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Title: Phobane complexes : restricted M-P rotation and their applications in catalysis
Author: Lister, Julia Margaret
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2013
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A series of alkyl phobane ligands PhobPR (R = nBu, iBu, sBu, sPn, ipn, CH2SiMe), menthyl, CH2C4H70) have been prepared by electrophilic Or nucleophilic routes as pure s- or a -isomers. Reaction of these ligands with [PtCI(NCIBu)2] or [PdCh(NCPh)2] gave square planar trans-[MCh(PhobPR)2] (M = Pt, Pd) complexes. Variable temperature 31p {H} NMR studies on the trans-[MC12(PhobPRh)2] complexes revealed restricted rotation about the M-P bond. The complexes generally existed in two forms: with R groups on opposite sides of the square plane (anti, C2h-symmelry) or on the same side (syn C2v-symmetry). Free energies of activation for the fluxional process of interconversion between the two rotamers were calculated ranging 8-17 kcal mol-1. The experimental hypotheses were supported by OFT calculations. Reaction of thc alkyl phobane ligands with ligands with [PtCb(COD)] gave square planar The cis-[Pt,CI2,(PhobPR)2] complexes displayed similar fluxionality to their analogous trans-{PtCI2(PhobPR)2] complexes showing anti (C2-symmetry) and syn (C3--symmetry) rotamers. Reaction of the alkyl phobane ligands with [Rh(diene2),] [BF4] (diene= nbd, COD) gave [Rh(diene)(PhobPR),][BF,l complexes. Steric effects were used to form pseudo-chelating ligands and this novel ligand design principle was applied to rhodium-catalysed asymmetric hydrogenation giving 40% enantioselectivity. Long chain B-branched tertiary phobane ligands were prepared by stoichiometric or catalysed routes as pure s- or a- isomers or as s/a mixtures. In order to gain an understanding of the B-effect, the platinum coordination chemistry was probed and the ligands were evaluated in cobalt-catalysed hydroformylation. The high molecular weight catalysts gave a higher percentage of the linear aldehyde product and a slightly lower paraffin make but also a lower rate of catalysis compared to low molecular weight PhobPR catalysts. C-centred and N-centred tripodal triphosphine ligands have been synthesised. The platinum and silver coordination chemistry was investigated generating some interesting results arising from the different bonding modes of tripodal ligands. The ligands have been tested in ruthenium-catalysed ester hydrogenation and palladium- and ruthenium-catalysed Il1cthoxycal'bonylation producing some promising initial results.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available