Structural Snapshots on Stepwise Anionic OxoboraneFormation: Access to an Acyclic BO Ketone Analogue and Its MetathesisChemistry with CO₂ and CS₂

In this work, we disclose the synthesis and characterization of non-acid/base-stabilized anionic oxoboranes [^MesTer₂BO]­[K­(L)] (^MesTer = –C₆H₃-2,6-(2,4,6-Me₃-C₆H₂)₂, L = [2.2.2]-cryptand or 18-crown-6), which are isoelectronic and isostructural with aryl-substituted ketones. The stepwise synthetic formation of these ion-separated oxoboranes is demonstrated on the one hand by the treatment of the parent borinic acid ^MesTer₂BOH with <i>N</i>-heterocyclic carbenes (NHCs) to give [^MesTer₂BO]­[HNHC] derivatives, and on the other hand by a deprotonation-sequestration sequence. Bearing polarized boron–oxygen moieties, their inherent reactivity toward both carbon disulfide and carbon dioxide reveals a unique π-bond metathesis reactivity to yield [(^MesTer)₂B-μ-E₂C=E]­[K­(L)] (E = O, S) derivatives.