Reversible C-H bond activation of a bifunctional phosphine bridging ligand across two unbonded metal centers

Reaction of [{Ir(mu-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(mu-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){mu-PPh(C6H4)-(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)(mu-Ph(2)PBzIm)], in solution. Abstraction of one chloride ligand from 1 with AgBF4 produces the deinsertion of the C-H bond yielding the cationic complex [{Ir(cod)}(2)(mu-Ph(2)PBzIm)(mu-Cl)]-BF4, which regenerates 1 upon addition of a chloride-soluble salt. The cationic complex [{Ir-(cod)}(2)(mu-Ph(2)PBzIm)(mu-Cl)]BF4 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)(CH3CN)(2)]BF4. A related binuclear sp(2)-C-H bond activation across two unbonded metals also occurs in the reaction of dppm with [{Ir(mu-Cl)(cod)}(2)] in a 1:1 molar ratio. This reaction leads to a mixture in equilibrium of [{IrCl(cod)}(2)(mu-dppm)] and the hydride complex [{IrCl(cod)(mu-PPh(C6H4)CH2-PPh2)}IrHCl(cod)] in a 1.5:1 molar ratio, respectively, in dichloromethane at 20 degrees C. The structure of the mixed-valence complex 1 was solved by X-ray diffraction studies.