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).