Synthesis, Structure and Reactivity of Phosphorus and Arsenic Heterocycles Darren Michael Charles Ould A thesis submitted to Cardiff University in candidature for the degree of Doctor of Philosophy March 2020 I. Acknowledgements To begin with, I would like to extend my thanks and gratitude to my supervisor Dr Rebecca Melen for firstly giving me the opportunity to undertake my PhD in her group and secondly for allowing me to present at a number of conferences both domestically and internationally. Travelling to Canada in the summers of both 2018 and 2019 as part of an exchange program and to present at the Canadian Chemistry Conference and Exhibition 2019 will undoubtedly go down as highlights of my PhD. Thanks must be given to the Melen group both past and present. In particular though to Dr Adam Ruddy, Dr Yashar Soltani and Jamie Carden for their help and suggestions, as well as providing a great working atmosphere. My further thanks to Dr Lewis Wilkins for his help and suggestions, but moreover for teaching me the basics of single crystal X-ray crystallography as well as solving a number of my early structures (compounds 6a, 7, 15a–c, 16a–c, 17 and 18). I am grateful for the hard work to the students I have supervised during the course of my PhD, Matthew de Vere-Tucker, Kayla Trafford, Emily Tansley, Dorothea Engl and especially Alex Rigby who helped me develop the initial diazaphosphole and diazarsole work, as well as helping me crystallise a number of complexes (6a, 7, 15a–c, 16a–c and 17). I am grateful to Cardiff University for funding and eight great years as an undergraduate and postgraduate. I have been fortunate enough to collaborate with a number of people throughout my PhD and wish to express my gratitude to them. Firstly, thanks to Thao Tran and Professor Jeremy Rawson (both at University of Windsor), who established some of the early work of the dithiaphospholes and dithiarsoles. Thao Tran had first synthesised the two paddlewheel structures and intermediates 9, 10, 11 and 12. Professor Jeremy Rawson has solved the crystal structures of 10 and 12, as well as providing helpful comments for my own structure refinements. Thanks to Dr John Davies (Cambridge University) for solving and refining crystal structures 3, 4, 14a and 14b. Appreciation must be given to Dr Samuel Adams and Professor Simon Pope for performing the absorption and emission spectroscopy (Chapter 3), Dr Emma Richards for the EPR spectroscopy measurements (Chapter 3) and Dr James Platts for the DFT calculations on the corresponding radical (Chapter 3) as well as teaching me how to perform Fluoride Ion Affinity calculations and generally introducing me to computational chemistry. Although not included in this thesis I would like to show my appreciation to Professor Thomas Wirth, Micol Santi and Dr Jan Wenz for our collaborative work on our paper titled Metal-Free Tandem Rearrangement/Lactonization: Access to 3,3-Disubstituted Benzofuran-2-(3H)-ones, which was published in Angew. Chem. Int. Ed. I would like to thank the technical support and professional services staff at Cardiff University, Dr Robert Jenkins, ii Simon Waller, Robin Hick, Tom Williams, Evelyn Blake and Jamie Cross. In addition, I would like to recognise Dr Benjamin Ward, Dr Angelo Amorroso and Dr Paul Newman, who although may not have directly contributed to this thesis have greatly helped and supported my time at Cardiff University. The challenges a PhD as well as life presents at times are difficult and I would like to personally acknowledge the wider inorganic department for always keeping me going by providing numerous amusing and upbeat moments. I would especially like to thank Siôn Edwards for the many lunch time adventures and conversations, which will certainly be sadly missed and Bria Thomas for providing entertaining moments and for proofreading this thesis. I would of course like to thank my family for their continuous support and belief in me, as well my friends from Cornwall (especially Sam Ringrose, Neil Sanders, Chris Lee and Anthony Donaghy) for always providing a welcomed distraction from PhD life. Lastly, I would like to express my upmost gratitude to Ella Carter for our many adventures during the past 3.5 years (and more), support and advice given. Thank you all! iii II. List of Publications Published work included in this thesis: 1. T. T. P. Tran, D. M. C. Ould, L. C. Wilkins, D. S. Wright, R. L. Melen and J. M. Rawson, CrystEngComm, 2017, 19, 4696–4699 (Chapters 2 and 3). 2. D. M. C. Ould, A. C. Rigby, L. C. Wilkins, S. J. Adams, J. A. Platts, S. J. A. Pope, E. Richards and R. L. Melen, Organometallics, 2018, 37, 712–719 (Chapters 2 and 3). 3. D. M. C. Ould and R. L. Melen, Chem. A Eur. J., 2018, 24, 15201–15204 (Chapter 4) 4. D. M. C. Ould, Thao T. P. Tran, J. M. Rawson and R. L. Melen, Dalton Trans., 2019, 48, 16922–16935 (Chapters 2, 3 and 4). Published work not included in this thesis: 1. A. J. Ruddy, D. M. C. Ould, P. D. Newman and R. L. Melen, Dalton Trans., 2018, 47, 10377–10381. 