CONSIDERATION OF THE MECHANISM OF THE TRANSITION-METAL CATALYZED OLEFIN METATHESIS REACTION - METATHESIS OF CIS,CIS-2,8-DECADIENE

The analysis of the scrambling pattern of the acyclic olefins resulting from the metathesis of 1, 7-diene systems allows a distinction to be made between two general classes of mechanisms of this reaction. This analysis requires no scrambling of the labels in the starting materials or products. These experimental restrictions are firmly established by examining the metathesis of a mixture of cis, cis-2, 8-decadiene and cis, cis-2, 8-decadiene-1, 1, 1, 10, 10, 10-d6. The 2-butene produced in this reaction has a cis/trans ratio of 5 at low conversion. The cis/trans ratio approaches an equilibrium value as the conversion of the diene approaches completion. Extrapolation of a plot of cis-/trans-2-butene vs. label ratio to zero stereoisomeric scrambling (trans/cis = 0) gives values of the isotopic label ratio resulting from zero scrambling. The extrapolated value is that expected for a one-carbon chain (carbene) mechanism. These studies allow distinctions between the mechanisms to be made at high (20-30%) conversions. © 1979, American Chemical Society. All rights reserved.