corresponding phosphine-selenides were present in the 31P{1H} NMR spectra, indicative of a competing process upon addition of alkyl/aryl phosphines.

78 79

S Ch 2 NHCiPr THF 2 dmbd Ch 2 Ar* P Ar* P P Ar* 2 Ch 2 Ch = S 50 °C Ar* P P NHCiPr Ch Ar* 2.4SiPr 2.3Ch 2.2Ch 2.5Ch

Ar* Ar* Ch DMAP P 2 Ch Ch + DMAP 3 Ar* P P Ar* Me2N N P + 2.3Ch THF, 50 °C Ch P P Ch Ar* Ch Ar* 2.3Ch 4.2Ch 4.1Ch

79 80

Taking all of the above into account, a possible mechanism for the formation of 4.1Ch can be envisioned (Scheme 4-2, bottom). The reaction most likely begins by breaking up of 2.3Ch that is induced either by the employed base (cf. formation of 2.4S) or simply by heating (cf. formation of 2.5Ch). In the presence of excess DMAP, the initial product should in both cases be the adduct 4.2Ch that could subsequently undergo insertion into 2.3Ch, leading to dissociation of DMAP and formation of 4.1Ch. This mechanism is experimentally supported by the appearance of free DMAP in the crude reaction mixture once 2.3S is fully consumed. Furthermore, heating samples of 2.3S without DMAP does not lead to the formation of 4.1S. However, as 4.1Se is formed even during the synthesis of 2.3Se, the potential energy surface for the formation of 4.1Ch is obviously not completely independent of the chalcogen atom.

Figure 4-4: 31P{1H} NMR stacked plot showing ring expansion attempts on 2.3Se using phosphine donors. Reaction conditions are shown on their respective plots. Each reaction indicates reactivity between PR3 and 2.3Se, however there is no evidence of ring expansion (chemical shift of 4.1Se is shown between dotted lines). Suggested SePR3 products are highlighted on their respective spectra.

80 81

The reaction pathway for forming 4.1S was examined using density functional theory at the PBE1PBE/TZVP level of theory augmented with an empirical dispersion correction. The calculations show that DMAP does not monomerize 2.3S as efficiently as was observed earlier in the case of an NHC. However, the calculated activation barrier for the formation of two stoichiometric equivalents of 4.2S (95 kJ mol-1) is in any case considerably lower than that found for the direct, heat induced, monomerization of 2.3S to two equivalents of 2.2S (124 kJ mol-1).27 Furthermore, while the formation of 2.2S is highly endergonic (118 kJ mol-1), the base-assisted monomerization of 2.3S to two equivalents of 4.2S is only slightly so (44 kJ mol-1). This shows that DMAP efficiently stabilizes the RP=S unit, as expected, but does it so that further reactivity of the monomer is not hindered. This is in contrast to what was observed for the NHC adduct 2.4S, the formation of which was calculated to be exergonic by as much as 106 kJ mol-1.

Having established the possible role of DMAP in stabilizing the transient RP=S monomer, we turned our attention to the formation of 4.1S. Many different mechanisms can be envisioned for this process, but the most likely one is a direct reaction between 2.3S and 4.2S. Computational work showed that the lowest energy pathway on this particular potential energy surface involves the break-up of one P-S bond in 2.3S to give 2.3S-b that then binds 4.2S and forms a 6-membered acyclic intermediate Int (Figure 4-5). This reaction is almost energy neutral and proceeds through a transition state that is comparable in energy (TS1, 103 kJ mol-1) to that found for the formation of 4.2S. The intermediate Int can subsequently close in on itself (TS2, 75 kJ mol-1), dissociating the coordinated DMAP and forming 4.1S. The calculations showed that 4.1S can adopt several conformers that are interconnected via low-energy transition states, with the experimentally observed chair conformer of 4.1S as the global energy minimum. In total, a reaction energy of -127 kJ mol-1 were obtained for the overall transformation of three equivalents of 2.3S to two equivalents of 4.1S, which confirms that the 6-membered rings are more stable than their 4-membered precursors.

As 4.1Se was found to form even during the synthesis of 2.3Se, there must also be a base-free mechanism for the formation of 4.1Ch. To allow comparison to extant data, we examined this possibility for 4.1S with computational methods (Figure 7-28). The

81 82 results show that 2.2S, being a highly reactive species, binds very easily to 2.3S via formation of two P-S interactions. This gives a stable intermediate Int2 that is 33 kJ mol-1 lower in energy compared to free 2.2S and 2.3S. The intermediate Int2 can subsequently form 4.1S via simple rearrangement of its P-S bonds (TS3, 57 kJ mol-1). Even though all of these transformations involve only low-energy transition states, such pathway is not feasible in practice due to the instability of the monomer 2.2S, in particular with respect to the dimer 2.3S; the conversion of two equivalents of 2.2S to 2.3S has a calculated barrier of only 6 kJ mol-1. Thus, simply heating 2.3Ch is unlikely to lead to the formation of significant amounts of 4.1Ch. However, as the synthesis of 2.3Ch proceeds via 2.2Ch, it is possible that some 4.1Ch forms during the process, as observed experimentally for Ch = Se.

4.2.2 Reactivity of P/Ch Heterocycles with Coinage Metals

Both 2.3Ch and 4.1Ch have a lone pair of electrons on each phosphorus, leaving a functional group for onwards reactivity, especially metal coordination. Our initial approach was to explore their reactivity as ligands to transition metals, firstly with Group 16 metal carbonyls (M = Cr, Mo, W). However, no reaction occurred upon reaction of the

(M(CO)5THF) precursor to either 2.3Ch or 4.1Ch, even after prolonged reaction times and varying reaction conditions. We hypothesized that the steric demand imposed by the m-terphenyl ligands prevented coordination. We then turned to the coinage metals (M = Cu, Ag, Au) because of their linear coordination modes and affinity for soft, phosphine donors (Scheme 4-3).

The addition of 2.3Ch to a metal salt (CuCl or AgOTf) in 3:2 stoichiometry at

31 1 room temperature showed single resonances in the P{ H} NMR spectra (Ch = S: Cu dP

= 89.2, Ag dP = 109.0; Ch = Se: Ag dP = 113.3; Figure 4-6, Figure 4-7). Slow layering of n-pentane onto a CH2Cl2 solution resulted in single crystals suitable for X-ray diffraction, which confirmed the structures to be ring-expansion products from the parent 2.3Ch, with the metal being bound to the phosphorus atoms in tripodal fashion (4.3ChM, Figure 4-8). The mechanism of this transformation was not examined computationally, but it can be easily envisaged that the coordination of a metal fragment to 2.3Ch leads to

82 83 weakening of P-S bonds, which provides a pathway for the formation of 2.2Ch stabilized by the coordinated metal centre.

83 84

Figure 4-5: Reaction coordinate diagram for DMAP-induced (RPS)n ring expansion (phosphorus atoms are coloured orange, sulfur yellow, and nitrogen blue). For simplicity, interconversion of different conformers of 4.1S is omitted (dashed arrow). Gibbs free energies are reported in kJ mol-1 and relative to 2.3S + 4.2S.

84 85

Although the addition of 2.3Ch with MX proceeds cleanly for 4.3SM and

4.3SeAg, the addition of 2.3Se to CuCl resulted in multiple products. However, a major product at dP = 72.3, which has been hypothesized to be 4.3SeCu (based on the similarity of the shift to 4.3SCu), and a minor product at dP = 87.8 (4.1Se), with a relative integration of 60:40, were dominant (Figure 4-7). The addition of more CuCl to the crude reaction mixture in an attempt to convert 4.1Se to 4.3SeCu did not proceed cleanly and resulted in multiple phosphorus containing products (Figure 7-29). Attempts to use a + different Cu source CuOTf[MeCN]4 yielded similar results as reactions performed with CuCl. As an alternative to the coinage metal induced ring expansion of 2.3Ch, the parent 6-membered rings 4.1Ch could be reacted directly with the metal species (CuCl, AgOTf) in 1:1 stoichiometry to yield 4.3ChM that were isolated in yields comparable to those obtained for reactions performed with 2.3Ch. Similar to the reactions with Cu and Ag, the low temperature addition of 2.3S to Me2SAuCl resulted in one major product (dP = 82.5). Leaving a solution at -35 °C for overnight in an attempt to grow single crystals resulted in numerous phosphorus-containing products (Figure 7-30) and repeated attempts to isolate the observed major product were met only with evidence for decomposition.

85 86

Scheme 4-3: Ring expansion of 2.3Ch (Ch = S, Se) using coinage metals (MX = CuCl,

AgOTf) resulting in 4.3ChM. Similar products were obtained from the addition of 4.1Ch to MX. Addition of excess CuCl to either 2.3Ch or 4.1Ch resulted in the formation of 4.4Ch.

31 1 Compounds 4.3SM contain a single resonance in the P{ H} NMR spectrum (Figure 4-6) as well as one set of terphenyl signals in the 1H NMR spectrum, indicating

19 3-fold symmetry amongst the 6-membered ring in solution. The F NMR of 4.3ChAg contained singlets with the chemical shifts reminiscent of a covalent cation-anion interaction (Ch = S: dF = -77.4; Ch = Se: dF = -76.4; c.f. [Bu4N][OTf]: dF = -79.0 (ionic)

28,29 31 1 and MeOTf: dF = -74.1 (covalent)). The P{ H} NMR spectrum of 4.3SAg displayed a broad singlet, likely indicating a dynamic process in solution. In contrast, the selenium

107 1 congener 4.3SeAg showed two sharp doublets with selenium satellites ( Ag: JAg-P =

109 1 1 185.8 Hz; Ag: JAg-P = 213.2 Hz; JSe-P = 151.8 Hz; Figure 4-7).

86 87

Figure 4-6: A stacked plot of 31P{1H} NMR spectra of different sulfur derivatives reported herein: parent 2.3S and ring expansion products 4.1S, 4.3SCu, 4.3SAg, and 4.4S.

The addition of excess CuCl to either 2.3Ch or 4.1Ch in CH2Cl2 resulted in the consumption of the starting material and the appearance of a broad resonance in the

31 1 P{ H} NMR spectrum (Ch = S: dP = 61.3; Ch = Se: dP = 45.9; Figure 4-6, Figure 4-7).

After removing the volatiles in vacuo and washing the crude powder with Et2O, the slow layering of a CH2Cl2 solution with n-pentane at -35 °C resulted in single crystals that confirmed the product to be 4.4Ch (Figure 4-8). Redissolving the single crystals in 31 1 CDCl3 gave the same broad P{ H} NMR resonance, consistent with the crude reaction mixture, and a 1H NMR spectrum that shows one distinct set of m-terphenyl signals indicating a symmetrical core on the NMR timescale. The structures are unexpected, but I a close examination shows insertion of Cu into 2.3Ch with Cu2Ch2 bridging another

P2Ch2Cu. Compound 4.4Ch can be interpreted as containing two bridging sulfur sites, four 3-coordinate sulfides and four CuI centres, where the cage is charge neutral.

87 88

Figure 4-7: A stacked plot of 31P{1H} NMR spectra of different selenium derivatives reported herein: parent 2.3Se and ring expansion products 4.1Se, 4.3SeCu, 4.3SeAg, and 4.4Se.

Recently the synthesis of polynuclear silver complexes stabilized by macrocyclic

(PNPCh)2 ligands and accommodating up to four metal centres have been reported by varying the metal:ligand ratio.7 In this respect, attempts to use a large excess of either

AgOTf or 2.3Ch did not influence the outcome of the reaction, and 4.3ChAg were the only appreciable products formed. The increased steric bulk at phosphorus (terphenyl vs. phenyl) could rationalize why sandwich metal complexes could not be formed. Although 4.1Ch displayed long-term stability when stored under ambient conditions (no decomposition after 2 months at room temperature for either chalcogen derivative) and high thermal stability (4.1S m.p. = 210-211 °C; 4.1Se decomposes at 215 °C), the metal- containing compounds 4.3ChM and 4.4Ch were found to be unstable at room temperature, with decomposition occurring either in the solid state or in solution (Figure

7-31 and Figure 7-32). This inherent instability of 4.3ChM and 4.4Ch precluded our ability to fully characterize these compounds.

88 89

4.2.3 X-ray Crystallography

Images of the solid-state structures are shown in Figure 4-2 and Figure 4-8, metrical parameters listed in Table 4-1 and important X-ray crystallographic details are found in Table 4-2. X-ray diffraction experiments were performed on 4.1Ch and 4.3SM where structure solutions were refined anisotropically and confirmed the ring expansion products. A structure solution of 4.3SeAg was obtained that verified atom connectivity, however the data was of poor quality and could only be refined isotropically (Figure 7-57) and therefore an in-depth analysis of this particular structure is not appropriate.

The solid-state structures of 4.1Ch confirmed the production of 6-membered ring expansion products from the parent P2Ch2 rings, and were observed to have alternating

89 90

P/Ch atoms that adopt a chair conformation with P-S-Pavg = 90.19(7)° and S-P-Savg =

102.15(7)° for 4.1S and P-Se-Pavg = 87.07(7)° and Se-P-Seavg = 102.37(7)° for 4.1Se. The average P-Ch bond length for 4.1S is 2.1393(2) Å, whereas significant lengthening of P- Ch occurred in 4.1Se with an average P-Se bond length of 2.285(2) Å. The 6-membered

P3Ch3 cores in both 4.1Ch were found to be occupationally disordered, with the major component occupying 79% for 4.1S and 78% for 4.1Se (Figure 7-57). The solid-state structures of 4.1Ch resemble those previously reported.23,25,26

The structures of 4.3SM confirm the formation of a ring expansion product from the parent 4-membered ring, and possess the same P3Ch3 cores as 4.1Ch. However, in

4.3SM the metal is bound by each phosphorus atom from within the 6-membered ring.

4.3SCu has P-S-Pavg = 89.32(7)° and S-P-Savg = 104.15(7)°, whereas 4.3SAg has P-S-Pavg

= 91.30(13)° and S-P-Savg = 103.35(13)°. This data is similar to that found for 4.1S. The same is true also for P-Ch bond distances in 4.3SCu, 4.3SAg, and 4.1S: 2.1334(16),

2.128(2) and 2.1393(2) Å, respectively. Compound 4.3SCu has an average P-Cu distance of 2.4603(16) Å that is considerably longer than that found for other tripodal phosphine

30–34 complexes bound to CuCl (2.246-2.359 Å). Compound 4.3SAg has an average P-Ag

90 91

Table 4-1: Selected metrical parameters for compounds reported in Chapter 4.

4.1S 4.1Se 4.3SCu 4.3SAg 4.4S 4.4Se 2.2569(1 P(1)-Ch(1) 2.1459(18) 2.3021(19) 2.1320(17) 2.131(3) 2.1258(10) 6) P(1)-Ch(3) 2.1367(19) 2.273(2) 2.1318(17) 2.125(3) - -

P(2)-Ch(1) 2.1352(17) 2.278(2) 2.1364(17) 2.128(4) - -

P(2)-Ch(2) 2.1556(19) 2.283(2) 2.1305(18) 2.132(3) - -

P(3)-Ch(2) 2.1395(17) 2.286(2) 2.1322(17) 2.141(3) - -

P(3)-Ch(3) 2.1455(18) 2.290(2) 2.1343(17) 2.112(4) - - 2.2757(1 P(1)-Ch(2) - - - - 2.1458(10) 5) 2.3948(1 Ch(1)-Cu(1) (avg) - - - - 2.3098(9) 0) P(1)-C(1) 1.854(4) 2.273(2) 1.850(4) 1.846(10) 1.859(3) 1.867(6)

P(2)-C(25) 1.855(4) 2.278(2) 1.853(4) 1.828(9) - -

P(3)-C(49) 1.860(4) 2.283(2) 1.862(5) 1.825(10) - - 2.2881(1 P(1)-M(1) - - 2.4535(16) 2.689(3) 2.2864(9) 7) P(2)-M(1) - - 2.4179(15) 2.705(3) - -

P(3)-M(1) - - 2.5095(16) 2.746(3) - -

91 92

Ag(1)-O(1) - - - 2.259(8) - -

P(1)-Ch(1)-P(2) 90.31(7) 86.36(8) 89.07(6) 91.10(14) - -

P(2)-Ch(2)-P(3) 90.39(7) 85.77(7) 89.56(6) 91.20(13) - -

P(3)-Ch(3)-P(1) 89.88(7) 89.09(7) 89.34(7) 91.61(13) - -

Ch(1)-P(2)-Ch(2) 102.01(7) 102.94(8) 104.16(7) 103.44(13) - -

Ch(2)-P(3)-Ch(3) 101.83(7) 102.55(8) 103.93(7) 103.74(15) - -

Ch(3)-P(1)-Ch(1) 102.62(7) 101.67(8) 104.37(7) 102.88(13) - -

P(1)-Ch(2)-P(1C) - - - - 92.92(9) 90.55(8)

C(1)-P(1)-Ch(1) 98.41(14) 96.83(15) 106.07(15) 107.0(13) - -

C(1)-P(1)-Ch(3) 105.84(14) 107.54(16) 99.74(16) 101.3(3) - -

C(25)-P(2)-Ch(1) 105.81(14) 106.73(16) 100.14(14) 100.9(3) - -

C(25)-P(2)-Ch(2) 99.02(14) 100.65(17) 106.12(15) 107.7(13) - -

C(49)-P(3)-Ch(2) 106.98(14) 107.23(17) 99.80(14) 100.2(3) - -

C(49)-P(3)-Ch(3) 98.03(14) 96.88(16) 106.15(16) 106.3(3) - - P(1)-M-X - - 135.49(6) 148.9(2) - -

P(2)-M-X - - 136.68(6) 130.3(2) - -

P(3)-M-X - - 133.59(6) 138.1(2) - - Bond lengths and angles are given in Ångstroms (Å) and degrees (°), respectively.

92 93

bond distance of 2.713(3) Å that is considerably longer than that found for one other reported tripodal phosphine-AgOTf complex (2.537 Å)35 and longer than P-Ag bonds in polynuclear silver(I)-phosphine compounds (average P-Ag bond distance of 2.676 Å).7

The structures of 4.4Ch are isomorphous and contain four 4-coordinate phosphorus atoms, four µ3-chalcogen centres, four 3-coordinate copper centres, and two µ2-chalcogen centres. Compounds 4.4Ch sit on a crystallographic centre of symmetry

3 with Ar*PCh2Cu representing the asymmetric unit. 4.4Ch has P-Ch(µ ) bond distances (S: 2.1258(10) Å, Se: 2.2559(16) Å) that are slightly different from P-Ch(µ2) distances (S: 2.1458(10) Å, Se: 2.2757(15) Å), but which all fall in the range of typical P-Ch single bond lengths (the sum of Pyykkö & Atsumi single bond covalent radii for P and S/Se is 36,37 2.14/2.27 Å) and vary only slightly from the parent 2.3Ch (2.3S, P-Savg = 2.1461(2) 24 Å; 2.3Se, P-Seavg = 2.303(2) Å). The P-Cu bond lengths in 4.4Ch are not significantly different (S: 2.2864(9) Å, Se: 2.2881(17) Å), whereas the Ch-Cu distances (S-Cu = 2.3098(9) Å and Se-Cu = 2.3948(10) Å) naturally depend on the identity of the employed chalcogen atom.

4.3 Conclusion

We have shown the successful synthesis of (c-RPCh)3 rings 4.1Ch: the sulfur derivative through ring expansion of the parent 4-membered rings 2.3Ch by the addition of DMAP, and the selenium derivative by cyclocondensation of Ar*PCl2 and Se(TMS)2. The mechanism for the formation of 4.1S was examined computationally, which lead to the identification of a feasible low-energy pathway in which DMAP functions to stabilize the fleeting monomeric RP=S unit. The calculations also suggested that the formation of

4.1Se involves a reaction between RP=Se and (RPSe)2. We have also showed coinage- metal induced ring expansion of 2.3Ch to 4.3ChM by the addition of CuCl or AgOTf, and the formation of 4.4Ch through the addition of excess CuCl to 2.3Ch or 4.1Ch. The 6- membered (c-RPCh)3 rings could undergo direct coordination to coinage metals that also resulted in the formation of 4.3ChM. Compounds 4.1Ch were found to be thermodynamically and thermally more stable than 2.3Ch.

