Aspects of the hydrozirconation-isomerisation reaction

Abstract

Aspects of the hydrozirconation-isomerization of nonfunctionalised olefins are discussed. Cyclooctene and 1-methyl-1-cyclohexene were previously reported not to react with Cp 2Zr(H)Cl. In the present work after treatment of the former with Cp 2Zr(D)Cl, and subsequent hydrolysis, no cyclooctane could be detected. Although the olefin seemed not to have reacted, it was deduced that the corresponding cyclooctylzirconium was in fact formed, since the amount of deuterium incorporated in cyclooctene was roughly the same as the amount of zirconium deuteride used. Total scrambling of deuterium was observed. Cycloheptene and 2,2,11,11-tetramethyl-6-dodecene gave similar results. 1-Methyl-1-cyclohexene, on the other hand, was very unreactive. No evidence for deuterium incorporation in the recovered olefin (80–90%) was obtained. When Z-5-decene was used as substrate, zirconium migration towards the terminal carbon, and cis-trans isomerisation, were slower than expected. No internal alkylzirconium derivatives could be trapped. Competing hydrogenation of 1- and Z-5-decene is favoured when a deficiency of the zirconium hydride is used.