Transition-Metal-Free Carbonyl Redox: A Ketene in Three Oxidation States

Area of Science:

• Organic Chemistry
• Redox Chemistry
• Carbene Chemistry

Background:

• Ketenes are versatile organic compounds with diverse reactivity.
• The redox chemistry of ketenes, especially stable radical anions and cations, is largely unexplored.
• Cyclic (alkyl)(amino)carbenes (CAACs) are potent ligands that stabilize reactive species.

Purpose of the Study:

• To isolate and characterize ketene species in multiple oxidation states, including radical anion and cation.
• To investigate the unique electronic and structural properties of these novel ketene radicals.
• To explore the reactivity of ketene radical anions and cations.

Main Methods:

• Synthesis and isolation of CAAC-derived ketene in three oxidation states.
• Characterization using IR, UV-vis, EPR spectroscopy, X-ray diffraction, and computational methods.
• Reactivity studies of the radical anion and cation.

Main Results:

• Successful isolation and characterization of a CAAC-derived ketene radical anion and radical cation.
• The radical anion exhibits a bent geometry, decoupling the radical from the CAAC.
• The radical cation arises from oxidation of the carbonyl group, showing parallels with transition metal carbonyls.
• Radical anion and cation display distinct reactivity: nucleophilic and radical pathways, respectively.

Conclusions:

• This study presents the first stable ketene radical anion and cation.
• The findings reveal unique electronic properties and reactivity patterns of ketene radicals.
• This work opens new avenues for redox chemistry of ketenes and carbene-based organocatalysis.