摘要
四丁基卤化铵(TBAX)离子液体与氨基酸铜配合物(CuAAs)在CO_(2)与环氧化物的环加成反应中表现出理想的协同催化活性.采用四种天然氨基酸(甘氨酸、丙氨酸、异亮氨酸和苯丙氨酸)和铜(Ⅱ)制备了相应的配合物并对其进行结构与形貌表征.以CuAAs为主催化剂,TBAX为助催化剂,研究了CuAAs/TBAX在CO_(2)与氧化苯乙烯环加成反应中的协同催化性能.实验结果表明,在CuAAs/TBAX协同催化体系中,环碳酸酯的收率可达71.3%~85.1%.基于密度泛函理论(DFT)计算,探讨了CuAAs和TBAX在CO_(2)环加成反应中的协同作用机制.DFT计算表明,氧化苯乙烯的开环过程是反应的决速步骤,甘氨酸铜/四丁基溴化铵协同催化体系具有较低的过渡态能垒(+19.4 kcal/mol).在氧化苯乙烯开环、CO_(2)插入和碳酸酯闭环过程中,CuAAs和TBAX的协同作用是不可或缺的,TBAX的协同作用可能主要影响氧化苯乙烯的开环和碳酸酯的闭环过程,CuAAs则可能更有利于CO_(2)的活化.利用CuAAs与TBAX的协同作用是构建系列简单可行的CO_(2)环加成催化体系的重要策略之一,这为CO_(2)化学转化绿色路径的设计提供了实验和理论支持.
CO_(2) capture,storage,and utilization technologies are essential for achieving carbon peaking and neutrality targets.The efficient conversion and utilization of CO_(2) as a feedstock contributes significantly to environmentally friendly and sustainable development goals.Among various CO_(2) conversion strategies,the cycloaddition of epoxides with CO_(2) represents a key transformation,yielding cyclic carbonates that serve as solvents,polycarbonate precursors,and fine chemicals.However,the chemical conversion of CO_(2) often requires harsh reaction conditions and highly active catalysts owing to its high thermodynamic stability and kinetic inertness.Therefore,the development of catalytic systems under mild conditions is imperative.Current CO_(2) cycloaddition reactions typically rely on homogeneous/heterogeneous catalysts,such as amino acid ionic liquids and MOFs.Copper amino acid complexes(CuAAs)have garnered significant attention in CO_(2) cycloaddition owing to their biocompatibility and CO_(2)-activating ability.Furthermore,quaternary ammonium salt(TBAX)ionic liquids exhibit significant advantages in C-O bond formation owing to their distinctive physicochemical properties.Nevertheless,the catalytic systems of both CuAAs and TBAX often exhibit inadequate performance in CO_(2) cycloaddition reactions.Notably,recent evidence indicates that TBAX can generate synergistic effects in catalytic systems composed of ionic liquids and metal catalysts for CO_(2) cycloaddition,although the precise mechanism remains unclear.Herein,four naturally occurring amino acids,including glycine(Gly),alanine(Ala),isoleucine(Ile),and phenylalanine(Phe),were coordinated with copper nitrate.The obtained CuAA complexes(CuGly,CuAla,CuIle,and CuPhe)were characterized employing Fourier transform infrared spectroscopy,powder X-ray diffraction,and X-ray photoelectron spectroscopy.The synergistic effects of CuAAs and TBAX in the cycloaddition of CO_(2) with styrene oxide(StO)under mild conditions(80℃,1 atm CO_(2))were investigated.Experimental results demonstrated cyclic carbonate yields of 71.3%-85.1%using this CuAAs/TBAX system.Density functional theory(DFT)calculations revealed three potential non-synergistic pathways and six synergistic routes for the cycloaddition,including epoxide ring opening,CO_(2) insertion,and carbonate ring closure.Surface electrostatic potential(ESP)analysis indicated that the maximum positive ESP energy for CuGly(+51.99 kcal/mol)exceeded those of other CuAAs.DFT calculations identified epoxide ring opening as the rate-limiting step for CO_(2) cycloaddition.Notably,the CuGly/TBAB system exhibited the lowest transition-state barrier(+19.4 kcal/mol)compared with that of CuAla(+21.2 kcal/mol),CuIle(+21.3 kcal/mol),and CuPhe(+28.3 kcal/mol),indicating superior catalytic efficiency in the ringopening step.In CuGly/TBAX(X=Cl,Br,I)catalytic systems,the ring-opening barriers of StO exhibited a reverse trend(Cl^(-):+13.6 kcal/mol<Br^(-):+19.4 kcal/mol<I^(-):+29.1 kcal/mol)compared with halide nucleophilicity(Cl^(-)>Br^(-)>I^(-)).By contrast,the carbonate ring-closing barriers(Cl^(-):+16.7 kcal/mol>Br^(-):+14.4 kcal/mol>I^(-):+13.1 kcal/mol)were consistent with halide leaving-group tendencies.These findings demonstrate that CuAAs and TBAX cooperatively promote ring-opening,CO_(2) insertion,and carbonate ring-closure.TBAX primarily accelerates epoxide ring-opening and carbonate cyclization,whereas CuAAs enhance CO_(2) activation.Independent gradient model based on Hirshfeld partition analysis indicated that weak intermolecular interactions within the catalytic system,such as hydrogen bonding and electrostatic effects,are essential for the observed synergistic catalysis.The CuGly/TBAB forms a spatially oriented platform that facilitates cooperative catalysis achieved via multiple attractive dispersion interactions between the catalyst and substrates,demonstrated that weak intermolecular interactions constitute the fundamental basis for synergistic catalysis.By combining experimental and theoretical results,this study elucidates the synergistic catalytic mechanism of CuAAs/TBAX in CO_(2) cycloaddition,providing experimental and theoretical foundations for green CO_(2) chemical conversion pathways.Furthermore,it offers a feasible technical solution for the resource utilization of CO_(2) aligning with“dual carbon”goals.
作者
肖自胜
刘思怡
宋涂暄
李丹
兰支利
肖毅
谭蓉
尹笃林
Zisheng Xiao;Siyi Liu;Tuxuan Song;Dan Li;Zhili Lan;Yi Xiao;Rong Tan;Dulin Yin(National&Local Joint Engineering Laboratory for New Petro-chemical Materials and Fine Utilization of Resources,College of Chemistry and Chemical Engineering,Hunan Normal University,Changsha 410081,China)
出处
《科学通报》
北大核心
2025年第26期4525-4537,共13页
Chinese Science Bulletin
基金
国家自然科学基金(22178093,22278122)
湖南省科技规划项目(2018TP1017)资助。
