Following the catalyst wherever she goes: Forays into the fundamental behavior of active, on-cycle intermediates in Ru-catalyzed olefin metathesis

Abstract

Ru-catalyzed olefin metathesis, an exceptionally versatile means of constructing new carbon-carbon bonds, has transformed org. synthesis in academia. Groundbreaking advances enabled by the N-heterocyclic carbene-stabilized, "second-generation" Ru catalysts (e.g. GII, HII; Chart 1) range from the RCM assembly of recent blockbuster hepatitis C virus therapeutics to the elaboration of renewable plant oils into value-added products and chems. Important limitations, however, arise from catalyst decompn. Notwithstanding an abundance of studies on the synthesis of new catalysts, and on the decompn. processes operative for the inactive, off-cycle species, the fundamental principles that govern activity and decompn. for the active, on-cycle intermediates (e.g. Ru-1, Ru-2; Chart 1) have been surprisingly little examd. A key reason for this is their high reactivity, which makes them elusive targets for study. Nonetheless, such understanding is an essential tool for informed catalyst and process redesign. Here we discuss recent insights into the reactivity and decompn. of active intermediates in metathesis, with emphasis placed on fundamental principles, and some solns.