Aryloxy complexes and cyclometallated aryloxy alkylidene complexes of tungsten (VI). Application to the metathesis of functionalized olefins

In this review article, the synthesis of aryloxy complexes of tungsten with the general formula W(OAr)_xCl_6-x is described together with that of aryloxy (chloro)neopentylidene-tungsten complexes. The properties of these compounds in the metathesis of non-functionalized and functionalized olefins are reviewed. The aryloxy complexes of tungsten are good air-stable precursor catalysts when combined with organotin or -lead cocatalysts. In particular, depending on the cocatalyst and substituents on the aryloxide ligands, one can achieve either linear or cross-linked polydicyclopentadienes. One can also govern the induction period for the obtention of cross-linked polydicyclopentadiene, a phenomenon compatible with the requirements of the RIM processing. The cyclometallated neopentylidene tungsten complex 1 can be synthesized by two different routes, either from the W(OAr)₂Cl₄ (OAr = -O-2,6-C₆H₃Cl₂ or -O-2,6-C₆H₃Ph₂) precursor or from the Schrock carbyne W(CCMe₃)(Cl₃)(dme). In both cases, when OAr = O-2,6-C₆H₃Ph₂, a metallation occurs by cleavage of the CH bond in one substituting phenyl group. Complex 1 is probably one of the most active and stereoselective catalysts for metathesis of cis- and trans-2-pentene (total retention of the configuration of the starting olefin). Similarly, it selectively transforms 1-methyl-norbornene to 100% cis, 100% headtail syndiotactic poly-1-methyl-norbornene. Complex 1 is also one of the most active catalysts for metathesis of functionalized olefins: with ethyl oleate 1 converts approximatively 250 equivalents of ethyl oleate into 9-octadecene and diethyl-9-octadecenedioate at 25°C. Compound 1 converts approximatively 100 equivalents of unsubstituted diallyl ether into the corresponding 2,5-dihydrofurane, and it (as well as the bicomponent catalysts) is able to realize metathesis of ω-unsaturated glucosides into the corresponding di-glucosides. It is also able to convert cyclic and acyclic double bonds with thio-ether functionalities to the corresponding polymer or cyclic products. For example, 1 converts diallyl sulphide or related compounds to the corresponding 2,5-dihydrothiophene derivatives. Similarly, phosphorus, silicon and tin diallyl derivatives can be transformed into the corresponding cyclic compound ECH₂CHCHCH₂, E = P, Si, Sn.