Composition vs catalytic properties of M(CO)(3)X(2)L(2) (M=Mo or W; X=Cl, Br or I; L=PPh(3), AsPh(3) or SbPh(3)) initiators in romp of norbornene

Catalytic properties of 18 air stable M(CO)(3)X(2)L(2) (M = Mo or W; X = Cl, Br or I; L = PPh(3), AsPh(3) or SbPh(3)) one-component initiators were screened in ring-opening metathesis polymerisation (ROMP) of norbornene. The rate of the polymerization, (V-p), varied between 7.8-32.9 mol dm(-3) h(-1) in the case of the tungsten containing initiators, with I/PPh(3) and Br/AsPh(3) ligand combinations representing the two extremes respectively. The cis/trans double bonds form at about equal probability (sigma(c) = 0.52). The presence of L = AsPh(3) as a ligand seems to favour higher activity, higher cis selectivity and moderate blockiness. The higher cis selectivity of the tungsten complexes (sigma(c) = 0.56-0.58) induced by the I ligand is associated with significantly diminished activity. The activity of the more trans directing (sigma(c) = 0.38) molybdenum catalysts was about two orders of magnitude smaller (V-p = 0.003-2.50 mol dm(-3) h(-1)) increasing in the order, L = PPh(3), AsPh(3), SbPh(3), while the cis content and the blockiness of the polymer follow a reverse tendency.