Chen Eugene Y-X
Department of Chemistry, Colorado State University, Fort Collins, CO, 80523-1872, USA,
Top Curr Chem. 2013;334:239-60. doi: 10.1007/128_2012_372.
Main-group classical and frustrated Lewis pairs (CLPs and FLPs) comprising strong Lewis acids (LAs) and strong Lewis bases (LBs) are highly active for polymerization of conjugated polar alkenes, affording typically high molecular weight polymers with relatively narrow molecular weight distributions. Especially effective systems are the Lewis pairs (LPs) consisting of the strong LA Al(C6F5)3 and strong LBs, such as achiral phosphines and chiral chelating diphosphines, N-heterocyclic carbenes, and phosphazene superbases, for polymerization of methacrylates and acrylamides as well as renewable α-methylene-γ-butyrolactones. Chain initiation involves cooperative addition of LPs to the monomer to generate zwitterionic active species, and chain propagation proceeds via a bimetallic, activated-monomer addition mechanism. Transition metal nucleophile/electrophile pairs comprising neutral metallocene bis(ester enolate)s and strong LAs E(C6F5)3 (E = Al, B) generate two drastically different polymerization systems, depending on the LA. With E = Al, catalyst activation and chain initiating events lead to dually active ion-pairs, thereby effecting ion-pairing polymerization that affords polymers with unique stereo-multiblock microstructures. With E = B, on the other hand, the FLP-induced catalyst activation generates metallacyclic cations paired with the hydridoborate anion HB(C6F5)3; uniquely, such ion-pairs effect catalytic polymerization of conjugated polar alkenes by an H-shuttling mechanism, with the cation catalyzing chain growth and the anion promoting chain transfer by shuttling the hydride between the cation and anion centers through the neutral borane.
由强路易斯酸（LAs）和强路易斯碱（LBs）组成的主族经典和受阻路易斯对（CLPs和FLPs）对共轭极性烯烃的聚合具有高活性，通常能得到具有相对窄分子量分布的高分子量聚合物。特别有效的体系是由强路易斯酸Al(C6F5)3和强路易斯碱组成的路易斯对（LPs），如非手性膦和手性螯合二膦、N-杂环卡宾和磷腈超强碱，用于甲基丙烯酸酯和丙烯酰胺以及可再生的α-亚甲基-γ-丁内酯的聚合。链引发涉及路易斯对（LPs）与单体的协同加成以生成两性离子活性物种，链增长通过双金属活化单体加成机理进行。由中性茂金属双（酯烯醇盐）和强路易斯酸E(C6F5)3（E = Al、B）组成的过渡金属亲核试剂/亲电试剂对根据路易斯酸的不同产生两种截然不同的聚合体系。当E = Al时，催化剂活化和链引发事件导致双重活性离子对，从而实现离子对聚合，得到具有独特立体多嵌段微观结构的聚合物。另一方面，当E = B时，受阻路易斯对（FLP）诱导的催化剂活化产生与氢化硼酸盐阴离子HB(C6F5)3配对的金属环阳离子；独特的是，这种离子对通过氢穿梭机理实现共轭极性烯烃的催化聚合，阳离子催化链增长，阴离子通过中性硼烷在阳离子和阴离子中心之间穿梭氢促进链转移。