93 94

4.4 Experimental

See Section 7.2 for general experimental and crystallographic procedures

4.4.1 General Experimental

The reagents CuCl, AgOTf, (Me2S)AuCl, and DMAP were purchased from Sigma Aldrich and used as received.

Multiple samples of spectroscopically pure 4.1S were sent for elemental analysis, however we could not obtain chemically sensible data. For this case, we have omitted EA data for this compound.

Note: Metal-coordination reactions were prepared with strict exclusion from ambient light as compounds 4.3ChM and 4.4Ch were found to be light-sensitive. 4.3ChM and 4.4Ch decomposed when left in solution overnight at room temperature or in the solid- state at room temperature for more than 2 days. These challenges precluded obtaining accurate elemental analyses and quaternary carbons in the corresponding 13C{1H} NMR spectra could not be identified. In the case of 4.4Ch, multiple samples were prepared for mass spectroscopic characterization, including the use of different ionization methods, however we could not obtain chemically sensible data.

4.4.2 Synthesis of 4.1S

Solid 4-dimethylaminopyridine (13 mg, 0.11 mmol) was added to a solution of 2.3S (20 mg, 0.027 mmol, 2 mL THF) and the mixture was heated for 16 hours at 50 °C. The volatiles were removed in vacuo and the yellow powder was dissolved in 1 mL CH2Cl2 and slowly concentrated leading to single crystals of 4.1S (yield: 13 mg, 70%). Alternatively, the reaction mixture could be heated at 35 °C for 7 days, which resulted in increased yields (> 90%). mp: 210.3-210.6 °C.

+ ESI-MS: 1151.4 m/z C72H75P3S3Na [M + Na] .

94 95

FT-IR (KBr, cm-1 (ranked relative intensities)): 625 (11), 732 (4), 750 (14), 807 (1), 845 (8), 906 (6), 1016 (5), 1216 (7), 1261 (13), 1374 (12), 1445 (2), 1559 (9), 1610 (10), 1643 (15), 2915 (3).

1 H NMR (C6D6, 400 MHz, δ): 2.02 (s, 36 H; Mes ortho-CH3), 2.27 (s, 18 H; Mes para- 3 3 CH3), 6.77 (d, JH-H = 7.4 Hz, 6H; Ar meta-CH), 6.83 (br s, 12 H; Mes CH), 7.02 (t, JH-H = 7.4 Hz, 3H; Ar para-CH).

13 1 C{ H} NMR (C6D6, 150.8 MHz, δ): 21.5, 21.8, 29.9, 130.1, 130.7, 133.6, 136.9, 137.8, 146.4.

31 1 P{ H} NMR (C6D6, 161.8 MHz, δ): 96.7 (s).

4.4.3 Synthesis of 4.1Se

A solution of Se(TMS)2 (264 mg, 1.17 mmol, 10 mL THF) was added to a solution of

Ar*PCl2 (487 mg, 1.17 mmol, 20 mL THF) portionwise over 3 hours. The volatiles were removed in vacuo, leading to an orange oil. The oil was washed with n-pentane (3 x 10 mL) and insoluble 2.3Se was filtered and collected (yield: 348 mg, 86%). The pentane fractions were combined, concentrated in vacuo, and 1 mL CH2Cl2 was added to the oil, which resulted in the precipitation of a yellow powder when left at -35 °C for 2 hours. X- ray quality single crystals of 4.1Se were grown by slow evaporation of a CH2Cl2 solution of 4.1Se (yield: 49 mg, 10%). mp: 215 °C (decomposes, turned dark brown).

+ ESI-MS: 1271.3 m/z C72H75P3Se3 [M ].

FT-IR (KBr, cm-1 (ranked relative intensities)): 85 (4), 159 (15), 236 (12), 321 (9), 391 (7), 414 (13), 576 (3), 738 (11), 1035 (6), 1302 (2), 1381 (8), 1576 (10), 1611 (5), 2915 (1), 3037 (14).

Elemental Analysis: Calculated 68.08% C, 5.95% H; Found 67.60% C, 6.48% H.

95 96

1 H NMR (C6D6, 600 MHz, δ): 2.08 (s, 36 H; Mes ortho-CH3), 2.30 (s, 18 H; Mes para- 3 3 CH3), 6.78 (d, JH-H = 7.5 Hz, 6H; Ar meta-CH), 6.84 (br s, 12 H; Mes CH), 7.03 (t, JH-H = 7.5 Hz, 3H; Ar para-CH).

13 1 C{ H} NMR (C6D6, 150.8 MHz, δ): 21.6, 21.8, 128.3, 130.1, 130.3, 137.0, 138.0, 146.0.

31 1 1 P{ H} NMR (C6D6, 161.8 MHz, δ): 87.8 (s, JSe-P = 136.6 Hz).

77 1 3 Se NMR (C6D6, 114.4 MHz, δ): 421.0 (ddd, JSe-P = 202.6, 133.3 Hz, JSe-P = 67.1 Hz).

4.4.4 General Methods for Coordination Chemistry with Coinage Metals

A solution of 2.3Ch in CH2Cl2 was added to a suspension of MX in CH2Cl2 and the mixture let stir at room temperature for 1 hour. The volatiles were removed in vacuo and the crude powder was washed with diethyl ether (3 x 5 mL), giving an insoluble powder that was collected.

4.4.5 Synthesis of 4.3SCu

Reagents: 2.3S (150 mg, 0.097 mmol, 4 mL CH2Cl2) and CuCl (12 mg, 0.13 mmol, 4 mL

CH2Cl2); yield: 55 mg, 61%. Single crystals were grown via vapour diffusion using

CH2Cl2/pentane. m.p. (nitrogen sealed capillary): 131 °C (decomposes, turned brown).

+ ESI-MS: 1191.4 m/z C72H75P3S3Cu [M - Cl] .

FT-IR (KBr, cm-1 (ranked relative intensities)): 733(4), 749 (12), 809 (7), 845 (6), 907 (5), 1030 (10), 1374 (8), 1448 (2), 1480 (14), 1562 (9), 1611 (3), 2853 (13), 2915 (1), 2944 (15), 2968 (11).

1 H NMR (CDCl3, 600 MHz, δ): 1.80 (s, 36 H; Mes ortho-CH3), 2.24 (s, 18 H; Mes para- 3 3 CH3), 6.81 (br s, 12 H; Mes CH), 6.90 (d, JH-H = 7.8 Hz, 6H; Ar meta-CH), 7.43 (t, JH-H = 7.8 Hz, 3H; Ar para-CH).

96 97

13 1 C{ H} NMR (CDCl3, 150.8 MHz, δ): 21.4, 21.6, 129.1, 130.8, 131.8, 136.3, 137.5, 146.0.

31 1 P{ H} NMR (CDCl3, 161.8 MHz, δ): 89.2 (s).

4.4.6 Synthesis of 4.3SAg

Reagents: 2.3S (75 mg, 0.097 mmol, 4 mL CH2Cl2) and AgOTf (16 mg, 0.065 mmol, 4 mL CH2Cl2); yield: 45 mg, 50%. Single crystals were grown via vapour diffusion using

CH2Cl2/pentane. m.p. (nitrogen sealed capillary): 141 °C (decomposes, turned dark grey).

+ ESI-MS: 1237.3 m/z C72H75P3S3Ag [M - OTf] .

FT-IR (KBr, cm-1 (ranked relative intensities)): 635 (9), 749 (13), 807 (11), 852 (7), 1027 (4), 1113 (14), 1162 (10), 1182 (15), 1232 (2), 1305 (8), 1377 (6), 1449 (3), 1563 (12), 1610 (5), 2918 (1).

1 H NMR (CDCl3, 400 MHz, δ): 1.82 (s, 36 H; Mes ortho-CH3), 2.25 (s, 18 H; Mes para- 3 3 CH3), 6.87 (br s, 12 H; Mes CH), 6.97 (d, JH-H = 7.6 Hz, 6H; Ar meta-CH), 7.53 (t, JH-H = 7.6 Hz, 3H; Ar para-CH).

13 1 C{ H} NMR (CDCl3, 150.8 MHz, δ): 21.2, 21.5, 128.8, 131.1, 132.8, 136.6, 138.6, 146.2.

19 1 F{ H} NMR (CDCl3, 376.3 MHz, δ): -77.4 (s).

31 1 P{ H} NMR (CDCl3, 161.8 MHz, δ): 109.0 (br s).

4.4.6.1 Synthesis of 4.3SeCu

Reagents: 2.3Se (80 mg, 0.094 mmol, 5 mL CH2Cl2) and CuCl (6 mg, 0.064 mmol, 5 mL

31 1 CH2Cl2). P{ H} NMR spectra of crude reaction mixture showed formation of 4.3SeCu

(δP = 72.3) and free 4.1Se (δP = 87.8). Attempts to separate 4.1Se and 4.3SeCu by

97 98

fractional crystallization were unsuccessful. Attempts to convert 4.1Se to 4.3SeCu resulted in multiple products in the 31P NMR spectrum, including 4.4Se (Figure 7-29).

4.4.7 Synthesis of 4.3SeAg

Reagents: 2.3Se (100 mg, 0.078 mmol, 4 mL CH2Cl2) and AgOTf (13 mg, 0.052 mmol, 4 mL CH2Cl2); yield: 54 mg, 69%. Single crystals were grown via vapour diffusion using

CH2Cl2/pentane. m.p. (nitrogen sealed capillary): 171 °C (decomposes, turned dark grey).

+ ESI-MS: 1379.2 m/z C72H75P3Se3Ag [M - OTf] .

FT-IR (KBr, cm-1 (ranked relative intensities)): 634 (3), 731 (5), 807 (8), 854 (6), 910 (13), 1024 (1), 1164 (10), 1213 (15), 1231 (2), 1303 (12), 1378 (11), 1448 (4), 1562 (14), 1608 (9), 2917 (7).

1 H NMR (CDCl3, 400 MHz, δ): 1.92 (s, 36 H; Mes ortho-CH3), 2.27 (s, 18 H; Mes para- 3 3 CH3), 7.03 (d, JH-H = 7.6 Hz, 6H; Ar meta-CH), 7.15 (s, 12 H; Mes CH), 7.63 (t, JH-H = 7.6 Hz, 3H; Ar para-CH).

13 1 C{ H} NMR (CDCl3, 150.8 MHz, δ): 20.9, 21.4, 129.7, 131.3, 133.7, 135.1, 136.8, 140.5, 146.4.

19 1 F{ H} NMR (CDCl3, 376.3 MHz, δ): -76.4 (s).

31 1 1 1 P{ H} NMR (CDCl3, 161.8 MHz, δ): 113.3 (d, J109Ag-P = 213.2 Hz, J107Ag-P = 185.8 Hz, 1 JSe-P = 151.8 Hz).

4.4.8 Synthesis of 4.4S

Reagents: 2.3S (50 mg, 0.066 mmol, 5 mL CH2Cl2) and CuCl (10 mg, 0.10 mmol, 5 mL

CH2Cl2). yield: 24 mg, 61%. Single crystals were grown via vapour diffusion using

CH2Cl2/pentane. m.p. (nitrogen sealed capillary): 119 °C (decomposes, turned brown).

98 99

FT-IR (KBr, cm-1 (ranked relative intensities)): 728 (3), 748 (12), 807 (5), 850 (2), 908 (6), 1031 (7), 1113 (13), 1182 (11), 1377 (9), 1443 (1), 1561 (10), 1609 (8), 2854 (14), 2914 (4), 2946 (15).

1 H NMR (CDCl3, 400 MHz, δ): 1.92 (s, 36 H; Mes ortho-CH3), 2.12 (s, 18 H; Mes para- 3 3 CH3), 6.78 (br s, 12 H; Mes CH), 6.88 (d, JH-H = 6.4 Hz, 6H; Ar meta-CH), 7.46 (t, JH-H = 6.4 Hz, 3H; Ar para-CH).

13 1 C{ H} NMR (CDCl3, 150.8 MHz, δ): 21.4, 22.2, 130.1, 130.8, 131.7, 132.1, 137.0, 146.7.

31 1 P{ H} NMR (CDCl3, 161.8 MHz, δ): 61.3 (s).

4.4.9 Synthesis of 4.4Se

Reagents: 2.3Se (50 mg, 0.0590 mmol, 7 mL CH2Cl2) and CuCl (10 mg, 0.10 mmol, 7 mL CH2Cl2); yield: 33 mg, 80%. Single crystals were grown via vapour diffusion using

CH2Cl2/pentane. m.p. (nitrogen sealed capillary): 160 °C (decomposes, turned black).

FT-IR (KBr, cm-1 (ranked relative intensities)): 719 (15), 748 (5), 807 (1), 846 (6), 1030 (2), 1090 (14), 1110 (10), 1183 (12), 1263 (7), 1376 (9), 1445 (3), 1562 (11), 1610 (8), 1720 (13), 2964 (4).

1 H NMR (CDCl3, 400 MHz, δ): 1.94 (s, 36 H; Mes ortho-CH3), 2.24 (s, 18 H; Mes para- 3 3 CH3), 6.82 (br s, 12 H; Mes CH), 6.86 (d, JH-H = 7.6 Hz, 6H; Ar meta-CH), 7.45 (t, JH-H = 7.6 Hz, 3H; Ar para-CH).

13 1 C{ H} NMR (CDCl3, 150.8 MHz, δ): 21.5, 22.0, 130.0, 130.8, 131.7, 132.0, 135.8, 136.9, 138.9, 146.5.

31 1 P{ H} NMR (CDCl3, 161.8 MHz, δ): 45.9 (br s).

99 100

4.4.10 Special Considerations for X-ray Crystallography

For compounds 4.1Ch, 4.3SCu, and 4.3SAg, severely disordered n-pentane solvates were present. Several attempts were made to model this disorder but chemically sensible solution could not be obtained. For this reason, the solvates were treated as a diffuse 38 contribution to the overall scattering by SQUEEZE/Platon. Compound 4.3SAg was twinned by merohedry and the twin fraction refined by BASF to 0.2327(2). Compounds

4.1Ch contained disordered P3Ch3 cores, with the major component refining to 79% for 4.1S and 78% for 4.1Se. In both cases, the minor component was refined anisotropically.

100 101

Table 4-2: Summary of X-ray diffraction collection and refinement details for the compounds reported in Chapter 4.

4.1S 4.1Se 4.3SCu 4.3SAg 4.4S 4.4Se CCDC # 1569577 1569578 1569579 1569580 1569581 1569582 Molecular Formula C72H75P3S3 C72H75P3Se3 C72H75P3S3CuCl C73H75AgF3O3P3S4 C96H100Cu4P4S6 C96H100Cu4P4Se6 Formula weight, gmol−1 1129.41 1270.11 1228.48 1386.35 1824.15 2105.55 Crystal system monoclinic triclinic triclinic monoclinic tetragonal tetragonal Space group Cc P-1 P-1 Cc I-4 I-4 T, K 120 110 110 110 110 110 a, Å 13.677(7) 13.071(9) 12.620(5) 16.224(4) 16.696(6) 16.894(3) b, Å 22.215(16) 13.139(9) 13.149(5) 21.380(4) 16.696(6) 16.894(3) c, Å 21.728(11) 22.123(10) 22.085(8) 24.567(4) 18.055(6) 18.282(3) α, ° 90 88.387(9) 89.399(13) 90 90 90 β, ° 93.935(14) 82.616(11) 76.619(12) 103.465(8) 90 90 γ, ° 90 67.19(2) 85.015(15) 90 90 90 V, Å3 6586(7) 3472(4) 3552(2) 8287(3) 5033(4) 5218(2) Z 4 2 2 4 2 2 F(000) 2392 1308 1298 2880 1896 2112 ρ, g cm−1 1.137 1.215 1.151 1.111 1.204 1.340 λ, Å 0.71073 0.71073 0.71073 1.54178 0.71073 1.54178 µ, cm−1 0.225 1.695 0.538 3.801 1.062 4.182 Measured fraction of data 0.999 0.997 0.998 0.996 0.998 0.998 Rmerge 0.0444 0.0911 0.1133 0.0467 0.0479 0.050 R1, wR2 0.0481, 0.1185 0.0634, 0.1458 0.0692, 0.1501 0.0599,0.1566 0.0332, 0.0890 0.0286, 0.0712 R (all data), 1 0.0564, 0.1232 0.1165, 0.1661 0.1513, 0.1823 0.0673, 0.1635 0.0399, 0.0921 0.0312, 0.0728 wR2 (all data) GOF 1.022 1.055 0.996 1.043 1.073 1.045

2 2 2 4 ½ 2 2 2 R1 = Σ( |Fo| - |Fc| ) / Σ Fo, wR2 = [ Σ( w( Fo - Fc ) ) / Σ(w Fo ) ] GOF = [ Σ( w( Fo - Fc ) ) / (No. of reflns. - No. of params. ) ]½

101 102

4.4.11 Computational Details

The ring expansion mechanism involving (RPS)n was investigated using DFT using PBE1PBE hybrid functional39–42 and TZVP basis sets.43 The calculations also employed Grimme’s dispersion correction with Becke-Johnson damping.44,45 The bulky Ar* groups were replaced by the parent terphenyl substituent to speed up the calculations. All computational work was performed using the Gaussian09 program.46

4.5 References (1) Gates, D. P.; Manners, I. J. Chem. Soc., Dalton Trans. 1997, 2525–2532. (2) Power, P. P. Nature 2010, 463, 171–177. (3) Driess, M.; Grützmacher, H. Angew. Chem., Int. Ed. 1996, 35, 828–856. (4) Chivers, T.; Manners, I. Inorganic Rings and Polymers of the p-Block Elements: From Fundamentals to Applications; RSC Publishing: Cambridge, UK, 2009. (5) He, G.; Shynkaruk, O.; Lui, M. W.; Rivard, E. Chem. Rev. 2014, 114, 7815–7880. (6) Chivers, T.; Ritch, J. S.; Robertson, S. D.; Konu, J.; Tuononen, H. M. Acc. Chem. Res. 2010, 43, 1053–1062. (7) Yogendra, S.; Hennersdorf, F.; Weigand, J. J. Inorg. Chem. 2017, 56, 8698–8704. (8) Alajarín, M.; Berná, J.; López-Leonardo, C.; Steed, J. W. Chem. Commun. 2008, 2337. (9) Cherkasov, R. A.; Kutyrev, G. A.; Pudovik, A. N. Tetrahedron 1985, 41, 2567– 2624. (10) Gray, I. P.; Bhattacharyya, P.; Slawin, A. M. Z.; Woollins, J. D. Chem. - Eur. J. 2005, 11, 6221–6227. (11) St. John Foreman, M.; Woollins, J. D. J. Chem. Soc., Dalton Trans. 2000, 1533– 1543. (12) Woollins, J. D. Synlett 2012, 23, 1154–1169. (13) Bhattacharyya, P.; Woollins, J. D. Tetrahedron Lett. 2001, 42, 5949–5951. (14) Baxter, I.; Hill, A. F.; Malget, J. M.; White, A. J. P.; Williams, D. J. Chem. Commun. 1997, 2049–2050. (15) Rothenberger, A.; Shi, W.; Shafaei-Fallah, M. Chem. - Eur. J. 2007, 13, 5974– 5981. (16) Hua, G.; Woollins, J. D. Angew. Chem., Int. Ed. 2009, 48, 1368–1377. (17) Ozturk, T.; Ertas, E.; Mert, O. Chem. Rev. 2007, 107, 5210–5278.

