Cp*RuCl-Vinyl Carbenes: Two Faces and the Bifunctional Role in Catalytic Processes

Abstract

Ruthenium vinyl carbenes derived from Cp/Cp*RuCl‐based complexes (Cp=cyclopentadiene, Cp*=1,2,3,4,5‐pentamethylcyclopentadiene) have been routinely invoked as key intermediates in tandem reactions involving a carbene/alkyne metathesis (CAM). A priori, these intermediates resemble the Grubbs‐type family of catalysts, but they exhibit a completely different reactivity pattern that few, if any, other catalytic system can reproduce so far. The reactivity of these species with α‐unsubstituted and α‐substituted alkynals showcases the peculiarities of these intermediates. Although Z‐vinyl dihydrooxazines are preferentially obtained with the former, Z‐vinyl epoxypyrrolidines are obtained with the latter. A combination of spectroscopic and computational data now prove that a η3‐coordination mode of the ruthenium vinyl carbene and the presence of a Lewis basic chloride ligand give rise to two markedly different stereoelectronic faces, which are responsible for the unconventional reactivity of these species.