Synthesis, Reactivity, and the Electronic Structures of Fluoro-and Hydridophosphazene Anions: X-ray Crystal Structure of [Li(THF)₃][N₃P₃F₂H(BEt₃)(η-C₅H₄)₂Fe]

The reaction of (NPF₂)₃ with 2.0 equiv of Li[BEt₃H] in THF at 25 °C yields a triethylborane-stabilized fluorophosphazene anion [N₃P₃F_sBEt₃]⁻. This species possesses a nucleophilic P(V) center that reacts readily with organic halides such as Mel or PhCH₂Br, with CF₃CH₂OH as a proton source, or with organometallic halides such as CpFe(CO)₂I to produce N₃P₃F₆Me, N₃P₃F₅CH₂Ph, N₃P₃F₅H, or N₃P₃F₅Fe(CO)₂Cp, respectively. The remaining fluorine atoms in these products were replaced by trifluoroethoxy groups to facilitate characterization. Reaction of (NPF₂)₃ with 3 equiv of Li[BEt₃H] in THF or reaction of the fluorophosphazene anion, [N₃P₃F₆BEt₃]⁻, with 1 equiv of Li[BEt₃H] generated a hy dridophosphazene anion [N₃P₃F₄HBEt₃]⁻. Similarly, reaction of the transannular ferrocenyl species N₃P₃F₄(η-C₅H₄)Fe with 3 equiv of Li[BEt₃H] in THF produced the hydridophosphazene anion [N₃P₃F₂H(BEt₃)(η-C₅H₄)₂Fe]⁻ in high yield. The electronic structures of the hydridophosphazene anions [N₃P₃F₄HBEt₃]⁻ or [N₃P₃F₂H(BEt₃)(η-C₆H₄)₂Fe]⁻ appear to differ significantly from that of the fluoro phosphazene anion [N₃P₃F₅BEt₃]⁻. Spectroscopic and reactivity studies suggest that the phosporus atom in the hydrido species exists in the +3 oxidation state, with the negative charge residing mainly on skeletal nitrogen. This situation is supported by the X-ray diffraction study of the hydridophosphazene anion [N₃P₃F₂H(BEt₃)(η-C₅H₄)₂Fe]⁻[Li(THF)₃]⁺, in which the lithium cation is coordinated to a skeletal nitrogen atom and is also surrounded by three THF molecules. Crystals of this compound are monoclinic, with a P2₁/c space group and with α = 11.363 (3) Å, b = 27.701 (9) Å, c = 11.667 (5) Å, β = 115.42 (4)°, V = 3316.8 ų, and Z = 4.