N-centered, yet persistent: isolation of N₂O-based radicals through FLP-type stabilization.

Area of Science:

• Organometallic Chemistry
• Radical Chemistry
• Boron Chemistry

Background:

• The electrochemical reduction of N-heterocyclic carbenes (NHCs) like 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IDipp) typically yields unstable radical anions.
• This instability limits their synthetic utility and detailed investigation.

Purpose of the Study:

• To stabilize the electrochemically generated radical anion of IDipp·N2O.
• To synthesize and characterize persistent radical species derived from NHCs.
• To investigate the electronic structure and stability of these novel radicals.

Main Methods:

• Electrochemical reduction of IDipp·N2O in the presence of Lewis acidic boranes.
• Chemical reduction for synthesis of the stabilized radicals.
• Electron paramagnetic resonance (EPR) spectroscopy (continuous-wave and pulsed).
• Theoretical electronic structure calculations.

Main Results:

• The one-electron reduction of IDipp·N2O, usually irreversible, becomes reversible upon stabilization with Lewis acidic boranes.
• Persistent radical species are successfully synthesized and characterized.
• These radicals exhibit a highly N-centered electronic structure.
• Remarkable persistence at room temperature under inert atmosphere was observed.

Conclusions:

• Lewis acidic boranes effectively stabilize transient NHC radical anions, transforming them into persistent radical species.
• The stabilized radicals possess a unique N-centered character and significant room-temperature stability.
• This work provides a new strategy for accessing and studying persistent NHC-based radicals.