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Interconversion between Ni and Pd bound n-heterocyclic carbenes and azolium salts: fundamental reactivity and applications to catalysis

Normand, Adrien 2008. Interconversion between Ni and Pd bound n-heterocyclic carbenes and azolium salts: fundamental reactivity and applications to catalysis. PhD Thesis, Cardiff University.

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Abstract

This thesis focuses on different aspects of the relationship between N-heterocyclic carbene (NHC) complexes of Ni and Pd and azolium salts, particularly imidazolium salts. Chapter one introduces the reader to the field of organometallic chemistry and homogeneous catalysis. General aspects of the chemistry of NHCs are then discussed. Chapter two describes studies aimed at optimising the recently discovered direct intermolecular coupling (via C-H activation and formation of an NHC hydride Ni(II) intermediate) of azolium salts with olefins. An extensive experimental study (in conjunction with DFT calculations conducted by Kirsty J. Hawkes and Brian F. Yates at the University of Tasmania) of the Ni(0)-catalysed reaction of l-propyl-3-methylimidazolium bromide ( pmimJBr) with ethylene revealed that the mechanism of this reaction changes with the size of the ancillary ligand. This reaction was further developed into an intramolecular version, allowing for the synthesis of fused-ring imidazolium salts bearing a chiral carbon atom. Extension of this chemistry to Lewis acid activated neutral azoles is also described, as well as the development of a Pd-catalysed version of the intermolecular coupling. In chapter three, the synthesis, solid-state (X-Ray) and solution phase (gs-NOESY) characterisation of a new family of cationic mixed phosphine/NHC Pd(II) 7t-allyl complexes of general formula Pd(7i-allyl)(NHC)PR3 BF4 are described. This family of compounds was designed to generate monoligated Pd-PR3 fragments upon thermal, solvent or olefin-mediated activation. For example, complex Pd(n3-C3H5)(tmiy)PCy3 BF4 (lb) was expected to generate an efficient catalyst for the Pd-catalysed coupling of olefins with azolium salts described in chapter two. Chapter four describes the catalytic activity of lb and studies of its activation mechanism. The serendipitous discovery of the reaction of lb with phenyl iodide, yielding a 2-phenylimidazolium salt and Pd(n3-C3H5)(I)PCy3) is reported as well as subsequent studies aimed at elucidating the scope and mechanism of this reaction.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303209765
Date of First Compliant Deposit: 30 March 2016
Last Modified: 12 Feb 2016 23:12
URI: http://orca-mwe.cf.ac.uk/id/eprint/54635

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