ADJUSTING THE FEATURES OF ACTIVE METALLOCENE ZIEGLER SYSTEMS FOR THEIR POTENTIAL USE AS CARBON-CARBON COUPLING CATALYSTS IN ORGANIC-SYNTHESIS

A variety of bent metallocene dichloride/methylalumoxane catalysts, de rived from the zirconocene complexes 10, 12-18, have been employed in intramolecular olefin-coupling reactions yielding monomeric or dimeric products. This was achieved by using optimized reaction conditions em ploying low substrate concentrations (1.0-1.8 M) and rather long react ion times. Under these particular conditions, 1,5-hexadiene was cyclod imerized to give 1-methylene-3-(cyclopentylmethyl)cyclopentane (11). 1 ,6-Heptadiene was cleanly converted to methylenecyclohexane, and cis-1 ,2-divinylcyclopentane (19) and cis-1,2-divinylcyclohexane (22) were c yclized to yield 2-methylenebicyclo[3.3.0]octane (20) and 7-methyleneb icyclo[4.3.0]nonane (23), respectively. In many cases, the cyclization products were accompanied by isomers originating from double-bond shi ft reactions that often occur rapidly at these catalyst systems under the specific reaction conditions chosen to keep the products in the mo nomeric regime.