Homoleptic Bismuth Alkynes: Isolable Reagents for Selective Alkynyl Radical Transfer.

Alkynyl radicals represent highly attractive building blocks in synthetic chemistry but keep posing considerable challenges to researchers in the field. While their existence in interstellar space, in combustion processes, and under matrix-isolation conditions has been documented, access under typical wet-chemical conditions remains limited. In this context, bismuth compounds are promising candidates as their ability to engage in controlled radical reactions has recently been brought into the focus of research efforts. Here, we present the first synthesis and full characterization of a series of homoleptic bismuth alkyne compounds, Bi(C≡CR)3 (R = alkyl, silyl, aryl). The isolable compounds readily and selectively release alkynyl radicals, as demonstrated by EPR spectroscopic studies. This reactivity has been harnessed in Glaser-type C-C homocoupling reactions, as well as in C-C, C-B, C-Se, and C-Te bond-forming events with external substrates, including transformations that commonly proceed through polar reaction pathways. The bismuth compounds complement existing strategies for the wet-chemical generation of alkynyl radicals in that they are transition-metal-free, avoid toxic components, proceed under mild conditions, can be operated via thermal activation, and do not require any additives or co-reagents.