Ruthenium’s Turn For Z-Selectivity

Peili Teo and Robert H. Grubbs of California Institute of Technology are reporting the preparation of ruthenium olefin cross-metathesis catalysts that improve selectivity for making Z (cis) alkenes, which are common in natural products and thus important to synthetic organic chemistry (Organometallics, DOI: 10.1021/om1007924). In the past, nearly all ring-opening and cross-metathesis reactions catalyzed by Grubbs’s ruthenium catalysts or by molybdenum catalysts such as those prepared by Massachusetts Institute of Technology’s Richard R. Schrock predominantly yielded E (trans) alkenes. Schrock, Amir H. Hovedya of Boston College, and coworkers recently developed molybdenum monoalkoxide-pyrrolide catalysts that are successful in selectively making Z alkenes (C&EN, Sept. 13, page 33). Teo and Grubbs have followed suit with ruthenium N-heterocyclic carbene catalysts that contain bulky sulfonate and phosphate ligands. For example, the sulfonate catalyst shown is easy to prepare, air-stable, and has higher reactivity and Z-selectivity than other known ruthenium catalysts in cross-metathesis reactions to make functionalized olefins. “Although these systems do not meet the levels of Z-selectivity of the best molybdenum catalysts, their ease of preparation and utilization should make them useful for a number of applications,” Teo and Grubbs write.