Redox‐Induced Reversible PP Bond Formation to Generate an Organometallic σ⁴λ⁴‐1,2‐Biphosphane Dication

Abstract

Twice the fun: Dimeric FeII diphosphonium bis(alkynyl) complexes are formed by oxidation of the corresponding FeII alkynyl phosphine complexes. The structure of these organometallic diphosphonium salts and their monomeric precursors were established by X‐ray crystallography. The PP bond can be cleaved by two‐electron reduction to regenerate the monomers.

Organophosphorus Compounds in Organic Electronics

“…Reversible formation of metalloethynylphosphane dimers ( 78 ; Figure ) through a dicationic P−P bridge provides access to a dinuclear iron complex through a C≡C−P−P−C≡C bridge . Monomeric ethynyl phosphane is fully recovered upon reduction, making this class of compounds interesting as molecular switches and wires and future studies will demonstrate the electronic communication across this ethynylbis(phosphane) bridge.…”

Reversible Redox Chemistry of Anionic Imidazole-2-thione-Fused 1,4-Dihydro-1,4-diphosphinines

“…Apart from cyclic P-systems, (acyclic) diphosphenes can be easily reduced to form anionic radical species, but again, no further studies were performed. 28 Electrochemical investigations of P–P (single) bond formation have been reported from both anodic and cathodic processes involving dimerization of phosphaalkene radical anions, cationic 1-phosphabutadiene radicals, or even R 3 P •+ centers, going back as far as Märkl et al 29 − 31 Other main group element redox systems that store energy in element–element bonds such as S–S bonds are the lithium–sulfur and sodium–sulfur storage batteries. 32 − 35 Herein, we report chemical and voltammetric investigations of the anionic 1,4-diphosphinine derivatives VII including their conversion into P–P coupled products and, subsequently, the successful chemical reduction to reform type VII salts, thus closing the redox cycle (also) in solution.…”

Easy and quantitative access to Fe(ii) and Fe(iii) di(aryl)alkynylphosphine oxides featuring [Fe(dppe)Cp*] endgroups: terminal PO functionality blocks the dimerisation of the Fe(iii) derivatives

“…New functional phosphines have always attracted attention because of their outstanding performance in selected metalcatalysed processes, 1 but research in phosphine chemistry has recently extended into many new and non-classical areas, for instance supramolecular phosphines. 13 We therefore present an enlarged study here that aims to treat the properties of the related Fe(III) phosphine oxides (3a-b[PF6]), a set of compounds whose saturated phosphorus valence shell is designed to allow the preparation of dimerisation-inert paramagnetic monomer oxides (3a-b; Scheme 2). Despite their low metal oxidation potentials (close to -0.15 V vs. SCE), 13 metallaphosphines 1a-c react cleanly in THF solution with an excess of hydrogen peroxide to provide nearly quantitative yields of the corresponding metallaphosphine oxides in the Fe(II) oxidation state.…”

“…13 We therefore present an enlarged study here that aims to treat the properties of the related Fe(III) phosphine oxides (3a-b[PF6]), a set of compounds whose saturated phosphorus valence shell is designed to allow the preparation of dimerisation-inert paramagnetic monomer oxides (3a-b; Scheme 2). Despite their low metal oxidation potentials (close to -0.15 V vs. SCE), 13 metallaphosphines 1a-c react cleanly in THF solution with an excess of hydrogen peroxide to provide nearly quantitative yields of the corresponding metallaphosphine oxides in the Fe(II) oxidation state. 15 The absence of any Fe(III) species formed by competitive oxidation of the electron-rich [Fe(dppe)(C5Me5)] centre is noteworthy, given that H2O2 is usually considered to be a powerful oxidant.…”

“…These were fully characterised (Scheme 1). 13 Whilst this result is encouraging, it is probably more interesting for coordination chemists to have a full understanding of the paramagnetic monomers 1a-b[PF 6 ] rather than the dimers 2a-b[PF 6 ] 2 , because such monomers will constitute the ligands that are generated when a suitable coordination compound of 1a-b is oxidised. 14 Preliminary cyclic voltammetry (CV) and UV-vis measurements indicate that these monomers are probably present in a strongly right-shifted equilibrium with the dimeric species 2a-b[PF 6 ] 2 (Scheme 1) whose massive dominance in solution complicates monomer identification and characterisation.…”