102 103

(18) Kaschel, J.; Schmidt, C. D.; Mumby, M.; Kratzert, D.; Stalke, D.; Werz, D. B. Chem. Commun. 2013, 4403–4405. (19) Liu, H.; Zhang, L.; Guo, Y.; Cheng, C.; Yang, L.; Jiang, L.; Yu, G.; Hu, W.; Liu, Y.; Zhu, D. J. Mater. Chem. C 2013, 1, 3104–3109. (20) Woollins, J. D.; Laitinen, R. Selenium and Tellurium Chemistry: From Small Molecules to Biomolecules and Materials; Springer Berlin Heidelberg, 2011. (21) Henne, F. D.; Watt, F. A.; Schwedtmann, K.; Hennersdorf, F.; Kokoschka, M.; Weigand, J. J. Chem. Commun. 2016, 2023–2026. (22) Lensch, C.; Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1984, 2855–2857. (23) Nordheider, A.; Chivers, T.; Schon, O.; Karaghiosoff, K.; Athukorala Arachchige, K. S.; Slawin, A. M. Z.; Woollins, J. D. Chem. - Eur. J. 2014, 20, 704–712. (24) Graham, C. M. E.; Pritchard, T. E.; Boyle, P. D.; Valjus, J.; Tuononen, H. M.; Ragogna, P. J. Angew. Chem., Int. Ed. 2017, 56, 6236–6240. (25) Baudler, V. M.; Koch, D.; Vakratsas, T.; Tollis, E.; Kipker, K. Z. Anorg. Allg. Chem. 1975, 413, 239–251. (26) Cetinkaya, B.; Hitchcock, P. B.; Lappert, M. F.; Thorne, A. J.; Goldwhite, H. J. Chem. Soc., Chem. Commun. 1982, 691–693. (27) The previously reported energies for the formation of 2.2S from 2.3S were obtained from calculations without dispersion correction, and consequently, differ from the numbers quoted herein. (28) Dutton, J. L.; Tuononen, H. M.; Ragogna, P. J. Angew. Chem., Int. Ed. 2009, 48, 4409–4413. (29) Tolstikova, L. L.; Shainyan, B. A. Russ. J. Org. Chem. 2006, 42, 1068–1074. (30) Knight, S. E.; Bezpalko, M. W.; Foxman, B. M.; Thomas, C. M. Inorganica Chim. Acta 2014, 422, 181–187. (31) Fife, D. J.; Mueh, H. J.; Campana, C. F. Acta Crystallogr. Sect. C Cryst. Struct. Commun. 1993, 49, 1714–1716. (32) Sircoglou, M.; Bontemps, S.; Bouhadir, G.; Nathalie, S.; Miqueu, K.; Gu, W.; Mercy, M.; Chen, C.-H.; Foxman, B. M.; Maron, L.; Ozerov, O. V; Bourissou, D. J. Am. Chem. Soc. 2008, 130, 16729–16738. (33) Wassenaar, J.; Siegler, M. A.; Spek, A. L.; De Bruin, B.; Reek, J. N. H.; Van Vlugt, J. I. Der. Inorg. Chem. 2010, 49, 6495–6508. (34) Kameo, H.; Kawamoto, T.; Bourissou, D.; Sakaki, S.; Nakazawa, H. Organometallics 2015, 34, 1440–1448. (35) Day, G. S.; Pan, B.; Kellenberger, D. L.; Foxman, B. M.; Thomas, C. M. Chem. Commun. 2011, 3634–3636. (36) Pyykkö, P.; Atsumi, M. Chem. - Eur. J. 2009, 15, 186–197. (37) Pyykkö, P.; Atsumi, M. Chem. - Eur. J. 2009, 15, 12770–12779.

103 104

(38) Spek, A. L. Acta Crystallogr. Sect. D Biol. Crystallogr. 2009, 65, 148–155. (39) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158–6170. (40) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997, 78, 1396. (41) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865–3868. (42) Perdew, J. P.; Ernzerhof, M.; Burke, K. J. Chem. Phys. 1996, 105, 9982. (43) Schäfer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829. (44) Grimme, S.; Ehrlich, S.; Goerigk, L. J. Comput. Chem. 2011, 32, 1456–1465. (45) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. J. Chem. Phys. 2010, 15, 154104– 154119. (46) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Marenichm, A. V.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakaji; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A. J.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 09, Revision D.01; Wallingford, CT, USA, 2009.

104 105

Chapter 5

5 Preparation and Characterization of P2BCh Ring Systems (Ch = S, Se) and Their Reactivity with N- Heterocyclic Carbenes 5.1 Introduction

The ability of low-coordinate and low-valent main group compounds to mimic the reactivity of transition metal complexes has pushed research in this area to the top of the inorganic chemistry agenda over the last decade.1 One strategy to isolate these reactive species is through donor stabilization of the low-valent main group centre, offering a doorway to explore the chemistry of these elusive intermediates. A common group of two electron σ-donors that have been used exhaustively over the last decade are N- heterocyclic carbenes. NHCs have stabilized p-block frameworks in many unusual bonding arrangements,2 including some noteworthy examples such as the homodiatomic main group allotropes (Figure 5-1, 5.A & 5.B),3–5 carbon (0) in carbodicarbenes/bent allenes (5.C),6 phosphinidenes (5.D),7–16 phosphaborenes (5.E),17 and phosphinidene sulfides (5.F).18 While NHCs offer thermodynamic stabilization, they are often used in conjunction with bulky substituents that aid in kinetic stability, rendering the low- coordinate and low-valent main group compounds “bottleable” and ready for onwards transformations.

While the interest in small strained inorganic rings is important for exploring the structural chemistry of main group heterocycles, these compounds have routinely acted as precursors to low-coordinate main group species that are otherwise difficult to isolate. The approach of using cyclic structures to gain access to otherwise inaccessible species 19,20 21 18 22 has been successful for P2B2, P2N2, P2S2, and B2N rings that upon thermolysis or addition of a Lewis base lead to degradation of their inorganic cores and formation of compounds with low-coordinate PB, PN, PS, and BN moieties (Figure 5-1, bottom).

105 106

Figure 5-1: Top: Examples of NHC-stabilized main group compounds: homodiatomic main group allotropes (5.A & 5.B), bent allenes (5.C), phosphinidenes (5.D), phosphaborenes (5.E), and phosphinidene sulfides (5.F). Bottom: Examples of base- /thermal-induced degradation of inorganic heterocycles yielding low-coordinate main group compounds (NR2 = TMP).

In recent years, we have been focused on incorporating pnictogen and chalcogen atoms into unique cyclic structures. While small phosphorus heterocycles with symmetrical cores dominate the literature,23 there are fewer examples of phosphorus- chalcogen rings.18,24,25 Moreover, small phosphorus-chalcogen heterocycles that display asymmetry with respect to the 4-membered core are even rarer. These include P-S-P-E (Figure 5-2, 5.G),26–28 P-Ch-P-C (Ch = S, Se, 5.H),29–31 P-S-C-S (5.I),32 and P-S-C-C structures (5.J),33 amongst others.34–39 Small ring cores that contain asymmetry in the presence of a P-P bond are by far the rarest, with published examples limited to only three species: P-P-C-N (5.K),40 P-P-C-O (5.L),37 and P-P-Si-N (5.M).41 In this context, we report the synthesis of small main group heterocycles containing a P2BCh core

(5.3Ch; Ch = S, Se) that possess a P–P bond. Compounds 5.3Ch were prepared through the combination of monomeric phosphinidene chalcogenides (2.2Ch) and

106 107

phosphaborenes (Mes*P=BNR2, 5.2). One could consider the formation of a P-P bond an expected outcome with the phosphorus in 2.2Ch as the electrophilic site and the phosphorus in 5.2 the nucleophilic one. However, the formation of a P-P bond is counterintuitive when considering the steric demand imposed by both phosphorus atoms as well as the electrophilicity of the boron atom in 5.2. In agreement with these notions, DFT calculations showed that the reaction begins with a P→B attack after which the resulting intermediate can follow multiple pathways with the most favourable ones lead to the formation of a P-P bond. The synthesized P2BCh main group rings can be monomerized at elevated temperatures in the presence of NHCs, reforming 2.2Ch and 5.2 as well as giving access to NHC-stabilized phosphinidenes.20

5.2 Results and Discussion

The 1:1 stoichiometric reaction of 2.3Ch and 5.1 in toluene at 80 °C resulted in the consumption of both starting materials after 2 hours and the appearance of two doublets in the 31P{1H} NMR spectrum (Scheme 5-1). Removing the volatiles in vacuo and slowly concentrating a n-pentane solution of the crude reaction mixture produced single crystals suitable for X-ray diffraction, which confirmed the products as 5.3Ch, four-membered heterocycles formed from the incorporation of monomeric units from

107 108

2.3Ch and 5.1 (Figure 5-3). The 31P{1H} NMR spectra of the redissolved single crystals of 5.3Ch displayed the same doublets as observed in the crude reaction mixture (5.3S: δP 1 1 1 = -29.8; -13.6, JP-P = 184.0 Hz; 5.3Se: δP = -33.5, JSe-P = 91.8 Hz, JP-P = 181.7 Hz; -

1 31.5, JP-P = 181.7 Hz), with both doublets shifted upfield from 2.3Ch and downfield from 5.1 (Figure 5-4). The 11B NMR spectra of both 5.3Ch displayed similar chemical shifts (5.3S: δB = 44.2; 5.3Se: δB = 42.3), as one would expect, and are indicative of three-coordinate boron centers. The solid-state structures of 5.3Ch confirmed the presence of P-P-B-Ch cores in butterfly conformation with P-P bond lengths of 2.2371(9) and 2.243(1) Å, and P-B bonds of 1.955(2) and 1.957(2) Å for 5.3S and 5.3Se, respectively (Figure 5-3). The B-Ch bond lengths in 5.3S and 5.3Se are 1.850(3) and 1.985(2) Å, respectively, whereas the corresponding P-Ch bond distances are 2.1301(8) and 2.267(1) Å.

Scheme 5-1: Synthesis of mixed main group rings 5.3Ch by combining monomeric phosphinidene chalcogenides (2.2Ch) and phosphaborene (5.2) units (NR2 = TMP).

The structures of 5.3Ch revealed the formation of a P-P bond, which is counterintuitive based on the steric demand at both phosphorus atoms and the electronic predisposition to form a P-B bond. In order to ascertain the mechanism of forming 5.3Ch, we turned to the aid of DFT calculations (Figure 5-5). For reasons of computational efficiency, the parent ligands Ar (m-diphenylbenzene) and Mes (2,4,6- trimethylphenyl) were used in the calculations and the formation of 5.3Ch was assumed to involve only monomeric ArP=S and MesP=B−NMe2 units.

108 109

Figure 5-3: Solid-state structures of 5.3S (left) and 5.3Se (right) with thermal ellipsoids at 50% probability. Hydrogen atoms and mesityl rings from terphenyl groups are omitted for clarity. Selected bond lengths [Å] and angles [°]. 5.3S: C(1)-P(1) 1.875(3), P(1)-P(2) 2.2371(9), P(1)-B(1) 1.955(2), P(2)-C(19) 1.862(2), P(2)-S(1) 2.1301(8), S(1)-B(1) 1.850(3), B(1)-N(1) 1.405(3), C(1)-P(1)-P(2) 118.15(8), C(1)-P(1)-B(1) 113.8(1), B(1)- P(1)-P(2) 83.50(8), P(1)-P(2)-S(1) 81.38(3), P(1)-P(2)-C(19) 110.69(8), P(2)-S(1)-B(1) 89.08(9), S(1)-B(1)-P(1) 96.9(1), S(1)-B(1)-N(1) 124.1(2), N(1)-B(1)-P(1) 138.7(2), C(19)-P(2)-S(1) 106.82(8). 5.3Se: C(1)-P(1) 1.885(2), P(1)-P(2) 2.243(1), P(1)-B(1) 1.957(2), P(2)-C(19) 1.861(2), P(2)-Se(1) 2.267(1), Se(1)-B(1) 1.985(2), B(1)-N(1) 1.414(2), C(1)-P(1)-P(2) 117.05(6), C(1)-P(1)-B(1) 113.03(9), P(1)-P(2)-C(19) 111.47(6), P(1)-P(2)-Se(1) 81.66(2), P(1)-B(1)-Se(1) 96.84(9), C(19)-P(2)-Se(1) 107.36(6), P(2)-Se(1)-B(1) 85.19(6), Se(1)-B(1)-P(1) 96.84(9), Se(1)-B(1)-N(1) 124.1(1), N(1)-B(1)-P(1) 138.6(2), B(1)-P(1)-P(2) 86.49(6).

The addition of ArP=S to MesP=B−NMe2 was found to proceed via transition state TS1 with a barrier of only 6 kJ mol–1 (38 kJ mol–1 without dispersion correction). The transition state shows an initial P→B attack that subsequently leads to the formation of the intermediate INT1 with a cyclic P−P−B core. This is understandable as the phosphorus atom in ArP=S is both nucleophilic and electrophilic, whereas the boron and

109 110

phosphorus atoms in MesP=B−NMe2 are electrophilic and nucleophilic, respectively. The optimized structure of INT1 shows that the Mes and Ar groups reside on opposite side of the plane of the three-membered ring, with the sulfur atom located on the same side of the plane as the Mes ligand.

31 1 Figure 5-4: A stacked plot of P{ H} NMR spectra of the P2BCh derivatives 5.3S, 5.3Se, and 5.7Se.

From the intermediate INT1, a one-step pathway to 5.3S was found that proceeds via TS2 with a barrier of 67(71) kJ mol–1. The reaction involves a straightforward insertion of the dangling sulfur atom into the P–B bond, forming the experimentally observed 2,3-isomer of 5.3S. Interestingly, no simple one-step pathway connecting INT1 to the 2,4-isomer of 5.3S was found. Instead, the intermediate three-membered ring first changes conformation from anti to syn via TS2b with a barrier of 53(56) kJ mol–1. The resulting intermediate INT2 can then undergo an insertion of the sulfur atom into the P−P bond via TS3 with a barrier of 111(89) kJ mol–1, giving INT3 that still needs to undergo an additional low-energy syn to anti conformation flip to form 2,4-5.3S via TS4. The calculations show that, despite the lower steric demand, 2,4-5.3S is 62(65) kJ mol–1

110 111 higher in energy than 2,3-5.3S, presumably due to the favourable S–B bond in 2,3-5.3S. This interaction also lowers the energy of the transition state TS2, bringing it significantly below that of TS3, the highest transition state on the path leading to 2,4- 5.3S. Furthermore, while INT2 is an intermediate en route to 2,4-5.3S, it can also form 2,3-5.3S via transition state TS3b that is 48(36) kJ mol–1 lower in energy than TS3. Consequently, the formation of 2,4-5.3S seems highly unlikely when considering the thermodynamic and kinetic favourability of the two competing pathways leading to 2,3- 5.3S.

Upon making the unique mixed main group rings 5.3Ch, we opted to explore their reactivity with strong Lewis bases, namely NHCs. Monitoring the addition of NHCiPr to 5.3Ch by 31P{1H} NMR spectroscopy revealed no reaction, even after heating the mixture at 80 °C for 3 days (Scheme 5-2). We hypothesized that the bulky aryl groups on phosphorus in combination with the sterically encumbered NHC resulted in “molecular frustration” and turned to an NHC with a lower steric demand.

Heating a solution of NHCMe and 5.3Ch at 80 °C for 16 hours resulted in consumption of the starting material and appearance of two phosphorus-containing 31 1 products in the P{ H} NMR spectra: two singlets at δP = 30.0 and 151.4 for Ch = S, Me corresponding to 2.4S and 5.4, and two singlets at δP = -76.7 and 151.4 for Ch = Se, corresponding to 5.4 and 5.5Me (Figure 5-6). The NHC-stabilized phosphaborene 5.4 has been reported as the product from the reaction of 5.1 with NHCMe and was therefore easily identified.20 Similarly, a derivative of an NHC-stabilized phosphinidene sulfide has also been reported by us, with a 31P{1H} NMR chemical shift similar to that observed for 2.4SMe.18 While 2.4SMe is stable and can be observed by NMR spectroscopy in crude reaction mixtures, there is no direct evidence of the analogous selenide 2.4SeMe (Figure 5-6). Instead, we observed the formation of an NHC-stablized phosphinidene 5.5Me and selenourea 5.6Me. The inherently weak “P=Se” moiety of 2.2Se likely makes 2.4SeMe an unstable intermediate that easily forms 5.5Me and 5.6Me in presence of excess NHC (Scheme 5-2).

111 112

Figure 5-5: Reaction coordinate diagram for the formation of 2,3 and 2,4 isomers of 5.3S. Gibbs free energies are reported in kJ mol–1 and relative to ArP=S + MesP=B-NMe2.

112 113

Scheme 5-2: Accessing low-coordinate phosphorus compounds from reacting 5.3S (top) Me 43 and 5.3Se (bottom) with NHC (NR2 = TMP).

Attempting the Lewis acid stabilization of low-coordinate phosphorus species, the addition of AuCl(THT) to 5.3S resulted in no reaction even after a prolonged period. However, the addition of one stoichiometric equivalent of AuCl(THT) to 5.3Se resulted

113 114 in full consumption of the starting material and the appearance of two new doublets in the 31 1 P{ H} NMR spectrum that were shifted downfield from the starting material (δP = -8.4, 1 1 1 JSe-P = 169.9 Hz, JP-P = 246.4 Hz; 10.3, JP-P = 246.4 Hz; Figure 5-4). Removing the volatiles in vacuo and leaving a concentrated solution in MeCN at -35 °C overnight resulted in single crystals suitable for X-ray diffraction that confirmed the product to be 5.7Se in which AuCl is coordinated by the P-Se phosphorus site (Scheme 5-3). The 31P{1H} NMR spectrum of the redissolved single crystals displayed the same doublets as observed in the crude reaction mixture while a broad singlet was noted in the 11B NMR spectrum (dB = 43.8). The solid-state structure revealed that the P2BSe core had remained intact retaining its butterfly conformation with relevant bond distances consistent with the parent structure 5.3Se (Figure 5-7). Compound 5.7Se is unstable if left in solution, giving a black precipitate along with a wide range of decomposition products, as indicated by 31P{1H} NMR spectroscopy. This instability is a marked departure from that of the parent ring 5.3Se that was found to be indefinitely stable, even at higher temperatures.

Scheme 5-3: Addition of Lewis acidic AuCl(THT) to 5.3Se, resulting in metal coordination.

Upon observing that the addition of an NHC to 5.3Ch resulted in dissociation of the rings and formation of base-stabilized low-coordinate phosphorus compounds 2.4SMe and 5.5Me, we then wondered if similar reactivity could also be observed with the parent P-Ch rings, 2.3Ch. Consequently, the 4:1 addition of NHCR (R = Me, iPr) to a THF solution of 2.3Se at room temperature resulted in the consumption of starting material

31 1 and the appearance of a singlet in the P{ H} NMR spectrum (dP = -76.7, R = Me; dP = - 75.0, R = iPr). Removing the volatiles in vacuo, dissolving the crude reaction mixture in a minimal amount of n-pentane, and leaving the solutions overnight at -35 °C resulted in single crystals suitable for X-ray diffraction. A subsequent structure analysis confirmed

114 115 the products as NHC-stabilized phosphinidenes 5.5Me and 5.5iPr (Figure 5-7), that is, similar species that were obtained via addition of NHCMe to 5.3Se.

Figure 5-7: Solid state structures of 5.5iPr (top left), 5.5Me (top right), 2.4SMe (bottom left), and 5.7Se (bottom right) with thermal ellipsoids drawn at 50% probability. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [°]. 5.5iPr: P(1)-C(1) 1.843(3), P(1)-C(25) 1.799(3), C(1)-P(1)-C(25) 101.53(11). 5.5Me: P(1)-C(1) 1.832(4), P(1)-C(25) 1.786(4), C(1)-P(1)-C(25) 99.10(17). 2.4SMe: P(1)-C(1) 1.867(3), P(1)-C(25) 1.852(3), P(1)-S(1) 2.0186(15), C(1)-P(1)-C(25) 97.01(14), C(1)-P(1)-S(1) 111.62(11), C(25)-P(1)-S(1) 100.48(12). 5.7Se: C(1)-P(2) 1.840(6), P(2)-P(1) 2.201(2), P(1)-C(25) 1.863(6), P(1)-B(1) 1.952(7), B(1)-N(1) 1.393(8), B(1)-Se(1) 2.007(7), P(2)- Se(1) 2.2492(18), P(2)-Au(1) 2.2344(17), Au(1)-Cl(1) 2.2978(17), C(1)-P(2)- Au(1)114.09(19), C(1)-P(2)-P(1)106.43(19), C(1)-P(2)-Se(1) 114.8(2), P(2)-P(1)-C(25) 112.66(18), P(2)-P(1)-B(1) 89.0(2), P(1)-B(1)-N(1) 137.1(5), P(1)-B(1)-Se(1) 96.7(3), B(1)-Se(1)-P(2) 86.3(2), Se(1)-P(2)-P(1) 83.33(7).

