Synthesis and applications of chiral, Group IV metallocenes

Bell, Jane Louise (1995) Synthesis and applications of chiral, Group IV metallocenes. University of Southampton, Doctoral Thesis.

Abstract

Zirconocene catalysed carbometallations of alkenes has been reviewed and the work of other research groups discussed.

The production of 1,4-dimagnesium reagents via the zirconium catalysed ethylmagnesiation reaction has been investigated. Extensions of the process to produce a range of alcohols, and a new method for the preparation of Grignard reagents from secondary amines, are presented.

The range of chiral titanocene and zirconocene complexes currently available from the literature has been surveyed. Several known, chiral zirconium complexes have been synthesised and applied to the asymmetric zirconium catalysed ethylmagnesiation of alkenes. Both the yields and enantiomeric excesses of the products were low to moderate (5 - 39% yield, up to 30% ee).

Using observations from the known complexes, a new class of cheap, chiral zirconocene catalysts was designed. The synthesis of the novel metallocenes was straightforward and an X-ray structural determination of one enantiomer of the complex obtained. The compounds were applied to the zirconium catalysed ethylmagnesiation of alkenes and the resolution of dihydrofurans. The complexes were found to be active and as little as 2 mol% of the chiral catalyst was required for product yields of up to 95%. The enantiomeric excesses of the elaborated products were good (up to 92%). By application to the ethylmagnesiation of an amine, the quantitative recovery of the catalyst was demonstrated.

The titanium analogue of the new zirconium complex was prepared and its synthesis is discussed. The titanocene complex has been applied to the reduction of enamines to furnish a chiral amine with a 30% enantiomeric excess.

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