Bismuth Amides Mediate Facile and Highly Selective Pn-Pn Radical-Coupling Reactions (Pn=N, P, As)

The controlled release of well-defined radical species under mild conditions for subsequent use in selective reactions is an important and challenging task in synthetic chemistry. We show here that simple bismuth amide species [Bi(NAr₂ )₃ ] readily release aminyl radicals [NAr₂ ]^. at ambient temperature in solution. These reactions yield the corresponding hydrazines, Ar₂ N-NAr₂ , as a result of highly selective N-N coupling. The exploitation of facile homolytic Bi-Pn bond cleavage for Pn-Pn bond formation was extended to higher homologues of the pnictogens (Pn=N-As): homoleptic bismuth amides mediate the highly selective dehydrocoupling of HPnR₂ to give R₂ Pn-PnR₂ . Analyses by NMR and EPR spectroscopy, single-crystal X-ray diffraction, and DFT calculations reveal low Bi-N homolytic bond-dissociation energies, suggest radical coupling in the coordination sphere of bismuth, and reveal electronic and steric parameters as effective tools to control these reactions.