115 116

The 31P{1H} NMR spectra of 5.5R displayed a single resonance, significantly upfield from the parent 2.3Se (DdP = 98), indicating the presence of an electron-rich phosphorus site.44 The 1H NMR spectra of 5.5R displayed a symmetric environment at phosphorus, indicated by one set of signals for the ortho-CH3 and para-CH3 groups on the terphenyl ligand, integrating to 12 and 6 hydrogen atoms, respectively, along with one set of signals for the NHC.45,46 The solid-state structures of 5.5R (Figure 5-7) displayed typical features for NHC-stabilized phosphinidenes, with a bent geometry at phosphorus (CAr-P-CNHC = 101.53(1) and 99.10(17)° for 5.5iPr and 5.5Me, respectively) and a short P– CNHC bond (1.799(3) and 1.786(4) Å for 5.5iPr and 5.5Me, respectively). In addition to the formation of 5.5R, selenoureas 5.6R were concomitantly formed during the reaction and their identities confirmed using X-ray diffraction and NMR spectroscopy.47

While we have already reported that the reaction of 2.3S and NHCiPr yields the NHC-stabilized phosphinidene sulfide 2.4SiPr,18 we repeated the same chemistry with the more sterically accommodating NHCMe (Scheme 5-4). In doing so, the 2:1 addition of NHCMe to 2.3S at -50 °C resulted in the consumption of starting material and appearance

31 1 of one signal in the crude P{ H} NMR spectrum (dP = 30.0) with a similar chemical

iPr shift as found for 2.4S (dP = 29.0). After removing the volatiles in vacuo, dissolving the crude reaction mixture in toluene, and slowly layering the solution with diethyl ether at - 35 °C, single crystals suitable for X-ray diffraction were obtained that confirmed the product to be 2.4SMe (Figure 5-7). The metrical parameters of 2.4SMe revealed two essentially identical P–C bond lengths (P–CNHC = 1.852(3) Å and P–CAr = 1.867(3) Å) and a short P–S bond of 2.0186(15) Å, that is, bond parameters that are similar to those in 2.4SiPr. The NHC-adduct 2.4SMe has a strikingly similar structure to the known methylenethioxophosphoranes (5.8, Scheme 5-4),48 however 2.4SMe contains a longer P– S bond (2.0186(15) Å vs. 1.928 Å)49 and a significantly longer P–C bond (P–CNHC in 2.4SMe 1.852(3) Å vs. 1.656 Å).49 The P–CNHC bond length is longer than expected for P=C,50–52 thus describing 2.4SMe as containing a multiply bound phosphorus atom is not appropriate.

The recently reported 6-membered phosphorus-chalcogen rings 4.1Ch53 (Scheme

5-4, bottom) contain the same general formula as 2.3Ch (e.g. (c-RPCh)n) and have long

116 117 been considered as precursors to phosphinidene chalcogenides,54 although no experimental evidence has supported this claim. We utilized the same approach employed for 2.3Ch and 5.3Ch, and attempted the degradation of these larger P-Ch heterocycles into base-stabilized phosphinidene chalcogenides using NHCs. Similar to 5.3Ch, the addition of NHCiPr to 4.1Ch at room temperature or elevated temperatures resulted in no reaction, even after prolonged reaction times. The use of a more sterically accommodating carbene NHCMe in 4:1 (Ch = S) or 6:1 (Ch = Se) stoichiometry, however, resulted in the formation of 2.4SMe (Ch = S) or 5.5Me and 5.6Me (Ch = Se) even at room temperature, indicating that strong sterically accommodating donors can indeed degrade these larger P-Ch heterocycles into their base-stabilized monomers.

Upon obtaining NHC-stabilized phosphinidenes 5.5R via multiple routes, we opted to test their onwards reactivity towards Lewis acids (Scheme 5-5). Although reports of such reactivity studies have been previously published,10–16 the coordination chemistry of NHC-stabilized phosphinidenes containing bulky terphenyl groups is currently unknown. The addition of 5.5iPr to BCF in THF resulted in immediate colour change from yellow to colourless. After concentrating the crude reaction mixture, precipitation with n-pentane gave an off-white powder that shows a singlet in the 31P{1H}

117 118

11 NMR spectrum (dP = -24.7), a singlet in the B NMR spectrum (dB = -2.9), indicating a four-coordinate boron centre, and three resonances in the 19F NMR spectrum, consistent with the ortho-, meta-, and para-fluorine resonances for tris(pentafluorophenyl)borane. An X-ray diffraction experiment on single crystals grown via THF/pentane vapour diffusion confirmed the structure of 5.9, indicating that a controlled ring-opening of THF iPr by 5.5 had occurred in the presence of the strongly Lewis acidic B(C6F5)3 (Figure 5-8). The ring-opened product 5.9 had a B–O bond length of 1.495(5) Å and two similar P–C bonds (CAr–P = 1.843(4) Å and CNHC–P = 1.839(4) Å), both of which are comparable to corresponding bond distances in 5.5iPr.

Direct coordination of a Lewis acidic transition metal was performed by adding two stoichiometric equivalents of AuCl(THT) to a solution of 5.5iPr (Scheme 5-5). After stirring for one hour at room temperature, the starting material was fully consumed and

31 1 one major product was observed in the P{ H} NMR spectrum (dP = -41.9). After removing the volatiles of the crude reaction mixture in vacuo, a CH2Cl2/pentane vapour diffusion of the crude reaction mixture yielded X-ray quality single crystals of 5.10. The resulting structure solution confirmed the product to be 5.10, where the phosphorus atom was bound to two AuCl fragments (Figure 5-8) with a coordination environment reminiscent of other NHC-stabilized phosphinidene compounds with a tetrahedral geometry at phosphorus.14,55 Significant lengthening of the CNHC–P bond from 1.799(3) Å in 5.5iPr to 1.856(4) Å in 5.10 is observed, which is likely induced by an increase in steric

118 119 interactions along with complete loss of backbonding with the inclusion of two AuCl units.

Figure 5-8: Solid state structures of 5.9 (left) and 5.10 (right) with thermal ellipsoids drawn at 50% probability. Mesityl groups and fluorine atoms from 5.9, and hydrogen atoms from both 5.9 and 5.10 have been omitted for clarity. Selected bond lengths [Å] and angles [°]: 5.9: P(1)-C(1) 1.843(4), P(1)-C(25) 1.839(4), P(1)-C(36), O(1)-B(1) 1.459(5), C(1)-P(1)-C(25) 100.59(16), C(1)-P(1)-C(36) 109.40(17), C(25)-P(1)-C(36) 99.36(17). 5.10: P(1)-C(1) 1.849(4), P(1)-C(25) 1.856(4), P(1)-Au(1) 2.2452(13), P(1)- Au(2) 2.2451(13), C(1)-P(1)-C(25) 102.64(18), C(1)-P(1)-Au(1) 115.96(14), C(1)-P(1)- Au(2) 111.54(13), C(25)-P(1)-Au(1) 103.71(14), C(15)-P(1)-Au(2) 111.54(13), Au(1)- P(1)-Au(2) 108.81(4).

5.3 Conclusion

In summary, we have demonstrated the synthesis of unique inorganic heterocycles containing group 13, 15, and 16 elements as 4-membered P2BCh rings (5.3Ch). The synthesis of 5.3Ch was accomplished via reaction between two highly reactive monomers: phosphinidene chalcogenide and phosphaborene. The P2BCh rings were found to be a source for low-coordinate phosphorus products, phosphinidene sulfides 2.4S and phosphinidenes 5.5R, from their reaction with NHCs at elevated temperatures.

Similar reactivity was also observed for the 4- and 6-membered (c-RPCh)n rings 2.3Ch and 4.1Ch. The coordination chemistry of NHC-stabilized phosphinidenes 5.5iPr was also explored, demonstrating their ability to ring-open THF and coordinate to Lewis acids via both lone pairs at phosphorus. Consequently, the controlled reactivity of monomeric units

119 120

(2.2Ch and 5.2), accessed from their parent dimers 2.3Ch and 5.1, has led to unique p- block rings that have eluded characterization until now. This method of forming novel heterocycles should allow for the synthesis of more asymmetric rings as well as the production of new low-coordinate main group compounds with possibly unforeseen structures and reactivity.

5.4 Experimental Section

5.4.1 General Experimental

AuCl(THT) was made following literature methods.56 Trispentafluorophenylborane was purchased from Strem Chemicals and sublimed overnight prior to use (50 °C, 0.01 mmHg, -10 °C cold finger).

5.4.2 General Method for the Synthesis of 5.3Ch

A mixture of 2.3Ch and 5.1 in benzene was heated at 80 °C for 2 hours after which the crude 31P{1H} NMR spectrum showed complete consumption of starting materials and appearance of two doublets. The volatiles were removed in vacuo and the crude reaction mixture was redissolved using 3 mL n-pentane and placed at -35 °C for 1 hour, leading to precipitation of a yellow powder.

5.4.3 Synthesis of 5.3S

Reagents: 2.3S (130 mg, 0.173 mmol) and 5.1 (148 mg, 0.173 mmol) in 5 mL benzene. Yield: 157 mg (57%). Single crystals suitable for X-ray diffraction were obtained by slowly concentrating an n-pentane solution via vapour diffusion. m.p. (argon sealed capillary): 254.0-254.3 °C.

+ ESI-MS: 803.49 m/z C51H72BNP2S [M] .

Elemental Analysis: Calculated 76.19% C, 9.03% H, 1.74% N; Found 76.32% C, 9.15% H, 1.80% N.

1 8 H NMR (THF-d , 500 MHz, δ): 0.92 (s, 6H; TMP C(CH3)2), 1.12 (s, 9H; Mes* ortho-

C(CH3)3), 1.21 (s, 6H; TMP C(CH3)2), 1.29 (s, 9H; Mes* para-C(CH3)3), 1.29-1.36 (m,

120 121

2H; TMP CH), 1.46-1.53 (m, 4H; TMP CH), 1.55 (s, 9H; Mes* ortho-C(CH3)3), 1.70 (br s, 6H; Mes ortho-CH3), 2.22 (s, 6H; Mes para-CH3), 2.28 (br s, 6H; Mes ortho-CH3), 3 6.64 (s, 2H; Mes CH), 6.82 (s, 2H; Mes CH), 6.89 (br d, JH-H = 7.5 Hz, 2H; Ar* meta-

3 CH), 7.32 (br s, 2H; Mes* CH), 7.37 (t, JH-H = 7.5 Hz, 1H; Ar* para-H).

13C{1H} NMR (THF-d8, 125 MHz, δ): 16.2, 21.0, 21.8, 22.9, 31.4, 33.5, 35.0 (br s), 35.2 (br s), 35.3, 39.9, 40.4, 40.7, 56.8, 122.8 (br s), 125.3, 128.2 (br s), 130.3, 130.7 (br s), 1 2 134.4 (br s), 136.6, 137.4 (br s), 139.6, 148.8 (br d, JP-C = 19 Hz), 150.6, 156.7 (d, JP-C = 30 Hz), 158.2.

11B NMR (THF-d8, 160 MHz, δ) 44.2 (br s).

31 1 8 1 1 P{ H} NMR (THF-d , 160 MHz, δ) -13.6 (d, JP-P = 184 Hz; P-P-S), -29.8 (d, JP-P = 184 Hz; P-P-B).

5.4.4 Synthesis of 5.3Se

Reagents: 2.3Se (31 mg, 0.037 mmol) and 5.1 (32 mg, 0.037 mmol) in 3 mL of benzene. Yield: 26 mg (84%). Single crystals suitable for X-ray diffraction were obtained by slowly concentrating an n-pentane solution via vapour diffusion. m.p. (nitrogen sealed capillary): 210.8-211.5 °C.

+ ESI-MS: 874.4 m/z C51H72BNP2SeNa [M + Na] .

Elemental Analysis: Calculated 71.99% C, 8.53% H, 1.65% N; Found 70.90% C, 9.09% H, 1.74% N.

1 H NMR (C6D6, 600 MHz, δ): 1.08 (s, 6H; TMP C(CH3)2), 1.29 (br s, 14H), 1.36 (s,

16H), 1.74 (s, 9H; Mes* ortho-C(CH3)3), 1.84 (s, 6H; Mes ortho-CH3), 2.29 (s, 6H; Mes 3 ortho-CH3), 2.54 (s, 6H; Mes para-CH3), 6.76 (s, 2H; Mes CH), 6.88 (d, JH-H = 7.6 Hz, 3 2H; Ar* meta-H), 6.95 (s, 2H; Mes CH), 7.09 (t, JH-H = 7.6 Hz, 1H; Ar* para-H), 7.49 (br s, 1H; Mes* CH), 7.54 (br s, 1H; ; Mes* CH).

121 122

13 1 C{ H} NMR (C6D6, 150.1 MHz, δ): 14.3, 15.8, 21.2, 21.9, 22.7, 23.2, 31.4, 32.0, 33.6, 34.9, 35.0, 35.4, 39.8, 40.0, 40.6, 57.4, 122.6 (br), 126.1, 128.4, 129.8, 130.0, 136.3, 136.9, 137.0, 137.2, 137.5, 139.7, 148.6, 148.7, 148.8, 150.1, 155.1, 155.2, 155.4, 157.8.

11 B NMR (CDCl3, 192.5 MHz, δ): 42.3 (br s).

31 1 1 1 P{ H} NMR (CDCl3, 242.3 MHz, δ): -33.5 (d, JP-P = 181.7 Hz, JSe-P = 91.8 Hz, 1P; P- 1 P-Se), -31.5 (d, JP-P = 181.7 Hz, 1P; P-P-B).

5.4.5 Synthesis of 2.4SMe

Me A solution of NHC (21 mg, 0.17) in 3 mL THF was added to a stirred solution of 2.3S (65 mg, 0.086) in 4 mL THF at -50 °C and let stir for 30 minutes before letting warm to room temperature. The volatiles were removed in vacuo, the crude powder was washed with cold n-pentane (3 x 5 mL), and the resulting yellow solid was collected. Yield: 52 mg (60%).

m.p. (nitrogen sealed capillary): 218.1-219.0 °C.

+ + ESI-MS: 1023.5 m/z C62H74P2N4S2 [(2 x M) + Na] , 523.2 m/z C31H37PN2S [M + Na] , + 469.3 m/z C31H37PN2 [M - S] .

1 H NMR (C6D6, 400 MHz, δ): 1.07 (s, 6H; NHC CH3), 2.12 (s, 6H; Mes ortho-CH3),

2.18 (s, 6H; Mes ortho-CH3), 2.43 (s, 6H; Mes para-CH3), 3.02 (br s, 6H; N-CH3), 6.69 3 (br s, 2H; Mes CH), 6.81 (br s, 2H; Mes CH), 6.89 (d, JH-H = 7.6 Hz, 2H; Ar* meta-CH), 3 7.11 (t, JH-H = 7.6 Hz, 1H; Ar* para-CH).

13 1 C{ H} NMR (C6D6, 100.5 MHz, δ): 7.7, 21.2, 21.5, 21.6, 21.9, 22.0, 130.1, 135.4, 136.2, 136.4, 140.4, 145.0 (br).

31 1 P{ H} NMR (C6D6, 161.8 MHz, δ): 30.0 (s).

5.4.6 General Method for the Synthesis of 5.5R

A solution of NHCR in THF was added to a solution of 2.3Se or 4.1Se in THF. The mixture was left to stir for 15 minutes after which the initial orange solution had changed

122 123 to dark red. The volatiles were removed in vacuo and the crude reaction mixture was dissolved in 5 mL n-pentane and left at -35 °C overnight, giving orange crystals.

5.4.7 Synthesis of 5.5iPr

Reagents: NHCiPr (38 mg, 0.21 mmol) in 3 mL THF and 2.3Se (45 mg, 0.053 mmol) in 3 mL THF. Yield: 37 mg (66%). Single crystals suitable for X-ray diffraction were obtained by leaving a concentrated n-pentane solution at -35 °C overnight. m.p. (nitrogen sealed capillary): 198.3-198.9 °C (orange powder turns red-orange at 155 °C).

+ ESI-MS: 525.3 m/z C35H45PN2 [M ].

Elemental Analysis: Calculated 80.11% C, 8.64% H, 5.34% N; Found 78.55% C, 8.65% H, 5.29% N.

1 3 H NMR (C6D6, 400 MHz, δ): 0.87 (d, JH-H = 6.8 Hz, 12H; iPr CH3), 1.54 (s, 6H; NHC 3 CH3), 2.22 (s, 6H; Mes para-CH3), 2.41 (s, 12H; Mes ortho-CH3), 5.24 (sept, JH-H = 7.2 3 Hz, 1H; iPr CH), 5.26 (sept, JH-H = 7.2 Hz, 1H; iPr CH), 6.87 (br s, 4H; Mes CH), 7.08 (overlapping multiplet, 3H).

13 1 C{ H} NMR (C6D6, 150.8 MHz, δ): 10.5 (br s), 21.5 (m), 52.3 (m), 123.4, 124.0, 129.2, 1 1 135.0, 136.1, 142.7, 147.3 (d, JP-C = 54.9 Hz), 149.3, 149.7, 171.0 (d, JP-C = 90.5 Hz).

31 1 P{ H} NMR (C6D6, 161.8 MHz, δ): -75.0 (s).

5.4.8 Synthesis of 5.5Me

Reagents: NHCMe (36 mg, 0.28 mmol) in 3 mL THF and 4.1Se (60 mg, 0.047 mmol) in 3 mL THF. Yield: 30 mg (44%). Single crystals suitable for X-ray diffraction were obtained by leaving a concentrated Et2O solution at -35 °C overnight. m.p. (nitrogen sealed capillary): 241.6-242.9 °C.

+ ESI-MS: 469.3 m/z C31H37PN2 [M ].

123 124

Elemental Analysis: Calculated 79.45% C, 7.96% H, 5.98% N; Found 78.38% C, 7.63% H, 6.04% N.

1 H NMR (C6D6, 400 MHz, δ): 1.22 (s, 6H; NHC CH3), 2.17 (s, 6H; Mes para-CH3), 2.42

(s, 12H; Mes ortho-CH3), 2.84 (s, 6H; NHC N-CH3), 6.79 (s, 4H; Mes CH), 7.03 (overlapping multiplet, 3H).

13 1 C{ H} NMR (C6D6, 150.8, MHz, δ): 8.5, 21.1, 21.2, 21.3, 33.8, 33.9, 122.0, 122.1, 1 1 122.2, 128.7, 134.4, 135.9, 142.4 (d, JP-C = 4.8 Hz), 144.4 (d, JP-C = 20.1 Hz).

31 1 P{ H} NMR (C6D6, 161.8 MHz, δ): -76.7 (s).

5.4.9 Synthesis of 5.7Se

A solution of 5.3Se (40 mg, 0.047 mmol) in 3 mL dichloromethane was added to a solution of AuCl(THT) (15 mg, 0.047 mmol) in 3 mL dichloromethane. The reaction vial was wrapped in aluminum foil to keep out ambient light. The reaction was let stir for 30 minutes and the volatiles were removed in vacuo. The crude reaction mixture was redissolved in 4 mL ether, passed through a Celite filter, and the filtrate was collected. The volatiles were removed in vacuo to yield 5.7Se (29 mg, 58%). Leaving a concentrated solution of 5.7Se in MeCN at -35 °C overnight yielded single crystals suitable for X-ray diffraction. m.p. (nitrogen sealed capillary): 118.8 °C (decomposed, turned black).

