Mixed-ligand platinum(II) complexes containing 2-(2′-pyridyl)phenyl and 8-quinolylphosphines: Synthesis and molecular structures in the crystals and in solution

A series of cyclometalated {2-(2′-pyridyl)phenyl}platinum(II) complexes having 8-quinolylphosphines, 8-(dimethylphosphino)quinoline (L1), 8-(diphenylphosphino)quinoline (L2), 2-methyl-8-(diphenylphosphino)quinoline (L3), and 2-phenyl-8-(diphenylphosphino)quinoline (L4), were prepared and their molecular structures and spectroscopic properties were investigated. The single-crystal X-ray analysis and the ³¹P{¹H} NMR spectra of the products, [Pt(ppy)(Ln)](BF₄ or OTf) {Cn; n = 1–4, ppy⁻ = 2-(2′-pyridyl)phenyl, OTf⁻ = trifluoromethanesulfonate} revealed the cis(P,C) configuration of the complex cations, although the square-planar Pt^II coordination geometry was considerably distorted. In particular, in the complexes C3 and C4 bearing sterically demanding 8-quinolylphosphines (L3 and L4), not only the tetrahedral distortion of the Pt^II coordination sphere but also a deviation of the Pt^II center from the planar chelate ring, i.e., an envelope-type distortion of the chelating quinolylphosphine coordination was observed. All complexes were stable in solution toward the addition of halide anions. However, a fluxional behavior of complexes C3 and C4, owing to the restricted inversion of the distorted coordination sphere, was observed in the temperature-dependent ¹H NMR spectra.