Use of the seven-coordinate complexes [MXY(CO) 3(NCMe)2] (M = Mo or W; X, Y = halide) and their derivatives in homogeneous catalysis

Abstract The seven-coordinate halocarbonyl complexes, [MXY(CO) 3 (NCMe) 2 ] (M=Mo or W; X, Y=halide) and their derivatives have been investigated in several types of homogeneous catalytic reactions. These include, the alkene metathesis polymerisation of norbornadiene using either, [MX 2 (CO) 3 (NCMe) 2 ] (M=Mo or W;X=Br or I), [MI 2 (CO) 3 (L′- P , P ′)] {M=Mo or W; L′=MeC(CH 2 PPh 2 ) 3 } or [MXY(CO)(L or L′- P, P ′)(η 2 -RC 2 R′)] {X,Y=Cl, Br or I; L=PhP(CH 2 CH 2 PPh 2 ) 2 ; R,R′=Me, Ph}. The isolation and characterisation of a key intermediate, [WI 2 (CO) 2 (η 4 -nbd)] ( 1 ) (nbd=norbornadiene) is also described. The development of water soluble polymerisation catalysts using water-solubilising pyridine ligands, and the biphasic polymerisation of styrene using [WI 2 (CO) 3 (NC 5 H 4 CO 2 Na-4) 2 ], ZrCl 4 , sodium lauryl sulphate and sodium hydrogen phosphate is also discussed. The room temperature polymerisation of phenylacetylene using [WX 2 (CO) 3 (NCMe) 2 ] (X=Cl, I), [WI 2 (CO) 3 (NCMe)L] (L=PPh 3 , AsPh 3 ) or [WBr 2 (CO)(NCMe)(η 2 -HC 2 Ph) 2 ] ( 4 ) is also described, and a mechanism is proposed for these polymerisation reactions.