Synthesis, isolation and application of a sila-ketenyl anion

Ynolates or ketenyl anions, [RCCO]−, are negatively charged reactive intermediates, which can be generated in situ and used for divergent chemical transformations. Ynolates can react either at the oxygen or carbon centres or across the C–C triple bond, making them useful in various applications in organic synthesis. Heavier analogues of ynolates or ketenyl anions ([RECO]−, E = group 14 element), however, have not been isolated or studied. Here we report the synthesis, isolation and characterization of [K(18-crown-6)]+[(tBu3Si)SiCO]−, a silicon analogue of a ketenyl anion. [K(18-crown-6)]+[(tBu3Si)SiCO]− is readily prepared through reaction of [K(18-crown-6)]+ coordinated silyl-radical anions with carbon monoxide, or by a reduction of a silyl-substituted silicon–carbonyl complex, [{(Me3Si)3Si}(tBu3Si)SiCO]. X-ray crystallographic and spectroscopic analyses coupled with quantum chemical calculations reveal that [K(18-crown-6)]+[(tBu3Si)SiCO]− predominately displays sila-ketenyl anion character. [(tBu3Si)SiCO]− was also demonstrated to be a competent ligand for a transition metal through reaction with Mo(CO)6. The heavy analogues of ynolates or ketenyl anions have not yet been studied. Here the synthesis, isolation and characterization of a sila-ketenyl anion, the silicon analogue of a ketenyl anion, are reported through the reaction of silyl-radical anions with CO.