Reactions of phosphines with electron deficient boranes

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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.