The origin of the chemoselectivity in the Cp2TiCl2/MAO catalyst for the polymerization of 1,3-butadiene explored by Density Functional Theory

摘要: Abstract A large variety of Ti catalysts are involved in the polymerization ethylene, propylene, 1,3 butadiene and other di-olefins. In present work we deal with reaction mechanism Cp 2 TiCl which combination methylaluminoxane (MAO) as alkylating agent produces a predominantly cis-1,4 poly(butadiene) (cis content about 80%). Different mechanisms have been proposed literature: η 5 coordination both ligands, formation carbene-like structure containing Ti-H bond, loss one ligands during process. We investigate systematic way all pathways by means Density Functional Theory calculations Car–Parrinello molecular dynamics. Calculations can rule out several catalytic that either thermodynamically or kinetically disfavored. The resulting energy profiles free energies differences suggest only compatible is ring process, previously suggested Miyazawa Suzuki [A. Miyazawa, Y. Suzuki, J. Chem. Res. (S) (2002) 503]. Within pathway also identified step responsible for chemoselectivity growing chain. calculated ratio between occurrence 1,2 produced polymer fair agreement experiments, gives polybutadiene.