Synthesis of potassium keteniminyl anions via PPh3/isocyanide exchange in metalated ylides (Route 1) and via N2/isocyanide exchange in diazomethanides formed from metalated ylides and nitrous oxide (Route 2). Yields in brackets refer to route 2, other yields to route 1. a NMR yields; all other are yields are isolated yields. successful PPh3/:CNR exchange. Nonetheless, the reaction was extremely sluggish, achieving only 45% conversion after heating the reaction mixture at 80 o C for one week. We hypothesized that electron-poor isocyanides might enhance the ligand exchange due to their increased acceptor properties which could enhance the attack of the nucleophilic metalated ylide. Therefore, we shifted our focus to aryl-substituted isocyanides. To our delight, the addition of phenyl isocyanide to a toluene solution of 1 at room temperature led to an immediate color change from orange to dark brown. Monitoring of the reaction by P{ 1 H} NMR spectroscopy confirmed the selective liberation of PPh3 along with the formation of the targeted keteniminyl anion 3a as characterized by a signal at δP = 7.0 ppm. However, isolation of the keteniminyl salt 3a-K from the reaction mixture proved challenging. To address this challenge, we repeated the reaction in the presence of 18crown-6 (18-c-6) for complexation of the potassium cation. The 18-c-6 complex of keteniminyl anion 3a turned out to being less soluble and precipitate from the reaction mixture, thus enabling its isolation as a brown solid in a high yield of 73 %. The structure of 3a could unambiguously be characterized by different spectroscopic and crystallographic methods (see below). To establish the generality of this method, we also investigated the reaction of other aryl isocyanides with yldiide 1. Treatment of 1 with 2,6-dichlorophenyl isocyanide in the presence of 18-c-6 successfully generated the corresponding potassium complex of keteniminyl anion 3b as brown solid in 75% isolated yield. However, attempts to obtain the 2,6-dimethylphenyl substituted keteniminyl anion using this method were unsuccessful. Addition of Xyl-NC (Xyl = 2,6-dimethylphenyl isocyanide) to 1 led to the protonation of the yldiide and reformation of the parent ylide. This observation can be explained by the high basicity of yldiide 1, which easily abstracts a proton from the ortho methyl group of the isocyanide. To address the challenges observed in the PPh3/isocyanide exchange, we pursued an alternative synthetic strategy. We hypothesized that the use of less basic diazomethanide 2 could mitigate undesired deprotonation, while providing an additional driving force for the exchange through the release of dinitrogen. Leveraging our recently developed method for synthesizing diazomethanides, we prepared diazo compound 2 from the metalated ylide 1 and N2O (Scheme 1). Addition of phenyl, xylyl or 2,6-dichlorophenyl isocyanide to a THF solution of 2 in the presence of 18-c-6 led to the clean formation of the keteniminyl anions via N2/:CNR exchange. To our delight, the 18-c-6 complexes of 3a, 3b and 3c could be isolated in high yields of more than 80 % through this protocol. We also tested the reaction of 2 with alkyl isocyanides. Compared to aryl isocyanides, the reaction of alkyl isocyanides with 2 is significantly slower, requiring several days of stirring at 45 o C to reach completion (4 days for cyclohexyl isocyanide and 14 days for tert-butyl isocyanide). Nonetheless, the 18-c-6 complexes of 3d could be isolated as crystalline solids in 53 % yield, thus proving the versatility of the developed protocol. Compound 3e was also formed in high yields but could not be cleanly isolated due to challenges in separating it from excess 18-crown-6. All keteniminyl anions are stable under an inert atmosphere at room temperature and show no tendency for decomposition or dimerization even after storage for weeks.