Structural Snapshots on Stepwise Anionic Oxoborane Formation: Access to an Acyclic BO Ketone Analogue and Its Metathesis Chemistry 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 N-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.