The First Low-Spin Nickel Complex with Two Coordinated Water Molecules, [Ni(o-MeO-dppp)(H2O)2](PF6)2 − Synthesis and Structural Characterization

A series of nickel complexes of the didentate ligand 1,3-bis[di(o-methoxyphenyl)phosphanyl]propane (o-MeO-dppp) has been synthesized and characterized. The first low-spin nickel complex containing two coordinated water molecules, [Ni(o-MeO-dppp)(H2O)2](PF6)2 (1), and compounds of the general formula [Ni(o-MeO-dppp)X2] [X = Cl, Br, I, or trifluoroacetate (TFA)] are reported. Complex 1 has been characterized by X-ray crystallography. The nickel ion resides in a square-planar coordination environment with two phosphorus donors and two water molecules in a cis configuration (Ni−P distance 2.19 Å; Ni−O distance 1.97 Å). The structure of this complex and its behavior in solution are quite different from those of the complexes [Ni(o-MeO-dppp)X2]. The halide complexes [Ni(o-MeO-dppp)Cl2] (2) and [Ni(o-MeO-dppp)Br2] (3) are seemingly mutually isostructural. In these complexes, the nickel ion also resides in a square-planar geometry, but with a significant tetrahedral distortion. The two different types of mono(o-MeO-dppp)nickel(II) complexes, i.e. [Ni(o-MeO-dppp)(H2O)2](PF6)2 (1) and [Ni(o-MeO-dppp)X2] [X = Cl (2), Br (3), I, or trifluoroacetate (TFA)] have been analyzed by electronic absorption and NMR spectroscopy. The differences in the crystal structures of 1 and 2 are helpful in rationalizing the fluxional behavior of these complexes, as has been studied by NMR spectroscopy.