The Cyanoketene Anion [NC3O]-

Abstract

Cumulenes and heterocumulenes with three or more cumulative multiple bonds are usually reactive species, that serve as valuable building blocks to more complex molecules but tend to isomerize or cyclize and therefore are difficult to isolate. Until to date, numerous (hetero)cumulenes have been detected in the interstellar medium and are assumed to be important intermediates in prebiotic chemistry, in particular when containing nitrogen and oxygen functionalities. Using a mild ligand exchange reaction at carbon in metalated ylides, we have now succeeded in the synthesis and gram-scale isolation of the so far elusive cyanoketene anion, [NC3O]-. Despite its assumed cumulene-like structure and the delocalization of the negative charge across the whole 5-atomic molecule, it features a bent geometry in solid state with a nucleophilic central carbon atom. Computational studies reveal an ambiguous bonding situation in the anion, which can only be illustrated by a combination of different resonance structures. Nonetheless, the anion features a remarkable stability, thus allowing the storage of its potassium salt and its application as highly functional synthetic building block. The cyanoketene anion readily reacts with a series of small molecules to more complex organic compounds including industrially valuable compounds such as cyanoacetate. This work demonstrates that reactive species found in the interstellar medium can be made accessible by novel synthesis methods and open up new pathways to more complex compounds through reaction with small molecules, an atom economic strategy sought in sustainable chemistry.