Reactions of phosphines with electron deficient boranes

Abstract

A series of classical B(C₆F₅)₃-phosphine adducts are shown to be reactive molecules. Reaction of (THF)B(C₆F₅)₃ with phosphines are shown to effect ring-opening of THF affording the zwitterionic phosphonium-borate species of the form R₂PH(C₄H₈O)B(C₆F₅)₃ and R₃P(C₄H₈O)B(C₆F₅)₃. Alternatively, treatment of (THF)B(C₆F₅)₃ with a lithium phosphide (R₂PLi, R = tBu, Ph Mes) affords species of the form [Li(THF)_x][R₂P(C₄H₈O)B(C₆F₅)₃]. Additionally, double THF ring-opening is also demonstrated to give species of the form [Li(THF)_x][R₂P(C₄H₈OB(C₆F₅)₃)₂]. In addition a series of classical borane-phosphine adducts are also shown to undergo thermal rearrangement reactions to give the zwitterionic products of aromatic substitution R₂PH(C₆F₄)BF(C₆F₅)₂ and R₃P(C₆F₄)BF(C₆F₅)₂. The mechanism of these substitutions is considered. A series of crystallographic studies of phosphine-borane adducts, THF ring-opened zwitterions and para-attack zwitterionic phosphonium borates are reported and discussed.