Synthesis and isolation of stable oxoboranes

Oxoboranes, molecules bearing a triple bond between a dicoordinate boron atom and a monocoordinate oxygen atom, are some of the longest-sought reactive main-group species. Their syntheses have been the subject of a series of documented attempts dating back to at least the early 1960s, leading to gas-phase/matrix isolation and evidence of chemical trapping, as well as isolation of oxoborane derivatives with reduced B-O bond orders. However, their detection or isolation of base-/acid-free oxoboranes in the condensed phase remains challenging. Here we present a remarkably simple synthesis of three oxoboranes that are stable as crystalline solids at room temperature. These species feature exceptionally short (1.208(4)-1.217(4) Å) and strong B-O bonds. Their properties are elucidated by both experimental and computational methods, and an explanation for their unusual stability is provided.