Electron-rich triarylphosphines, namely 4-(methoxyphenyl)diphenylphosphine (MMTPP) and tris(4-trimethoxyphenyl)phosphine (TMTPP), outperform commonly used triphenylphosphine (TPP) in catalyzing oxa-Michael additions. A matrix consisting of three differently strong Michael acceptors and four alcohols of varying acidity was used to assess the activity of the three catalysts. All test reactions were performed with 1 mol % catalyst loading, under solvent-free conditions and at room temperature. The results reveal a decisive superiority of TMTPP for converting poor and intermediate Michael acceptors such as acrylamide and acrylonitrile and for converting less acidic alcohols like isopropanol. With stronger Michael acceptors and more acidic alcohols, the impact of the more electron-rich catalysts is less pronounced. The experimental activity trend was rationalized by calculating the Michael acceptor affinities of all phosphine–Michael acceptor combinations. Besides this parameter, the acidity of the alcohol has a strong impact on the reaction speed. The oxidation stability of the phosphines was also evaluated and the most electron-rich TMTPP was found to be only slightly more sensitive to oxidation than TPP. Finally, the catalysts were employed in the oxa-Michael polymerization of 2-hydroxyethyl acrylate. With TMTPP polymers characterized by number average molar masses of about 1200 g/mol at room temperature are accessible. Polymerizations carried out at 80 °C resulted in macromolecules containing a considerable share of Rauhut–Currier-type repeat units and consequently lower molar masses were obtained.

中文翻译：

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富电子三芳基膦作为 oxa-Michael 反应的亲核催化剂


富电子三芳基膦，即 4-(甲氧基苯基)二苯基膦 (MMTPP) 和三(4-三甲氧基苯基)膦 (TMTPP) 在催化 oxa-Michael 加成方面优于常用的三苯基膦 (TPP)。使用由三种不同强度的迈克尔受体和四种不同酸度的醇组成的基质来评估三种催化剂的活性。所有测试反应均在无溶剂条件下和室温下以 1 mol% 催化剂负载量进行。结果表明，TMTPP 在转化丙烯酰胺和丙烯腈等弱迈克尔受体和中间迈克尔受体以及转化异丙醇等弱酸性醇方面具有决定性的优势。随着迈克尔受体的增强和酸性醇的增多，富电子催化剂的影响就不那么明显了。通过计算所有膦-迈克尔受体组合的迈克尔受体亲和力，使实验活性趋势合理化。除了这个参数之外，醇的酸度对反应速度也有很大影响。还评估了膦的氧化稳定性，发现最富电子的 TMTPP 对氧化的敏感性仅比 TPP 稍高。最后，将该催化剂用于丙烯酸2-羟乙酯的氧杂-迈克尔聚合反应。使用TMTPP，可以获得在室温下数均摩尔质量约为1200 g/mol的聚合物。在 80 °C 下进行的聚合导致大分子含有相当大比例的 Rauhut-Currier 型重复单元，因此获得了较低的摩尔质量。