The Careful Combination of Bismuth Compounds and CAAC: Formal Halonium and Nitrenium Transfer via Radical Pathways.

Cyclic (alkyl)(amino)carbenes (CAACs) are key compounds en route to a plethora of unprecedented low-valent and radical complexes of transition metals and main group elements. For p-block elements of the sixth period, however, low-valent and radical complexes of CAACs are extremely rare, and even simple adducts with CAACs are difficult to access. Here we report the full characterization of the first adduct between a CAAC and a bismuth trihalide, [BiCl(CAAC)] (1), which has previously only been spectroscopically characterized. 1 and its in situ generated bromido analog form intensely colored solutions in solvent molecule (THF) and undergo formal halonium ion (i.e., X) transfer from the Bi atom to the carbene carbon atom to give the complex cations [CAAC─X] (X = Cl, Br). Starting from bismuth amide complexes, formal nitrenium ion (i.e., [NR]) transfer reactions are observed to give [CAAC─NR]. EPR spectroscopic reaction monitoring indicates the viability of radical processes and suggests the involvement of unprecedented α-aminyl radicals and mononuclear Bi species. Our investigations reveal easily accessible radical pathways via peerless molecular complexes, which proceed in the absence of external reducing agents, as a key factor on the way to exploit the full potential of carbene ligands in the chemistry of sixth row p-block elements.