A Radical Mechanism for Frustrated Lewis Pair Reactivity

Article abstract of DOI:10.1016/j.chempr.2017.05.022

The frustrated Lewis pairs (FLPs) derived from tBu₃P and E(C₆F₅)₃ (E = B, Al) react with pO₂C₆Cl₄ and Ph₃SnH to give [tBu₃POC₆Cl₄OE(C₆F₅)₃] (E = B 1, Al 2), [tBu₃PSnPh₃][HB(C₆F₅)₃] 3, and [tBu₃PSnPh₃][(μ-H)(Al(C₆F₅)₃)₂] 4. These products form via the accepted two-electron process involving a transient “encounter complex.” In contrast, the corresponding reactions of Mes₃P and E(C₆F₅)₃ (E = B, Al) with pO₂C₆Cl₄ give [(Mes₃POC₆Cl₄OE(C₆F₅)₃] (E = B 8, Al 9); however, the identification of the intermediates [Mes₃P·]₂[(C₆F₅)₃EOC₆Cl₄OE(C₆F₅)₃] (E = B 5, Al 6) supports a mechanism that proceeds via a single-electron transfer process. This is further supported by the reactions of Mes₃P and E(C₆F₅)₃ (E = B, Al) with Ph₃SnH, which yielded [Mes₃PH][HB(C₆F₅)₃] 10 and [Mes₃PH][(μ-H)(Al(C₆F₅)₃)₂] 11, respectively, with the concurrent formation of Ph₃SnSnPh₃.