Anderson, D. R.; Ung, T.; Mkrtumyan, G.; Bertrand, G.; Grubbs, R. H.; Schrodi, Y. A Kinetic Selectivity of Olefin Metathesis Catalysts Bearing Cyclic (Alkyl)(Amino)Carbenes Organometallics, 2008, 27, 563-566.
Ethenolysis, the efficient cross metathesis of an internal olefin with ethylene while avoiding non-productive self-metathesis—the cross metathesis of the internal olefin with itself—remains a significant challenge for catalyst development. There’s a delicate selectivity balance between ethenolysis activity and undesired self-metathesis activity. For example, 1st generation Grubbs catalysts are generally selective for ethenolysis, but overall less reactive (turnover numbers (TON) <15,000), while 2nd generation Grubbs catalysts are more active overall but form fewer products from ethenolysis.
From the collaborative effort between the research groups of Robert H. Grubbs, Guy Bertrand, and Materia, a notable advancement towards efficient ethenolysis reactions have been made using a group of novel cyclic(alkyl)(amino) carbene (CAAC) ruthenium catalysts. These CAAC catalysts seem to give the best of both worlds: the selectivities of 1st generation Grubbs catalysts and the reactivity of 2nd generation catalysts. The catalyst shown below gave the highest ethenolysis TON to date (>35,000).
The development of novel catalysts with high activity and selectivity is an ongoing research effort. New ligand design and synthesis appear to be the key to achieving these goals.