Palladium(II) 2-diphenylphosphinohydroquinone (H2pphq) complexes: preparation and structures of a novel cluster, [{PdBr(Hpphq)}4]·2H2O, and a phosphine–phosphinite complex, cis-[PdBr2{C6H3(OH)-1,PPh2-3,PPh2O-4}]·2H2O

Abstract

The complexes [PdCl₂(PPh₃)L²](L²= 1,4-dimethoxy-2-diphenylphosphinobenzene), [PdCl(bipy)L²]⁺(bipy = 2,2′-bipyridine) and [PdCl₂(mpy)L²](mpy = 4-methylpyridine) have been prepared and their reactions with BBr₃ studied. The first two complexes afforded products resulting from protolytic cleavage of the phosphinohydroquinone ligand whereas reactions of the last with BBr₃ produced [PdBr(mpy)(Hpphq-O,P)](H₂pphq = H₂L¹= 2-diphenylphosphinohydroquinone) when quenched with methanolic sodium carbonate or, when quenched with methanol alone, a mixture which contains the novel tetrameric cluster [{PdBr(HL¹)}₄] and slowly deposits an unexpected phosphine–phosphinite complex, cis-[PdBr₂{C₆H₃(OH)-1,PPh₂-3,PPh₂O-4}]·H₂O, on standing. The crystal structures of the last two complexes have been determined. The palladium tetramer was also formed when [PdBr(mpy)(HL¹-O,P)] was treated with hydrobromic acid. The NMR spectra suggest that in solution the tetramer is in equilibrium with monomeric solvato complexes, [PdBr(solv)(HL¹-O,P)](solv = solvent).