Regio- and stereochemistry of the first insertion step in the 1,3-butadiene polymerization catalyzed by CpTiCl3-MAO

CpTiCl₃-MAO (methylaluminoxane) catalytic system promotes the butadiene polymerization leading to 85% of 4,1-cis polymer. The generally well accepted homopolymerization mechanism involves a diene insertion on a π-allylic terminal growing chain. In α-olefin-diene copolymerizations, diene monomer can also insert on a σ carbon-metal bond.In order to simulate an insertion of a conjugated diene on a σ chain, experimental and theoretical studies, relative to the first insertion step, are reported. Unexpectedly 56% of 1,2-primary and 44% of 4,1-trans first inserted units were obtained, by using as catalyst CpTiCl₃/MAO/Al(¹³CH₃)₃. The experimental results were rationalized by DFT (Density Functional Theory) calculations, by including a solvent molecule coordinated to the catalytic site during the first insertion step.