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

Article abstract of DOI:10.1021/om0001671

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(Ph₂-PBzIm)(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-Ph₂ PBzIm)(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)CH₂-PPh₂)}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.