Abstract
The use of aryloxide ligand for the obtention of highly active tungsten-based metathesis catalysts is now widely accepted. Indeed, it is easy to control the coordination sphere of the metal center with such ligands, which compare very well with alkoxides. Their electron-withdrawing effects can be modified or adapted by varying the substituents on the aromatic ring. In addition, the bulkiness of groups attached at ortho and ortho’ position of the aromatic rings allows a better check of steric effects around the tungsten atom. In the first generation of such catalysts, bicomponent systems were obtained by association of the precursor W(OAr)xCl6−x with MR4, where MR4 is a tetraalkyl-tin or -lead component. The second family of these complexes are “well defined catalysts”. A stable carbene has been isolated after alkylation of W(OAr)2Cl4 (OAr=O-2,6-C6H3Ph2) with 1 eq. of MgNp2·dioxane. Recently we developped a new route to obtain the same complex W(OAr)(OAr)(=CHCMe3)Cl(OEt2) by using a Schrock carbyne intermediate. Under special conditions, this complex seems to adopt a dimeric configuration and shows then a remarkable air stability and a good activity for the metathesis reaction.