Electrochemical reduction of phosphonium cations in media of low proton availability

Savéant, Jean Michel; Binh, Su Khac

doi:10.1021/jo00427a032

Cited by 47 publications

(26 citation statements)

References 14 publications

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“…Homolytic dediazoniation prevails in more nucleophilic solvents or conditions 43 and more particularly when electron is transferred to the aryldiazonium salt as in the case of electrografting processes. In the following we consider, as generally admitted, 44 that NP radicals, denoted Ar • , are generated from the irreversible electrochemical reduction of NBD according to a concerted electron transfer bond-breaking process following Savéant's denomination: 45 NBD + e k ⎯⎯ → Ar • + N 2 (10) The NBD consumption at the electrode is described either by mass-transfer limitation or by kinetic limitation from the charge transfer process associated to the rate constant k (in cm s -1 ). The flux of consumed NBD is then given, on the one hand, from a Butler-Volmer-like relationship in the case of kinetic limitation:…”

Section: Simplified Kinetic Model For Nbd Electrograftingmentioning

confidence: 99%

Mapping fluxes of radicals from the combination of electrochemical activation and optical microscopy

et al. 2013

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The coating of gold (Au) electrode surfaces with nitrophenyl (NP) layers is studied by combination of electrochemical actuation and optical detection. The electrochemical actuation of the reduction of the nitrobenzenediazonium (NBD) precursor is used to generate NP radicals and therefore initiate the electrografting. The electrografting process is followed in situ and in real time by light reflectivity microscopy imaging, allowing for spatio-temporal imaging with sub-micrometer lateral resolution and sub-nanometer thickness sensitivity of the local growth of a transparent organic coating onto a reflecting Au electrode. The interest of the electrochemical actuation resides in its ability to finely control the grafting rate of the NP layer through the electrode potential. Coupling the electrochemical actuation with microscopic imaging of the electrode surface allows quantitative estimates of the local grafting rates and subsequently a real time and in situ mapping of the reacting fluxes of NP radicals on the surface. Over the 2 orders of magnitude range of grafting rates (from 0.04 to 4 nm s(-1)), it is demonstrated that the edge of Au electrodes are grafted -1.3 times more quickly than their centre, illustrating the manifestation of edge-effects on flux distribution at an electrode. A model is proposed to explain the observed edge-effect, it relies on the short lifetime of the intermediate NP radical species.

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Section: Simplified Kinetic Model For Nbd Electrograftingmentioning

confidence: 99%

Mapping fluxes of radicals from the combination of electrochemical activation and optical microscopy

et al. 2013

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“…Va rious products have been identified as resulting from two different types of electron transfer: a one-electron pathway leading to dimerization and/or disproportionation of the released radical or a twoelectron pathway providing the formation of ylides, phosphine oxides or Hofmann degradation products. [67] Interestingly, Kampmeier and Nalli reported that phosphoranyl radical intermediates generated by arylation of triphenylphosphine can act as reducing agents with iodonium and sulfonium salts. [59] Along with these electrochemical studies, photolysis of phosphonium salts was investigated by Griffin and Kaufman (Scheme 17).…”

Section: Homolytic Reduction Of Phosphoniumsmentioning

confidence: 99%

Homolytic Reduction of Onium Salts

Fensterbank

Goddard

Malacrìa

et al. 2012

Chimia

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Onium salts have proved to be efficient sources of carbon-centered radicals. They can undergo homolytic reduction by single electron transfer (SET) and participate in subsequent synthetic transformations. This review aims to provide an overview on the behavior of onium salts including diazonium, sulfonium, selenonium, telluronium, phosphonium and iodonium cations toward various reductive methods such as radiolysis, electrolysis, photolysis or the use of SET reagents. Mechanistic and synthetic aspects are presented. Applications in polymers and materials science are not covered.

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“…Their fragmentation rates, determined electrochemically [300] or by pulse radiolysis 13011 range from 1O'O s-l for phenyl halides to s-' for some halonitrobenzenes. The rate of the reaction for some aryl halide radical anions is too high to be measured electrochemically, the fragmentation of more stable radical anions such as those of 1-bromo-and 1-iodoanthraquinone [302], p -[303] and m-bromo-13041 and p-[303] and rn-chloronitrobenzenes 13041 occurs at considerably lower rates and the reaction is favored from their photoexcited state.…”

Section: R = H Hexylmentioning

confidence: 99%

Electron‐transfer Reactions of Aromatic Compounds

Gescheidt¹,

Khan²

2001

Electron Transfer in Chemistry

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Aromatic molecules are inclined to undergo electron-transfer reactions. The additional charges introduced by the electron-transfer process are efficiently stabilized by delocalization. Nevertheless rearrangements of the molecular skeleton or followup reactions can occur. The course of the electron-transfer reactions and the properties of the species thus formed are the subject of this section.In particular, we concentrate on the species formed after an one-electron transfer reaction. Starting from closed-shell diamagnetic precursors, paramagnetic stages, i.e. radical cations or radical anions are formed in this first step. To understand the properties and reactivity of these species, detailed knowledge in terms of charge and spin delocalization and electronic structure is an important prerequisite. This information is preferably derived from electronic and paramagnetic resonance (EPR and electron-nuclear multiple resonance-techniques such as ENDOR or Triple spectroscopy). It has recently been shown that the experimental results can be substantiated by the use of quantum-chemical calculations. In addition to Hartree-Fock-based ab initio procedures, calculations on the density-functional level of theory have been established as rather efficient tools. Therefore, before representing examples of electron-transfer-generated radicals a short survey of the computational methods is given.Another substantial factor directing the kinetic and thermodynamic stability of charged radicals is ion pairing. This phenomenon, although well established for many years, is often not directly distinct in experiments. To establish the importance of ion pairing, or, in other words, supramolecular interactions, a separate introductory chapter is dedicated to these aspects.The references are selected particularly from recent publications, without, however, ignoring some 'classical' contributions. In some sections topics are included which do not strictly represent aromatic molecules but involve interactions of ztype orbitals.

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Electrochemical reduction of phosphonium cations in media of low proton availability

Cited by 47 publications

References 14 publications

Mapping fluxes of radicals from the combination of electrochemical activation and optical microscopy

Mapping fluxes of radicals from the combination of electrochemical activation and optical microscopy

Homolytic Reduction of Onium Salts

Electron‐transfer Reactions of Aromatic Compounds

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