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Title: Complexes of chromium, vanadium and tantalum bearing monoanionic bidentate ligands : potential catalysts for the polymerisation of ethylene and a-olefins
Author: Chew, Kong Chin
Awarding Body: Imperial College London (University of London)
Current Institution: Imperial College London
Date of Award: 2000
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This thesis describes studies into the chemistry of chromium(VI) bis(imido), vanadium(V) and tantalum(V) in-Lido complexes with monoanionic bidentate ligands. The vanadium and tantalum complexes were targeted as potential catalysts in the polymerisation of ethylene and α-olefins. Chapter 1 highlights several important electronic and structural aspects of the imido ligand, along with the isolobal analogy between Group 4 bent metallocene, Group V imido-cyclopentadienyl and Group VI bis(imido) fragments. Several important polymerisation systems are briefly reviewed, in addition to the discussion of some monoanionic bidentate ligand systems which have been used in the design of the catalysts. Chapter 2 focuses on the syntheses of chromium(VI) bis(imido) complexes bearing [O-O]-, [N-O]- and [N-N]- ligands. A model NMR-scale reaction of Cr(NAr)2(ArN=CHC4H3N)Cl.MeCN (6) with A1Me3 showed that the bidentate ligand is abstracted by the aluminium reagent. The diazoalkane complex Cr(NAr)2(N2CHPh)(PMe3) (11) was isolated from the reaction of Cr(NAr)2(PMe3)2 with phenyldiazomethane. Chapter 3 describes the syntheses of similar derivatives of vanadium(V). McAlCl2 was found to be the most efficient co-catalyst for these systems in the absence of halocarbon promoters, giving very high activities with significantly longer catalytic lifetimes. Mass spectrometry analyses however revealed that the bidentate ligands were abstracted by the activator. The syntheses of the identified aluminium species were subsequently carried out and their influence in the ethylene polymerisation of the vanadium systems was investigated. Chapter 4 describes similar chemistry of tantalum(V). Four model compounds were prepared and these were subsequently methylated. The previously unreported Ta (N A r) Me3 (thf) (32) was isolated as a mixture in the reaction of Ta(NAr){McC(NAr)CHCOMe}C12(thf) (31) with McMgCI. The reaction of the compound Ta{McC(NAr)CHCOMe}C14 (34) with tBuNHSiMe3 showed that this was an alternative route into such imido derivatives. Chapter 5 outlines the experimental details for chapters 2,3 and 4.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available