Capturing carbon monoxide-Accessing bis(boryl)ketones through direct B-B bond carbonylation

Carbon monoxide (CO) readily attacks the B-B bonds of the cyclic tetra(amino)tetraborane B₄(NCy₂)₄ [cyclohexyl (Cy)], which led to insertion and ring expansion, creating tetraboron analogs of cyclopentanone and cyclohexane-1,3-dione. These intriguing molecules are rare instances of stable CO diborylation products that were made accessible by direct CO capture. While the monocarbonyl product shows remarkable thermal stability, the dicarbonyl product rearranges into a bicyclic tetraborylethylene structure under thermal stress. Combined analytical and theoretical efforts clearly highlight the unique electronic, spectroscopic, and structural characteristics of these carbonyl compounds. The cyclopentanone analog engages in stepwise one- and two-electron reduction processes to yield radical monoanion and dianion species while preserving the five-membered ring structure and the boron-boron bonds. Together, these boron heterocycles expand the limited class of stable boryl ketones containing direct boron-carbonyl carbon bonds, thus offering valuable opportunities for exploring the fundamental chemistry and synthetic applications of this functionality.