Facile tungsten alkylidene synthesis: alkylidene transfer from a phosphorane to a tungsten imido complex

A number of transition-metal complexes catalyze the ring-opening metathesis polymerization (ROMP) of a variety of cyclic olefins. Notable among these catalysts are the titanacyclobutane derivatives and certain alkylidene complexes of tungsten: molybdenum, tantalum, and rhenium. The highly reactive tungsten alkylidene complexes developed by Schrock, Osborn, and Basset are particularly useful for the synthesis of unsaturated polymers such as novel conducting polymers and soluble precursors and derivatives of polyacetylene. Recent applications of these catalytic systems involve the polymerization of acyclic alkynes and dienes In addition, the use of tungsten alkylidene complexes as Wittig-type reagents in organic synthesis holds considerable promise