Synthesis, Structure, and Reactivity of Pentamethylcyclopentadienyl 2,4,6-Triphenylphosphinine Iron Complexes

The potassium salt [K([18]­crown-6)­(THF)₂]­[Cp*Fe­(η⁴-2,4,6-triphenyl­phosphinine)}] (<b>K1</b>, Cp* = C₅Me₅) can be isolated in 68% yield by reacting the anionic naphthalene complex [K([18]­crown-6)­{Cp*Fe­(η⁴-C₁₀H₈)}] (C₁₀H₈ = naphthalene) with 2,4,6-triphenylphosphinine. Compound <b>K1</b> reacts with water to afford [K([18]-crown-6)]­{Cp*Fe­(η⁴-2,4,6-triphenyl-2,3-dihydrophosphinine 1-oxide)}] (<b>K2</b>) with a novel 2,3-dihydrophosphinine 1-oxide ligand. Oxidation of <b>K1</b> with one equivalent of ferrocenium hexafluorophosphate yields the P–P-bonded diphosphinine complex [Cp*Fe­(η⁵-2,4,6-triphenyl­phosphinine)]₂ (<b>3</b>), while the iodide salt [Cp*Fe­(η⁶-2,4,6-triphenyl­phosphinine)]­I (<b>4</b>) can be obtained by reacting <b>K1</b> with one equivalent of iodine. Reactions of <b>4</b> with LiNMe₂, Cp*Li, LiBHEt₃, and Ga­(nacnac^Dipp) (nacnac^Dipp = HC­{C­(Me)­N­(C₆H₃-2,6-<i>i</i>Pr₂)}₂) afford [Cp*Fe­(η⁵-1-dimethylamino-2,4,6-triphenyl­phosphacyclohexadienyl)] (<b>5</b>), [Cp*Fe­(η⁵-1-(η¹-Cp*)-2,4,6-triphenyl­phosphacyclohexadienyl)] (<b>6</b>), [Cp*Fe­(η⁵-1-hydro-2,4,6-triphenyl­phosphacyclohexadienyl)] (<b>7</b>), and [Cp*Fe­((η⁵-1-{Ga­(nacnac^Dipp)­I}-2,4,6-triphenyl­phosphacyclohexadienyl] (<b>8</b>). The molecular structures of <b>5</b>–<b>8</b> display η⁵-coordinated λ³σ³-phosphinine anions. All new complexes were fully characterized by spectroscopic techniques (¹H, ¹³C, and ³¹P NMR, UV–vis, and IR spectroscopy), elemental analysis, and X-ray crystallography. The electronic structures of these new phosphinine complexes were investigated theoretically at the DFT level, using molecular orbital and population analyses. The nature of the electronic transitions observed in the UV–vis spectra was analyzed using TD-DFT calculations