Adjusting the Features of Active Metallocene Ziegler Systems fot Their Potential Use as Carbon–Carbon Coupling Catalysts in Organic Synthesis

A variety of bent metallocene dichloride/methylalumoxane catalysts, derived 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 employing low substrate concentrations (1.0-1.8 M) and rather long reaction times. Under these particular conditions, 1,5-hexadiene was cyclodimerized 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-divinylcylohenxane (22) were cyclized to yield 2-methylenebicyclo[3.3.0]octane (20) and 7-methylenebicyclo[4.3.0]nonane (23), respectively. In many cases, the cyclization products were accompanied by isomers originating from double-bond shift reactions that often occur rapidly at these catalyst systems under the specific reaction conditions chosen to keep the products in the monomeric regime.