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 (Ph2PBzIm) gives the yellow complex [IrCl(Ph2PBzIm)(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(C6H4)BzIm}IrHCl(cod)] (1). Complex 1 is in equilibrium with the mononuclear complex [IrCl(Ph2PBzIm)(cod)] and the active species undergoing the sp2-C−H activation, [{IrCl(cod)}2(μ-Ph2PBzIm)], 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(μ-Ph2PBzIm)(μ-Cl)]BF4, which regenerates 1 upon addition of a chloride-soluble salt. The cationic complex [{Ir(cod)}2(μ-Ph2PBzIm)(μ-Cl)]BF4 is inactive for the above-mentioned sp2-C−H bond activation and can be prepared alternatively from the reaction of 2 with [Ir(cod)(CH3CN)2]BF4. A related binuclear sp2-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(C6H4)CH2PPh2)}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.