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‡

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AbstractEfficient 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.