1 H NMR (CDCl3, 600 MHz, δ): 1.09 (s, 6H; TMP C(CH3)2), 1.17 (s, 3H; TMP C(CH3)),

1.29 (s, 6H), 1.33 (s, 9H; Mes* ortho-C(CH3)3), 1.42 (s, 9H; Mes* ortho-C(CH3)3), 1.50-

1.55 (br m, 6H; TMP CH), 1.64 (s, 9H; Mes* para-C(CH3)3), 1.75 (3H; Mes ortho-CH3),

1.87 (s, 3H; Mes ortho-CH3), 2.28 (s, 3H; Mes ortho-CH3), 2.38 (s, 3H; Mes para-CH3),

2.70 (s, 3H; Mes para-CH3), 6.55 (s, 1H; Mes CH), 6.80 (s, 1H; Mes CH), 6.92 (br, 3H), 3 3 4 7.13 (br d, JH-H = 7.6 Hz, 1H; Ar* meta-CH), 7.35 (br d, JH-H = 7.6 Hz, JP-H = 1.2 Hz,

3 5 1H; Ar* meta-CH), 7.43 (dt, JH-H = 7.6 Hz, J(P-H = 1.2 Hz, 1H; Ar* para-CH), 7.57 (s, 1H; Mes* CH).

124 125

13 1 C{ H} NMR (CDCl3, 150.1 MHz, δ): 15.7, 16.5, 21.0, 21.4, 22.0, 22.5, 23.4, 27.9, 31.3, 33.8, 34.4, 34.5, 35.2, 35.3, 36.6, 36.7, 39.7, 39.8, 40.6, 41.2, 57.4, 58.1, 123.6, 123.7, 127.6, 127.9, 128.1, 129.1, 131.0, 131.2, 131.7, 132.3, 132.4, 132.4, 135.7, 136.3,

1 137.1, 137.6, 138.0, 138.4, 138.5, 138.6, 147.0, 147.9 (d, JP-C = 22.6 Hz), 152.2, 154.5 2 2 (d, JP-C = 4.9 Hz), 154.8 (d, JP-C = 4.9 Hz), 157.6.

11 B NMR (CDCl3, 192.5 MHz, δ): 43.8 (br s).

31 1 1 1 P{ H} NMR (CDCl3, 161.8 MHz, δ): -8.4 (d, JP-P = 245.6 Hz, JSe-P = 169.9 Hz, 1P; P- 1 P-Se), 10.3 (d, JP-P = 246.4 Hz, 1P; P-P-B).

5.4.10 Synthesis of 5.9

A solution of 5.5iPr (50 mg, 0.095 mmol) in 3 mL THF was added to a solution of trispentafluorophenylborane (49 mg, 0.095 mmol) in 3 mL THF. After 30 minutes, the initial orange solution had turned colourless and the volatiles were removed in vacuo. The crude powder was washed with n-pentane (3 x 3 mL) and the resulting white solid was collected. Yield: 94 mg (89%). Single crystals suitable for X-ray diffraction were obtained by pentane/THF vapour diffusion at -35 °C overnight. m.p. (nitrogen sealed capillary): 212.1 °C (decomposed, turned grey).

+ ESI-MS: 1131.4 m/z C57H53BF15N2OPNa [M + Na] , 597.4 m/z C39H53N2OP [M – + B(C6F5)3] .

Elemental Analysis: Calculated 60.07% C, 4.69% H, 2.46% N; Found 60.83% C, 5.29% H, 2.43% N.

1 3 3 H NMR (CDCl3, 600 MHz, δ): 0.80 (d, JH-H = 6.6 Hz, 3H; iPr CH3), 1.13 (d, JH-H = 3 3 6.6 Hz, 3H; iPr CH3), 1.20 (d, JH-H = 6.6 Hz, 3H; iPr CH3), 1.32 (d, JH-H = 6.6 Hz, 3H; iPr CH3), 1.75-1.84 (br m, 6H; CH2), 2.21 (br s, 9H), 2.26 (s, 3H; Mes ortho-CH3), 2.28

(s, 6H; Mes ortho-CH3), 2.29 (s, 6H; Mes para-CH3), 2.78 (br m, 1H; alkyl CH), 2.89 (br

3 3 m, 1H; alkyl CH), 4.61 (septet, JH-H = 6.6 Hz, 1H; iPr CH), 4.77 (septet, JH-H = 6.6 Hz, 3 1H; iPr CH), 6.82 (br s, 2H), 6.96 (br s, 4H), 7.44 (t, JH-H = 7.5 Hz, 1H; Ar* para-CH).

125 126

13 1 C{ H} NMR (CDCl3, 100.5 MHz, δ): 10.5, 10.8, 14.2, 20.0, 21.0, 21.1, 21.2, 21.9, 22.4, 22.5, 22.9, 24.5, 24.6, 24.8, 34.3, 53.3, 53.6, 62.2, 129.0, 129.2, 129.7, 129.8, 130.4, 132.0, 132.2, 132.6, 137.6, 138.8, 145.7, 146.3, 147.0 (br), 149.1 (br).

11 B NMR (CDCl3, 128.3 MHz, δ): -2.9 (s).

19 3 F NMR (CDCl3, 376.3 MHz, δ): -168.1 (br t, JF-F = 20.0 Hz, 6F; ortho-CF), -165.2 (t, 3 3 JF-F = 20.0 Hz, 3F; para-CF), -133.4 (br d, JF-F = 20.0 Hz, 6F; meta-CF).

31 1 P{ H} NMR (CDCl3, 161.8 MHz, δ): -24.7 (s).

5.4.11 Synthesis of 5.10

A solution of 5.5iPr (65 mg, 0.12 mmol) in 3 mL THF was added dropwise to a well stirred solution of AuCl(THT) (30 mg, 0.25 mmol) in 3 mL THF. After the addition of 5.5iPr was complete, the orange colour had disappeared and the crude reaction mixture remained colourless. After 30 minutes, the volatiles were removed in vacuo, the crude powder was washed with n-pentane (3 x 3 mL), and the resulting white solid was collected. Yield: 71 mg (58%). Single crystals suitable for X-ray diffraction were grown via dichloromethane/ether vapour diffusion at -35 °C. m.p. (nitrogen sealed capillary): 184.0 °C (decomposed, turned black).

+ ESI-MS: 1195.1 m/z C35H45PN2Au2I2Na [M - 2 Cl + 2 I + Na] , 1011.2 m/z + C35H45PN2Au2Cl2Na [M + Na] .

1 H NMR (CDCl3, 600 MHz, δ): 1.14 (br s, 6H; NHC CH3), 1.39 (br s, 6H; iPr CH3), 2.29

(s, 18H; Mes CH3), 2.32 (s, 3H; iPr CH3), 2.45 (s, 3H; iPr CH3), 5.56 (br m, 2H; iPr CH),

3 6.98 (br m, 3H), 7.11 (br s, 2H; Mes CH), 7.34 (br s, 1H; Mes CH), 7.52 (t, JH-H = 7.8 Hz, 1H; Ar* para-CH).

13 1 C{ H} NMR (CDCl3, 150.8 MHz, δ): 11.5, 14.2, 20.7 (br), 22.5, 22.8, 29.5, 29.8, 31.4, 32.1, 34.3, 38.3, 54.0, 128.4, 129.2, 130.0, 130.6, 130.7, 130.9, 131.4, 131.7, 132.6, 137.9, 139.5, 143.8, 144.1, 146.6, 148.1.

31 1 P{ H} NMR (CDCl3, 161.8 MHz, δ): -41.9 (s).

126 127

5.4.12 Special Considerations for X-ray Crystallography

For compounds 5.3Ch, 2.4SMe, 5.5R, 5.7Se, 5.9, and 5.10, the non-hydrogen atoms were well ordered and refined with anisotropic thermal parameters. In the case of 5.7Se, a MeCN solvate was found in the asymmetric unit that could not be refined anisotropically but isotropically.

127 128

Table 5-1: Summary of X-ray diffraction collection and refinement details for the compounds reported in Chapter 5. 5.3S 5.3Se 2.4SMe 5.5iPr 5.5Me 5.7Se 5.9 5.10 CCDC # 1573801 1573802 1573805 1573808 1573806 1573804 1573807 1573803 Molecular C51H72BNP2Se C35H45N2P C57H53BF15 C51H72BNP2S C51H72BNP2Se C31H37N2PS C35H45N2P C31H37N2P Formula AuCl Au2Cl2 N2OP Formula weight, 803.90 850.80 500.65 704.99 468.59 1124.27 1108.79 1074.46 Crystal system triclinic triclinic monoclinic monoclinic monoclinic monoclinic monoclinic monoclinic Space group P-1 P-1 P 21/n P 21/n P 21/n P 21/c P 21/c P 21/n T, K 120 110 110 110 110 110 110 110 a, Å 10.5497(3) 10.659(4) 14.210(9) 10.385(2) 8.1612(14) 22.336(10) 12.0327(19) 11.761(4) b, Å 11.6827(3) 11.656(5) 13.487(8) 25.443(5) 14.097(2) 12.111(6) 24.751(6) 18.934(7) c, Å 20.6959(9) 20.814(10) 14.962(10) 11.697(2) 22.886(4) 19.246(10) 17.504(4) 17.851(5) α, ° 91.087(3) 91.060(9) 90 90 90 90 90 90 β, ° 97.928(3) 98.491(14) 105.345(14) 95.521(14) 98.229(5) 90.939(14) 98.043(6) 109.13(2) γ, ° 111.357(3) 111.449(8) 90 90 90 90 90 90 V, Å3 2346.24(15) 2373.0(18) 2765(3) 3076.2(10) 2605.9(8) 5206(4) 5161.9(18) 3756(2) Z 2 2 4 4 4 4 4 4 F(000) 872 908 1072 1536 1008 2288 2288 2072 ρ, g cm−1 1.138 1.191 1.203 1.522 1.194 1.434 1.427 1.900 λ, Å 0.71073 0.71073 0.71073 1.54178 1.54178 0.71073 1.54178 0.71073 µ, cm−1 0.171 0.892 0.197 1.138 1.080 3.674 1.333 8.159 Measured 0.999 0.998 0.999 0.994 0.999 0.998 0.997 0.998 fraction of data Rmerge 0.1713 0.0423 0.0768 0.0322 0.0564 0.1206 0.0512 0.0566 0.0567, 0.0410, 0.0731, 0.0583, 0.0461, 0.0454, 0.0626, 0.0302, R wR 1, 2 0.1379 0.1039 0.2098 0.1542 0.111 0.0819 0.1727 0.0624 R1 (all data), 0.0708, 0.0568, 0.1113, 0.0622, 0.0621, 0.0926, 0.0795, 0.0449, wR2 (all data) 0.1423 0.1138 0.2393 0.1615 0.1257 0.0957 0.1892 0.0665 GOF 1.021 1.031 1.057 1.047 1.095 1.003 1.047 1.021

2 2 2 4 ½ 2 2 2 ½ R1 = Σ( |Fo| - |Fc| ) / Σ Fo, wR2 = [ Σ( w( Fo - Fc ) ) / Σ(w Fo ) ] GOF = [ Σ( w( Fo - Fc ) ) / (No. of reflns. - No. of params. ) ]

128 129

5.4.13 Computational details

Calculations were performed using the PBE1PBE57–60 density functional with the Gaussian0961 program package. Ahlrichs’ TZVP basis sets were used for all atoms.62 The importance of dispersion interactions was examined by performing optimizations both with and without Grimme’s GD3BJ empirical dispersion correction.63,64 The bulky Ar* and Mes* groups were replaced with Ar (meta-diphenylbenzene) and Mes (2,4,6- trimethylphenyl), respectively, to speed up the calculations. Similarly, 2,2,6,6- tetramethylpiperidine was replaced with dimethylamine throughout calculations.

5.5 References (1) Power, P. P. Nature 2010, 463, 171–177. (2) Martin, C. D.; Soleilhavoup, M.; Bertrand, G. Chem. Sci. 2013, 4, 3020. (3) Wilson, D. J. D.; Dutton, J. L. Chem. - Eur. J. 2013, 19, 13626–13637. (4) Wang, Y.; Xie, Y.; Wei, P.; King, B.; Schaefer, H.; Schleyer, P. V. R.; Robinson, G. H. Science 2008, 321, 1069–1071. (5) Wang, Y.; Xie, Y.; Wei, P.; King, R. B.; Schaefer, H. F.; Schleyer, P. V. R.; Robinson, G. H. J. Am. Chem. Soc. 2008, 130, 14970–14971. (6) Dyker, C. A.; Lavallo, V.; Donnadieu, B.; Bertrand, G. Angew. Chem., Int. Ed. 2008, 47, 3206–3209. (7) Wang, Y.; Xie, Y.; Abraham, M. Y.; Gilliard, R. J.; Wei, P.; Schaefer, H. F.; Schleyer, P. V. R.; Robinson, G. H. Organometallics 2010, 29, 4778–4780. (8) Arduengo, A. J.; Calabrese, J. C.; Cowley, A. H.; Dias, H. V. R.; Goerlich, J. R.; Marshall, W. J.; Riegel, B. Inorg. Chem. 1997, 36, 2151–2158. (9) Cicač-Hudi, M.; Bender, J.; Schlindwein, S. H.; Bispinghoff, M.; Nieger, M.; Grützmacher, H.; Gudat, D. Eur. J. Inorg. Chem. 2016, 649–658. (10) Tondreau, A. M.; Benkö, Z.; Harmer, J. R.; Grützmacher, H. Chem. Sci. 2014, 1545–1554. (11) Doddi, A.; Bockfeld, D.; Bannenberg, T.; Jones, P. G.; Tamm, M. Angew. Chem., Int. Ed. 2014, 53, 13568–13572. (12) Bispinghoff, M.; Tondreau, A. M.; Grützmacher, H.; Faradji, C. A.; Pringle, P. G. Dalton Trans. 2016, 5999–6003. (13) Liu, L.; Ruiz, D. A.; Dahcheh, F.; Bertrand, G. Chem. Commun. 2015, 12732– 12735. (14) Arduengo III, A. J.; Carmalt, C. J.; Clyburne, J. A. C.; Cowley, A. H.; Pyati, R. Chem. Commun. 1997, 981–982.

129 130

(15) Lemp, O.; von Hänisch, C. Phosphorus. Sulfur. Silicon Relat. Elem. 2016, 191, 659–661. (16) Beil, A.; Gilliard, R. J.; Grützmacher, H. Dalton Trans. 2016, 2044–2052. (17) Price, A. N.; Cowley, M. J. Chem. - Eur. J. 2016, 22, 6248–6252. (18) Graham, C. M. E.; Pritchard, T. E.; Boyle, P. D.; Valjus, J.; Tuononen, H. M.; Ragogna, P. J. Angew. Chem., Int. Ed. 2017, 56, 6236–6240. (19) Arif, A. M.; Boggs, J. E.; Cowley, A. H.; Lee, J. G.; Pakulski, M.; Power, J. M. J. Am. Chem. Soc. 1986, 108, 6083–6084. (20) Price, A. N.; Nichol, G. S.; Cowley, M. J. Angew. Chem., Int. Ed. 2017, 56, 9953– 9957. (21) Burford, N.; Dyker, C. A.; Phillips, A. D.; Spinney, H. A.; Decken, A.; McDonald, R.; Ragogna, P. J.; Rheingold, A. L. Inorg. Chem. 2004, 43, 7502–7507. (22) Eversheim, E.; Englert, U.; Boese, R.; Paetzold, P. Angew. Chem., Int. Ed. 1994, 33, 201–202. (23) He, G.; Shynkaruk, O.; Lui, M. W.; Rivard, E. Chem. Rev. 2014, 114, 7815–7880. (24) Gray, I. P.; Bhattacharyya, P.; Slawin, A. M. Z.; Woollins, J. D. Chem. - Eur. J. 2005, 11, 6221–6227. (25) Cherkasov, R. A.; Kutyrev, G. A.; Pudovik, A. N. Tetrahedron 1985, 41, 2567– 2624. (26) Yoshifuji, M.; An, D. L.; Toyota, K.; Yasunami, M. Tetrahedron Lett. 1994, 35, 4379–4382. (27) Kilián, P.; Marek, J.; Marek, R.; Jiøí, T.; Humpa, O.; Woollins, J. D. J. Chem. Soc., Dalton Trans. 1998, 1175–1180. (28) Beckmann, H.; Ohms, G.; Großmann, G.; Kriiger, K.; Klostermann, K.; Kaiser, V. Heteroat. Chem. 1996, 7, 111–118. (29) Jochem, G.; Karaghiosoff, K.; Plank, S.; Dick, S.; Schmidpeter, A. Chem. Ber. 1995, 128, 1207–1219. (30) Toyota, K.; Yoshifuji, M.; Hirotsu, K. Chem. Lett. 1990, 643–646. (31) Elder, P. J. W.; Chivers, T. Inorg. Chem. 2013, 52, 7791–7804. (32) Oshida, H.; Ishii, A.; Nakayama, J. Tetrahedron Lett. 2004, 45, 1331–1334. (33) Foreman, M. R. S. J.; Slawin, A. M. Z.; Woollins, J. D. Chem. Commun. 1997, 855–856. (34) Villalba Franco, J. M.; Schnakenburg, G.; Espinosa Ferao, A.; Streubel, R. Dalton Trans. 2016, 13951–13956. (35) Fulde, M.; Reid, W.; Bats, J. W. Helv. Chim. Acta 1989, 72, 139–147. (36) Te, S.; Ome, P.; Chadha, R. K.; Drake, J. E.; Mcmanus, N. T.; Quinlan, B. A.; Sarkar, A. B. Organometallics 1987, 6, 813–819.

130 131

(37) Weiber, M.; Lang, S. Z. Anorg. Allg. Chem. 1994, 620, 1397–1402. (38) Driess, M.; Pritzkow, H.; Rell, S.; Winkler, U. Organometallics 1996, 15, 1845– 1855. (39) Burford, N.; Mason, S.; Spence, R. E. v H.; Whalen, J. M.; Richardson, J. F.; Rogers, R. D. Organometallics 1992, 11, 2241–2250. (40) Huy, N. H. T.; Ricard, L.; Mathey, F. Heteroat. Chem. 1998, 9, 597–600. (41) Villinger, A.; Westenkirchner, A.; Wustrack, R.; Schulz, A. Inorg. Chem. 2008, 47, 9140–9142. (42) Weber, L.; Buchwald, S.; Lentz, D.; Preugschat, D.; Stammler, H.-G.; Neumann, B. Organometallics 1992, 11, 2351–2353. (43) We are representing the NHC-adducts as the charge-separated species, rather than the dative bonding structures. While we understand that other resonance structures contribute to the bonding of 2.4S, 5.4, 5.5, 5.9, and 5.10, we have only indicated one species for brevity. (44) Back, O.; Henry-Ellinger, M.; Martin, C. D.; Martin, D.; Bertrand, G. Angew. Chem., Int. Ed. 2013, 52, 2939–2943. (45) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics 1997, 2, 1920–1925. (46) Twamley, B.; Sofield, C. D.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1999, 121, 3357–3367. (47) Verlinden, K.; Buhl, H.; Frank, W.; Ganter, C. Eur. J. Inorg. Chem. 2015, 2416– 2425. (48) Niecke, E.; Wildbredt, D. A. J. Chem. Soc., Chem. Commun. 1981, 72–73. (49) Bond lengths for methylenethioxophosphoranes were taken as an average from the reported structures from: Toyota, K.; Takahashi, H.; Shimura, K.; Yoshifuji, M. Bull. Chem. Soc. Jpn. 1996, 69, 141–145; Caira, M.; Neilson, R. H.; Watson, W. H.; Wisian-Neilson, P; Xie, Z. M. J. Chem. Soc., Chem. Commun. 1984, 698-699; Miyake, H.; Sasamori, T.; Tokitoh, N. Phosphorus. Sulfur. Silicon Related. Elem. 2015, 190, 1247-1250; Yoshifuji, M.; Takahashi, H.; Shimura, K.; Toyota, K. Heteroat. Chem. 1997, 8, 375-382. (50) Gudimetla, V. B.; Ma, L.; Washington, M. P.; Payton, J. L.; Cather Simpson, M.; Protasiewicz, J. D. Eur. J. Inorg. Chem. 2010, No. 6, 854–865. (51) Pyykkö, P.; Atsumi, M. Chem. - Eur. J. 2009, 15, 12770–12779. (52) Pyykkö, P.; Atsumi, M. Chem. - Eur. J. 2009, 15, 186–197. (53) Graham, C. M. E.; Valjus, J.; Boyle, P. D.; Pritchard, T. E.; Tuononen, H. M.; Ragogna, P. J. Inorg. Chem. 2017, 56, 13500–13509. (54) Henne, F. D.; Watt, F. A.; Schwedtmann, K.; Hennersdorf, F.; Kokoschka, M.; Weigand, J. J. Chem. Commun. 2016, 2023–2026. (55) Adiraju, V. A. K.; Yousufuddin, M.; Dias, H. V. R. Dalton Trans. 2015, 4449–

131 132

4454. (56) Uson, R.; Laguna, A.; Laguna, M. Inorg. Synth. 1989, 26, 85–91. (57) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158–6170. (58) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997, 78, 1396. (59) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865–3868. (60) Perdew, J. P.; Ernzerhof, M.; Burke, K. J. Chem. Phys. 1996, 105, 9982. (61) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Marenichm, A. V.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakaji; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A. J.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 09, Revision D.01; Wallingford, CT, USA, 2009. (62) Schäfer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829. (63) Grimme, S.; Ehrlich, S.; Goerigk, L. J. Comput. Chem. 2011, 32, 1456–1465. (64) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. J. Chem. Phys. 2010, 15, 154104– 154119.

