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The special role of B(C₆F₅)₃ in the single electron reduction of quinones by radicals.

ABSTRACT: In the presence of two molar equiv. of B(C₆F₅)₃ p-benzoquinone reacts with persistent radicals TEMPO, trityl or decamethylferrocene by single electron transfer to give doubly O-borylated benzosemiquinone radical anions with TEMPO⁺, trityl or ferrocenium counter cations. All three [(C₆F₅)₃B]₂-semiquinone radical anion salts were characterized by X-ray diffraction. The addition of donor reagent THF or DMSO induced rapid back electron transfer, in the case of the [(C₆F₅)₃B]₂-semiquinone radical anion oxoammonium salt giving rise to the formation of the (C₆F₅)₃B-DMSO (or THF) Lewis adduct, p-benzoquinone and the TEMPO radical. The reaction of 9,10-anthraquinone or acenaphthenequinone with either the Gomberg dimer or in 1 : 1 stoichiometry in the presence of two molar equiv. of B(C₆F₅)₃ gave the respective two-fold O-B(C₆F₅)₃ containing 9,10-anthrasemiquinone or acenaphthene-semiquinone radical anion salts with either Ph₃C⁺ or counter cations. These products were also characterized by X-ray diffraction. The salts showed analogous back electron shuttling behavior upon treatment with DMSO. 9,10-Phenanthrenequinone reacted analogously with B(C₆F₅)₃ and the electron rich ferrocene. The [(C₆F₅)₃B]₂-9,10-phenanthrene-semiquinone salt was characterized by X-ray diffraction. The radical anions were characterized by ESR spectroscopy.

SUBMITTER: Tao X

PROVIDER: S-EPMC6202917 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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The special role of B(C6F5)3 in the single electron reduction of quinones by radicals.

Tao Xin X Daniliuc Constantin G CG Knitsch Robert R Hansen Michael Ryan MR Eckert Hellmut H Lübbesmeyer Maximilian M Studer Armido A Kehr Gerald G Erker Gerhard G

Chemical science 20180820 41

In the presence of two molar equiv. of B(C6F5)3 p-benzoquinone reacts with persistent radicals TEMPO, trityl or decamethylferrocene by single electron transfer to give doubly O-borylated benzosemiquinone radical anions with TEMPO+, trityl or ferrocenium counter cations. All three [(C6F5)3B]2-semiquinone radical anion salts were characterized by X-ray diffraction. The addition of donor reagent TH ...[more]

PMID: 30450185

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Project description:Long-distance electron transfer in marine environments couples physically separated redox half-reactions, impacting biogeochemical cycles of iron, sulfur and carbon. Bacterial bio-electrochemical systems that facilitate electron transfer via conductive filaments or across man-made electrodes are well-known, but the impact of abiotic currents across naturally occurring conductive and semiconductive minerals is poorly understood. In this paper I use cyclic voltammetry to explore electron transfer between electrodes made of common iron minerals (magnetite, hematite, pyrite, pyrrhotite, mackinawite, and greigite), and hydroquinones-a class of organic molecules found in carbon-rich sediments. Of all tested minerals, only pyrite and magnetite showed an increase in electric current in the presence of organic molecules, with pyrite showing excellent electrocatalytic performance. Pyrite electrodes performed better than commercially available glassy carbon electrodes and showed higher peak currents, lower overpotential values and a smaller separation between oxidation and reduction peaks for each tested quinone. Hydroquinone oxidation on pyrite surfaces was reversible, diffusion controlled, and stable over a large number of potential cycles. Given the ubiquity of both pyrite and quinones, abiotic electron transfer between minerals and organic molecules is likely widespread in Nature and may contribute to several different phenomena, including anaerobic respiration of a wide variety of microorganisms in temporally anoxic zones or in the proximity of hydrothermal vent chimneys, as well as quinone cycling and the propagation of anoxic zones in organic rich waters. Finally, interactions between pyrite and quinones make use of electrochemical gradients that have been suggested as an important source of energy for the origins of life on Earth. Ubiquinones and iron sulfide clusters are common redox cofactors found in electron transport chains across all domains of life and interactions between quinones and pyrite might have been an early analog of these ubiquitous systems.

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The special role of B(C₆F₅)₃ in the single electron reduction of quinones by radicals.

Publications

The special role of B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> in the single electron reduction of quinones by radicals.

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