Bis-coordination of <i>N</i>-(Alkyl)-<i>N</i>‘-(2,6-diisopropylphenyl) Heterocyclic Carbenes to Grubbs Catalysts

Abstract

N-(Alkyl)-N'-(2,6-diisopropylphenyl) carbenes display an exceptional tendency toward bis(NHC) coordination in their reaction with the Grubbs complex [RuCl2(CHPh)(PCy3)2]. The resulting bis(NHC) complexes show substantial olefin metathesis activity at elevated temperature. One NHC ligand is expected to dissociate from the metal center for the catalyst to be activated. This NHC ligand lability is confirmed by the observation that both NHCs are exchangeable when the complexes are treated with an excess of PCy3. In addition, the isolation of a new mono(NHC) complex is described, as well as its reactivity in the ring-opening metathesis polymerization (ROMP) of cycloocta-1,5-diene and the ring-closing metathesis (RCM) of diethyl diallylmalonate.