ZIRCONOCENE-(MU-ORGANYL)BORATE BETAINES DERIVED BY TREATMENT OF A (SIGMA-ALKENYL)(SIGMA-ALKYNYL)ZIRCONOCENE COMPLEX WITH TRIS(PENTAFLUOROPHENYL)BORANE

Hydrozirconation of propyne followed by treatment with propynyllithium yields the (sigma-propenyl)(sigma-propynyl)zirconocene complex 11. It s treatment with the organometallic Lewis acid B(C6F5)(3) results in t ransfer of the sigma-propynyl group from zirconium to boron followed b y insertion of the alkynylborate triple bond into the zirconium carbon bond of the remaining metallaallyl cation to furnish the zirconocene( mu-hydrocarbyl)borate betaine complex 14. This reacts with three molar equivalents of tert-butyl isocyanide to give 16. Complex 16 contains a five-membered carbocyclic ring, formed by carbon-carbon coupling of the former propenyl and propynyl groups with the C=N-R reagent, to whi ch a (eta(2)-iminoacyl)(kappa-tert-butyl isocyanide)zirconocene moiety is attached. Complex 16 was characterized by an X-ray crystal structu re analysis.