A series of classical B(C(6)F(5))(3)-phosphine adducts are shown to be reactive molecules. Reaction of (THF)B(C(6)F(5))(3) with phosphines are shown to effect ring-opening of THF affording the zwitterionic phosphonium-borate species of the form R(2)PH(C(4)H(8)O)B(C(6)F(5))(3) and R(3)P(C(4)H(8)O)B(C(6)F(5))(3). Alternatively, treatment of (THF)B(C(6)F(5))(3) with a lithium phosphide (R(2)PLi, R = tBu, Ph Mes) affords species of the form [Li(THF)(x)][R(2)P(C(4)H(8)O)B(C(6)F(5))(3)]. Additionally, double THF ring-opening is also demonstrated to give species of the form [Li(THF)(x)][R(2)P(C(4)H(8)OB(C(6)F(5))(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 R(2)PH(C(6)F(4))BF(C(6)F(5))(2) and R(3)P(C(6)F(4))BF(C(6)F(5))(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.