The polymerization mechanism of 2-vinylpyridine catalyzed by cationic yttrium complexes with diverse ancillary ligands, specifically [L¹Y(CH₂SiMe₃)(THF)]⁺ [L¹ = (2,6-Et₂C₆H₃)NC(Me)CHC(Me)N(2,6-Et₂C₆H₃)] (Y-1), [L²Y(CH₂SiMe₃)(THF)]⁺ [L² = (2,6-Cl₂C₆H₃)NC(Me)CHC(Me)N(2,6-Cl₂C₆H₃)] (Y-2), and [L³Y(CH₂SiMe₃)(THF)]⁺ [L³ = (2,6-C₆H₅)NC(Me)CHC(Me)N(2,6-ⁱPr₂C₆H₃)] (Y-3), was studied using density functional theory (DFT) calculations. Having achieved an agreement between theory and experiment, it is found that isotactic selectivity induced by Y-1 or Y-2 results from a combination of smaller deformation of the catalyst and stronger electronic effects. Conversely, the Y-3 complex exhibits comparable energy barriers for proceeding via either isotactic or syndiotactic pathways, aligning with the production of atactic polymers as seen experimentally. To examine the steric effects on the kinetic and thermodynamic properties, a computational model of an analogue complex [L⁴Y(CH₂SiMe₃)(THF)]⁺ [L⁴ = (2,6-Cl₂C₆H₃)NC(Me)CHC(Me)N(ⁱPr₂C₆H₃)] (Y-4), featuring increased steric hindrance, was analyzed. Distortion–interaction and topographic steric map analyses further affirmed that steric hindrance significantly influences stereoselectivity. A direct relationship was identified between the energy barriers of isotactic insertion transition states and the bulkiness of ancillary ligands; greater distortion energy of the catalyst correlates with higher barriers for isotactic polymerization. These findings enhance the mechanistic comprehension of 2-vinylpyridine polymerization and are expected to contribute valuable insights for the improvement of catalytic polymerization systems of 2-vinylpyridine.

中文翻译：

---

不同辅助配体阳离子钇配合物催化2-乙烯基吡啶立体选择性聚合的理论研究

阳离子钇与不同辅助配体的配合物催化2-乙烯基吡啶的聚合机理，具体为[ L ¹ Y(CH ₂ SiMe ₃ )(THF)] ⁺ [ L ¹ = (2,6-Et ₂ C ₆ H ₃ )NC (Me)CHC(Me)N(2,6-Et ₂ C ₆ H ₃ )] ( Y-1 ), [ L ² Y(CH ₂ SiMe ₃ )(THF)] ⁺ [ L ² = (2,6 -Cl ₂ C ₆ H ₃ )NC(Me)CHC(Me)N(2,6-Cl ₂ C ₆ H ₃ )]( Y-2 )、[ L ³ Y(CH ₂ SiMe ₃ )(THF) ] ⁺ [ L ³ = (2,6-C ₆ H ₅ )NC(Me)CHC(Me)N(2,6- ⁱ Pr ₂ C ₆ H ₃ )] ( Y-3 )，使用密度泛函进行研究理论（DFT）计算。理论与实验一致，发现Y-1或Y-2诱导的全同立构选择性是催化剂较小变形和较强电子效应相结合的结果。相反，Y-3络合物通过全同立构或间同立构途径表现出相当的能量势垒，与实验中观察到的无规聚合物的生产一致。为了检查对动力学和热力学性质的空间效应，模拟配合物的计算模型 [ L ⁴ Y(CH ₂ SiMe ₃ )(THF)] ⁺ [ L ⁴ = (2,6-Cl ₂ C ₆ H ₃ ) NC(Me)CHC(Me)N( ⁱ Pr ₂ C ₆ H ₃ )] ( Y-4），以空间位阻增加为特征，进行了分析。畸变相互作用和地形空间图分析进一步证实了空间位阻显着影响立体选择性。确定了全同立构插入过渡态的能垒与辅助配体的体积之间的直接关系；催化剂的畸变能越大，全同立构聚合的势垒越高。这些发现增强了对2-乙烯基吡啶聚合机理的理解，并有望为改进2-乙烯基吡啶催化聚合体系提供有价值的见解。