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A series of phosphine-stabilized phosphoranimine cations [[[R.sub.3]P.P[R.sub.2]-[double bond]NSi[Me.sub.3]].sup.+] are prepared and the reactivities are studied. The density functional theory studies have shown that the difference in the [super 1][J.sub.pp] couplings are related to the electronegativity of the R- substituents at the phosphoranimine phosphorous center rather than the strength of the donor-acceptor P-P bond.

A series of phosphine-stabilized phosphoranimine cations [R3P· PR′2=NSiMe3]+, which can be regarded as derivatives of the proposed transient reactive intermediate [PR′2=NSiMe3]+ in the thermal condensation polymerization of phosphoranimines (R"O)PR′2=NSiMe3 to form poly(alkyl/arylphosphazenes) [PR′2=N]n at 180-200 °C, have been prepared. The bromide salts [R3P·PR′2=NSiMe3]Br[R′ = Me ([6]+), OCH2CF3 ([8]+); R3P = Me3P (a), Et3P (b), nBu3P (C), dmpm (d, dmpm = dimethylphosphinomethane), dmpe (e, dmpe = dimethyiphosphinoethane)] were prepared from the direct reactions between BrMe2P=NSiMe3 (5) and Br(CF3CH2O)2P=NSiMe3 (7) and the corresponding tertiary phosphines R3P or the diphosphines Me2P(CH2)nPMe2 (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·PR2=NSiMe3]Br [R = Me ([9]+), OCH2CF3 ([10]+)]. Cations [6]+ with Br anions are particularly labile: for example, (6a]Br slowly releases PMe3, BrSiMe3, and forms cyclic phosphazenes such as [Me2P=N]4. Anion exchange reactions between the salts [6b]Br or [8c]Br and AgOTf (OTf = CF3SO3) quantitatively afforded the corresponding and more stable triflate salts [6b]OTf and [8c]OTf. Phosphine ligand abstraction reactions with B(C6F5)3 were observed for the bromide salts [6b]Br and [8c]Br, which regenerated the phosphoranimines 5 and 7, respectively, and formed the adduct R3P·B(C6F5)3. In contrast, the triflate salts [6b]OTf and [8c]OTf were unreactive under the same conditions. X-ray structural analysis of the P-donor stabilized cations revealed longer P-P and P-Nbond lengths and smaller P-N-Si bond angles for cations [6]+ compared to analogs [8]+. These structural differences were rationalized using the negative hyperconjugation bonding model. In addition, the ¹Jpp coupling constants for the cations [6]+ observed by both solution and solid-state 31P NMR are remarkably small (13-25 Hz), whereas those for [8]+ are substantially larger and positive (276-324 Hz) and are as expected for P(IV)+-P(V) systems. DFT studies suggest that the significant difference in ¹Jpp couplings observed for [6]+ and [8]+ appears to be related to the electronegativity of the R′ substituents at the phosphoranimine phosphorus center rather than the strength of the donor-acceptor P-P bond, which is slightly weaker in [6]+ relative to that in [8]+, as indicated by the X-ray data and reactivity studies. [ABSTRACT FROM AUTHOR]