Phiphob Naweephattana,a Khanittha Walaijai,b Chompoonut Rungnim,c

Torsak Luanphaisarnnont,a Anyarat Watthanaphanit,a Supanan Patthamasang,b

Phairat Phiriyawirutb and Panida Surawatanawong*a,d

aDepartment of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.

bSCG Chemicals, Co., Ltd., 1 Siam Cement Road, Bangsue, Bangkok, 10800, Thailand

cNational Electronics and Computer Technology Center (NECTEC), National Science and Technology Development Agency (NSTDA), Pathum Thani 12120, Thailand

dCenter of Sustainable Energy and Green Materials, Mahidol University, Salaya, Nakhon Pathom 73170, Thailand

*E-mail: panida.sur@mahidol.ac.th

Alkyl aluminium plays a primary role in activating Ti within Ziegler–Natta (ZN) catalysts for propylene polymerization. We performed density functional calculations to explore the additional roles of AlEt3 and AlEt2Cl, in conjunction with diisobutyl phthalate (DIBP) internal donor and dicyclopentyl dimethoxysilane (DCPDMS) external donor, to enhance the stereoselectivity of propene insertion. Based on our calculated adsorption energies on the (MgCl2)13/TiCl2iBu cluster model for the ZN catalyst, the presence of DIBP on the cluster essentially facilitated AlEt2Cl adsorption while AlEt2Cl also promoted the adsorption of DIBP. The reaction between AlEt3 and DIBP on the cluster led to the extraction of DIBP, creating an available site for DCPDMS adsorption. While the stereoselectivity, represented by the difference in the activation energies between 1,2-re and 1,2-si insertions of propene, was negligible on the cluster containing only DIBP, it became significant on the clusters containing both AlEt2Cl and DIBP (and DCPDMS). AlEt2Cl plays a pivotal role in imposing steric effects near the Ti active site, thereby increasing stereoselectivity. Our findings suggest the importance of including AlEt2Cl alongside DIBP (and DCPDMS) in the ZN cluster model to investigate stereoselective propene insertion. Considering AlEt2Cl adsorption and AlEt3 reaction with internal donors is essential in developing Ziegler–Natta catalysts.