Dioxygen Reactivity with a Ferrocene–Lewis Acid Pairing: Reduction to a Boron Peroxide in the Presence of Tris(pentafluorophenyl)borane

Abstract

Ferrocenes, which are typically air‐stable outer‐sphere single‐electron transfer reagents, were found to react with dioxygen in the presence of B(C6F5)3, a Lewis acid unreactive to O2, to generate bis(borane) peroxide. Although several Group 13 peroxides have been reported, boron‐supported peroxides are rare, with no structurally characterized examples of the BO2B moiety. The synthesis of a bis(borane)‐supported peroxide anion and its structural and electrochemical characterization are described.

Reduction of Dioxygen by Radical/B(p‐C6F4X)3 Pairs to Give Isolable Bis(borane)superoxide Compounds

“…TheN MR spectra (see the Supporting Information for details) indicated the formation of ap aramagnetic reaction product. [9] (the 2a·2CH 2 Cl 2 structure is depicted in the Supporting Information). TheX-ray structure analysis revealed the formation of the bis(borane)superoxideradical anion with one oxoammonium countercation, [C 5 H 6 Me 4 N = O] + {O 2 [B(C 6 F 5 ) 3 ] 2 }C À and two dichloromethane solvent molecules.T he O1ÀO2 bond in compound 2a·(2 CD 2 Cl 2 )i ss ignificantly shorter than the oxygen-oxygen linkage in the BÀOÀOÀBb is-(borane)peroxide compound 1a (Dd = 0.18 ).…”

“…Thec yclic voltammogram (Figure 4) showed the strong signal of the Fc* + /Fc* redox couple at À0.59 V(vs.Fc/ Fc + ), followed by the weak trityl cation/trityl radical redox feature (À0.16 V) and the bis(borane)superoxide radical anion/bis(borane)peroxide signal at + 0.22 V. [9] We note from an independent experiment (for details,s ee the Supporting Information) that the latter value is almost identical with the oxoammonium/ TEMPO redox potential, which is in accord with the apparently facile back-electron transfer under suitable conditions (see above). Therefore,w e added as light excess of decamethylferrocene to the solution of 2c,w hich served as ap re-reductant and an internal standard.…”

“…Therefore,w e added as light excess of decamethylferrocene to the solution of 2c,w hich served as ap re-reductant and an internal standard. TheX-ray structure analysis (see the Supporting Information for details and the depicted molecular structure) revealed that compound 1c features aB À O À O À Bb is(borane)peroxide dianion with two trityl counter cations similar to that previously observed by Agapie et al in the respective bis(ferrocenium) systems [9] (d(OÀO): 1.488(2) (1c), 1.485 (2) (1a)). [20] Tr eatment of compound 2c generated in situ with an additional molar equivalent of trityl radical led to the formation of the trityl cation/bis(borane)peroxided ianion salt 1c,f eaturing tetra-coordinate borate NMR signals (Scheme 4; 11 B: d = À2.1, Dd 19 F m,p = 2.9 ppm {O 2 [B-(C 6 F 5 ) 3 ] 2 } 2À ;for the depicted NMR spectra and experimental details,s ee the Supporting Information).…”

“…[8] Agapie et al recently described the reduction of dioxygen by two molar equivalents of ferrocenes in the presence of the strong boron Lewis acid B(C 6 F 5 ) 3 to yield the bis(ferrocenium) bis(borane)peroxides 1a,b (Scheme 1). [9,10] Thecyclic voltammogram of 1a showed the redox potential of the [B] 2 O 2 2À /[B] 2 O 2 C À pair being at av alue close to the TEMPO/ TEMPO + pair. This let us speculate that it might be possible to reduce triplet oxygen [11] by suitable persistent radicals to the superoxide state (or beyond) in the presence of the strong B(C 6 F 5 ) 3 Lewis acid.…”

Novel Surface Passivation for Stable FA0.85MA0.15PbI3 Perovskite Solar Cells with 21.6% Efficiency

“…TPFPB is a strong organometallic Lewis acid, which could interact with organic cations in perovskite through the strong B—N and H—F interaction . To better understand the interaction between TPFPB and perovskite, a liquid‐state 1 H NMR titration measurement in the solution is performed, with results shown in Figure a.…”