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Title: E-H bond activation by d⁰ and d¹⁰ metal centres
Author: Nako, Adi Edmund
ISNI:       0000 0004 6059 1332
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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In recent years there has been a drive to study the catalytic dehydrocoupling of various protic and hydridic partners that contain E-H bonds (E = C, N, P, B, Si, Sn). This is in part due to the high atom-efficiency of these reactions as well as their ability to release dihydrogen in a controlled and potentially reversible manner. Transition metal complexes have historically been employed as catalysts for these reactions. Nevertheless, in recent years there has been growing interest in using complexes of the rare earth and main group metals to the same end. For these redox reluctant metals, the lack of multiple stable oxidation states makes σ-bond metathesis the predominant mechanistic step. This contrasts with the common two-electron and one-electron pathways often observed for transition metals. A diverse selection of mechanistic pathways have emerged with complementary activities and selectivities often reported for transition metal and non-transition metal systems. This thesis describes the activation of various E-H (E = C, Si, N, Al, Zn) bonds by do and d10 metal centres in both catalytic and stoichiometric regimes. The [Y{N(SiMe3)2}3] catalysed C-H silylation of triphenylphosphonium methylide with phenylsilane to give Ph3PCHSiH2Ph is reported. This is the first known example of C-H silylation of an ylide, and was found to be highly dependent on the nature of the pre-catalyst. Whilst exploring the reaction chemistry of the same yttrium complex, the first known example of the catalytic dehydrocoupling of Al-H/N-H bonds was discovered. This latter reaction offers a new synthetic route to form Al-N σ-bonds from sterically hindered alane and amine partners. The yttrium mediated dehydrocoupling of Si-H/N-H bonds is also documented with an emphasis on the potential for ligand acceleration of catalysis by a cyclometalated phosphonium ylide complex. As part of these studies, the synthesis of a series of structurally diverse aluminium hydride complexes is discussed. These complexes were not only investigated in the aforementioned dehydrocoupling reaction, but also as ligands for transition metals in their own right. The coordination of both Al-H and related Zn-H σ-bonds to copper(I) was observed in both solution and the solid state and this interaction was characterised by a number of spectroscopic techniques.
Supervisor: Crimmin, Mark ; Long, Nicholas Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral