Reversible C−H Bond Activation of a Bifunctional Phosphine Bridging Ligand across Two Unbonded Metal Centers

Reaction of [{Ir(μ-Cl)(cod)} 2 ] with the short-bite bifunctional N,P-donor ligand (1-benzyl-2-imidazolyl)diphenylphosphine (Ph 2 PBzIm) gives the yellow complex [IrCl(Ph 2 PBzIm)(cod)] ( 2 ). A further addition of [{Ir(μ-Cl)(cod)} 2 ] to 2 results in the reversible metalation of a phenyl ring across two unbonded iridium centers to give orange crystals of [IrCl(cod){μ-PPh(C 6 H 4 )BzIm}IrHCl(cod)] ( 1 ). Complex 1 is in equilibrium with the mononuclear complex [IrCl(Ph 2 PBzIm)(cod)] and the active species undergoing the sp 2 -C−H activation, [{IrCl(cod)} 2 (μ-Ph 2 PBzIm)], in solution. Abstraction of one chloride ligand from 1 with AgBF 4 produces the deinsertion of the C−H bond yielding the cationic complex [{Ir(cod)} 2 (μ-Ph 2 PBzIm)(μ-Cl)]BF 4, which regenerates 1 upon addition of a chloride-soluble salt. The cationic complex [{Ir(cod)} 2 (μ-Ph 2 PBzIm)(μ-Cl)]BF 4 is inactive for the above-mentioned sp 2 -C−H bond activation and can be prepared alternatively from the reaction of 2 with [Ir(cod)(CH 3 CN) 2 ]BF 4 . A related binuclear sp 2 -C−H bond activation across two unbonded metals also occurs in the reaction of dppm with [{Ir(μ-Cl)(cod)} 2 ] in a 1:1 molar ratio. This reaction leads to a mixture in equilibrium of [{IrCl(cod)} 2 (μ-dppm)] and the hydride complex [IrCl(cod){μ-PPh(C 6 H 4 )CH 2 PPh 2 )}IrHCl(cod)] in a 1.5:1 molar ratio, respectively, in dichloromethane at 20 °C. The structure of the mixed-valence complex 1 was solved by X-ray diffraction studies.