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Title: An investigation of the phosphonium salts [R'P(CH₂Ph)₃]X and [R'P(NHR)₃]Br as potential tripodal ligands
Author: Barrett, Tony
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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Our interest in developing new ligands for asymmetric catalysis by octahedral metal complexes has led us to consider ways in which tripodal ligands may be used to reduce their symmetry to C3 and thus provide three homotopic coordination sites for substrate coordination opposite the ligand. Initial attempts at producing our desired coordination mode concentrated on using the system [C(NR)3]2- as an isoelectronic analogue of the well established trimethylenemethane ligand. However, although these proved to be interesting chelating and bridging ligands, the distortion from planarity required for the h3-coordination of such Y-shaped ligands is precluded by the energy associated with the in-plane p-bonding in such systems. In order to address this problem we have begun employing ligands centred on tetrahedral rather than planar atoms which effectively have the required distortion built in to the ligand before coordination. The synthesis and characterisation of the phosphonium salts [R'P(CH2R)3]Cl and [R'P(NHR)3]Br as precursors to such ligands is described herein. Studies of the identified phosphonium salts were then carried out in order to prove that a proton can be removed from all three of the potential donor atoms, and that formation of the dilithiates [R'P(CHR)Li2] and [R'P(NR)Li2] results on treatment of the phosphonium salts with three equivalents of n-butyllithium. Methylation studies and in-situ NMR proved formation of the dilithiates but attempts to obtain crystallographic evidence of the dilithiate form of the ligand were unsuccessful, with only double deprotonated (monolithiate) species being observed. Reactions of the nitrogen donor ligands [R'P(NR)3]2- with various metal precursors are highlighted in Chapter 4. Chromium, ruthenium, rhodium and palladium complexes containing the phosphorous centred nitrogen donor ligands have been crystallographically analysed. All complexes isolated contain the nitrogen donor ligands in a h2-coordination mode. Reactions of the carbon donor ligands [R'P(CHR)3]2- with various metal precursors are highlighted in Chapter 5. Chromium, ruthenium, rhodium and platinum complexes containing the phosphorous centred carbon donor ligands have been crystallographically analysed. The complexes isolated have shown the carbon donor ligands to be flexible and versatile chelating ligands, but the desired h3-coordination mode was not observed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available