Ferrocene‐Based Phosphenium Ion with Intramolecular Phosphine Coordination

Abstract

A bis(ferrocenyl)phosphenium ion with intramolecular phosphine‐coordination, incorporated within [2]ferrocenophane framework, was synthesized as an air‐stable compound. Although it can be thought as a phosphino‐phosphonium derivative, considering the potential rotation of the cyclopentadienyl group of the ferrocene moiety, the isolated compound should be a masked phosphenium ion with intramolecular phosphine coordination. The redox behavior of the isolated phosphine‐coordinated phosphenium ion has been revealed by CV measurements and the theoretical calculations, suggesting its oxidation at the ferrocenyl moieties and reduction at the phosphorus center consecutively giving the corresponding phosphinyl radical and phosphide ion.

Gradual Donor Stabilization of a Transient Ferrocene Bridged Bisphosphanyl Phosphenium Cation

“…It is worth mentioning that insertion reaction of low valent silicon species was reported into the strained P 4 cage and into the non-strained P 5 ring of [Cp*Fe(η 5 -P 5 )]. 32 Finally, the formal connection in terms of redox states between the fully reduced phosphanide anion 7 on the one side and the originally targeted cation (8) on the other side is remarkable, as the proposed silylene phosphonium cation may be considered formally as an oxidized form of 7 (Scheme 4). The signal of the terminal phosphanyl group splits into a doublet of doublets due to the direct P−P coupling and the 3 J PP coupling (57 Hz) with the opposite phosphanyl unit, showing a doublet signal at −33.4 ppm.…”

“…Similar to other low-valent species, successful isolation usually requires sufficient thermodynamic or kinetic stabilization of the low-valent center. Thermodynamic stabilization is usually achieved by at least one strongly π-donating substituent (e.g., amino or thiolate group) sparking numerous investigations since the discovery of the first thermodynamically stabilized phosphenium ions in 1972, independently reported by Fleming et al, and Maryanoff and Hutchins. ,, However, thermodynamically stabilized phosphenium ions by inter- or intramolecular coordination or N -heterocyclic phosphenium ions of the type [R 2 N–P–NR 2 ] + with π-electron donating groups are less reactive due to reduced electrophilicity. ,− …”

Synthesis and Structure of a Ferrocenylsilane-Bridged Bisphosphine

“…According to literature procedures, 1-bromo-1′-dicyclohexylphosphinoferrocene was prepared [20,21]. 1-Lithio-1′-dicyclohexylphosphinoferrocene (Li-fc-PCy2) was prepared by the reaction of 1-bromo-1′-dicyclohexylphosphinoferrocene with n-BuLi in THF at -60 °C.…”

“…According to literature procedures, 1-bromo-1 -dicyclohexylphosphinoferrocene was prepared [20,21]. 1-Lithio-1 -dicyclohexylphosphinoferrocene (Li-fc-PCy 2 ) was prepared by the reaction of 1-bromo-1 -dicyclohexylphosphinoferrocene with n-BuLi in THF at -60 • C. When an excess of Si(OMe) 4 was added to the THF solution of Li-fc-PCy 2 at -60 • C, the corresponding ferrocenyltrimethoxysilane (1) was isolated in 42% yield (Scheme 1).…”

“…All melting points were determined on a Büchi Melting Point Apparatus M-565 and are uncorrected. 1-Bromo-1 -dicyclohexylphosphinoferrocene was prepared according to a reported procedure [20,21].…”