Institut des Sciences Moléculaires UMR CNRS 5255, Université de Bordeaux, 351 cours de la Libération, 33405 Talence, France.
Chemistry. 2010 Apr 12;16(14):4196-205. doi: 10.1002/chem.200902912.
The mechanism of the ring-opening polymerization (ROP) of lactide catalyzed by two partner hydrogen-bonding organocatalysts was explored. New amidoindoles 4 a,c, thioamidoindoles 4 b,d, amidobenzimidazoles 5 a,c, and thioamidobenzimidazoles 5 b,c were synthesized and used as activators of the monomer. In the solid state and in solution, compounds 4 and 5 showed a propensity for self-association, which was evaluated. (Thio)Amides 4 and 5 do catalyze the ROP of lactide in the presence of a cocatalyst, tertiary amine 3 a or 3 b, which activates the growing polymer chain through hydrogen-bonding. Reactions were conducted in 2-24 h at 20 degrees C; conversion yields ranged between 22 and 100 %. A detailed study of the intermolecular interactions undertaken between the participating species showed that, as expected, simultaneous weak hydrogen bonds do exist to activate the reagents. Moreover, interactions have been revealed between the partner catalysts 4/5+3. ROP catalyzed by these partner activators is thus governed by multiple dynamic equilibria. The latter should be judiciously adjusted to fine-tune the catalytic properties of (thio)amides and organocatalysts, more generally.
两种氢键相互作用的有机催化剂协同催化丙交酯开环聚合（ROP）的机理得到了研究。新的酰胺吲哚 4a,c、硫代酰胺吲哚 4b,d、酰胺苯并咪唑 5a,c 和硫代酰胺苯并咪唑 5b,c 被合成并用作单体的活化剂。在固态和溶液中，化合物 4 和 5 表现出自身缔合的倾向，对其进行了评估。（硫）酰胺 4 和 5 在助催化剂三乙胺 3a 或 3b 的存在下确实可以催化丙交酯的 ROP，助催化剂通过氢键激活生长的聚合物链。反应在 20°C 下进行 2-24 小时；转化率在 22%至 100%之间。对参与物种之间的分子间相互作用进行了详细研究，结果表明，正如预期的那样，确实存在同时的弱氢键来激活试剂。此外，还揭示了伴侣催化剂 4/5+3 之间的相互作用。这些伴侣活化剂催化的 ROP 受到多种动态平衡的控制。应该谨慎调整这些平衡，以微调（硫）酰胺和有机催化剂的催化性能，更普遍地说。
