Date of Award
Doctor of Philosophy
The ligand amphos forms square planar Rh(I) complexes which catalyze the asymmetric homogeneous hydrosilation of ketones in up to 72% optical yield. Initially, modifications of the aminophosphine ligand, N,N-dimethyl-1-(o-(diphenylphosphino)phenyl)ethylamine, amphos, were prepared and their Rh complexes were tested as catalysts for the asymmetric hydrosilation of ketones. In the second approach x-ray crystallography, spectroscopic techniques, and conformational energy calculations were used to investigate the relationship between catalyst shape and efficiency.;Three modifications of the amphos ligand were prepared. In the first two the phenyl substituents on P were replaced by either cyclohexyl groups, dicyphos, or tert-butyl groups dibutphos. In the third modification one of the N-methyl groups in amphos was replaced by CH(,2)CH(,2)N(CH(,3))(,2) to produce the tridentate ligand diamphos. Neutral Rh complexes of amphos, dicyphos, and dibutphos and neutral and cationic Rh complexes of diamphos were tested as asymmetric hydrosilation catalysts. Two silanes and four ketones were employed as substrates to investigate the relationship between the shape and bulk of substrate substituents and the chemical and optical yields produced.;Four Rh-norbornadiene complexes of these ligands and the complex Ni(R-dicyphos)(NCS)(,2) were prepared and structurally characterized using x-ray crystallographic techniques. Preliminary results for the complex RhCl(,3)(R-diamphos) are also presented. Variable temperature ('1)H nmr spectroscopy and ('31)P nmr spectroscopy have been used to investigate the conformation and fluxionality of the metal-chelate ring in solution. Non-bonded potential energy calculations and molecular mechanics conformational energy minimization calculations have been performed for a selection of these complexes to identify the predominant conformation(s) in solution and the structural features which give rise to these conformations. The combined results of these two approaches provide the basis for an explanation of the optical efficiencies of the various catalysts in terms of their shapes and conformational rigidities in solution.
Mckay, Ian Douglas, "Studies In Asymmetric Hydrosilation" (1986). Digitized Theses. 1511.