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Catalyzing pyramidal inversion: configurational lability of P-stereogenic phosphines via single electron oxidation
Kyle D Reichl1, Daniel H Ess, Alexander T Radosevich
1Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
Abstract:
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.
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