Stereochemistry and catalysis with zirconium complexes

Abstract

Mono- and bis(η-cyclopentadienyl)zirconium complexes show interesting stereochemical featureswith regard to their use in organometallic and organic synthesis as well as in catalysis. An example is described where the zirconocene unit serves to stabilize a planar tetracoordinate carbon center. Next, various building blocks (a metal carbonyl, an organic carbonyl compound, a conjugated diene, plus one or two organic alkylating electrophiles) are assembled at the Cp2Zr-moiety and stereoselectively coupled to give new functionalized heteroatom stabilized carbene complexes or directly organic products. Chiral (R*Cp)2Zr-derived metallocene/alumoxane Ziegler-type catalysts have been used for propene polymerization. It is shown that chain end control and enantiomorphic site control are not operating independently for determining the product stereochemistry. Additivity effects have been disclosed in a series of [Cp-CHRlR2]2rCl2-derived olefin polymerization catalysts with regard to the degree of stereocontrol exercised by the chiral metallocene unit. Finally, the preparation of the new chiral Lewis acid “(diboma-Cp)zirconium trichloride” and applications in enantioselective catalysis are described. © 1991 IUPAC