DFT Studies on Isoprene/Ethylene Copolymerization Catalyzed by Cationic Scandium Complexes Bearing Different Ancillary Ligands  

作　　者：Xiaojie Hu Xiaohui Kang Guangli Zhou Xingbao Wang Zhaomin Hou Yi Luo 

机构地区：[1]State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China [2]Organometallic Chemistry Laboratory and Center for Sustainable Resource Science, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan [3]College of Pharmacy, Dalian Medical University, Dalian, Liaoning 116044, China

出　　处：《Chinese Journal of Chemistry》2017年第5期723-732,共10页中国化学（英文版）

摘　　要：The isoprene/ethylene copolymerization catalyzed by cationic rare earth metal complexes [（η5-C5Me5）Sc（CH2SiMe3）]＋ （A） had afforded alternating isoprene-ethylene copolymer with rich 3,4-polyisoprene microstructures,whereas no isoprene-ethylene copolymer was observed by using analogous [（PNpPh）Nc（CH2SiMe3）]＋ （B） under the same conditions.Theoretical calculations in this work have revealed that,in the case of A,successive 3,4-insertion of isoprene resulted in a noncovalent interaction between the C =C double bond of penultimate unit and the metal center,suppressing the further insertion of monomers due to higher energy barrier and endergonic character.On the other hand,the ethylene pre-inserted species with alkyl active site is more suitable for the subsequent kinetically and thermodynamically favorable isoprene insertion and copolymerization is therefore realized.In the case of B,the experimentally observed cis-l,4-specific homopolymerization of isoprene was the outcome of both kinetic and thermodynamic control.And,the unfavorable ethylene insertion into the isoprene pre-inserted species with allyl active site could account for the experimental finding that no isoprene-ethylene copolymer was obtained.These computational results are expected to provide some hints for the design of rare earth copolymerization catalysts.The isoprene/ethylene copolymerization catalyzed by cationic rare earth metal complexes [（η5-C5Me5）Sc（CH2SiMe3）]＋ （A） had afforded alternating isoprene-ethylene copolymer with rich 3,4-polyisoprene microstructures,whereas no isoprene-ethylene copolymer was observed by using analogous [（PNpPh）Nc（CH2SiMe3）]＋ （B） under the same conditions.Theoretical calculations in this work have revealed that,in the case of A,successive 3,4-insertion of isoprene resulted in a noncovalent interaction between the C =C double bond of penultimate unit and the metal center,suppressing the further insertion of monomers due to higher energy barrier and endergonic character.On the other hand,the ethylene pre-inserted species with alkyl active site is more suitable for the subsequent kinetically and thermodynamically favorable isoprene insertion and copolymerization is therefore realized.In the case of B,the experimentally observed cis-l,4-specific homopolymerization of isoprene was the outcome of both kinetic and thermodynamic control.And,the unfavorable ethylene insertion into the isoprene pre-inserted species with allyl active site could account for the experimental finding that no isoprene-ethylene copolymer was obtained.These computational results are expected to provide some hints for the design of rare earth copolymerization catalysts.

关 键 词：DFT ethylene/isoprene copolymerization rare earth metal 

分 类 号：O631.5[理学—高分子化学] TQ333.3[理学—化学]