Boron — A Key Element in Radical Reactions

Abstract

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.

Tri-n-Butylborane/WaterComplex-Mediated Copolymerization of Methyl Methacrylate with Proteinaceous Materials and Proteins: A Review

“…Borane derivatives are now becoming key reagents in radical chemistry, and have been used to develop an attractive new procedure for the reduction of radicals with alcohol and water [17]. To clarify the mechanism of grafting of trialkylborane-initiated MMA resins with protein materials, we review here the results of our previous studies [18][19][20] on the basis of published materials and current knowledge.…”

“…More recently, Penaud et al [17] have reported that homolytic substitution at borane moieties does not proceed with carbon-centered radicals, and that many different types of heteroatom-centered radicals (e.g., alkoxyl radicals) react efficiently with organoboranes. The first step of homolytic substitution is the formation of a Lewis acid-base complex between the borane and the radical.…”

“…This complex can then undergo -fragmentation, producing the alkyl radical. The use of triethylborane and other organoboranes as chain-transfer reagents has been reviewed previously [17]. In these processes, the organoborane acts as an initiator and as a reagent that propagates the chain.…”

In search of the X2BO and X2BS (X = H, F) free radicals: Ab initio studies of their spectroscopic signatures

“…4 Boron derivatives have been characterized as key reagents in radical chemistry, and triethylborane is used as an effective low temperature initiator in radical reactions. 5 Boron has long been regarded as a good candidate for rocket fuel additives, due to its high energy density, and its incorporation results in complex high temperature chemistry involving boron radicals. 6 In these contexts, information on new boron radicals is both interesting and scientifically valuable.…”

Amine–borane complex-initiated SF5Cl radical addition on alkenes and alkynes

“…The SF 5 Cl addition on unsaturated compounds goes through a free-radical mechanism, and is promoted by the radical activation of SF 5 Cl by Et 3 B, which leads to the formation of the propagating species SF 5 • [ 32 – 33 ]. Trialkylboranes are common low-temperature radical initiators, and Et 3 B is one of the most used in the literature [ 34 – 35 ]. The use of the reagent allows the radicals to form, even at very low temperature, due to its strong reactivity with oxygen.…”