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)}]
(K1, 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 K1 reacts with water to afford [K([18]-crown-6)]­{Cp*Fe­(η4-2,4,6-triphenyl-2,3-dihydrophosphinine 1-oxide)}] (K2) with a novel 2,3-dihydrophosphinine 1-oxide ligand. Oxidation
of K1 with one equivalent of ferrocenium hexafluorophosphate
yields the P–P-bonded diphosphinine complex [Cp*Fe­(η5-2,4,6-triphenyl­phosphinine)]2 (3), while the iodide salt [Cp*Fe­(η6-2,4,6-triphenyl­phosphinine)]­I
(4) can be obtained by reacting K1 with
one equivalent of iodine. Reactions of 4 with LiNMe2, Cp*Li, LiBHEt3, and Ga­(nacnacDipp)
(nacnacDipp = HC­{C­(Me)­N­(C6H3-2,6-iPr2)}2) afford [Cp*Fe­(η5-1-dimethylamino-2,4,6-triphenyl­phosphacyclohexadienyl)]
(5), [Cp*Fe­(η5-1-(η1-Cp*)-2,4,6-triphenyl­phosphacyclohexadienyl)] (6), [Cp*Fe­(η5-1-hydro-2,4,6-triphenyl­phosphacyclohexadienyl)]
(7), and [Cp*Fe­((η5-1-{Ga­(nacnacDipp)­I}-2,4,6-triphenyl­phosphacyclohexadienyl] (8). The molecular structures of 5–8 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.