Di-Mesoionic Carbene-Bridged Complexes of Rh2, Ir2, and RhIr: A Stepwise Metalation Strategy for the Synthesis of di-MIC-Bridged Mixed-Metal Systems

A meta-substituted benzene-bridged ditriazolium salt has been prepared using copper-catalyzed azide–alkyne cycloaddition (CuAAC or “click” chemistry) and methylation protocols. Metalation of this dicationic species by basic-ligand-containing [Rh­(μ-OMe)­(COD)]2 and [Ir­(μ-OMe)­(COD)]2 precursors provides homobimetallic complexes of Rh and Ir bridged by a 1,2,3-triazol-5-ylidene-type di-mesoionic carbene (di-MIC) via an “internal-base” strategy. By using only 1/2 equiv of the internal-base precursor, mononuclear MIC-anchored/pendent-triazolium intermediates have been isolated, in which only one end of the ditriazolium salt has been deprotonated and attached to Rh or Ir. Reaction of these pendent intermediates with another 1/2 equiv of an internal-base precursor affords either the aforementioned homobimetallic products or an analogous di-MIC-bridged, mixed-metal Ir/Rh complex.