CO<sub>2</sub>/ethylene oxide copolymerization and ligand variation for a highly active salen–cobalt(<scp>iii</scp>) complex tethering 4 quaternary ammonium salts
作者:Jong Yeob Jeon、Jung Jae Lee、Jobi Kodiyan Varghese、Sung Jae Na、S. Sujith、Min Jeong Go、Junseong Lee、Myung-Ahn Ok、Bun Yeoul Lee
DOI:10.1039/c2dt31854g
日期:——
A cobalt(III) complex (1) of a salcy-type ligand tethering 4 quaternary ammonium salts, which is thought to act as a highly active catalyst for CO2/propylene oxide (PO) copolymerization, also shows high activity (TOF, 25â900 hâ1; TON, 518â000; 2.72 kg polymer per g cat) and selectivity (>98%) for CO2/ethylene oxide (EO) copolymerization that results in high-molecular-weight polymers (Mn, 200â000â300â000) that have strictly alternating repeating units. The related cobalt(III) complexes 11â14 were prepared through variations of the ligand framework of 1 by replacing the trans-1,2-diaminocyclohexane unit with 2,2-dimethyl-1,3-propanediamine, trans-1,2-diaminocyclopentane, or 1,1â²-binaphthyl-2,2â²-diamine or by replacing the aldimine bond with ketimine. These ligand frameworks are thought to favour the formation of the cis-β configuration in complexation, and the formation of the cis-β configuration in 11â14 was confirmed through NMR studies or X-ray crystallographic studies of model complexes not bearing the quaternary ammonium salts. Complexes 11, 13, and 14, which adopt the cis-β configuration even in DMSO did not show any activity for CO2/PO copolymerization. Complex 12, which was constructed with trans-1,2-diaminocyclopentane and fluctuated in DMSO between the coordination and de-coordination of the acetate ligand as observed for 1, showed fairly high activity (TOF, 12â400 hâ1). This fluctuating behaviour may play a role in polymerization. However, complex 12 did not compete with 1 in terms of activity, selectivity, and the catalyst cost.
被认为是二氧化碳/环氧丙烷(PO)共聚的高活性催化剂的盐类配体钴(III)配合物(1),在二氧化碳/环氧乙烷(EO)共聚方面也显示出高活性(TOF,25900 h1;TON,518000;2.72 kg polymer per g cat)和选择性(>98%),可用于二氧化碳/环氧乙烷(EO)共聚,产生具有严格交替重复单元的高分子量聚合物(Mn,200â000â300â000)。通过将反式-1,2-二氨基环己烷单元替换为 2,2-二甲基-1,3-丙二胺、反式-1,2-二氨基环戊烷或 1,1â²-联萘-2,2â²-二胺,或将醛亚胺键替换为酮亚胺,制备出了相关的钴(III)配合物 11â14。这些配体框架被认为有利于在络合过程中形成顺δ构型,11â14 中顺δ构型的形成已通过核磁共振研究或不含季铵盐的模型络合物的 X 射线晶体学研究得到证实。即使在二甲基亚砜(DMSO)中也采用顺δ² 构型的络合物 11、13 和 14 没有显示出任何 CO2/PO 共聚活性。络合物 12 是用反式-1,2-二氨基环戊烷构建的,在二甲基亚砜中乙酸配体的配位和去配位之间起伏不定,正如在 1 中观察到的那样,它显示出相当高的活性(TOF,12â400 hâ1)。这种波动行为可能在聚合过程中起了作用。不过,就活性、选择性和催化剂成本而言,复合物 12 无法与 1 竞争。