Key interactions in heterogeneous Ziegler-Natta catalytic systems: Structure and energetics of TiCl4-Lewis base complexes

Extensive calorimetric investigations on the interaction of TiCl4 with some Lewis bases are presented. Some of the bases were chosen for their industrial relevance in heterogeneous Ziegler-Natta polymerization of propene (ethyl benzoate, L2, diisobutyl phthalate, L3, (2R,3S)-diethyl 2,3-diisopropylsuccinate, L6, (2S,3S)-diethyl 2,3-diisopropylsuccinate, L7, and 9,9-bis(methoxymethyl)-9H-fluorene, L13) while other bases were chosen as probe molecules to explore the electronic and steric effects on the complexation energy (ethyl acetate, L1, diethyl phthalate, L4, diethyl succinate, L5, tetrahydrofuran, L8, dimethoxyethane, L9, dimethoxypropane, L10, dimethoxybutane, L11, and 3,3-bis(methoxymethyl)-2,6-dimethylheptane, L12). 1,1,2,2,-Tetrachloroethane was selected as the solvent for its low donating properties, which allows the focus to be on the metal-donor interaction. The calorimetric data are discussed and compared with the efficiency of the derived catalysts. Further understanding is obtained by comparison of the experimental results with theoretical calculations based on density functional theory (DFT). The performance of different computational approaches was validated by comparison of the calculated and experimental complexation energies.