We report the first quantum chemical description of the initial steps of Ziegler–Natta olefin polymerization catalysis involving all the relevant catalyst components. TiCl₄ binds on the (1 0 4) surface of MgCl₂ as a binuclear Ti₂Cl₈ and on the (1 1 0) surface as a mononuclear TiCl₄, both binding modes being stabilized by octahedral six-coordination of Ti and Mg. Aluminum alkyl (triethylaluminum) coordinates to the MgCl₂ surface via an unsaturated Cl to initiate catalyst alkylation reactions, thermodynamically driven by dimerization of the chlorinated aluminum alkyl. Addition of an internal donor (dimethyl phthalate) greatly stabilizes the (1 0 4) and (1 1 0) surfaces, ending up directing the alkylation reactions to the binuclear (1 0 4) site. External donor (dimethoxydimethylsilane) further assists the process, stabilizing similarly both catalytic surfaces. The spatial requirements of the donors are shown to be greater on the (1 1 0) surface than on the (1 0 4) surface, rationalizing the role of Lewis bases in the stereocontrol of polyolefins.

我们报告了涉及所有相关催化剂组分的齐格勒-纳塔烯烃聚合催化反应初始步骤的第一个量子化学描述。TiCl ₄以双核Ti ₂ Cl _8的形式结合在MgCl ₂的（1 0 4）表面和以单核TiCl _4的形式结合在（1 1 0）的表面上，两种结合方式均通过Ti和Mg的八面体六配位而稳定。烷基铝（三乙基铝）与MgCl _2配位通过不饱和Cl在表面上引发催化剂烷基化反应，该反应是由氯化烷基铝的二聚作用热力学驱动的。添加内部供体（邻苯二甲酸二甲酯）可极大地稳定（1 0 4）和（1 1 0）表面，最终将烷基化反应导向双核（1 0 4）位点。外部给体（二甲氧基二甲基硅烷）进一步辅助了该过程，类似地稳定了两个催化表面。显示给体的空间需求在（1 1 0）表面大于（1 0 4）表面，这使路易斯碱在聚烯烃的立体控制中的作用合理化。