Multiple complexation of CO and related ligands to a main-group element

Transition metal–ligand fragments are often able to bind and release several carbon monoxide molecules, such as the catalysts used in industrial-scale acetic acid synthesis and the active sites of hydrogenase enzymes, but main-group elements have never shown an ability to bind more than one carbon monoxide molecule; here a boron-based compound stable to moisture and air is synthesized and shown to contain multiple carbon monoxide units bound to the central boron atom.