Synthesis and Structure of Molybdenum and Tungsten Bisphosphine Carbonyl Dimers

The synthesis of two bisphosphine ligands (R2P)2C6H4 with a para-disubstituted phenyl moiety is described (R = Cy (3), i-Pr (4)). Solutions of M(CO)3(C7H8) (C7H8 = η6-cycloheptatriene, M = Mo and W) and 3 or 4 were reacted under CO affording dimeric compounds of the general formula [M2(CO)8((R2P)2C6H4)2] (M = W, R = Cy (5); M = Mo, R = Cy (6); and M = W, R = i-Pr (7)). When the same reactions are carried out in the presence of H2, similar W−H2 analogues of the general formula [W2(CO)6((R2P)2C6H4)2(H2)2], R = Cy (8), R = i-Pr (9), can be observed by 1H and 31P NMR spectroscopy. Compounds 8 and 9 are not isolable, due to facile ligand redistribution forming 5 and 7, respectively.