Reactions of phosphines with electron deficient boranes

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.