Mechanism of <i>Z</i>‑Selective Olefin Metathesis Catalyzed by a Ruthenium Monothiolate Carbene Complex: A DFT Study

A ruthenium monothiolate carbene complex (2cat) readily derived from the Grubbs–Hoveyda system is among the newly developed catalysts for Z-selective olefin metathesis reactions. We have performed density functional theory calculations (B3LYP and M06) to elucidate the detailed mechanism of 2cat-catalyzed homometathesis of terminal olefins. The five-coordinate 2cat dissociates to a tetrahedral intermediate, from which two consecutive metathesis events via the bottom-bound olefin attack mechanism lead to (Z)-olefins as major products. The Z selectivity stems from the bulky thiolate ligand, which sterically forces both olefinic substituents to the far side of the metallacyclobutane ring to achieve a Z geometry in the resulting olefin product.