132 133

Chapter 6 6 Summary, Conclusions, and Future Work 6.1 Summary and Conclusions

This dissertation encompasses a discussion surrounding the synthesis and reactivity of phosphorus-chalcogen heterocycles and use of these compounds to obtain systematic access to low-coordinate phosphorus species. The target compounds for this study were phosphinidene chalcogenides – a low-coordinate phosphorus species that have escaped the recent agenda within Groups 15 and 16. Literature examples of phosphinidene chalcogenides are known for oxygen and sulfur derivatives, and the examples reported here have expanded on this field to include thorough analysis of new sulfur and selenium derivatives. We have also reported on a method of in situ generation of phosphinidene chalcogenides at room temperature that we anticipate being useful for the heavier pnictogens/chalcogens.

The synthesis of 2.3S and 2.3Se were the first reported examples of phosphorus- chalcogen heterocycles that contained a P2Ch2 core with phosphorus in the +3 oxidation state. These species represent cyclic dimers of the monomeric phosphinidene chalcogenide. The potential to use these heterocycles as sources of their monomeric form was tested by gently heating 2.3Ch in the presence of dmbd and alkynes, that generated the cycloadducts 2.5Ch, 3.1, and 3.2, indicating that the monomer 2.2Ch can be accessed from their parent dimers – the selenium congener being nonexistent in the literature. Additionally, the room temperature addition of NHCR to 2.3Ch resulted in the base stabilized phosphinidene sulfide (2.4SR) for Ch = S, and an NHC stabilized phosphinidene (5.5R) for Ch = Se. These systems were probed computationally and revealed that breaking apart the dimers (2.3Ch) into their monomers (2.2Ch) are energetically feasible and confirm the experimental results.

Further reactivity of 2.3Ch was tested with Lewis acids and Lewis bases, that resulted in ring expansion of the dimer (c-RPCh)2 to larger trimers (c-RPCh)3 (4.1Ch). In the examples using Lewis acids, the coinage metal used to induce ring expansion

133 134 remained in the structure and were bound to each phosphorus atom in the 6-membered ring (4.3ChM; Ch = S, Se; M = Cu, Ag). The results from the addition of Lewis bases were dependent on the nature of the base. For example, the addition of DMAP to 2.3Ch resulted in ring expansion to 4.1Ch. The addition of a stronger base (e.g. NHCMe) to 4.1Ch yielded the low-coordinate phosphorus derivatives 2.4SMe and 5.5Me, indicating that these less strained rings can also be used as sources of phosphinidene chalcogenides. In the case of Lewis bases, a computational pathway was detected that involved the DMAP-stabilized phosphinidene chalcogenide (4.2Ch) as an intermediate, indicating that the low-coordinate phosphorus-chalcogen species play a role in forming 4.1Ch from the parent 4-membered rings.

The reaction of multiple low-coordinate phosphorus species was investigated through the combination of phosphinidene chalcogenides and phosphaborenes. These low-coordinate compounds were thermally generated in situ from their parent dimers and resulted in the quantitative formation of 5.3Ch. The mechanism of generating these heterocycles was probed computationally, that revealed favourable pathways in forming a P-P bond by the combination of 2.2Ch and 5.2 – an unexpected result since both phosphorus atoms are bound to bulky ligands. The reactivity of 5.3Ch was probed via the addition of both Lewis acids and Lewis bases. The addition of AuCl(THT) to 5.3Se resulted in the direct coordination of AuCl to one phosphorus atom from the P2BSe core (5.7Se). The addition of NHCMe resulted in degradation of 5.3Ch and formation of low- coordinate phosphorus compounds 2.4SMe, 5.4, and 5.5Me – similar to the results of NHC and either 2.3Ch or 4.1Ch. Reactivity of the isolated NHC-stabilized phosphinidene (5.5iPr) was investigated using Lewis acids, that resulted in coordination to transition metal centres from both lone pairs at phosphorus (5.10). FLP type behaviour of 5.5iPr was discovered from the ring-opening of THF in the presence of a strong Lewis acid (BCF).

The work detailed in this thesis describes not only the synthesis and reactivity of new phosphorus-chalcogen heterocycles, but also the ability to use main group heterocycles as storage forms for reactive species. The phosphorus-chalcogen heterocycles reported here have been utilized as sources for phosphinidene chalcogenides, and represent the first example of obtaining these reactive units from

134 135

cyclic structures – most notably (c-RPCh)n rings. Our findings indicated that, in general, cyclic dimers and trimers of phosphinidene chalcogenides can be used as precursors to the low-coordinate phosphorus-chalcogen compounds, and the sulfur derivatives were much more stable to their selenium counterparts. For this reason, the selenium chemistry has been less developed and remains a target for future work. These results contribute to the vast understanding of phosphorus-chalcogen chemistry and aims to motivate discussion regarding the true electronic nature of phosphinidene chalcogenides, and the chemistry surrounding these rare species.

6.2 Future Work

6.2.1 Bulky Ligands to Stabilize RP=Ch

We have suggested that upon the addition of Ar*PCl2 and S(TMS)2 free monomeric phosphinidene chalcogenides are formed, which dimerize to yield the parent 4-membered heterocycles 2.3Ch. It appears that the bulk of the m-terphenyl ligand is sufficient to kinetically stabilize a PIII centre, but not bulky enough to prevent the dimerization of Ar*P=Ch. We now propose that using this same method but replacing the m-terphenyl ligand with a more sterically encumbered group will lead to the stabilization of monomeric phosphinidene chalcogenides.

Germanium and tin halides ([M(Cl){2,6-Mes2C6H3}]2) that contain the same m- terphenyl ligand have been reported as bridged dimers, similar in structure to 2.3Ch.1 When the sterics of the terphenyl ligand are increased by replacing the flanking Mes groups with Trip (Ar#), the ligand stabilized monomers (e.g. E-X; E = Ge, Sn) are formed.2 This clearly indicates that the bulkier ligand can be used to stabilize the main group element monomer, and should be adopted for P-Ch systems. With this in mind, using bulkier ligands than the ones utilized in this thesis is an appropriate starting point in attempting to isolate monomeric phosphinidene chalcogenides. The phosphorus precursor # 3 Ar PCl2 (6.1) is a literature known compound and should be a synthetically viable starting point for using a bulkier ligand. The addition of Ch(TMS)2 to 6.1 will potentially result in the ligand stabilized phosphinidene chalcogenide (6.2, Scheme 6-1) and will allow for the thorough investigation of this virtually unknown molecular unit.

135 136

Ch PCl2 P

Trip Trip Ch(TMS)2 Trip Trip

6.1 6.2

Scheme 6-1: Using bulkier m-terphenyl ligands to stabilize phosphinidene chalcogenides

Alternative to using terphenyl ligands, bulky amido groups developed by Cameron Jones and coworkers have been reported to adopt similar reactivity profiles to these extremely bulky terphenyl ligands used by Power.4 The chemistry surrounding phosphinidene chalcogenides and bulky amido ligands has more room for experimental curiosity, seeing as the R groups on the silane can be easily tuned to contain various alkyl or aryl groups. Some cases have demonstrated that the silyl groups are prone to cleavage,5 therefore substituting silanes for other aryl groups might be necessary to enhance the stability of the ligand. Nevertheless, the chemistry surrounding amido ligands are well known, and these systems can be tuned to whatever the need may be. The synthetic strategy for incorporating phosphorus into the bulky amido group can follow literature known procedures (Scheme 6-2).4 The same methodology will be applied as used with terphenyls, with the addition of Ch(TMS)2 to 6.4 yielding the ligand stabilized monomer 6.5. It would be interesting to explore both the bulky terphenyls in addition to the amido derivatives, and (in the event both can stabilize RP=Ch) generate enough data for simple comparison of the terminal P=Ch. In addition, applying these ligands to create the heavier pnictogens (arsenic and antimony) could be useful since these new ligands would offer a larger steric demand to aid in stabilizing the more unstable heavier main group elements.

136 137

R3Si R3Si PCl2 R3Si P Ch NH N N

Ph Ph 1) nBuLi Ph Ph Ch(TMS)2 Ph Ph Ph Ph Ph Ph Ph Ph 2) PCl3

6.3 6.4 6.5

Scheme 6-2: Synthesis of phosphinidene chalcogenides stabilized by bulky amido ligands.

6.2.2 Electron-Withdrawing Ligands to Stabilize RP=Ch

Phosphinidene chalcogenide derivatives discussed thus far have been constructed around sterically accommodating ligands (simple alkyl/aromatic groups) and bulky ligands (Mes, Mes*, Ar*). Aside from one report of an electronically stabilized ligand 6 (2,6-(OMe)2-C6H3) with RP=S, this realm of phosphinidene chalcogenide chemistry is nonexistent. One potentially viable ligand is perfluorophenyl (-C6F5) since it is inherently electron withdrawing, the ligand precursor is commercially available, and phosphorus functionality can easily be added onto this group. Literature methods are known (and have been safely reproduced in our lab) for generating C6F5PCl2, therefore creating the materials needed for this study should not be problematic.7 In preliminary studies in our F F lab, the addition of Ph PCl2 and S(TMS)2 yields the tetramer (Ph PS)4 in almost stoichiometric amounts in a matter of hours. The formation of the tetramer indicates that the perfluoro group is able to briefly stabilize the reactive PhFP=S unit, but clearly not strongly electron withdrawing enough to stabilize the monomer on its own. Additionally, it appears that the steric bulk of the m-terphenyl ligand was necessary to generate the more strained 4-membered rings – as opposed to the trimers and tetramers previously reported in the literature. This ligand appears to be a new candidate for stabilizing the transient phosphinidene sulfide and should be applied to the heavier chalcogen atoms as well. The chemistry involving cycloadditions, metal coordination, and addition of strong bases would be useful to compare the effects of perfluorophenyl and m-terphenyl for stabilizing phosphinidene chalcogenides.

137 138

6.2.3 In situ Generation of Phosphinidene Chalcogenides

In Chapter 3, we discussed an alternative method of generating phosphinidene chalcogenides. Rather than degrading the dimers (2.3S) into their monomeric units, the addition of the parent dichlorophosphine (Ar*PCl2) with S(TMS)2 generates Ar*P=S, which could be trapped with alkynes, and generated similar products from the thermolysis of 2.3S in the presence of trapping reagents. This method circumvents the isolation of the dimeric heterocycles, and projects to be useful for the heavier pnictogens and chalcogens – since the heterocycles bearing strict bond angles are imagined to be unfavourable for the heavier elements. This instability was evident with 2.3Se, with significant decomposition occurring when leaving the sample for a period of time. Although exploring the heterocycles is interesting from a structural standpoint, the end goal of generating phosphinidene chalcogenides might not need to depend on generating these cyclic structures. The scope of our system, until now, has been limited to m- terphenyl derivatives, however when utilizing our new condensation route, we can apply this to any alkyl/aryl dichlorophosphine – some of which are commercially available.

Applying this method to the heavier chalcogens, preliminary results from using

Ar*PCl2 and Se(TMS)2 in the presence of phenylacetylene appears to generate the 1,2- selenaphosphetene (6.6) based on its NMR signature (Scheme 6-3), however numerous other phosphorus containing products were present in the 31P{1H} NMR spectrum. Not surprisingly, the thermolysis of 2.3Se with phenylacetylene yielded the same major product in the 31P NMR spectrum. In generating RP=Ch, the selenium congener appears to mimic alkene type behaviour from the phosphinidene selenide unit, where the phosphinidene sulfide has displayed both carbene and alkene-type reactivity. These results align directly with those proposed by Niecke and Schoeller, that carbene character becomes less prominent, and alkene character becomes dominant when the main group element multiply bound to phosphorus becomes less electronegative.8 Although these results are preliminary, it appears that the condensation route of dichlorophosphines and chalcogenides appears to be promising for generating solution accessible phosphinidene chalcogenides, and predicts to be important for exploring the chemistry of the heavier chalcogens.

138 139

Ar* Se Ph P Ph Ar*PCl2 + Se(TMS)2 Ar* P P Ar* RT Se 60 °C Se Ph 6.6

Scheme 6-3: Generation and trapping of phosphinidene selenides.

6.2.4 Kinetic Studies to Probe the Presence of Phosphinidene Chalcogenides

In Chapter 2 and 3, we discussed the ability to access either free phosphinidene chalcogenides, or at least degrade 2.3Ch into units that comprise of the molecular unit Ar*PCh. The clear drawback for this chemistry is determining whether the “free” phosphinidene chalcogenides are actually solution accessible from the condensation or thermolysis routes, or if other mechanisms are in practice. As previously discussed, although we are able to obtain and transfer molecular units comprised of the Ar*PCh framework, understanding the mechanism is pivotal for fully developing this chemistry and being able to progress in this field. In order to better understand the thermolysis and condensation routes, kinetic studies are imperative. In doing so, probing the dependence of the reaction with the concentration of trapping reagent will allow us to understand the role of the trapping reagent – whether it assists in the degradation of 2.3Ch, or if it reacts with the “free” RP=Ch generated in this system.

6.2.5 Frustrated Lewis Pair Chemistry Based on NHC- Phosphinidenes

The last discussion is a clear outlier from the rest of this section and involves using low-coordinate phosphorus derivatives reported here in FLP chemistry. In Chapter 5, we reported the synthesis of NHC-stabilized phosphinidenes from the degradation of P-Se heterocycles with NHCs. In exploring the reactivity of these compounds, reacting 5.5iPr and BCF in the presence of THF resulted in the controlled ring opening of the solvent THF. The interesting component of this process is that there is no convincing evidence (based on preliminary data) that a typical Lewis acid-base interaction occurs when treating 5.5iPr with BCF in non-coordinating solvent. It is believed that the steric bulk of the NHC, the m-terphenyl group, and the borane itself is not accommodating

139 140 enough for a P®B interaction to occur. With these results in mind, this appears to be a perfect candidate for FLP chemistry.

Traditional FLP systems adopt a bulky phosphorus centre with one lone pair of electrons and a bulky Lewis acid that enables for the activation of a small molecule e.g.

H2, which could further be used for transition-metal free hydrogenations. When using NHC-stabilized phosphinidenes as the Lewis base in an FLP system, two lone pairs of electrons are available at phosphorus, and one could imagine the simultaneous activation of two equivalents of H2 (6.7, Scheme 6-4). This allows for the potential of transferring two equivalents of H2 to a substrate, rather than one in a traditional FLP system. The reactivity of both lone pairs of electrons has been demonstrated in Chapter 5 using AuCl, therefore it is clear that both lone pairs of electrons can simultaneously act as donors. If successful, this would represent a unique system where low-coordinate phosphorus compounds are used as Lewis bases in FLP chemistry.

H H Ar* P Ar* P N 2 H2, 2 BCF N 2 [HB(C6F5)3] N N

6.7

Scheme 6-4: Using NHC-phosphinidenes for FLP chemistry.

6.3 References (1) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics 1997, 2, 1920–1925. (2) Pu, L.; Olmstead, M. M.; Power, P. P.; Schiemenz, B. Organometallics 1998, 17, 5602–5606. (3) Twamley, B.; Sofield, C. D.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1999, 121, 3357–3367. (4) Li, J.; Stasch, A.; Schenk, C.; Jones, C. Dalton Trans. 2011, 10448–10456. (5) Hicks, J.; Hadlington, T. J.; Schenk, C.; Li, J.; Jones, C. Organometallics 2012, 32, 323–329. (6) Qian, H.; Gaspar, P. P.; Rath, N. P. J. Organomet. Chem. 1999, 585, 167–173.

140 141

(7) Orthaber, A.; Fuchs, M.; Belaj, F.; Rechberger, G. N.; Kappe, C. O.; Pietschnig, R. Eur. J. Inorg. Chem. 2011, 2588–2596. (8) Schoeller, W. W.; Niecke, E. J. Chem. Soc., Chem. Commun. 1982, 569–570.

141 142

Chapter 7 7 Appendices 7.1 Synthesis of m-terphenyl phosphines

The synthesis of 2.3Ch were the starting point for all of the chemistry detailed in

Chapters 2-5. While the synthesis of these strained P2Ch2 rings was not overly troublesome, the progression of these synthetic chapters was initially bottlenecked by the synthesis of the phosphorus starting material Ar*PCl2. Although this is a literature known compound and the first procedures detailing its synthesis were reported in the 1990’s, there were some inconsistencies when repeating these literature procedures. For instance, the reported preparation of Ar*PCl2 calls for the addition of nBuLi to Ar*I (7.1), yielding lithiated terphenyl 7.2, which can be isolated as a stable powder (or generated in situ), 1,2 and reacted with PCl3 to yield 7.3 in excellent yields (upwards to 80%; Scheme 7-1).

While the lithiation of 7.1 proceeds as reported, the addition of 7.2 to PCl3 consistently yielded two products: Ar*PCl2 and Ar*Cl in a ratio of roughly 1:4. Varying the solvent, reaction time, dilution, and temperature did not mitigate the formation of Ar*Cl. This product was problematic since its solubility was nearly identical to that of 7.3, and even a

95:5 mixture of Ar*PCl2:Ar*Cl negatively affected subsequent chemistry.

I Li PCl2 Mes Mes Mes Mes Mes Mes nBuLi PCl3

7.1 7.2 7.3

F F F F F F nBuLi -50 °C ClP(NEt2)2 F H F Li F P(NEt ) -50 °C to RT 2 2 F F F F F F

Scheme 7-1: Top: General procedure for generating terphenyl phosphines. Bottom: Stepwise approach for selective P-C bond formation.

142 143

In order to move forward and explore the chemistry of these hypothesized P2Ch2 rings, we had to develop a method that allowed for the clean and scalable synthesis of

Ar*PCl2. Pietschnig and coworkers reported a method of selective P-C bond formation

3,4 using a “protected” phosphorus starting material, ClP(NEt2)2. This protected phosphine contains only one unit of functionality therefore mitigating the potential issue of over- substitution – a common issue when using PCl3 as a starting material in making dichlorophosphines. The resulting R-PN2 could be treated with HCl to cleave the P-N bonds and install the desired PCl2 functionality onto the ligand (Scheme 7-1, bottom).

