TUNGSTEN CARBONYL-COMPLEXES AS OLEFIN METATHESIS CATALYSTS

Different tungsten carbonyl complexes: [W(CO)4L2], [NEt4][W(CO)4LX] and [WX2(CO)3L2], where L = CH3CN, pip, PPh2H, PPh3, bipy, dppe, Zr(PPh2)2cp2, Zr(PPh2C5H4)2Cl2, X = Cl-, Br-, can be transformed into catalysts for olefin metathesis in the presence of certain Group 4, 13 or 14 element halides (AX(n)). The process of transformation of these systems into catalytically active complexes is a multistage one. The first stage is based upon the interaction of the tungsten complex with AX(n) as Lewis acid, which abstracts one ligand from the coordination sphere of tungsten, thus freeing a coordination site for the attachment of an olefin ligand. Catalytic activity of the system depends upon ligand L and X in the tungsten complex and element A in AX(n). In the series of halides studied, the most active proved to be ZrCl4, whose activity could be explained by its high Lewis acidity at the most stable metal halide bond.