text: Gessner et al. first revealed a synthetic route for stabilized ketenyl anion using metalated ylides in 2022. In their paper, upon introducing CO, metalated ylide with posassium cation exchange CO with phosphine group R, also known for carbonylation of ylide. Their isolated ketenyl anion [K(PPh(=S)CCO]  is stable solid for a week under inert atmosphere, and its crystal structure was characterized. An alternate synthetic pathway for synthesizing ketenyl anion from ylide, shown in Figure 2, includes sulfuration on diphenylphosphine group, deprotonation on carbon center, and CO substitution in exchange of triphenylphosphine leaving. This synthesis resulted in 88% isolation of the product. Later in their studies, the ketenyl anion product upon carbonylation can be selective by changing electron-withdrawing ability on a certain leaving group and Lewis acidity of coordinated alkali metal cation. In their example with ylide containing phosphine group and tosyl group (Ts), Gessner et al. was able to produce the ketenyl anion product more selective by modifying those parameters, shown in Figure 2. As R group is more electron-withdrawing group, it becomes more likely to leave than tosyl group. For example, changing R group from cyclohexyl group (Cy) to phenyl group (Ph) favored the ketenyl anion product with R group leaving by 76%. This is because phenyl group is less electron rich and less nucleophilic compared to cyclohexyl group, resulting in more stable by itself. For alkali metal cation trend, when triphenylphosphine group is present, changing from M = Li to M = K favored in phosphine group leaving by 9%. Although it is a small effect compared to leaving group effect, this is due to Lewis acidity on metal cations because a stronger Lewis acidic metal cation (Li > K in Lewis acidity) attracts tosyl group to interact, resulting in increasing leaving group ability. 
  Inoue et al. presented synthetic route of stabilizing ketene via silica-carbonyl anion, silicon analogue of ketene. They motivated this goals from recent reactivity study of silylene and disilane activating CO and isolating intermediate, hypothesizing that silica-ketenyl anion is also capable to stabilize ketene. While Gessner et al. uses ylides to accept CO, Inoue et al. uses silylene anion with another silyl group substituted to afford insertion of CO or carbonylation at room temperature in exchange of silyl group.
  Liu et al. had another approach to stabilize and isolate ketene by using carbene coordinated by phosphinidene. Carbene coordinated by 2,6-diisopropylphenyl(Dipp)-substituted phosphinidene and dinitrogen (N) perform N/CO ligand exchange. The starting material is similar to N-heterocyclic carbene with bulky substituents, invented by Bertrand. In their studies, this reaction is concerted and thermodynamically favorable (-47.4 kcal/mol relative to N-coordinated carbene) on coordinating CO ligand to NHC. This product is stable at room temperature inert atmosphere for a month, and no decomposition while heating in THF at 80 °C for 12 hours was observed.