Taking the lead from these results, we treated 7.2 with ClP(NEt2)2 and observed the quantitative formation of 7.4, which was easily isolated by filtering off the resulting LiCl and washing the crude powder with a small amount of cold n-pentane (Scheme 7-2). Treating 7.4 with gaseous HCl resulted in the quantitative formation of 7.3, which was

31 1 easily detected in the P{ H} NMR spectrum (dP = 160.6; Figure 7-1). This new process allowed us to access analytically pure 7.3 on scales up to 50 g, that enabled the scalable synthesis of 2.3Ch, and compounds therefrom.

I Li Mes Mes Mes Mes nBuLi

7.1 7.2

ClP(NEt2)2

PCl2 P(NEt2)2 Mes Mes HCl Mes Mes

7.3 7.4

Scheme 7-2: Synthetic approach used in this thesis for generating 7.3.

143 144

Figure 7-1: A 31P{1H} NMR stacked plot displaying the spectra for each phosphorus starting material.

7.1.1 Experimental

PCl3 was purchased from Sigma Aldrich and distilled prior to use. HNEt2 was 5 6 purchased from Alfa Aesar and distilled from KOH prior to use. ClP(NEt2)2, Ar*I, and Ar*Li7 were made following literature procedures. HCl gas was generated in situ by dropping neat H2SO4 to CaCl2, bubbling this through an H2SO4 bubbler and then through the reaction mixture, and the residual acid was neutralized through a NaHCO3 exit bubbler.

7.1.2 Synthesis of 7.4

A solution of ClP(NEt2)2 (9.40 g, 44.6 mmol) in 50 mL Et2O was slowly added to a suspension of Ar*Li (13.09 g, 40.6 mmol) in 25 mL Et2O at -78 °C for 4 hours and allowed to warm to room temperature overnight. The solution was concentrated to half of its original volume, and 100 mL of n-pentane was added, and the LiCl precipitate was filtered through Celite, and washed with 3 x 10 mL n-pentane. Leaving a concentrated

Et2O solution at -35 °C overnight resulted in the bulk crystallization of 7.4 (14.65 g, 74%

144 145 yield). Concentrating the supernatant and leaving it at -35 °C for 2 days resulted in the recovery of additional 7.4 (total yield = 89%). m.p. (nitrogen sealed capillary): 112.1-113.4 °C.

FT-IR (KBr, cm-1 (ranked relative intensity)): 636 (12), 665 (8), 717 (15), 750 (10), 804 (7), 850 (5), 909 (4), 1014 (1), 1190 (3), 1371 (6), 1445 (9), 1559 (14), 1610 (13), 2360 (11), 2963 (2).

+ + ESI-MS: 489.3 m/z C32H45PN2 [M + H] , 345.2 m/z C24H25P [M – 2 NEt2 + H] .

1 3 H NMR (CDCl3, 400 MHz, δ): 0.84 (t, JH-H = 7.2 Hz, 12H; CH2-CH3), 2.24 (s, 6H;

Mes p-CH3), 2.26 (s, 12H; Mes o-CH3), 2.52-2.58 (m, 4H; CH2-CH3), 2.69-2.81 (m, 4H; 3 4 CH2-CH3), 6.84 (dd, JH-H = 7.2 Hz, JP-H = 2.4 Hz, 2H; Ar* meta-CH), 6.88 (br s, 4H; 3 Mes CH), 7.10 (t, JH-H = 7.2 Hz, 1H; Ar* para-CH).

13 1 C{ H} NMR (CDCl3, 150 MHz, δ): 15.3, 21.2, 21.7, 45.3, 127.4, 128.1, 130.6, 135.6, 136.2, 136.3, 140.8, 141.9, 144.1.

31 1 P{ H} NMR (C6D6, 161.8 MHz, δ): 100.5 (s).

7.1.3 Synthesis of 7.3

Neat H2SO4 (6.99 g, 71.2 mmol) was slowly dropped into a 3-neck round bottom flask charged with CaCl2 (10.48 g, 94.4 mmol), and the resulting HCl gas was bubbled through a solution of 7.4 (8.49 g, 17.4 mmol) in 50 mL of toluene at room temperature. After the complete addition of H2SO4, the reaction mixture was let stir for 3 hours at room temperature. The ammonium hydrochloride precipitate was filtered off using a medium frit, the precipitate was washed 3 x 10 mL of n-pentane, and the volatiles were removed in vacuo, yielding 7.3 (6.97 g, 96%). The spectroscopic data matches those previously reported.1

1 H NMR (C6D6, 600 MHz, δ): 2.10 (s, 12H; Mes o-CH3), 2.17 (s, 6H; Mes p-CH3), 6.80

3 4 (dd, JH-H = 7.6 Hz, JP-H = 3.2 Hz, 2H; Ar* meta-CH), 6.83 (br s, 4H; Mes CH), 7.09 (t, 3 JH-H = 7.6 Hz, 1H; Ar* para-CH).

145 146

31 1 P{ H} NMR (C6D6, 161.8 MHz, δ): 160.6 (s).

7.2 Experimental Methods

7.2.1 General Experimental Methods

All manipulations were performed under inert atmosphere either in a nitrogen- filled MBraun Labmaster 130 Glovebox or on a Schlenk line. Solvents were obtained from Caledon and dried using an MBraun Solvent Purification System. Dried solvents were collected under vacuum in a flame dried Straus flask and stored over 4 Å molecular sieves. Solvents for NMR spectroscopy (CDCl3, C6D6) were stored in the drybox over 4 Å molecular sieves.

7.2.2 General Instrumentation

Solution 1H, 13C{1H}, 11B{1H}, 31P{1H} Nuclear Magnetic Resonance (NMR) spectroscopy was recorded on a Varian INOVA 400 MHz spectrometer (1H 400.09 MHz, 31P{1H} 161.8 MHz, 11B{1H} 128.2 MHz, 13C{1H} 100.5 MHz) unless otherwise noted. All 13C{1H} spectra were recorded on a Varian INOVA 600 MHz spectrometer (13C{1H} 150.8 MHz) and referenced to the 13C signal of the solvent relative to tetramethylsilane

1 (CDCl3; δC = 77.1, C6D6; δC = 128.06). All samples for H NMR spectroscopy were referenced to the residual protons in the deuterated solvent relative to tetramethylsilane 1 1 11 (CDCl3; H δ = 7.26, C6D6; H δ = 7.16). The chemical shifts for B (BF3 Et2O; δB = 19 31 1 0.0), F (CF3COOH; δF = -76.6), and P{ H} (85% H3PO4; δP = 0.0) NMR spectroscopy were referenced using an external standard. FT-IR spectroscopy was performed on samples as KBr pellets using a Bruker Tensor 27 FT-IR spectrometer, with a 4 cm-1 resolution. Mass spectrometry was recorded in house in positive- and negative-ion modes using electrospray ionization Micromass LCT spectrometer. Melting or decomposition points were determined by flame-sealing the sample in capillaries and heating using a Gallenkamp Variable Heater. Elemental analysis was performed at the University of Montreal and is reported as an average of two samples weighed under air and combusted immediate thereafter.

146 147

7.2.3 General Crystallographic Methods

Single crystal X-ray diffraction studies were performed at the Western University X-ray Facility. Crystals were selected under Paratone(N) oil, mounted on a MiTeGen polyimide micromount, and immediately put under a cold stream of nitrogen for data to be collected on a Bruker and Nonius Apex II detectors using Mo-Kα radiation (λ = 0.71073 Å) or Cu-Kα radiation (λ = 1.54178 Å). The Bruker and Nonius instruments operate Bruker’s Apex2 software. The data collection strategy was a number of ϕ and ω scans which collected data up to 2q. The frame integration was performed using SAINT.8 The resulting raw data was scaled and absorption corrected using a multi-scan averaging of symmetry equivalent data using SADABS.9 The structure was solved by using a dual space methodology using the SHELXT program.10 All non-hydrogen atoms were obtained from the initial solution. The hydrogen atoms were introduced at idealized positions and were allowed to ride on the parent atom. The structural model was fit to the data using full matrix least-squares based on F. The calculated structure factors included corrections for anomalous dispersion from the usual tabulation. The structures were refined using the SHELXL program from the SHELXTL suite of crystallographic software.9,11 The majority of solid-state structures reported were well refined and converged to one single solution, where restraints were not necessary. In the situations where special refinement cycles were necessary, these details have been included in the experimental section in their corresponding chapter.

7.3 Copyrights and Permissions

7.3.1 John Wiley and Sons License Agreement

TERMS AND CONDITIONS

This copyrighted material is owned by or exclusively licensed to John Wiley & Sons, Inc. or one of its group companies (each a"Wiley Company") or handled on behalf of a society with which a Wiley Company has exclusive publishing rights in relation to a particular work (collectively "WILEY"). By clicking "accept" in connection with completing this licensing transaction, you agree that the following terms and conditions apply to this transaction (along with the billing and payment terms and conditions

147 148 established by the Copyright Clearance Center Inc., ("CCC's Billing and Payment terms and conditions"), at the time that you opened your RightsLink account (these are available at any time at http://myaccount.copyright.com).

Terms and Conditions

The materials you have requested permission to reproduce or reuse (the "Wiley Materials") are protected by copyright.

You are hereby granted a personal, non-exclusive, non-sub licensable (on a stand-alone basis), non-transferable, worldwide, limited license to reproduce the Wiley Materials for the purpose specified in the licensing process. This license, and any CONTENT (PDF or image file) purchased as part of your order, is for a one-time use only and limited to any maximum distribution number specified in the license. The first instance of republication or reuse granted by this license must be completed within two years of the date of the grant of this license (although copies prepared before the end date may be distributed thereafter). The Wiley Materials shall not be used in any other manner or for any other purpose, beyond what is granted in the license. Permission is granted subject to an appropriate acknowledgement given to the author, title of the material/book/journal and the publisher. You shall also duplicate the copyright notice that appears in the Wiley publication in your use of the Wiley Material. Permission is also granted on the understanding that nowhere in the text is a previously published source acknowledged for all or part of this Wiley Material. Any third party content is expressly excluded from this permission.

With respect to the Wiley Materials, all rights are reserved. Except as expressly granted by the terms of the license, no part of the Wiley Materials may be copied, modified, adapted (except for minor reformatting required by the new Publication), translated, reproduced, transferred or distributed, in any form or by any means, and no derivative works may be made based on the Wiley Materials without the prior permission of the respective copyright owner. For STM Signatory Publishers clearing permission under the terms of the STM Permissions Guidelines only, the terms of the license are extended to include subsequent editions and for editions in other languages, provided such editions

148 149 are for the work as a whole in situ and does not involve the separate exploitation of the permitted figures or extracts,You may not alter, remove or suppress in any manner any copyright, trademark or other notices displayed by the Wiley Materials. You may not license, rent, sell, loan, lease, pledge, offer as security, transfer or assign the Wiley Materials on a stand-alone basis, or any of the rights granted to you hereunder to any other person.

The Wiley Materials and all of the intellectual property rights therein shall at all times remain the exclusive property of John Wiley & Sons Inc, the Wiley Companies, or their respective licensors, and your interest therein is only that of having possession of and the right to reproduce the Wiley Materials pursuant to Section 2 herein during the continuance of this Agreement. You agree that you own no right, title or interest in or to the Wiley Materials or any of the intellectual property rights therein. You shall have no rights hereunder other than the license as provided for above in Section 2. No right, license or interest to any trademark, trade name, service mark or other branding ("Marks") of WILEY or its licensors is granted hereunder, and you agree that you shall not assert any such right, license or interest with respect thereto

NEITHER WILEY NOR ITS LICENSORS MAKES ANY WARRANTY OR REPRESENTATION OF ANY KIND TO YOU OR ANY THIRD PARTY, EXPRESS, IMPLIED OR STATUTORY, WITH RESPECT TO THE MATERIALS OR THE ACCURACY OF ANY INFORMATION CONTAINED IN THE MATERIALS, INCLUDING, WITHOUT LIMITATION, ANY IMPLIED WARRANTY OF MERCHANTABILITY, ACCURACY, SATISFACTORY QUALITY, FITNESS FOR A PARTICULAR PURPOSE, USABILITY, INTEGRATION OR NON-INFRINGEMENT AND ALL SUCH WARRANTIES ARE HEREBY EXCLUDED BY WILEY AND ITS LICENSORS AND WAIVED BY YOU.

WILEY shall have the right to terminate this Agreement immediately upon breach of this Agreement by you.

You shall indemnify, defend and hold harmless WILEY, its Licensors and their respective directors, officers, agents and employees, from and against any actual or

149 150 threatened claims, demands, causes of action or proceedings arising from any breach of this Agreement by you.

IN NO EVENT SHALL WILEY OR ITS LICENSORS BE LIABLE TO YOU OR ANY OTHER PARTY OR ANY OTHER PERSON OR ENTITY FOR ANY SPECIAL, CONSEQUENTIAL, INCIDENTAL, INDIRECT, EXEMPLARY OR PUNITIVE DAMAGES, HOWEVER CAUSED, ARISING OUT OF OR IN CONNECTION WITH THE DOWNLOADING, PROVISIONING, VIEWING OR USE OF THE MATERIALS REGARDLESS OF THE FORM OF ACTION, WHETHER FOR BREACH OF CONTRACT, BREACH OF WARRANTY, TORT, NEGLIGENCE, INFRINGEMENT OR OTHERWISE (INCLUDING, WITHOUT LIMITATION, DAMAGES BASED ON LOSS OF PROFITS, DATA, FILES, USE, BUSINESS OPPORTUNITY OR CLAIMS OF THIRD PARTIES), AND WHETHER OR NOT THE PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. THIS LIMITATION SHALL APPLY NOTWITHSTANDING ANY FAILURE OF ESSENTIAL PURPOSE OF ANY LIMITED REMEDY PROVIDED HEREIN.

Should any provision of this Agreement be held by a court of competent jurisdiction to be illegal, invalid, or unenforceable, that provision shall be deemed amended to achieve as nearly as possible the same economic effect as the original provision, and the legality, validity and enforceability of the remaining provisions of this Agreement shall not be affected or impaired thereby.

The failure of either party to enforce any term or condition of this Agreement shall not constitute a waiver of either party's right to enforce each and every term and condition of this Agreement. No breach under this agreement shall be deemed waived or excused by either party unless such waiver or consent is in writing signed by the party granting such waiver or consent. The waiver by or consent of a party to a breach of any provision of this Agreement shall not operate or be construed as a waiver of or consent to any other or subsequent breach by such other party.

This Agreement may not be assigned (including by operation of law or otherwise) by you without WILEY's prior written consent.

150 151

Any fee required for this permission shall be non-refundable after thirty (30) days from receipt by the CCC.

These terms and conditions together with CCC's Billing and Payment terms and conditions (which are incorporated herein) form the entire agreement between you and WILEY concerning this licensing transaction and (in the absence of fraud) supersedes all prior agreements and representations of the parties, oral or written. This Agreement may not be amended except in writing signed by both parties. This Agreement shall be binding upon and inure to the benefit of the parties' successors, legal representatives, and authorized assigns.

In the event of any conflict between your obligations established by these terms and conditions and those established by CCC's Billing and Payment terms and conditions, these terms and conditions shall prevail.

WILEY expressly reserves all rights not specifically granted in the combination of (i) the license details provided by you and accepted in the course of this licensing transaction, (ii) these terms and conditions and (iii) CCC's Billing and Payment terms and conditions.

This Agreement will be void if the Type of Use, Format, Circulation, or Requestor Type was misrepresented during the licensing process.

This Agreement shall be governed by and construed in accordance with the laws of the State of New York, USA, without regards to such state's conflict of law rules. Any legal action, suit or proceeding arising out of or relating to these Terms and Conditions or the breach thereof shall be instituted in a court of competent jurisdiction in New York County in the State of New York in the United States of America and each party hereby consents and submits to the personal jurisdiction of such court, waives any objection to venue in such court and consents to service of process by registered or certified mail, return receipt requested, at the last known address of such party.

WILEY OPEN ACCESS TERMS AND CONDITIONS

151 152

Wiley Publishes Open Access Articles in fully Open Access Journals and in Subscription journals offering Online Open. Although most of the fully Open Access journals publish open access articles under the terms of the Creative Commons Attribution (CC BY) License only, the subscription journals and a few of the Open Access Journals offer a choice of Creative Commons Licenses. The license type is clearly identified on the article.

The Creative Commons Attribution License

The Creative Commons Attribution License (CC-BY) allows users to copy, distribute and transmit an article, adapt the article and make commercial use of the article. The CC-BY license permits commercial and non-

Creative Commons Attribution Non-Commercial License

The Creative Commons Attribution Non-Commercial (CC-BY-NC)License permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.(see below)

Creative Commons Attribution-Non-Commercial-NoDerivs License

The Creative Commons Attribution Non-Commercial-NoDerivs License (CC-BY-NC- ND) permits use, distribution and reproduction in any medium, provided the original work is properly cited, is not used for commercial purposes and no modifications or adaptations are made. (see below)

Use by commercial "for-profit" organizations

Use of Wiley Open Access articles for commercial, promotional, or marketing purposes requires further explicit permission from Wiley and will be subject to a fee.

Further details can be found on Wiley Online Library http://olabout.wiley.com/WileyCDA/Section/id-410895.html

152 153

7.3.1.1 Chapter 2

This Agreement between Western University -- Cameron Graham ("You") and John Wiley and Sons ("John Wiley and Sons") consists of your license details and the terms and conditions provided by John Wiley and Sons and Copyright Clearance Center. License Number 4243131477423 License date Dec 06, 2017 Licensed Content Publisher John Wiley and Sons Licensed Content Publication Angewandte Chemie International Edition Licensed Content Title Trapping Rare and Elusive Phosphinidene Chalcogenides Licensed Content Author Cameron M. E. Graham, Taylor E. Pritchard, Paul D. Boyle, Juuso Valjus, Heikki M. Tuononen, Paul J. Ragogna Licensed Content Date Jan 10, 2017 Licensed Content Pages 5 Type of use Dissertation/Thesis Requestor type Author of this Wiley article Format Print and electronic Portion Full article Will you be translating? No Title of your thesis / dissertation Exploring the Synthesis, Structure, and Reactivity of Phosphorus-Chalcogen Heterocycles Expected completion date Feb 2018 Expected size (number of pages) 250 Requestor Location Western University 1151 Richmond St

London, ON N6A3K7 Canada Attn: Western University Publisher Tax ID EU826007151 Billing Type Invoice Billing Address Western University 1151 Richmond St

London, ON N6A3K7 Canada Attn: Western University Total 0.00 CAD

153 154

7.3.1.2 Chapter 3

License Number 4307920091318 License date Mar 14, 2018 Licensed Content John Wiley and Sons Publisher Licensed Content Chemistry - A European Journal Publication Licensed Content Title Addressing the Nature of Phosphinidene Sulfides via the Synthesis of P−S Heterocycles Licensed Content Cameron M. E. Graham,Charles L. B. Macdonald,Paul D. Author Boyle,James A. Wisner,Paul J. Ragogna Licensed Content Date Dec 7, 2017 Licensed Content Pages 7 Type of use Dissertation/Thesis Requestor type Author of this Wiley article Format Print and electronic Portion Full article Will you be translating? No Title of your thesis / Exploring the Synthesis, Structure, and Reactivity of dissertation Phosphorus-Chalcogen Heterocycles Expected completion Feb 2018 date Expected size (number 250 of pages) Requestor Location Western University 1151 Richmond St

London, ON N6A3K7

154 155

Canada Attn: Western University Publisher Tax ID EU826007151 Total 0.00 USD

7.3.1.3 Chapter 5 License Number 4307911444642 License date Mar 14, 2018 Licensed Content John Wiley and Sons Publisher Licensed Content Chemistry - A European Journal Publication Licensed Content Title Preparation and Characterization of P2BCh Ring Systems (Ch=S, Se) and Their Reactivity with N-Heterocyclic Carbenes Licensed Content Author Cameron M. E. Graham,Clément R. P. Millet,Amy N. Price,Juuso Valjus,Michael J. Cowley,Heikki M. Tuononen,Paul J. Ragogna Licensed Content Date Dec 12, 2017 Licensed Content Pages 9 Type of Use Dissertation/Thesis Requestor type Author of this Wiley article Format Print and electronic Portion Full article Will you be translating? No Title of your thesis / Exploring the Synthesis, Structure, and Reactivity of dissertation Phosphorus-Chalcogen Heterocycles Expected completion Feb 2018 date Expected size (number of 250 pages) Attachment Requestor Location Western University 1151 Richmond St

London, ON N6A3K7

155 156

Canada Attn: Western University Publisher Tax ID EU826007151

Total 0.00 USD

The work presented in Chapter 2 has been reproduced with permission from C. M. E. Graham, T. E. Pritchard, P. D. Boyle, J. Valjus, H. M. Tuononen, P. J. Ragogna, Angew. Chem., Int. Ed. 2017, 56, 6236-6240. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. http://onlinelibrary.wiley.com/wol1/doi/10.1002/anie.201611196/full

The work presented in Chapter 3 has been reproduced with permission from C. M. E. Graham, C. L. B. Macdonald, P. D. Boyle, J. A. Wisner, P. J. Ragogna, Chem – Eur. J. 2017 DOI: 10.1002/chem.201705198. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. http://onlinelibrary.wiley.com/wol1/doi/10.1002/chem.201705198/full

The work presented in Chapter 5 has been reproduced with permission from C. M. E. Graham, C. R. P. Millet, A. N. Price, J. Valjus, M. J. Cowley, H. M. Tuononen, P. J. Ragogna, Chem – Eur. J. 2017 DOI: 10.1002/chem.201704337. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. http://onlinelibrary.wiley.com/wol1/doi/10.1002/chem.201704337/full

7.3.2 American Chemical Society’s policy on theses and dissertations

If your university requires you to obtain permission, you must use the RightsLink permission system. See RightsLink instructions at http://pubs.acs.org/page/copyright/permissions.html.

