Z-Selective Ruthenium Metathesis Catalysts
Stereocontrol in olefin metathesis is an ongoing challenge because of the thermodynamic preference for E-olefin products. Here, we describe the preparation of new ruthenium metathesis catalysts formed via the carboxylate-induced C-H activation of an N-heterocyclic carbene ligand. These catalysts adopt a unique geometry that results in unprecedented selectivity for Z-olefins in a variety of reactions including cross-metathesis, macrocyclic ring-closing metathesis, and ring-opening metathesis polymerization. Moreover, we show that they are effective at low catalyst loadings and can survive prolonged exposure to dioxygen, water, and a variety of common functional groups. Finally, we present extensive experimental and theoretical investigations into the mechanism of this new class of ruthenium metathesis catalysts and the origin of their remarkable Z-selectivity.