Activation of C–H and H–H bonds by dinuclear iridium complexes. Oxidative addition to highly active unsaturated 32e− diiridium species

Reactions of [(Cp∗Ir)2(μ-dmpm)(μ-H)2][OTf]2 (1) with NaOtBu in aromatic solvent at room temperature give [(Cp∗Ir)(H)(μ-dmpm)(μ-H)(Cp∗Ir)(Ar)][OTf] [Ar = Ph (3), p-Tol (4a), m-Tol (4b), 2-furyl (5a), 3-furyl (5b)] via intermolecular aromatic C–H activation. Treatment of [(Cp∗Ir)2(μ-dppm)(μ-H)2][OTf]2 (2) with weak base (Et2NH) results in intramolecular C–H activation of a phenyl group in the dppm ligand to give [(Cp∗Ir)(H){μ-PPh(C6H4)CH2PPh2}(μ-H)(Cp∗Ir)][OTf] (6). Reaction of 1 with NaOtBu in tetrahydrofuran under H2 (1 atm) results in activation of the H–H bond to give [{(Cp∗Ir)(H)}2(μ-dmpm)(μ-H)][OTf] (7). Reaction of 1 with NaOtBu in dichloromethane under carbon monoxide (1 atm) gives a carbonyl-bridged IrII–IrII complex, [(Cp∗Ir)2(μ-dmpm)(μ-H)(μ-CO)][OTf] (8-OTf). These results strongly suggest that the active species in C–H and H–H bond activation starting with 1 and 2 would be unsaturated 32e− diiridium species. The structures of 3, 5a, 6, 7, and 8-BPh4 have been determined by X-ray diffraction methods.

Highly active unsaturated 32e− diiridium species were generated by the deprotonation of dihydrido-bridged diiridium complexes. Oxidative addition of C–H bond in aromatic molecules and H–H bonds of hydrogen to such active species occurred under ambient conditions. Mechanistic aspects of the activation reactions are also demonstrated.Figure optionsDownload as PowerPoint slide