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Title: Synthesis and characterisation studies of organozinc carboxylate complexes
Author: Harris, Jonathan Edward
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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The motivation for this project lies in furthering the understanding of the structure and properties of organozinc carboxylate complexes, both as discrete complexes and as coordination compounds. The thesis centres on the interaction between organozinc complexes and CO2, the insertion of which forms an organozinc carboxylate complex. A series of arylzinc carboxylate species, of the general form [ArZn(O2CR)], have been synthesised and their solution structures have been studied by NMR spectroscopy (Ar = Ph, C6F5; R = Me, Ph, C6F5). NMR experiments indicate that the ligand stoichiometry of the complexes depends on the nature of the solvent (coordinating vs non-coordinating) and, in the case of Ar = R = C6F5, can alter the Schlenk equilibrium present in this species, shifting the equilibrium towards a single heteroleptic product. The reaction of discrete diorganozinc complexes of the form ZnR2 (R = Et, Ph, C6F5, C3H5) and CO2 has also been explored. It was found that CO2 inserts cleanly into the Zn-R bond of all the investigated complexes, however the purity of the CO2 is extremely important due to the propensity for organozinc complexes to react with water. The kinetics of the insertion reaction were monitored using 1H NMR spectroscopy and the reaction was found to be first-order in all cases, with an order of reactivity for the series of Zn(C3H5)>ZnPh2>ZnEt2>Zn(C6F5)2. Finally, a series of N,N,O-phenolate zinc complexes of the form 2-tert-butyl-4-R-6-{[(2ʹ-dimethylaminoethyl)methylamino]methyl}-phenyl-ZnRʹ (R = tert-Bu, OMe, NO2; Rʹ = H, Et, Ph) have been synthesised. The structure of the complexes was studied, and it was found that the hydride complexes are a rare example of mononuclear zinc terminal hydrides, as indicated by both NMR and X-ray diffraction experiments. As well as characterising their structure, these complexes were also tested for their reactivity towards CO2. It was observed that the hydride complexes reacted extremely rapidly to yield formate complexes, only limited by diffusion of CO2 into the reaction solvent. However, the phenyl and ethyl complexes showed little reactivity at 298 K, but if heated to 398 K, the phenyl complexes did insert CO2.
Supervisor: Williams, Charlotte ; Shaffer, Milo Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available