Preparation, crystal structures, and spectroscopic and redox properties of nickel(II) complexes containing phosphane-(amine or quinoline)-type hybrid ligands and a nickel(I) complex bearing 8-(diphenylphosphanyl)quinoliney

Nickel(II) complexes containing P-N-type bidentate hybrid ligands of 2-aminoethylphosphanes (RR'Pea; RR' = Ph₂ or MePh) or 8-quinolylphosphanes (RR'Pqn), namely [Ni(P-N)₂](BF₄) ₂ [P-N = Ph₂Pea (1), MePhPea (2), Ph₂Pqn (3), or MePhPqn (4)] have been prepared, and their structural, spectroscopic, and electrochemical properties determined. The crystal structure analysis indicates that: the 2-amlnoethylphosphane complexes (1 and 2) have a square-planar coordination geometry around the Ni^II center with a cis(P,P) configuration, whereas the 8-quinolylphosphane complexes (3 and 4) exhibit a severe tetrahedral distortion because of the steric repulsion between the ortho-H atoms in the mutually cis-positioned quinolyl rings, Complexes 1 and 2 maintain their diamagnetic square-planar four-coordinate structure on acetonitrile solution, whereas complexes 3 and 4 show paramagnetic behavior. Spectroscopic and electrochemical measurements suggest that the ligand-field strengths of these four PN-type ligands increase in the order Ph₂Pqn (3) < MePhPqn (4) < Ph₂Pea (1) < MePhPea (2). The Ph ₂Pqn complex 3 is readily reduced by Zn powder to afford the corresponding nickel(I) complex [Ni(Ph₂Pqn)₂]BF ₄ (5), The crystal structure of complex 5 reveals that the Ni ^I ion adopts a distorted tetrahedral coordination geometry with slightly longer (≈ 0.05 Å) Ni-P and. Ni-N bond lengths than those in the corresponding Ni^II complex 3.