Ring-Opening Polymerization of ε-Caprolactone Initiated by Multinuclear Aluminum Methanetris(aryloxido) Complexes
Ring-Opening Polymerization of ε-Caprolactone Initiated by Multinuclear Aluminum Methanetris(aryloxido) Complexes
复制标题
多核甲烷三(芳氧基)铝配合物引发ε-己内酯的开环聚合
DOI：
10.1021/acs.organomet.9b00540
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发表时间：
2019
期刊：
影响因子：
2.8
通讯作者：
Nomura Nobuyoshi
中科院分区：
文献类型：
--
作者：
Oishi Masataka;Ichinose Yuri;Iwata Naomi;Nomura Nobuyoshi
在四氢呋喃溶剂中对相应的三核铝配合物（1a和1b）进行脱铝处理，合成了甲烷（芳基氧化物）负载的双核铝配合物（2a-/2b-THF）。甲基铝衍生物1a1和2a- thf用一等量的苯甲醇处理，分别形成单酶氧化酶3a1和4a4，核不变。研究了这些多核铝配合物对ε-己内酯的开环聚合（ROP），发现以4a为引发剂时，ε-己内酯具有良好的聚合活性和分子量控制。在ROP过程中，通过1h NMR观察到支持配体的三个芳基氧化物部分是等效的，反映了al2中心与路易斯碱之间的快速配位平衡。合成了酯系链烷烃6 - 9并进行了结构表征。在酯加合物结构的基础上，用DFT计算对甲氧基醚的合合物和反cl加合物进行了探讨。对4a引发的ROP进行了动力学研究，发现反应速率决定步骤是由聚合条件决定的。这些结果表明，活性al2中的两个铝中心协同作用，作为路易斯碱（CL）的配位位点和醇氧末端插入的稳定位点。
Dinuclear aluminum complexes (2a-/2b-THF) supported by a methanetris(aryloxide) were synthesized by dealuminumation of the corresponding trinuclear aluminum complexes (1aand1b) in THF solvent. Treatment of methylaluminum derivatives1aand2a-THF with one equivalent of benzyl alcohol led to the formation of monobenzyloxides3aand4awith no nuclearity change, respectively. Ring-opening polymerization (ROP) of ε-caprolactone by these multinuclear aluminum complexes were studied, and good polymerization activity and molecular weight control were observed when4awas employed as the initiator. During the ROP, the three aryloxide moieties of the supporting ligand were observed to be equivalent by1H NMR spectroscopy, reflecting the rapid equilibrium of coordination between Al2centers and a Lewis base. Ester-tethered alkoxides6–9were synthesized and structurally characterized. On the basis of the ester adduct structures, bothsyn- andanti-CL adducts of methoxide10were probed using DFT calculation. Kinetic study for the4a-initiated ROP was performed and revealed that the rate-determining step is switched by polymerization conditions. These results suggest that the two aluminum centers in the active Al2species cooperatively work as a coordination site toward Lewis bases such as CL and as a stabilization site for the insertion of an alkoxide terminus.