A New, Highly Active Bimetallic Grubbs–Hoveyda–Blechert Precatalyst for Alkene Metathesis

A new Grubbs−Hoveyda−Blechert alkene metathesis catalyst, in which the benzylidene ligand has been coordinated to a highly electron-withdrawing tricarbonylchromium moiety, is presented. The structure of the complex provides evidence for a so far unreported attractive interaction between the benzylidene hydrogen atom and one of the mesityl substituents at the Arduengo carbene ligand. Screening of the catalytic properties shows that the activity of the new catalyst in ring-closing, enyne, cross, and homo metathesis of alkenes is comparable and in some cases better than that of known catalysts.