Bismuth radical catalysis in the activation and coupling of redox-active electrophiles

Radical cross-coupling reactions represent a revolutionary tool to make C( sp 3 )–C and C( sp 3 )–heteroatom bonds by means of transition metals and photoredox or electrochemical approaches. However, the use of main-group elements to harness this type of reactivity has been little explored. Here we show how a low-valency bismuth complex is able to undergo one-electron oxidative addition with redox-active alkyl-radical precursors, mimicking the behaviour of first-row transition metals. This reactivity paradigm for bismuth gives rise to well-defined oxidative addition complexes, which could be fully characterized in solution and in the solid state. The resulting Bi(III)–C( sp 3 ) intermediates display divergent reactivity patterns depending on the α-substituents of the alkyl fragment. Mechanistic investigations of this reactivity led to the development of a bismuth-catalysed C( sp 3 )–N cross-coupling reaction that operates under mild conditions and accommodates synthetically relevant NH-heterocycles as coupling partners. The use of main-group elements in radical cross-coupling reactions has been little explored. Now, a low-valency bismuth complex has been shown to emulate the behaviour of first-row transition metals and undergo single-electron-transfer oxidative addition to redox-active electrophiles, leading to the development of a bismuth-catalysed C–N coupling reaction between amines and carboxylic acids.