2. M. Santi, D. M. C. Ould, J. Wenz, Y. Soltani, R. L. Melen and T. Wirth, Angew. Chem. Int. Ed., 2019, 58, 7861–7865. 3. T. A. Gazis, B. A. Mohajeri, D. Willcox, D. M. C. Ould, J. Wenz, J. M. Rawson, M. S. Hill, T. Wirth and R. L. Melen, Chem Commun., 2020, 56, 3345-3348. 4. Y. Soltani, A. Dasgupta, T. A. Gazis, D. M. C. Ould, E. Richards, B. Slater, K. Stefkova, V. Y. Vladimirov, L. C. Wilkins, D. Willcox and R. L. Melen, Cell Rep. Phys. Sci., 2020, 100016. 5. D. M. C. Ould, J. L. Carden and R. L. Melen, Turning the alane key: novel synthesis and reactivity of triarylalanes, manuscript in revision. 6. D. M. C. Ould and R. L. Melen, Chem. A. Eur. J., 2020, doi.org/10.1002/chem.202001734 iv III. Abbreviations °C degrees Celcius Å Angstrom AN acceptor number BCF tris(pentafluorophenyl)borane Bn benzyl BSSE basis set superposition effect C concentration ca. circa, about cf. confer, compared with CAAC 1-(2,6-diisopropylphenyl)-3,3,5,5- tetramethylpyrrolidin-2-ylidene COD 1,5-cyclooctadiene Cp cyclopentadiene Cp* pentamethylcyclopentadiene CSD Cambridge structural database DABCO 1,4-diazabicyclo[2.2.2]octane DAP diazaphospholene DFB 1,2-difluorobenzene DFT density functional theory Dipp 2,6-diisopropylphenyl Dur 2,3,5,6-tetramethylphenyl ECP effective core potential EI electron ionisation EPC electrophilic fluorophosphonium cation EPR electron paramagnetic resonance v ES electrospray equiv equivalent FIA fluoride ion affinity FLP frustrated Lewis pair GEI global electrophilicity index GIMC gauge-including magnetically induced current HBpin pinacolborane HMDS bis(trimethylsilyl)amide HOMHED harmonic oscillator model of heterocyclic electron delocalisation HOMO highest occupied molecular orbital HPLC high performance liquid chromatography hr hour HRMS high resolution mass spectrometry LA Lewis acid LANL2DZ Los Alamos National Laboratory 2-double-zeta LUMO lowest unoccupied molecular orbital M molar, mol dm-3 M06-2X Minnesota 06 MO molecular orbital MP2 Møller–Plesset perturbation theory NBO natural bond orbital NHC N-heterocyclic carbene NHP N-heterocyclic phosphenium nm nanometre NMR nuclear magnetic resonance vi OLED organic light emitting diode PCM polarisable continuum solvation model Ph phenyl PMB p-methoxybenzyl ppm parts per million RI Resolution of Identity approximation r.t. room temperature SV(P) split valence polarization tBu tert-butyl TD time dependent THF tetrahydrofuran TMSOTf trimethylsilyl trifluoromethanesulfonate TZP triple zeta valence polarization UV ultraviolet vs. versus VT variable temperature vii IV. Aims The overriding theme of this thesis is to produce a series of new benzo-fused-phosphole and benzo-fused-arsole derived compounds. By introducing sulfur, nitrogen and oxygen heteroatoms into the pnictole ring core, an interesting comparison and exploration into the fundamental properties and reactivity of this highly interesting but ultimately underexplored class of compound will be achieved. To elaborate further, a multitude of modern-day techniques, including multinuclear NMR spectroscopy, EPR spectroscopy, absorption and emission spectroscopy, single crystal X-ray diffraction and DFT calculations will be employed to bring this class of heterocycle into the 21st century. In Chapter 2 the aim is to synthesise a series of novel benzo-fused-phosphole and benzo- fused-arsole derived compounds, which bear a halogen co-ligand. This will create a library of complexes which will be used to explore the structural and electronic properties as well as provide pre-cursors to use in subsequent reactions. The aims of Chapter 3 are firstly to look at performing substitution of the chloride co-ligand to generate a N-centred paddlewheel. Secondly, the compounds from Chapter 2 will be used to synthesise the corresponding phosphenium and arsenium cations, and as they are 10π aromatic, investigate the optical properties. Lastly, the final objective is to reduce the benzo- fused diaza-chloro-phosphole and benzo-fused diaza-chloro-arsole to form the corresponding dimeric complex. Chapter 4 is inspired by the recent use of the closely related diazaphospholene complexes as pre-catalysts in hydroboration reduction catalysis. Thus, Chapter 4 has the main aim of using the phosphorus and arsenic compounds from Chapters 2 and 3, as well as producing a benzyloxy-phosphosphole and benzyloxy-arsole, to undergo hydroboration catalysis and give a comparison on the catalytic performance of using phosphorus vs. arsenic. viii V. Nomenclature Phosphane: The saturated hydrides of trivalent phosphorus of the general formula PnH2n+1. The simplest phosphane is PH3. Arsane: The saturated hydrides of trivalent arsenic of the general formula AsnH2n+1. The simplest arsane is AsH3. Phosphine: Organophosphorus compounds derived from PH3 by replacing one, two or three of the hydrogen atoms.