Preparation and reactivity of mononuclear and dinuclear carbene-alkene complexes of tungsten

Abstract Reaction of W(CO) 6 with 4-penten-1-yllithium gives the pentenyl-methoxycarbene complex (CO) 5 WC(OCH 3 )CH 2 CH 2 CH 2 CHCH 2 which upon heating gives the isomerized, double bond coordinated, carbene complex (CO) 4 WC(OCH 3 )CH 2 CHCHCH 3 . An analogous complex is obtained from 3-buten-1-yllithium. The reactivity of these complexes towards external ligands is compared to the reactivity of the dinuclear μ-alkylidene complex (CO) 9 W 2 (CHCHCMe 2 ) which bears a coordinated double bond; the same reactivity patterns are observed. Moreover, in the case of alkynes, the dinuclear complex leads to stable insertion products. A mechanism for the polymerization of cycloalkenes and alkynes around two metal centers is outlined.