Abstract This contribution illustrates the significant influence of the Al-catalyzed e-caprolactone (e-CL) and δ-valerolactone (δ-VL) ring-opening polymerizations. A series of β-pyridyl-enamino aluminum complexes [AlLMe2] 1–6 {L = [(2-C5H4N)-C(H) C(Ph) N(Ar) ], Ar = C6H5 (1), 2,6-Me2C6H3 (2), 2,6-Et2C6H3 (3), 2,6-iPr2C6H3 (4), 4-FC6H4 (5), C6F5 (6)} were synthesized and characterized by NMR spectroscopy and single-crystal X-ray diffraction. The catalytic activities the polymerization of e-caprolactone (e-CL) and δ-valerolactone (δ-VL) correlated with the substituent’s character of the ortho and para groups on the Ar moieties of the β-pyridyl-enamino ligands. For the polymerizations of the both cyclic esters, complexes 1, 5 and 6 displayed excellent catalytic activities in the presence of the initiator benzyl alcohol, while complexes 2–4 exhibited much lower activities under the same conditions. Kinetic studies revealed that complex 5 polymerized e-CL at a faster rate in comparison to 1 and 6, where highlighted a cumulative effect of both the electronic and steric effect on the ligands. By contrast, for the ROP of δ-VL, complex 1 was found to be more active than the catalysts 5 and 6. This unusual result was suggested the rate-determined step was the “insertion” step in e-CL and δ-VL polymerization, the former’s insertion rate is faster than the latter’s.

中文翻译：

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β-吡啶基-烯氨基铝配合物催化ε-CL和δ-VL开环聚合反应中意外取代基对催化活性的影响

摘要 这一贡献说明了铝催化的ε-己内酯（e-CL）和δ-戊内酯（δ-VL）开环聚合的显着影响。一系列β-吡啶基-烯氨基铝配合物[AlLMe2] 1-6 {L = [(2-C5H4N)-C(H) C(Ph) N(Ar) ], Ar = C6H5 (1), 2,6 -Me2C6H3 (2), 2,6-Et2C6H3 (3), 2,6-iPr2C6H3 (4), 4-FC6H4 (5), C6F5 (6)} 合成并通过核磁共振光谱和单晶X射线表征衍射。ε-己内酯（e-CL）和δ-戊内酯（δ-VL）的聚合催化活性与β-吡啶基-烯氨基配体的Ar部分上的邻位和对位基团的取代基特征相关。对于两种环酯的聚合，配合物 1、5 和 6 在引发剂苯甲醇存在下表现出优异的催化活性，而在相同条件下，复合物 2-4 的活性要低得多。动力学研究表明，与 1 和 6 相比，复合物 5 以更快的速率聚合 e-CL，其中突出了电子和空间效应对配体的累积效应。相比之下，对于 δ-VL 的 ROP，发现配合物 1 比催化剂 5 和 6 更具活性。这一不寻常的结果表明速率决定步骤是 e-CL 和 δ-VL 中的“插入”步骤聚合时，前者的插入速度比后者快。