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根据茂金属和水杨酸亚胺基后过渡金属催化聚合烯烃反应机理的密度泛函计算化学研究结果,从反应物和过渡态的角度论述了烯烃催化聚合体系中Mulliken位置电荷与区位选择性的相关性。反应物和过渡态对反应的区位选择性有不同影响。反应物通过位置电荷影响前线分子轨道,进而决定反应的区位选择性;过渡态通过位置电荷的离域程度决定反应的区位选择性。不同的区位选择性导致两种不同的聚合反应机理:1,2-和2,1-插入反应。1,2-插入反应机理生成正碳离子中间体,2,1-插入反应机理生成负碳离子中间体。过渡态中正碳离子电荷离域程度大的发生1,2-插入反应活化能小;过渡态中负碳离子电荷离域程度大的发生2,1-插入反应活化能小。不同催化体系构型由此产生不同区位选择性;而构型与区位选择性的关系与体系Mulliken电荷分布相关。只有Mulliken电荷给出最好的相关,可能是由于Mulliken电荷是通过轨道系数得到的。材料设计是科学研究中的重要课题。Mulliken位置电荷与区位选择性的相关性规律对高分子聚烯烃材料的设计有重要意义。
According to the results of density functional calculations of metallocene and salicylic acid post-transition metal catalyzed polymerization of olefins, Mulliken site charge and site-selectivity of olefin-catalyzed polymerization systems are discussed from the perspective of reactants and transition states Correlation. Reactants and transition states have different effects on the site selectivity of the reaction. The charge of the reactant affects the frontier molecular orbital through the site charge and thus determines the site selectivity of the reaction. The transition state determines the site selectivity of the reaction through the degree of delocalization of the site charge. Different site selectivity leads to two different polymerization mechanisms: 1,2- and 2,1-insertion reactions. The 1,2-insertion reaction mechanism generates a positive carbon ion intermediate and a 2,1-insertion reaction mechanism generates a negative carbon ion intermediate. In the transitional state, the 1,2-insertion reaction has a small activation energy, and the negative charge of the carbanion in the transition state is large. Different catalysis system configurations result in different site selectivity. The relationship between configuration and site selectivity is related to Mulliken charge distribution. Only the Mulliken charge gives the best correlation, probably because the Mulliken charge is obtained by the orbital coefficient. Material design is an important issue in scientific research. Mulliken location charge and location selectivity of the law for the design of polymer polyolefin materials is of great significance.