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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >A computational insight into a metal mediated pathway for the ring-opening polymerization (ROP) of lactides by an ionic {(NHC)_2Ag} ~+X~- (X = halide) type N-heterocyclic carbene (NHC) complex
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A computational insight into a metal mediated pathway for the ring-opening polymerization (ROP) of lactides by an ionic {(NHC)_2Ag} ~+X~- (X = halide) type N-heterocyclic carbene (NHC) complex

机译：对金属离子介导的{{NHC）_2Ag}〜+ X〜-（X =卤化物）型N-杂环卡宾（NHC）络合物对丙交酯开环聚合（ROP）的金属介导途径的计算洞察力

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摘要

A metal mediated coordination-insertion pathway for the ring-opening polymerization (ROP) of l-lactide by an ionic {(NHC)_2Ag} ~+X~- (X = halide) type silver complex of N-heterocyclic carbene (NHC) has been investigated using the density functional theory (DFT) method. A clear insight into the lactide insertion process could be obtained by modeling two consecutive monomer addition steps with the first one mimicking chain initiation with the second representing a propagation step. In particular, in each of the cycles, the reaction initiates with the formation of a lactide coordinated species, [1+LL] and [2+LL] that transforms into a metal bound cyclic lactide intermediate, I([1+LL] → 2) and I([2+LL] → 3), which subsequently ring opens to give the lactide inserted products, 2 and 3. The estimated overall activation barrier for the initiation step is 42.0 kcal mol~(-1) while the same for the propagation step is 31.5 kcal mol ~(-1). Studies on higher monomer insertions showed a decrease in the relative product energies as anticipated for an addition polymerization pathway.
机译：N杂环卡宾（NHC）的离子型{（NHC）_2Ag}〜+ X〜-（X =卤化物）型银配合物对L-丙交酯的开环聚合（ROP）的金属介导配位插入途径已经使用密度泛函理论（DFT）方法进行了研究。可以通过对两个连续的单体添加步骤进行建模来获得对丙交酯插入过程的清晰了解，其中第一个模仿链引发，第二个代表传播步骤。特别是，在每个循环中，反应均以丙交酯配位物种[1 + LL]和[2 + LL]的形成开始，该物种转变为金属键合的环状丙交酯中间体I（[1 + LL]→ 2）和I（[2 + LL]→3），随后开环给出插入丙交酯的产物2和3。估计起始步骤的总活化势垒为42.0 kcal mol〜（-1），而相同传播步骤的分子量为31.5 kcal mol〜（-1）。对较高单体插入的研究表明，如加成聚合途径所预期的，相对产物能量降低了。

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