σ-Complexes of transition metals are key intermediates in metal-mediated bond activation, but have traditionally been isolable only when chelating or when one of the participating atoms is hydrogen. Here, a complex is isolated with an unsupported borirene ligand bound not through the unsaturated C=C bond, but exclusively via a B–C single bond.
- Holger Braunschweig
- Peter Brenner
- Alfredo Vargas
