Synthesis and Characterization of a N,C,N-Carbodiphosphorane Pincer Ligand and Its Complexes

The reaction of 2-pyridiyldiphenylphosphine (2) with tetrachloromethane and subsequent dehalogenation of the intermediate chloro phosphonium salt [(CDPPy2)­Cl]Cl (3) with tris­(1-pyrrolidyl)­phosphine results in the formation of a new type of carbodiphosphorane N,C,N pincer ligand, sym-bis­(2-pyridyl)­tetraphenylcarbodiphosphorane, CDPPy2 (1). It crystallizes in a triclinic crystal system with a crystallographic point group of P1̅. This neutral double-ylidic N,C,N ligand is capable of stabilizing a wide range of metal coordination polyhedra, varying from square planar [(CDPPy2)­PdCl]Cl (4), octahedral mer-[(CDPPy2)­TiCl3] (5) and fac-[(CDPPy2)­Cr­(CO)3] (6) to trigonal-bipyramidal [(CDPPy2)­MnCl2] (9) and [(CDPPy2)­CoCl2] (10) complexes. Unprecedented dinuclear complexes are formed with molybdenum and nickel carbonyls. 1 reacts with [Mo­(CO)3(NCMe)3] to form the symmetric κ3-N,C,N-[(CDPPy2)­Mo­(CO)3(μ-CO)­Mo­(CO)3] (7) with one bridging carbonyl next to a bridging central carbon atom with its two lone pairs. In contrast, an unsymmetrical coordination mode with only one coordinated pyridine is observed in κ2-N,C-[(CDPPy2)­Ni­(CO)­(μ-CO)­Ni­(CO)2] (8). Carbodiphosphorane-based ligands are unique due to their σ,π four-electron-donor character of the central carbon atom toward one metal and alternatively their 2σ four-electron-donor character toward two vicinal metal atoms.