Structure/Properties Relationship for Bis(phenoxyamine)Zr(IV)-Based Olefin Polymerization Catalysts: A Simple DFT Model To Predict Catalytic Activity

The productivity of a number of bis­(phenoxyamine)­Zr­(IV)-based catalysts (bis­(phenoxyamine) = N,N′-bis­(3-R1-5-R2-2-O-C6H2CH2)-N,N′-(R3)2-(NCH2CH2N)) in ethene and propene polymerization was evaluated for different R1/R2/R3 combinations. In previous studies on this class we demonstrated that the cations that form upon precatalyst activation (e.g., by methylalumoxane) adopt a “dormant” mer-mer geometry, and an endothermic isomerization to the active fac-fac geometry is the necessary first step of the catalytic cycle. Herewith we report a clear correlation between catalyst activity and the DFT-calculated energy difference ΔEi between the active and dormant state. The correlation only holds when the calculations are run on ion pairs, which is less obvious than it may appear because the anion in these systems is not at the catalyst front. This finding provides a comparatively simple and fast method to predict the activity of new catalysts of the same class.本研究针对一系列双(苯氧胺)合锆(IV) (bis(phenoxyamine)Zr(IV))基催化剂展开乙烯与丙烯聚合性能评价，所涉催化剂的双(苯氧胺)配体结构为N,N′-双(3-R¹-5-R²-2-O-C₆H₂CH₂)-N,N′-(R³)₂-(NCH₂CH₂N)，并考察了不同R¹/R²/R³取代基组合对催化活性的影响。此前针对该类催化剂的研究表明，预催化剂经活化（如使用甲基铝氧烷 (methylalumoxane)）后生成的阳离子会采取“休眠”的经式-经式 (mer-mer)构型，而由休眠态向活性面式-面式 (fac-fac)构型的吸热异构化过程是催化循环的必要起始步骤。本文明确报道了催化剂活性与密度泛函理论 (Density Functional Theory，DFT)计算得到的活性态与休眠态之间的能量差ΔEi之间存在显著相关性。该相关性仅在以离子对为模型开展计算时成立，而这一结论的成立条件并不直观，究其原因在于该类体系中的阴离子并不位于催化剂活性前沿区域。上述发现为预测同类型新型催化剂的催化活性提供了一种相对简便快捷的方法。