Interception of intermediates in phosphine oxidation by mesityl nitrile-N-oxide using frustrated Lewis pairs

Abstract

Phosphine oxidation by MesCNO is rapid; however, an FLP strategy intercepts the 1,3 addition products including [MesC(R₃P)NOB(C₆F₅)₃] (R = Ph 1, p-tol 2), [MesC(Mes₂PH)NOB(C₆F₅)₃] 3 (MesC(NOB(C₆F₅)₃)Ph₂P)₂(CH₂)_n (n = 2: 4, 3: 5) and [MesC(Ph₃P)NOB(C₆F₄H)₃] 6. These species are shown to react with tBuOK or [Bu₄N]F permitting the oxidation to proceed via a process involving borane dissociation. Similarly, the equilibrium established by 1 with B(C₆F₄H)₃ and 6 with B(C₆F₅)₃ provides experimental support for the “Cummins mechanism” for these phosphine oxidations.