The Interplay\nof Cyclometalated-Ir and Mesoionic Imines:\nStoichiometric and Catalytic Reactivities

Triazole-based mesoionic imines (MIIs) make up a new\nclass of compounds\nthat possess ambivalent electronic structures and unusual chemical\nreactivities. We present here two MIIs that display strong intra-\nand intermolecular hydrogen bonding. Whereas the former is responsible\nfor the selectivity of C–H activation reactions in these molecules,\nthe latter strongly determines their UV–vis signatures. The\ncyclometalated iridium complexes with MIIs form either coordinatively\nunsaturated compounds (with Mes substituents) or undergo dimerization\n(for Ph substituents) through the “imine-N” atom of\nthe MIIs. The coordinatively unsaturated cyclometalated Cp*Ir-MII\ncomplex reacts with several substrates such as PPh<sub>3</sub>, CO,\nazide, and ethyl. The CO and, in particular, the ethyl-bound Cp*Ir\ncomplex are rare cases of stable and crystallographically characterized\nCp*Ir complexes with these ligands. Additionally, the IrCp*-MII complex\nundergoes double C–H activation through the coordination of\na second IrCp* fragment. Intriguingly, the cyclometalated IrCp*-MII\ncomplexes react with 3 equiv of an activated alkyne to produce an\nunusual bicyclic compound that contains one six-membered and one eight-membered\niridacycle. Furthermore, the coordinatively unsaturated IrCp*-MII\ncomplex is an active transfer hydrogenation catalyst. The first comprehensive\nreport on the reactions of transition metal complexes of MIIs shows\nthe potential of these new ligands in organometallic reactivity.