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. [Figure not available: see fulltext.].