Stereocontrolled Radical Polymerization of Acrylamides by Ligand-Accelerated Catalysis
Stereocontrolled Radical Polymerization of Acrylamides by Ligand-Accelerated Catalysis
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配体加速催化丙烯酰胺立体控制自由基聚合
DOI：
10.1038/s41428-020-00444-0
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
S.
中科院分区：
文献类型：
--
作者：
Park;B.; Imamura;Y.; Yamago;S.
阐明了乙醇在Yb(OTf)3-和Y(OTf)3催化的丙烯酰胺立体选择性自由基聚合中的作用。在N，N-二乙基丙烯酰胺的聚合中，醇与金属三氟酸盐配位生成一种新的络合物，与不含醇的金属三氟酸盐相比，它提高了聚合速率和立体控制。虽然三氟化镧催化的丙烯酰胺在甲醇中的立体选择性聚合已经得到很好的合成，但这是第一个证明醇类配位催化剂作为活性催化剂形成的例子。JOB作图表明，Yb(OTf)3和MeOH的化学计量比为1：2。当用MeOD代替MeOH时，聚合速率略有下降，二次同位素效应为1.14，强烈表明羟基对提高反应活性的重要性。相反，没有观察到明显的二次同位素效应影响立体选择性。乙醇配体的手性不影响立体选择性，说明立体化学很可能受倒数第二个效应的控制，这一点已经被提出。此外，这些条件与有机碲引发的自由基聚合条件高度兼容，成功地实现了相对分子质量和规整度的双重控制。
The role of alcohol in the Yb(OTf)3- and Y(OTf)3-catalyzed stereoselective radical polymerization of acrylamides is clarified. The coordination of an alcohol to the metal triflate generates a new complex, which increases both the polymerization rate and stereocontrol compared to those achieved by the metal triflate without an alcohol in the polymerization ofN,N-diethylacrylamide. While the lanthanide triflate-catalyzed stereoselective polymerization of acrylamides in MeOH has already been well established synthetically, this is the first example that proves the formation of an alcohol-coordinated catalyst as the active catalyst. Job’s plot suggests that the stoichiometry between Yb(OTf)3and MeOH in the complex is 1:2. The polymerization rate decreases slightly when MeOD is used instead of MeOH, with a secondary isotope effect of 1.14, strongly suggesting the importance of hydroxyl groups for increasing the reactivity. In contrast, no apparent secondary isotope effect is observed to affect the stereoselectivity. The chirality of the alcohol ligand does not affect the stereoselectivity, illustrating that the stereochemistry is most likely controlled by the penultimate effect, which has already been proposed. Furthermore, the conditions are highly compatible with those for organotellurium-mediated radical polymerization, and the dual control of molecular weight and tacticity is successfully achieved.