Scandium-catalyzed regio- and stereospecific cis -1,4-polymerization of 1,3-cyclohexadiene and copolymerization with ethylene

In the presence of an activator such as [Ph₃C][B(C ₆F₅)₄] or [PhMe₂NH][B(C ₆F₅)₄], the half-sandwich scandium dialkyl complexes Cp'Sc(CH₂SiMe₃)₂(THF) (Cp' = C ₅Me₄SiMe₃ (1), C₅Me₅ (2), C₅H₃(SiMe₃)₂ (3)) showed excellent regio- and stereoselectivity for the polymerization of 1,3-cyclohexadiene (CHD) and its copolymerization with ethylene. The homopolymerization of CHD afforded soluble crystalline cis-1,4-linked poly(CHD)s with very high stereoselectivity (tacticity up to 99 mol %). The copolymerization of CHD with ethylene gave the corresponding copolymers with a wide range of CHD contents (10-67 mol %) in a regio- and stereospecific 1,4-cis fashion.