Crystalline Keteniminyl Anions

The synthesis, characterization, and reactivity of keteniminyl anions [R ¹ C = C = NR ² ] ⁻ , a hitherto uncharted functional group, are the primary focus of this study. Our comprehensive analyses, including NMR spectroscopy, X-ray crystallography, and density functional theory calculations, have illuminated the distinct electronic characteristics of these anions. They are characterized by their nucleophilic/basic anionic carbon and π electrons, which are extensively delocalized along the PCCN chain. These anions undergo a range of facile reactions, such as protonation, alkylation, silylation, and metalation at the carbon site, leading to various ketenimine derivatives. They also participate in hydroamination reactions, yielding amino enamide functional groups. Additionally, the phosphino substituent in keteniminyl anions acts as a previously underappreciated weak π-electron acceptor when the phosphorus atom is in a pyramidalized state, thereby facilitating the stabilization of the electron-rich anionic carbon. The isolation of phosphino and thiophosphino keteniminyl anions not only represents a significant synthetic achievement but also heralds the potential for the future isolation of novel electron-rich species featuring phosphino substituents.