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

In this work, we disclose the synthesis and characterization of non-acid/base-stabilized anionic oxoboranes [TerBO][K(L)] (Ter = -CH-2,6-(2,4,6-Me-CH), 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 TerBOH with -heterocyclic carbenes (NHCs) to give [TerBO][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 [(Ter)B-μ-EC=E][K(L)] (E = O, S) derivatives.