Tin-Free Radical Reactions Mediated by Organoboron Compounds

Darmency, Vincent; Renaud, Philippe

doi:10.1007/128_030

Cited by 82 publications

(47 citation statements)

References 124 publications

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“…[193] The interaction of the Lewis acidic alkyl catcholborane with TEMPO provides adduct 75, which can fragment to radical RC and boric acid ester 40. The radical RC is then trapped by a second equivalent of TEMPO to give the corresponding alkoxyamine 74.…”

Section: Nitroxides In Free-radical Chemistry 421 Trapping Of C-cementioning

confidence: 99%

Nitroxides: Applications in Synthesis and in Polymer Chemistry

2011

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This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures.

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Section: Nitroxides In Free-radical Chemistry 421 Trapping Of C-cementioning

confidence: 99%

Nitroxides: Applications in Synthesis and in Polymer Chemistry

2011

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“…The use of triethylborane and other organoboranes as chain-transfer reagents has been recently reviewed [8]. In these processes, the organoborane acts as an initiatior and as a reagent that propagates the chain.…”

Section: Triethylborane As a Chain-transfer Reagentmentioning

confidence: 99%

“…This complex can then undergo a β-fragmentation leading to the alkyl radical. This process is of particular interest for the development of radical chain reactions [8].…”

Section: Introductionmentioning

confidence: 99%

Boron: A key element in radical reactions

Renaud

Beauseigneur

Brecht‐Forster

et al. 2007

Pure and Applied Chemistry

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Boron derivatives are becoming key reagents in radical chemistry. Here, we describe reactions where an organoboron derivative is used as a radical initiator, a chain-transfer reagent, and a radical precursor. For instance, B-alkylcatecholboranes, easily prepared by hydroboration of alkenes, represent a very efficient source of primary, secondary, and tertiary alkyl radicals. Their very high sensitivity toward oxygen-and heteroatom-centered radicals makes them particularly attractive for the development of radical chain processes such as conjugate addition, allylation, alkenylation, and alkynylation. Boron derivatives have also been used to develop an attractive new procedure for the reduction of radicals with alcohols and water. The selected examples presented here demonstrate that boron-containing reagents can efficiently replace tin derivatives in a wide range of radical reactions.

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“…[21][22][23] As a result of the complexation of water molecules with boryl radicals, one of the current authors 24 has considered the lowered LUMO O-H of the water molecule as an efficient receiver for the radical located firstly at the boron atom, in parallel with Rablen's 10 conclusion.…”

Section: Introductionmentioning

confidence: 89%

The water–boryl radical as a proton-coupled electron transfer reagent for carbon dioxide, formic acid, and formaldehyde — Theoretical approach

et al. 2013

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The thermochemistry of the hydrogen atom transfer reactions from the H 2 O-BX 2 radical system (X = H, CH 3 , NH 2 , OH, F) to carbon dioxide, formic acid, and (or) formaldehyde, which produce hydroxyformyl, dihydroxymethyl, and hydroxymethyl radicals, respectively, were investigated theoretically at ROMP2/6-311+G(3DF,2P)//UB3LYP/6-31G(D) and UG3(MP2)-RAD levels of theory. Surprisingly, in the cases of a strong Lewis acid (X = H, CH 3 , F), the spin transfer process from the water-boryl radical to the carbonyl compounds was barrier-free and associated with a dramatic reduction in the B-H bond dissociation energy (BDE) relative to that of isolated water-borane complexes. Examining the coordinates of these reactions revealed that the entire hydrogen atom transfer process is governed by the proton-coupled electron transfer (PCET) mechanism. Hence, the elucidated mechanism has been applied in the cases of weak Lewis acids (X = NH 2 , OH), and the variation in the accompanied activation energy was attributed to the stereoelectronic effect interplaying in CO 2 and HCOOH compared with HCHO. We ascribed the overall mechanism as a SA-induced five-center cyclic PCET, in which the proton transfers across the so-called complexationinduced hydrogen bond (CIHB) channel, while the SOMO B -LUMO C=O= interaction is responsible for the electron migration process. Owing to previous reports that interrelate the hydrogen-bonding and the rate of proton-coupled electron-transfer reactions, we postulated that "the rate of the PCET reaction is expected to be promoted by the covalency of the hydrogen bond, and any factor that enhances this covalency could be considered an activator of the PCET process." This postulate could be considered a good rationale for the lack of a barrier associated with the hydrogen atom transfer from the water-boryl radical system to the carbonyl compounds. Light has been shed on the water-boryl radical reagent from the thermodynamic perspective.Key words: -boryl radical, complexation-induced hydrogen bond (CIHB), proton-coupled electron transfer (PCET), B-H bond dissociation energies (BDEs).Résumé : Faisant appel à des calculs théoriques effectués aux niveaux ROMP2/6-311+G(3DF,2P)//UB3LYP/6-31G(D) et UG3(MP2)-RAD de la théorie, on a effectué une étude de la thermochimie des réactions de transfert d'atomes d'hydrogène de systèmes radicalaires H 2 O-BX 2 vers le dioxyde de carbone, l'acide formique et (ou) le formaldéhyde qui conduisent respectivement à la formation de radicaux hydroxyformyle, dihydroxyméthyle et hydroxyméthyle. D'une façon surprenant, dans les cas d'acides de Lewis forts (X = H, CH 3 , F) les processus de transferts de spin des radicaux eau-boryle vers les composés carbonylés ne comportent aucune barrière et ils sont associés à une réduction dramatique de l'énergie de la dissociation de la liaison (EDL) B-H relative à celle des complexes eau-boranes isolés. L'examen des coordonnées de la réaction de ces réactions révèle que, le processus de transfert de l'atome d'hydrogène est gouverné par le mé...

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Tin-Free Radical Reactions Mediated by Organoboron Compounds

Cited by 82 publications

References 124 publications

Nitroxides: Applications in Synthesis and in Polymer Chemistry

Nitroxides: Applications in Synthesis and in Polymer Chemistry

Boron: A key element in radical reactions

The water–boryl radical as a proton-coupled electron transfer reagent for carbon dioxide, formic acid, and formaldehyde — Theoretical approach

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