Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
J Am Chem Soc. 2013 Jun 26;135(25):9354-7. doi: 10.1021/ja404943x. Epub 2013 Jun 17.
We report that pyramidal inversion of trivalent phosphines may be catalyzed by single electron oxidation. Specifically, a series of P-stereogenic (aryl)methylphenyl phosphines are shown to undergo rapid racemization at ambient temperature when exposed to catalytic quantities of a single electron oxidant in solution. Under these conditions, transient phosphoniumyl radical cations (R3P(•+)) are formed, and computational models indicate that the pyramidal inversion barriers for these open-shell intermediates are on the order of ∼5 kcal/mol. The observed 10(20)-fold rate enhancement over uncatalyzed pyramidal inversion opens new opportunities for the dynamic stereochemistry of phosphines and may hold additional implications for the configurational stability of P-stereogenic phosphine ligands on high-valent oxidizing transition metals.
我们报告说，三价膦的三角锥形反转可能被单电子氧化催化。具体来说，一系列 P-手性（芳基）甲基苯基膦在溶液中暴露于催化量的单电子氧化剂时，在环境温度下会迅速外消旋。在这些条件下，瞬态磷鎓基自由基阳离子（R3P(•+)）形成，计算模型表明这些开壳中间体的三角锥形反转势垒约为 5 kcal/mol。与未经催化的三角锥形反转相比，观察到的 10(20)倍速率增强为膦的动态立体化学开辟了新的机会，并且可能对高价氧化过渡金属上 P-手性膦配体的构型稳定性具有额外的意义。
