Synthesis and characterization of a series of novel nickel(II)/nickel(I) complexes. Crystal structures of [NiCl2(dcpm)], [Ni(dcpm)2](NO3)2·2EtOH, [Ni2Cl2(μ-dcpm)2(μ-H)] and [Ni2(μ-PCy2)2(PCy2Me)2]; dcpm=bis(dicyclohexylphosphino)methane

The complexes [(dcpm)NiCl2] (1), [Ni2Cl2(μ-dcpm)2(μ-H)] (3), [Ni2(μ-PCy2)2(PCy2Me)2] (4) and [Ni(dcpm)2](NO3)2·2EtOH (2), dcpm=bis(dicyclohexylphosphino)methane, have been prepared and characterized by 31P, 1H NMR (or EPR) as well as X-ray crystallography. The salt NiCl2·6H2O was found to react with dcpm to form the monomeric, four-coordinate, diamagnetic complex [(dcpm)NiCl2] (1). Compound 1 was then reduced with nBu3SnH (or LiH with heating) in toluene at room temperature to form the air sensitive ‘A-frame’ complex [Ni2Cl2(μ-dcpm)2(μ-H)] (3). The NiNi bond distance for 3 was found to be 2.904(3) Å showing a lack of any NiNi metal bonding. [Ni2(μ-PCy2)2(PCy2Me)2] (4) was then formed by the reaction of 1 and excess LiH, heating to 90°C in an oil bath. [Ni2Cl2(μ-dcpm)2(μ-H)] (3) was shown to be an intermediate in the synthesis of the bridging phosphido nickel complex. The NiNi bond distance in 4 is 2.3910(8) Å corresponding to a single NiNi metal bond. The reaction of Ni(NO3)2·6H2O with dcpm in ethanol yields the square planar complex [Ni(dcpm)2](NO3)2·2EtOH (2).