Synthesis and Reactivity of Phosphine-Stabilized Phosphoranimine Cations, [R3P center dot PR2 '=NSiMe3](+)

作者: Keith Huynh , Alan J. Lough , Michelle A. M. Forgeron , Martin Bendle , Alejandro Presa Soto

DOI: 10.1021/JA900256G

关键词: PhosphineReactivity (chemistry)BromideNegative hyperconjugationMedicinal chemistryChemistryMolecular geometryLigandDiphosphinesInorganic chemistryTrifluoromethanesulfonate

摘要: A series of phosphine-stabilized phosphoranimine cations [R(3)P x PR'(2)=NSiMe(3)](+), which can be regarded as derivatives the proposed transient reactive intermediate [PR'(2)=NSiMe(3)](+) in thermal condensation polymerization 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 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, dimethylphosphinomethane), dmpe (e, dimethylphosphinoethane)] were prepared from direct reactions between BrMe(2)P=NSiMe(3) (5) and Br(CF(3)CH(2)O)(2)P=NSiMe(3) (7) corresponding tertiary phosphines or diphosphines Me(2)P(CH(2))(n)PMe(2) (n 1, 2). Cations type [6](+) [8](+), with electron-donating -withdrawing groups phosphorus center, respectively, undergo facile phosphine ligand substitution strong N-donor 4-dimethylaminopyridine (DMAP) yield DMAP-stabilized [DMAP PR(2)=NSiMe(3)]Br [R ([9](+)), ([10](+))]. Br(-) anions are particularly labile: for example, [6a]Br slowly releases PMe(3), BrSiMe(3), forms cyclic phosphazenes such [Me(2)P=N](4). Anion exchange [6b]Br [8c]Br AgOTf (OTf CF(3)SO(3)) quantitatively afforded more stable triflate [6b]OTf [8c]OTf. Phosphine abstraction B(C(6)F(5))(3) observed [8c]Br, regenerated 5 7, formed adduct B(C(6)F(5))(3). In contrast, [8c]OTf unreactive under same conditions. X-ray structural analysis P-donor stabilized revealed longer P-P P-N bond lengths smaller P-N-Si angles compared analogs [8](+). These differences rationalized using negative hyperconjugation bonding model. addition, (1)J(PP) coupling constants by both solution solid-state (31)P NMR remarkably small (13-25 Hz), whereas those [8](+) substantially larger positive (276-324 Hz) expected P(IV)(+)-P(V) systems. DFT studies suggest that significant difference couplings appears related electronegativity R' substituents center rather than strength donor-acceptor bond, is slightly weaker relative indicated data reactivity studies.

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