From the reaction of metal—carbene complexes with cyclic enol ethers to the synthesis and structure of μ-alkylidene complexes of tungsten and their possible implication in the olefin metathesis reaction

Abstract

Reaction of heteroatom or non-heteroatom stabilized alkylidene complexes of tungsten with cyclic enol ethers allowed us to observe products that arise from the insertion of the metal into the carbon—carbon double bond of the unsaturated starting compound. This reaction is compared with the ring opening polymerization of cyclic olefins. The reaction of a metathesis catalyst prepared from W(CO) 6/CCl 4/hν with such cyclic enol ethers gives products arising from the probable insertion of a dichlorocarbene complex of tungsten into the carbon—carbon double bond. Attempts to prepare dialkyl substituted alkylidene complexes of tungsten, starting from Fischer-type carbenes, and to trap them with cyclic enol ethers failed; instead, a new kind of stabilization of these complexes by the formation of dinuclear μ-alkylidene complexes was observed. The chemistry of these new complexes, as well as the possibility of their occurence in the olefin metathesis reaction, is outlined.