Mono and dinuclear palladium complexes of o-alkyl substituted arylphosphane ligands: Solvent-dependent syntheses, NMR-spectroscopic characterization and X-ray crystallographic studies

Palladium(II) chloride complexes of o-alkyl substituted phosphanes were prepared in various solvents with the phosphane ligands o-methylphenyldiphenylphosphane, o-ethylphenyldiphenylphosphane, o-isopropylphenyldiphenylphosphane, o-cyclohexylphenyldiphenylphosphane and o-phenylphenyldiphenylphosphane. The structures of the complexes were characterized by 1H NMR and 31P NMR spectroscopy and elemental analysis. The X-ray structures of PdCl2(o-methylphenyldiphenylphosphane)2, PdCl2(o-isopropylphenyldiphenylphosphane)2, PdCl2(o-cyclohexylphenyldiphenylphosphane)2, PdCl2(o-phenylphenyldiphenylphosphane)2, [PdCl2(o-methylphenyldiphenylphosphane)]2, [PdCl2(o-ethylphenyldiphenylphosphane)]2 and [PdCl2(o-cyclohexylphenyldiphenylphosphane)]2 were also determined. We report a systematic, solvent-dependent method to prepare palladium(II) complexes of the aryl phosphines o-methylphenyldiphenylphosphane, o-cyclohexylphenyldiphenylphosphane and o-phenylphenyldiphenylphosphane with a desired nuclearity. We demonstrated that chlorinated solvents promote the formation of dinuclear chlorine-bridged palladium complexes for all five ligands. The ligands preferentially form mononuclear palladium complexes in other solvents where the starting materials are only weakly soluble in the solvent.