文献类型：期刊文献

英文题名：Aluminum methyl and isopropoxide complexes with ketiminate ligands: Synthesis, structural characterization and ring-opening polymerization of cyclic esters

作者：Altaf, Cigdem Tuc;Wang, Haobing;Keram, Maryam;Yang, Yang;Ma, Haiyan[1]

机构：[1]E China Univ Sci & Technol, Shanghai Key Lab Funct Mat Chem, Shanghai 200237, Peoples R China; E China Univ Sci & Technol, Lab Organomet Chem, Shanghai 200237, Peoples R China

年份：2014

卷号：81

起止页码：11

外文期刊名：POLYHEDRON

收录：;EI(收录号：20233414575671);WOS:【SCI-EXPANDED(收录号:WOS:000343339600003)】；

基金：This work is subsidized by the National Natural Science Foundation of China (NNSFC, 20604009 and 21074032), and the Fundamental Research Funds for the Central Universities (WK1214048, WD1113011). All the financial supports are gratefully acknowledged. H. Ma also thanks the very kind donation of a Braun glove-box by AvH foundation.

语种：英文

外文关键词：Aluminum; Ketiminate ligand; Catalyst; Cyclic ester; Ring-opening polymerization

摘要：Mono(ketiminate) aluminum dimethyl complexes 1a-5a and bis(ketiminate) aluminum methyl complex 2b were synthesized via the reactions of AlMe3 with various N-aryl substituted ketimine compounds in a 1:1 or 1:2 molar ratio, respectively. The reaction of Al((OPr)-Pr-i)(3) with the ketimine compound (LH)-H-2 resulted in a bis(ketiminate) aluminum isopropoxide complex 2c. All the complexes were characterized by H-1 and C-13{H-1} NMR spectroscopy, either EA or HRMS analysis. X-ray diffraction measurement of complexes 2a and 3a confirmed that in the solid state both 2a and 3a exist as a tetrahedron structure with the aluminum atom center surrounded by the oxygen and nitrogen donors of the bis-chelating ketiminate ligand as well as two methyl groups. Besides, a triligated aluminum complex 3 (Al(L-3)(3)) with a six-coordinated metal core and a dinuclear aluminum isopropoxide complex 6d [(L-6)(2)Al(mu-(OPr)-Pr-i)(2)Al((OPr)-Pr-i)(2)] with C-2-symmetry were isolated and characterized by X-ray diffraction studies. All aluminum methyl complexes behaved as active initiators in the ring-opening polymerization (ROP) of rac-lactide (rac-LA), affording isotactic-enriched polylactides (PLAs) with high molecular weights and broad molecular weight distributions at 70 degrees C. The steric and electronic characters of the ancillary ligands show significant effects both on the activity and the stereoselectivity. The introduction of an electron-withdrawing group on the para-position of N-aryl ring of the ligand resulted in an increase of the catalytic activity. However, the electronic character of ancillary ligands showed a neglectable effect on the ROP of epsilon-CL initiated by these aluminum complexes. For both monomers, bis(ketiminate) aluminum complex 2b was found to be more active than the corresponding mono(ketiminate) complex 2a of the same ligand. Aluminum isopropoxide complex 2c exerted better control for the polymerizations of both monomers, providing polymers with narrower molecular weight distributions and smaller molecular weights which are comparable to the theoretical values (C) 2014 Elsevier Ltd. All rights reserved.