Photooxidation of Mixed Aryl and Biarylphosphines

Arylphosphines and dialkylbiarylphosphines react with singlet oxygen to form phosphine oxides and phosphinate esters. For mixed arylphosphines, the most electron-rich aryl group migrates to form the phosphinate, while for dialkylbiarylphosphines migration of the alkyl group occurs. Dialkylbiarylphosphines also yield arene epoxides, especially in electron-rich systems. Phosphinate ester formation is increased at high temperature, while protic solvents increase the yield of epoxide. The product distribution provides evidence for Buchwald’s recent conformational model for the aerobic oxidation of dialkylbiarylphosphines.

芳基膦(Arylphosphines)与二烷基二芳基膦(dialkylbiarylphosphines)均可与单线态氧(singlet oxygen)发生反应，生成氧化膦(phosphine oxides)与次膦酸酯(phosphinate esters)。对于混合芳基膦(mixed arylphosphines)而言，反应中富电子芳基会发生迁移以生成次膦酸酯；而针对二烷基二芳基膦，则为烷基发生迁移反应。二烷基二芳基膦还可生成芳烃环氧化物(arene epoxides)，在富电子反应体系中该产物的生成尤为突出。高温条件下次膦酸酯的产率会有所提升，而质子溶剂(protic solvents)则可提高环氧化物的产率。该产物分布为布赫瓦尔德(Buchwald)近期提出的二烷基二芳基膦需氧氧化(aerobic oxidation)构象模型提供了实验证据。