This is regarding request for permission to include your paper(s) or portions of text from your paper(s) in your thesis. Permission is now automatically granted; please pay special attention to the implications paragraph below. The Copyright Subcommittee of the Joint Board/Council Committees on Publications approved the following:

ACS extends blanket permission to students to include in their theses and dissertations their own articles, or portions thereof, that have been published in ACS journals or

156 157 submitted to ACS journals for publication, provided that the ACS copyright credit line is noted on the appropriate page(s).

Publishing implications of electronic publication of theses and dissertation material

Students and their mentors should be aware that posting of theses and dissertation material on the Web prior to submission of material from that thesis or dissertation to an ACS journal may affect publication in that journal. Whether Web posting is considered prior publication may be evaluated on a case-by-case basis by the journal’s editor. If an ACS journal editor considers Web posting to be “prior publication”, the paper will not be accepted for publication in that journal. If you intend to submit your unpublished paper to ACS for publication, check with the appropriate editor prior to posting your manuscript electronically.

Reuse/Republication of the Entire Work in Theses or Collections:

Authors may reuse all or part of the Submitted, Accepted or Published Work in a thesis or dissertation that the author writes and is required to submit to satisfy the criteria of degree-granting institutions. Such reuse is permitted subject to the ACS’ “Ethical Guidelines to Publication of Chemical Research” (http://pubs.acs.org/page/policy/ethics/index.html); the author should secure written confirmation (via letter or email) from the respective ACS journal editor(s) to avoid potential conflicts with journal prior publication*/embargo policies. Appropriate citation of the Published Work must be made. If the thesis or dissertation to be published is in electronic format, a direct link to the Published Work must also be included using the ACS Articles on Request author-directed link − see http://pubs.acs.org/page/policy/articlesonrequest/index.html

* Prior publication policies of ACS journals are posted on the ACS website at http://pubs.acs.org/page/policy/prior/index.html

The work presented in Chapter 4 has been reproduced with permission from “C. M. E. Graham, J. Valjus, T. E. Pritchard, P. D. Boyle, H. M. Tuononen, P. J. Ragogna, Inorg. Chem. 2017, 56, 13500-13509 Copyright 2017 American Chemical Society.”

157 158

7.4 Supplementary Information for Chapter 2

1 Figure 7-2: H NMR spectrum of 2.3S in C6D6.

13 1 Figure 7-3: C{ H} NMR spectrum of 2.3S in CDCl3.

158 159

31 1 Figure 7-4: P{ H} NMR spectrum of 2.3S in C6D6..

1 Figure 7-5: H NMR spectrum of 2.3Se in C6D6.

159 160

13 1 Figure 7-6: C{ H} NMR spectrum of 2.3Se in C6D6.

31 1 Figure 7-7: P{ H} NMR spectrum of 2.3Se in C6D6.

160 161

77 1 Figure 7-8: Se{ H} NMR spectrum of 2.3Se in C6D6.

1 Figure 7-9: H NMR spectrum of 2.4S in CDCl3.

161 162

13 1 Figure 7-10: C{ H} NMR spectrum of 2.4S in CDCl3.

31 1 Figure 7-11: P{ H} NMR spectrum of 2.4S in CDCl3.

162 163

1 Figure 7-12: H NMR spectrum of 2.6S in CDCl3.

13 1 Figure 7-13: C{ H} NMR spectrum of 2.6S in CDCl3.

163 164

31 1 Figure 7-14: P{ H} NMR spectrum of 2.6S in CDCl3.

1 Figure 7-15: H NMR spectrum of 2.6Se in CDCl3.

164 165

13 1 Figure 7-16: C{ H} NMR spectrum of 2.6Se in CDCl3.

31 1 Figure 7-17: P{ H} NMR spectrum of 2.6Se in CDCl3.

165 166

Table 7-1: Frontier orbital interactions (isovalue ± 0.05) relevant to the dimerization of 2.2S to 2.3S.

166 167

7.5 Supplementary Information for Chapter 3

Table 7-2: M06-2X/TZVP calculated energetic and thermochemical data for 3- and 4-membered ring isomers of Ar’PS(C2R2). M06-2x In au in kJ mol-1 calcs E (with Ar’ Models H(298.15) S(cal/molK) G(298.15) DE(rxn) DH(rxn) DS(rxn) DG(rxn) ZPVE)

H-C≡C-H

- 3-mem -1667.392951 1667.36690 171.585 -1667.448433

- 3-mem → 4-mem -1667.421373 1667.39585 166.411 -1667.474921 -74.62 -76.00 -0.02 -69.54 4-mem 4

Me-C≡C-Me

- 3-mem -1745.971033 1745.94230 182.752 -1746.029138

3-mem → 4-mem -1745.988935 -1745.96007 182.763 -1746.046906 -47.00 -46.64 0.00 -46.65 4-mem H-C≡C-Ph

- 3-mem -1898.354579 193.559 -1898.415862 1898.32389

167 168

-1898.380914 - 194.995 -1898.443027 3-mem → -69.14 -69.53 0.01 -71.32 4-mem 1898.35037 4-mem 9 Ph-C≡C-Ph

- 3-mem -2129.315437 2129.28008 214.229 -2129.381872

- 3-mem → 4-mem -2129.330546 2129.29606 208.607 -2129.395184 -39.67 -41.97 -0.02 -34.95 4-mem 8

Table 7-3: (U)M06-2X/TZVP calculated energetic and thermochemical data for 3- and 4-membered ring isomers of HPS(C2R2).

H models for mechanism

E(with ZPVE) H(298.15) S(cal/molK) G(298.15) DE(rxn) DH(rxn) DS(rxn) DG(rxn)

H-C≡C-H -77.294881 -77.2912 47.544 -77.3138

H-P=S -740.082922 -740.079 59.263 -740.107

3-mem product -817.404201 -817.399 69.943 -817.432 Reacts. → Prod. -69.31 -74.99 -0.15 -29.01

168 169

4-mem product -817.437824 -817.433 68.706 -817.465 Reacts. → Prod. -157.59 -164.04 -0.16 -116.51

3-mem TS -817.36647 -817.361 72.328 -817.395 Reacts. → TS 29.75 25.29 -0.14 68.30

4-mem TS -817.341274 -817.335 74.822 -817.371 Reacts. → TS 95.91 91.49 -0.13 131.39

4-mem TS SDR -817.348218 -817.343 71.711 -817.377 Reacts. → TS 77.68 72.66 -0.15 116.44

169 170

Figure 7-18: 1H-31P HMBC spectrum of 3.2a. Cross peaks indicate P-H coupling.

1 Figure 7-19: H NMR spectrum of 3.1a in C6D6.

170 171

13 1 Figure 7-20: C{ H} NMR spectrum of 3.1a in C6D6.

31 Figure 7-21: P NMR spectrum of 3.1a in C6D6.

171 172

1 Figure 7-22: H NMR spectrum of 3.2a in C6D6.

13 1 Figure 7-23: C{ H} NMR spectrum of 3.2a in C6D6.

172 173

31 Figure 7-24: P NMR spectrum of 3.2a in C6D6.

1 Figure 7-25: H NMR spectrum of 3.2b in C6D6.

173 174

13 1 Figure 7-26: C{ H} NMR spectrum of 3.2b in C6D6.

31 Figure 7-27: P NMR spectrum of 3.2b in C6D6.

174 175

7.6 Supplementary Information for Chapter 4

Figure 7-28: Reaction coordinate for the base-free ring expansion of 2.3S to 4.1S.

175 176

Figure 7-30: Attempted synthesis of 4.3SAu. Major product at dP = 81 decomposed when left at -35 °C overnight. The chemistry of 4.3ChAu were no longer pursued.

Figure 7-31: 31P{1H} NMR stacked plot showing the decomposition of 4.4S left in the solid state at room temperature for 2 days.

176 177

31 1 Figure 7-32: P{ H} NMR stacked plot showing the decomposition of 4.3SCu left in the solid state at room temperature for 2 days.

1 Figure 7-33: H NMR spectrum of purified 4.1S in C6D6.

177 178

13 1 Figure 7-34: C{ H} NMR spectrum of purified 4.1S in C6D6.

31 1 Figure 7-35: P{ H} NMR spectrum of purified 4.1S in C6D6.

178 179

1 Figure 7-36: H NMR spectrum of purified 4.1Se in C6D6.

13 1 Figure 7-37: C{ H} NMR spectrum of purified 4.1Se in C6D6.

179 180

31 1 Figure 7-38: P{ H} NMR spectrum of purified 4.1Se in C6D6.

77 1 Figure 7-39: Se{ H} NMR spectrum of purified 4.1Se in C6D6.

180 181

1 Figure 7-40: H NMR spectrum of purified 4.3SCu in CDCl3.

13 1 Figure 7-41: C{ H} NMR spectrum of 4.3SCu in CDCl3.

181 182

31 1 Figure 7-42: P{ H} NMR spectrum of 4.3SCu in CDCl3.

1 Figure 7-43: H NMR spectrum of 4.3SAg in CDCl3.

182 183

13 1 Figure 7-44: C{ H} NMR spectrum of 4.3SAg in CDCl3.

19 Figure 7-45: F NMR spectrum of 4.3SAg in CDCl3.

183 184

31 1 Figure 7-46: P{ H} NMR spectrum of 4.3SAg in CDCl3.

1 Figure 7-47: H NMR spectrum of 4.3SeAg in CDCl3.

184 185

13 1 Figure 7-48: C{ H} NMR spectrum of 4.3SeAg in CDCl3.

19 Figure 7-49: F NMR spectrum of 4.3SeAg in CDCl3.

185 186

31 1 Figure 7-50: P{ H} NMR spectrum of 4.3SeAg in CDCl3.

1 Figure 7-51: H NMR spectrum of 4.4S in CDCl3.

186 187

13 1 Figure 7-52: C{ H} NMR spectrum of 4.4S in CDCl3.

31 1 Figure 7-53: P{ H} NMR spectrum of 4.4S in CDCl3.

187 188

1 Figure 7-54: H NMR spectrum of 4.4Se in CDCl3.

13 1 Figure 7-55: C{ H} NMR spectrum of 4.4Se in CDCl3.

188 189

31 1 Figure 7-56: P{ H} NMR spectrum of 4.4Se in CDCl3.

Figure 7-57: Thermal ellipsoid plots for P3Ch3 cores of 4.1S (left) and 4.1Se (centre), with the minor component of the disorder indicated with a dashed line. Isotropic structure of 4.3SeAg (right). Thermal ellipsoids have been drawn at 50% probability.

189 190

7.7 Supplementary Information for Chapter 5

Figure 7-58: 1H NMR spectrum of 5.3S in THF-d8.

Figure 7-59: 13C{1H} NMR spectrum of 5.3S in THF-d8.

190 191

Figure 7-60: 11B NMR spectrum of 5.3S in THF-d8.

Figure 7-61: 31P{1H} NMR spectrum of 5.3S in THF-d8.

191 192

1 Figure 7-62: H NMR spectrum of 5.3Se in C6D6.

13 1 Figure 7-63: C{ H} NMR spectrum of 5.3Se in C6D6.

192 193

11 Figure 7-64: B NMR spectrum of 5.3Se in C6D6.

31 1 Figure 7-65. P{ H} NMR spectrum of 5.3Se in C6D6.

193 194

1 Me Figure 7-66: H NMR spectrum of 2.4S in C6D6.

13 1 Me Figure 7-67: C{ H} NMR spectrum of 2.4S in C6D6.

194 195

31 1 Me Figure 7-68: P{ H} NMR spectrum of 2.4S in C6D6.

1 iPr Figure 7-69: H NMR spectrum of 5.5 in C6D6.

195 196

13 1 iPr Figure 7-70: C{ H} NMR spectrum of 5.5 in C6D6.

31 1 iPr Figure 7-71: P{ H} NMR spectrum of 5.5 in C6D6.

196 197

1 Figure 7-72: H NMR spectrum of 5.7Se in CDCl3.

13 1 Figure 7-73: C{ H} NMR spectrum of 5.7Se in CDCl3.

197 198

11 Figure 7-74: B NMR of 5.7Se in CDCl3.

31 1 Figure 7-75: P{ H} NMR spectrum of 5.7Se in CDCl3.

198 199

1 Figure 7-76: H NMR spectrum of 5.9 in CDCl3.

13 1 Figure 7-77: C{ H} NMR spectrum of 5.9 in CDCl3.

199 200

11 Figure 7-78: B NMR spectrum of 5.9 in CDCl3.

19 Figure 7-79: F NMR spectrum of 5.9 in CDCl3.

200 201

31 1 Figure 7-80: P{ H} NMR spectrum of 5.9 in CDCl3.

1 Figure 7-81: H NMR spectrum of 5.10 in CDCl3.

201 202

13 1 Figure 7-82: C{ H} NMR spectrum of 5.10 in CDCl3.

31 1 Figure 7-83: P{ H} NMR spectrum of 5.10 in CDCl3.

202 203

7.8 References (1) Urnezius, E.; Protasiewicz, J. D. Main Gr. Chem. 1996, 1, 369–372. (2) Overlander, C.; Tirree, J. J.; Nieger, M.; Niecke, E.; Moser, C.; Spirk, S.; Pietschnig, R. Appl. Organometal. Chem. 2007, 21, 46–48. (3) Orthaber, A.; Belaj, F.; Albering, J. H.; Pietschnig, R. Eur. J. Inorg. Chem. 2010, 1, 34–37. (4) Orthaber, A.; Fuchs, M.; Belaj, F.; Rechberger, G. N.; Kappe, C. O.; Pietschnig, R. Eur. J. Inorg. Chem. 2011, 2588–2596. (5) King, R. B.; Sundaram, P. M. J. Org. Chem. 1984, 49, 1784. (6) Du, C.-J. F.; Hart, H.; Ng, K.-K. D. J. Org. Chem 1986, 51, 3162–3165. (7) Ruhlandt-Senge, K.; Ellison, J. J.; Wehmschulte, R. J.; Pauer, F.; Power, P. P. J. Am. Chem. Soc 1993, 115, 11353–11357. (8) SAINT v2013.8. Bruker AXS INC; Madison, WI, USA, 2013. (9) SADABS v2012.1. Bruker AXS INC; Madison, WI, USA, 2012. (10) Sheldrick, G. M. Acta Crystallogr. Sect. A Found. Crystallogr. 2015, 71, 3–8. (11) Linden, A. Acta Crystallogr. Sect. C Struct. Chem. 2015, 71, 1–2.

203 204

Curriculum Vitae Cameron M. E. Graham

Education Western University – London, ON 2013 - 2018 PhD in Synthetic Inorganic Chemistry Exploring the Synthesis, Structure, and Reactivity of Strained Phosphorus-Chalcogen Heterocycles Supervisor: Dr. Paul J. Ragogna

Brock University – St. Catharines, ON 2008 - 2013 BSc (Honours) in Chemistry Investigating Carbon-Carbon Decarboxylative Coupling Mediated by Lead Tetracarboxylates Supervisor: Dr. Tomáš Hudlicky

Honours and Awards

• OUA academic achievement award (baseball, 2011 – 2016)

• Western University Bronze “W” Award (baseball, 2015)

• Brock University President’s Award (2011 – 2013, $500/a)

• Mary Rixey Richardson Bursary (2012, $500)

• Donna Vukmanic Memorial Scholarship (2012, $1000)

Publications

1. C. M. E. Graham, C. L. B. Macdonald, P. D. Boyle, P. J. Ragogna “Addressing the nature of phosphinidene sulfides via the synthesis of P-S heterocycles” Chemistry – A European Journal 2017, 24, 743-749. 2. C. M. E. Graham, C. R. P. Millet, A. N. Price, J. Valjus, M. J. Cowley, H. M.

Tuononen, P. J. Ragogna “Preparation and characterization of P2BCh ring systems (Ch = S, Se) and their reactivity with N-Heterocyclic carbenes” Chemistry - A European Journal 2017, 24, 672-680.

204 205

3. C. M. E. Graham, J. Valjus, P. D. Boyle, T. E. Pritchard, H. M. Tuononen, P. J. Ragogna “Phosphorus-chalcogen ring expansion and metal coordination” Inorganic Chemistry 2017, 56, 13500-13509. 4. C. M. E. Graham, C. L. B. Macdonald, P. P. Power, Z. D. Brown, P. J. Ragogna

“Transition metal functionalization of P4 using a diarylgermylene anchor” Inorganic Chemistry 2017, 56, 9111-9119. 5. C. M. E. Graham, T. E. Pritchard, P. D. Boyle, J. Valjus, H. M. Tuononen, P. J. Ragogna “Trapping rare and elusive phosphinidene chalcogenides” Angewandte Chemie International Edition 2017, 56, 6236-6240. 6. J. W. Dube, C. M. E. Graham, C. L. B. Macdonald, Z. D. Brown, P. P. Power, P.

J. Ragogna “Reversible, photoinduced activation of P4 by low-coordinate main group compounds” Chemistry - A European Journal 2014, 20, 6739-6744.

Conference Presentations 1. C. M. E. Graham, T. E. Pritchard, J. Valjus, A. N. Price, C. R. P. Millet, M. J. Cowley, H. M. Tuononen, P. J. Ragogna “Synthesis and Reactivity of Phosphorus-Chalcogen Heterocycles” at the 12th International Conference on Heteroatom Chemistry, Vancouver, BC, June 2017. 2. C. M. E. Graham, T. E. Pritchard, J. Valjus, H. M. Tuononen, P. J. Ragogna “Synthesis and Reactivity of Phosphorus Containing Ring Systems” at the 100th Canadian Chemistry Conference and Exhibition, Toronto, ON, May 2017. 3. C. M. E. Graham, T. E. Pritchard, J. Valjus, H. M. Tuononen, P. J. Ragogna “Phosphorus-Chalcogen Rings: They Key to Unlocking Low-coordinate Phosphorus Compounds” at the 49th Inorganic Discussion Weekend, Hamilton, ON, November 2016. 4. C. M. E. Graham, T. E. Pritchard, P. J. Ragogna “Synthesis and reactivity of Pnictogen-Chalcogen Rings” at the 99th Canadian Chemistry Conference and Exhibition, Halifax, NS, May 2016.

205