Phosphine-Based Z-Selective Ruthenium Olefin Metathesis Catalysts

Abstract

Whereas a number of highly Z-selective ruthenium-based olefin metathesis catalysts bearing N-heterocyclic carbene ligands have been reported in recent years, Z-selectivity has so far been difficult to achieve for phosphine-based catalysts. Guided by predictive density functional theory (DFT) calculations, we have developed phosphine-based ruthenium olefin metathesis catalysts giving 70–95% of the Z-isomer product in homocoupling of terminal alkenes such as allylbenzene, 1-octene, allyl acetate, and 2-allyloxyethanol. Starting from a moderately selective catalyst, [P(Cy)3](-S-2,4,6-Ph-C6H2)ClRu(═CH-o-OiPrC6H4) (4, Cy = cyclohexyl, iPr = isopropyl), obtained by substituting a chloride of the Hoveyda–Grubbs first-generation catalyst with 2,4,6-triphenylbenzenethiolate, we moved on to replace Cl and PCy3 by chelating, anionic phosphine ligands. Such ligands increase selectivity by limiting rotation around the P–Ru bond and by specifically directing the steric bulk of the phosphine substituents toward the sele...