Stereoselectivity of cycloolefin polymerization with WCl 6-based catalytic systems

Abstract

The stereochemistry of ring-opening metathesis polymerization of several cycloolefins (cyclopentene, cyclooctene, 1,5-cyclooctadiene, cyclododecene) in the presence of WCl 6-based catalysts (WCl 6/iBu 3Al/epichlorohydrin, WCl 6/iBu 3Al/chloranil, WCl 6/phenylacetylene, WCl 6/Ph 4Sn, WCl 6/allyl 4Si, WCl 6/iBu 2AlOAliBu 2) has been carefully examined. The product stereoselectivity and polymer microstructure were greatly dependent on the nature of the catalytic system and reaction conditions; the nature of the cycloolefin also influenced the steric course of the reaction. An important stereochemical consequence was that the cis and trans content of the polyalkenamer greatly depended on the oxidation state of the W-atom, catalyst activity and reaction temperature. The relationship between the microstructure of several polyalkenamers (polypentenamer, polyoctenamer, polydodecenamer) obtained with the above catalytic systems and cycloolefin reactivity or catalyst nature is fully illustrated. The role of the ligand as well as of the cocatalyst and activator is also shown. The particular stereochemical behaviour of cycloolefins in the presence of the studied WCl 6-based catalytic systems is discussed in terms of the metallacarbene—metallacyclobutane mechanism. The steric effects induced by the coordinating cycloolefin and the existing ligands at the transition metal are also considered.