The Interplay of Cyclometalated-Ir and Mesoionic Imines: Stoichiometric and Catalytic Reactivities

Triazole-based mesoionic imines (MIIs) make up a new class of compounds that possess ambivalent electronic structures and unusual chemical reactivities. We present here two MIIs that display strong intra- and intermolecular hydrogen bonding. Whereas the former is responsible for the selectivity of C-H activation reactions in these molecules, the latter strongly determines their UV-vis signatures. The cyclometalated iridium complexes with MIIs form either coordinatively unsaturated compounds (with Mes substituents) or undergo dimerization (for Ph substituents) through the "imine-N" atom of the MIIs. The coordinatively unsaturated cyclometalated Cp*Ir-MII complex reacts with several substrates such as PPh₃, CO, azide, and ethyl. The CO and, in particular, the ethyl-bound Cp*Ir complex are rare cases of stable and crystallographically characterized Cp*Ir complexes with these ligands. Additionally, the IrCp*-MII complex undergoes double C-H activation through the coordination of a second IrCp* fragment. Intriguingly, the cyclometalated IrCp*-MII complexes react with 3 equiv of an activated alkyne to produce an unusual bicyclic compound that contains one six-membered and one eight-membered iridacycle. Furthermore, the coordinatively unsaturated IrCp*-MII complex is an active transfer hydrogenation catalyst. The first comprehensive report on the reactions of transition metal complexes of MIIs shows the potential of these new ligands in organometallic reactivity.