Hoveyda and Schrock showed recently that monoaryloxide-pyrrolide Mo catalysts are Z selective for selected internal olefins and polymerization of norbornenes.1 In this new paper they show that similar Mo- or W-catalysts can be used to effect self-cross metathesis of terminal olefins with very high Z-selectivity.2 Highly Z-selective homocoupling of terminal olefins to make acyclic products has never been observed before.
The coupling was demonstrated with different substrates and works with as little as 0.2 mol% catalyst. As a general rule, the W catalysts were shown to be more selective than Mo systems. A number of reactions proceeded with >90% Z-selectivity and in good yields. The selectivity of the reaction is attributed to the large aryloxide ligand, which serves two purposes. First, it allows only the formation of metallacyclobutenes with adjacent cis substituents. Second, it causes the isomerization of the Z-product to the E-product to be slow.
1Flook, M. M.; Jiang, A. J.; Schrock, R. R.; Müller, P.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 7962.
2Jiang, A. J.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H.; J. Am. Chem. Soc. 2009, 131, 16630.