Deactivation of Z-selective olefin metathesis catalyst via 1,2-sulfide shift

Abstract

Since the advent of olefin metathesis, stereoselective olefin metathesis catalysts have been sought after for use in academic and industrial applications. The most recently reported Ru-complex for Z-selective olefin metathesis features a catechothiolate ligand, and this catalyst has been shown to be esp. useful in ring-opening metathesis polymn. and ringopening-cross metathesis. However, this catalyst is prone to deactivation, as the electron-rich sulfur in the catechodithiolate ligand is susceptible to undergo a 1,2-shift to the neighboring electrophilic alkylidene, which effectively deactivates the catalyst. Hoveyda et al. used electroneg. groups on the dithiolate ligand to diminish the rate of the proposed isomerization and thus favor olefin metathesis towards high-value Z-allylic alc. products. However, a deeper study of the mechanism of deactivation and a further anal. of the electronic structure is necessary in order to understand the deactivation pathway and tune the catalyst to disfavor this 1,2-shift. Guided by expts., we present a computational study of the reaction pathway and present results on the electronic nature of the catalytically active species. We study the propensity for the catalytic species to undergo deactivation by analyzing the altered electronic structure that results from substrate coordination and alkylidene substitution. This work serves as grounds for understanding the reactivity of this new class of Ru-complexes and we propose design principles for further development of these catalysts for academic and industrial use.