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.