Imidazol(in)ium‐2‐Carboxylates as N‐Heterocyclic Carbene Ligand Precursors for Ruthenium Metathesis Initiators

Abstract

AbstractSummary: Imidazol(in)ium‐2‐carboxylates were used as N‐heterocyclic carbene (NHC) ligand precursors to convert the [RuCl2(p‐cymene)]2 dimer into three ruthenium‐arene complexes of the [RuCl2(p‐cymene)(NHC)] type. The decarboxylation of NHC · CO2 betaines also provided a convenient synthetic path to prepare five well‐known ruthenium‐NHC catalysts for olefin metathesis and related reactions, including the second generation Grubbs and Hoveyda–Grubbs catalysts, via ligand exchange with phosphine‐containing, first generation ruthenium‐benzylidene or indenylidene complexes. Both procedures are particularly attractive from a practical point of view, because NHC · CO2 adducts are stable zwitterionic compounds that can be stored and handled with no particular precautions.