Effect of ligand and solvent on chloride ion coordination in anti-tumour copper(I) diphosphine complexes: synthesis of [Cu(dppe)(2)]Cl and analogous complexes (dppe = 1,2-bis(diphenylphosphino)ethane)

Complexes formed between copper(I) and 1,2-bis(diphenylphosphino)ethane (L-1) have previously been isolated. as salts of the [CuL21](+) cation if only non-coordinating anions are present, or as [Cu2Cl2L31] if chloride is present. We describe the synthesis of [CuL21] the stoichiometry of which is confirmed by elemental analysis, FAB mass spectroscopy and conductivity. Polar solvents (water-ethanol mixtures) lead to isolation of the latter, whereas solvents of lower polarity (CHCl3, CH2Cl2) lead to isolation of the complexes containing coordinated chloride. Related ligands such as cis-1,2-bis(diphenylphosphino) ethene, 1,2-bis(diethylphosphino) ethane, 1,2-bis(dimethylphosphino) ethane and 1,2-bis(hydroxymethylphosphino) ethane, give salts [CuL2]Cl. This behaviour, and that of other 1,2-bisphosphine ligands, is rationalised in terms of competition between chloride and phosphine ligands for binding sites on the metal with the equilibrium position determined by solvent polarity, ligand structure and rigidity, and steric and electronic properties of the ligands.