Single electron reduction of NHC-CO₂-borane compounds.

Area of Science:

• Inorganic Chemistry
• Organic Chemistry
• Electrochemistry

Background:

• The carbon dioxide radical anion ([CO2˙-]) is a crucial reactive species in chemistry.
• Generating [CO2˙-] typically requires very negative reduction potentials, limiting its practical applications.
• Frustrated Lewis Pairs (FLPs) offer a novel approach to activate small molecules like CO2.

Purpose of the Study:

• To investigate the generation and stabilization of [CO2˙-]-like species using FLP chemistry.
• To explore the electrochemical properties and reactivity of these novel adducts.
• To demonstrate the advantages of FLP systems for accessing challenging radical anions.

Main Methods:

• Formation of N-heterocyclic carbene (NHC)-CO2-borane (BR3) adducts via FLP activation.
• Electrochemical reduction of the adducts to generate radical anions.
• Characterization using Electron Paramagnetic Resonance (EPR) spectroscopy and single-crystal X-ray diffraction.
• Density Functional Theory (DFT) calculations to understand electronic structure.

Main Results:

• NHC-CO2-BR3 adducts were reduced at significantly less negative potentials compared to free CO2.
• A stable radical anion, [CAAC-CO2-B(C6F5)3˙-], was generated and characterized.
• DFT calculations revealed spin density localized on the CO2 moiety due to the Lewis acid's electron-withdrawing effect.
• The generated species exhibited reactivity similar to [CO2˙-] towards DMPO.

Conclusions:

• FLP-mediated activation facilitates the generation of [CO2˙-]-like species at accessible potentials.
• These stabilized radical anions offer a promising platform for synthetic applications.
• This work highlights the power of FLP chemistry in stabilizing and utilizing reactive intermediates.