文献类型：期刊文献

英文题名：Amidinate aluminium complexes: Synthesis, characterization and ring-opening polymerization of rac-lactide

作者：Qian, Feng[1]; Liu, Keyin[1]; Ma, Haiyan[1]

机构：[1] Laboratory of Organometallic Chemistry, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China

年份：2010

卷号：39

期号：34

起止页码：8071

外文期刊名：Dalton Transactions

收录：EI(收录号：20103413187231)

语种：英文

外文关键词：Ligands - Synthesis (chemical) - X ray diffraction - Catalyst activity - Geometry - Molecular weight distribution - Aluminum compounds

摘要：A series of aluminium alkyl complexes {PhC(NR′)(NR′′)} AlR2 (4a-n, R′ = 2,6-iPr2C 6H3, 2,6-Me2C6H3; R′′ = aryl groups with various ortho-, para- or meta-substituents, tert-butyl; R = methyl, ethyl) bearing non-symmetrically N-substituted benzamidinate ligands were synthesized via the reaction of trialkylaluminium and the corresponding benzamidine proligands. Complex 5 bearing symmetric amidinate ligand was also obtained for comparison purposes. The X-ray diffraction studies of complexes 4b, 4c and 5 show in each case a distorted tetrahedral geometry around the aluminium center. All the amidinate aluminium complexes were found to catalyze the ring-opening polymerization (ROP) of rac-lactide with moderate activities. The steric and electronic characteristics of the ancillary ligands have a significant influence on the polymerization performance of the corresponding aluminium complexes. The introduction of electron-withdrawing substituents at the ortho-positions of N-phenyl ring of the ligands resulted in an obvious increase in catalytic activity. Complex 4b showed the highest activity among the investigated aluminium complexes due to the high electrophilicity of the metal center induced by the ortho-chloro substituents on the phenyl ring. The existence of ortho-substituents of small steric bulkiness is also beneficial for the increase of activity of these catalysts. However, further increase of steric hindrance of the ligands by introducing bulky ortho-substituents onto the phenyl moieties resulted in a decrease of activity and an increase in the isotactic bias of the obtained polylactides. The broad molecular weight distributions (PDI = 1.13-2.02) of the polymer samples indicated that the ROP of rac-lactide initiated by these complexes was not well-controlled. ? 2010 The Royal Society of Chemistry.