An Investigation of Novel Heterobimetallic Carbido Complexes

Abstract

Chapter One comprehensively reviews low nuclearity mu-carbido complexes. Compound classes are introduced emphasising synthetic routes while recounting examples of reactivity that demonstrate capability of mu-carbidos given further development. Specific attention is paid to metallacarbynes and ultimately introduces the premise of this thesis: the first dedicated study of Class B mu2-carbido complexes. Chapter Two explores the relationship between halocarbynes and metallacarbynes. Halocarbynes are reviewed, in advance of investigations into the pi-coordination of [M(CX)(CO)2(Tp*)] (M = Mo, W; X = Cl, Br) to late transition metals (AuI, Pt0) to provide a series of mu2-halocarbynes. The conversion of mu2-halocarbynes to mu2-carbidos via C-halogen activation is then described, supported by computational studies to explore halocarbyne bonding in the context of Fischer-Schrock paradigms. Chapter Three expands the range of metallacarbyne complexes through ligand substitution reactions of [WPt(mu2-C)Br(PPh3)2(CO)2(Tp*)] facilitated by the development of a multi-gram synthesis. Study of this library, which varies according to charge and ligand donors, allows the identification of trends. Chapter Four investigates substitution of [WPt(mu2-C)Br(PPh3)2(CO)2(Tp*)] with isocyanides, to increase electron density and reduce steric protection for further reactivity. A strong solvent dependence was observed whereby non-polar media provide the expected species whilst polar media afforded previously unknown mu2-iminoketenylidene (mu2-CCNR) ligands. Chapter Five explores reactions of [WPt(mu2-C)Br(PPh3)2(CO)2(Tp*)] with organometallic nucleophiles. Halide metathesis occurs with MeLi and n-BuLi, however the latter provides cis-[WPt(mu2-C)(n-Bu)(PPh3)2(CO)2(Tp*)] that undergoes beta-hydride elimination to generate a rare parent mu2-methylidyne [WPt(mu2-CH)(PPh3)2(CO)2(Tp*)]. Chapter Six explores cross-coupling reactions of halocarbynes akin to Sonogashira, Suzuki-Miyaura and Stille processes. Key palladium carbidos [MPd(mu2-C)Br(PPh3)2(CO)2(Tp*)] (M = Mo, W) are spectroscopically observable but evolve upon isolation to halo-bridged dimers, a process that may be diverted by introduction of chelating diphosphines. Suzuki-Miyaura cross-coupling of halocarbynes was optimised to produce functionalised carbynes. During catalysis, phosphoniocarbynes act as counter-productive tangents and undergo reactions with sulfur to produced novel thiocarbonylphosphorane and arsorane species. Chapter Seven utilises stannylcarbyne transmetallation to yield gold(I) and mercury(II) metallacarbynes. Optimisation of the known tetrameric species [W(CAu)(CO)2(Tp*)]4 afforded access to mononuclear gold(I) metallacarbynes disaggregated with nucleophiles such as phosphines, isocyanides and N-heterocyclic carbenes. Mercury(II) metallacarbynes bearing aryl substituents (Hg-C bonds) form complex mixtures due to dynamic equilibria, however under careful control of stoichiometry, [HgCl2] provides trimetallic [W2Hg(mu2-C)2(CO)4(Tp*)2], tetrametallic [WHg(mu2-C)Cl(CO)2(Tp*)]2 or hexametallic [W2Hg2(HgCl)2(mu3-C)2Cl2(CO)4(Tp*)2] complexes. The complex [W2Hg(mu2-C)2(CO)4(Tp*)2] presents a well-defined carbyne transfer agent, in addition to a dithiocarbamate analogue [WHg(mu2-C)(S2CNMe2)(CO)2(Tp*)] useful for further studies. Chapter Eight explores the application of [W2Hg(mu2-C)2(CO)4(Tp*)2] and [WHg(mu2-C)(SCNMe2)(CO)2(Tp*)] as reagents towards further mu-carbido species through two different processes. Firstly, oxidative addition of reactive Hg-C bonds in [WHg(mu2-C)(S2CNMe2)(CO)2(Tp*)] results in a family of heterobimetallic metallacarbynes spanning the metals Pt, Pd, Ni, Ir, Rh and Ru. Secondly, reluctant reactions of osmium with the dithiocarbamate precursor is overcome via hydride abstraction with [W2Hg(mu2-C)2(CO)4(Tp*)2] to produce the first osmium mu2-carbido complex of any sub-class as a versatile precursor to a family of osmium metallacarbynes. Show more