Use of electron-rich η 6-arylphosphine complexes of molybdenum(O) as ligands in group 6 metal carbonyl complexes

Abstract

The reactions of M(CO) 6 M = Cr, Mo, W and Mo(η 6-PhPPh 2)(dppe)(L), dppe = PPh 2CH 2CH 2PPh 2, L = CO, ( L 1CO ), L = PMe 3, ( L 1P ) in benzene under photolysis lead to the following dimeric species M(CO) 5( L 2CO ) and M(CO) 5( L 1P ). Here the free phosphorus of the donor complex coordinates to M(CO) 5 without metalmetal bond formation; a CottonKraihanzel force constant analysis indicates that the ordering of e-donor ability is L 2P > L 1CO >PPh 3. Similarly treating the new complex Mo(η 6-PhPMePh)(dppe)(P(OMe) 3), ( L 2P ) with Mo(CO) 6 under photolysis gives the dimer Mo(CO) 5( L 2P ). Heating individual solutions of complexes L 1CO , L 1P Mo(η 6-PhPMePh)(dppe)(CO), ( L 2CO ) and L 2P in the presence of stoichiometric equivalents of M(CO) 4(pip) 2, M = Mo or W, pip = piperidine yields Mo(CO) 4(pip)( L 1CO ), W(CO) 4(pip)( L 1CO ), Mo(CO) 4(pip)( L 1P ), W(CO) 4(pip)( L 2CO ) and Mo(CO) 4(pip)( L 2P ). The further thermal reactions of W(CO) 4(pip)( L 1CO ), W(CO) 4(pip)( L 2CO ) and Mo(CO) 4(pip)( L 2P ) with phosphines or phosphite results in the substitution of the piperidine ligand and formation of W(CO) 4(PMe 2Ph)( L 1CO ), W(CO) 4(PMe 2Ph)( L 2CO ), Mo(CO) 4(P(OMe) 3)( L 2P ) and Mo (CO) 4(PMe 3)( L 2P ). Complexes are characterised by IR, 1H and 31P{ 1H} NMR spectroscopy. The cone angle for L 1CO is determined to be 155± 5° by comparing the cis / trans equilibrium ratio for its complex (W(CO) 4(PMe 2Ph)( L 2CO ) to literature values for other W(CO) 4(PMe 2Ph)(L) complexes. The bimetallics containing L 1CO or L 2CO show an irreversible one electron oxidation wave associated with the metallophosphine ligand; those containing L 1P or L 2P show one reversible oxidation at a more positive potential to that of the free metallophosphine ligands and a second irreversible oxidation.