Chang Meng-Chih, Lu Wei-Yi, Chang Heng-Yi, Lai Yi-Chun, Chiang Michael Y, Chen Hsing-Yin, Chen Hsuan-Ying
Department of Medicinal and Applied Chemistry, Kaohsiung Medical University , Kaohsiung, Taiwan 80708, R.O.C.
Department of Chemistry, National Sun Yat-sen University , Kaohsiung, Taiwan 80424, R.O.C.
Inorg Chem. 2015 Dec 7;54(23):11292-8. doi: 10.1021/acs.inorgchem.5b01858. Epub 2015 Nov 17.
A series of Al complexes bearing Schiff base and thio-Schiff base ligands were synthesized, and their application for the ring-opening polymerization of ε-caprolactone (CL) and l-lactide (LA) was studied. It was found that steric effects of the ligands caused higher polymerization rate and most importantly the Al complexes with N,S-Schiff base showed significantly higher polymerization rate than Al complexes with N,O-Schiff base (5-12-fold for CL polymerization and 2-7-fold for LA polymerization). The reaction mechanism of CL polymerization was investigated by density functional theory (DFT). The calculations predicted a lower activation energy for a process involved with an Al complex bearing an N,S-Schiff base ligand (17.6 kcal/mol) than for that of an Al complex bearing an N,O-Schiff base ligand (19.0 kcal/mol), and this magnitude of activation energy reduction is comparable to the magnitude of rate enhancement observed in the experiment. The reduction of activation energy was attributed to the catalyst-substrate destabilization effect. Using a sulfur-containing ligand to decrease the activation energy in the ring-opening polymerization process may be a new strategy to design a new Al complex with high catalytic activity.
合成了一系列带有席夫碱和硫代席夫碱配体的铝配合物，并研究了它们在ε-己内酯（CL）和L-丙交酯（LA）开环聚合反应中的应用。研究发现，配体的空间效应导致聚合速率更高，最重要的是，含N,S-席夫碱的铝配合物的聚合速率显著高于含N,O-席夫碱的铝配合物（CL聚合反应中高5-12倍，LA聚合反应中高2-7倍）。采用密度泛函理论（DFT）研究了CL聚合反应的机理。计算结果预测，含N,S-席夫碱配体的铝配合物参与的反应过程的活化能（17.6 kcal/mol）低于含N,O-席夫碱配体的铝配合物（19.0 kcal/mol），且这种活化能降低的幅度与实验中观察到的速率提高幅度相当。活化能的降低归因于催化剂-底物失稳效应。使用含硫配体降低开环聚合过程中的活化能可能是设计具有高催化活性的新型铝配合物的一种新策略。
