Reactions of phosphine oxides with bromophosphoranimines; synthesis and unusual rearrangements of O-donor stabilized phosphoranimine cations.

Reaction of phosphine oxides R(3)P═O [R = Me (1a), Et (1c), (i)Pr (1d) and Ph (1e)], with the bromophosphoranimines BrPR'R''P═NSiMe(3) [R' = R'' = Me (2a); R' = Me, R'' = Ph (2b); R' = R'' = OCH(2)CF(3) (2c)] in the presence or absence of AgOTf (OTf = CF(3)SO(3)) resulted in a rearrangement reaction to give the salts [R(3)P═N═PR'R''O-SiMe(3)]X (X = Br or OTf) ([4]X). Reaction of phosphine oxide 1a with the phosphoranimine BrPMe(2)═NSiPh(3) (5) with a sterically encumbered silyl group also resulted in the analogous rearranged product [Me(3)P═N═PMe(2)O-SiPh(3)]X ([8]X) but at a significantly slower rate. In contrast, the direct reaction of the bulky tert-butyl substituted phosphine oxide, (t)Bu(3)P═O (1b) with 2a or 2c in the presence of AgOTf yielded the phosphine oxide-stabilized phosphoranimine cations [(t)Bu(3)P═O·PR'(2)═NSiMe(3)](+) ([3](+), R' = Me (d), OCH(2)CF(3) (e)).

Synthesis and reactivity of phosphine-stabilized phosphoranimine cations, [R3P x PR'2=NSiMe3]+.

A series of phosphine-stabilized phosphoranimine cations [R(3)P x PR'(2)=NSiMe(3)](+), which can be regarded as derivatives of the proposed transient reactive intermediate [PR'(2)=NSiMe(3)](+) in the thermal condensation polymerization of phosphoranimines (R''O)PR'(2)=NSiMe(3) to form poly(alkyl/arylphosphazenes) [PR'(2)=N](n) at 180-200 degrees C, have been prepared. The bromide salts [R(3)P x PR'(2)=NSiMe(3)]Br [R' = Me ([6](+)), OCH(2)CF(3) ([8](+)); R(3)P = Me(3)P (a), Et(3)P (b), (n)Bu(3)P (c), dmpm (d, dmpm = dimethylphosphinomethane), dmpe (e, dmpe = dimethylphosphinoethane)] were prepared from the direct reactions between BrMe(2)P=NSiMe(3) (5) and Br(CF(3)CH(2)O)(2)P=NSiMe(3) (7) and the corresponding tertiary phosphines R(3)P or the diphosphines Me(2)P(CH(2))(n)PMe(2) (n = 1, 2). Cations of the type [6](+) and [8](+), with electron-donating and -withdrawing groups at the phosphoranimine phosphorus center, respectively, undergo facile phosphine ligand substitution with the strong N-donor 4-dimethylaminopyridine (DMAP) to yield the corresponding DMAP-stabilized salts [DMAP x PR(2)=NSiMe(3)]Br [R = Me ([9](+)), OCH(2)CF(3) ([10](+))].