Two Different, Metal-Dependent Coordination Modes of a Dicarbene Ligand

The bisimidazolium salt H₂-1(PF₆)₂ featuring a bridging 1,4-phenylene group reacts with 0.5 equiv of [PdCl­(allyl)]₂ in the presence of Cs₂CO₃ to give the dinuclear complex [2]­(PF₆)₂, whereas the reaction of the same bisimidazolium salt with 0.5 equiv of [Ir­(Cl)₂(Cp*)]₂ yields the mononuclear orthometalated complex [3]­PF₆ with one remaining imidazolium unit. The unreacted imidazolium group in complex [3]­PF₆, however, can also be metalated with Rh^III to yield the doubly orthometalated heterobimetallic complex [4]. In complex [4], each M^III center (M = Ir^III and Rh^III) is coordinated by one NHC unit and orthometalates the central aryl ring of the ligand.