Highly active and stereoselective olefin polymerization catalysts generated by the transfer-epimetallation of olefins or acetylenes with dialkyltitanium(IV) complexes: three-membered metallocycles as active catalyst sites



Efficient transfer-epimetallations of simple olefins and acetylenes by R2TiL2 reagents (R = Bun, But; L = X) are readily achieved in THF at −78°C to generate titanacyclopropa(e)ne intermediates, readily capable of inserting various unsaturated addends (olefin, acetylene, nitrile). Analogous epimetallations conducted in hydrocarbons lead to the isotactic stereoselective polymerization of 1-alkenes and the cyclotrimerization of acetylenes. In place of the widely accepted Arlman-Cossee model for the active catalytic site, namely a Ti-C bond on the TiCl3 crystal lattice, the 2-substituted-1-halotitanacyclopropyl cation formed in hydrocarbon media is proposed as the active site for stereoselective olefin polymerization.