Stereoselective Olefin Polymerization Catalysts Generated by the Transfer-Epimetalation of Olefins or Acetylenes with Dialkyltitanium(IV) Complexes:  Three-Membered Metallocycles as Proposed Chiral Sites¹

Efficient transfer-epimetalations of simple olefins and acetylenes by R₂TiL₂ reagents (R = Buⁿ, Bu^t; 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 epimetalations conducted in hydrocarbons lead to the stereoselective polymerization of 1-alkenes and the cyclotrimerizations of acetylenes. The 2-substituted-1-halotitanacyclopropyl cation is proposed as the active site for stereoselective olefin polymerization.