Boryl radical-mediated halogen-atom transfer enables arylation of alkyl halides with electrophilic and nucleophilic coupling partners

Abstract

Traditional metal-catalysed cross-couplings of alkyl halides for C(sp³)–C(sp²) bond formation are often challenging to achieve. Processes where the alkyl halide is initially converted into a radical species can provide valuable complementarity. So far, these strategies are almost exclusively orchestrated by silicon-based reagents, which can be expensive, have low atom economy and are sensitive to steric factors. Here we report the use of the stable Lewis acid–Lewis base complex Me₃N–BH₃, which, upon conversion into its corresponding amine-ligated boryl radical, enables nickel- and copper-catalysed cross-coupling of alkyl iodides and bromides with electrophilic aryl bromides and nucleophilic aryl boronic acids. Mechanistically, this method uses the amine borane radical’s propensity to activate halides via halogen-atom transfer through highly polarized transition states. This reactivity features mild conditions and broad tolerability of functional groups and engages sterically hindered alkyl halides.