Electronic and steric effects of substituents in series of Zn²⁺ asymmetrical bis-Schiff-base ligands complexes on catalytic ring-opening copolymerization of CHO and MA

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• 作者：Jing Wu ; Dengfeng Liu ; Liying Wu ; Xingmei Zhang ; Luqun Zhu ; Daidi Fan ; Xingqiang L眉 ; Qi Shi
• 关键词：Electronic and steric effect ; Zn2+ asymmetrical bis-Schiff-base complexes ; Copolymerization from CHO and MA ; Polyester ; Poly(ester-co-ether)
• 刊名：Journal of Organometallic Chemistry
• 出版年：1 January, 2014
• 年：2014
• 卷：749
• 期：Complete
• 页码：302-311
• 全文大小：891 K

文摘

Based on the half-unit Schiff-base ligand HL and series of asymmetrical bis-Schiff-base ligand H₂Lⁿ (n聽=聽1-6) in situ synthesized from the reaction of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP), o-phenylenediamine, and/or different salicylaldehyde derivatives, complexes [Zn(L)₂] (1) and series of [Zn(Lⁿ)] (n聽=聽1-6, 2-7) are obtained, respectively. Complex 1 proves to be inactive, resulting from its saturated octahedral coordination environment around the central Zn²⁺ ion, while in complexes 2-7, the unsaturated coordination environment for the catalytic active centers (Zn²⁺ ions) permits the monomer insertion for the effective bulk or solution copolymerization of CHO (cyclohexene oxide) and MA (maleic anhydride). As to the electron and steric effect in complexes 2-7 on the catalytic behaviors, the copolymerization results show that the introduction of withdrawing -Br substituent para to the phenoxide group endows higher reactive activity, while the bulkiness effect of the encumbering substituent (-Br, -OMe or tert-butyl) ortho to the phenoxide groups is in favor of the chain growth of the copolymers. Moreover, all the bulk copolymerizations in 2-7/DMAP (4-(dimethylamino)pyridine) systems afford poly(ester-co-ether)s, while lower catalyst and co-catalyst concentration for 3/DMAP system is helpful for the formation of perfectly alternating polyester in solution. Of the three co-catalysts, DMAP is found to be the most efficient, while an excess thereof is detrimental for the chain growth of the copolymers.