Exploiting Pnictogen σ/π-Hole Interactions for Visible-Light-Induced Radical Transformations.

Area of Science:

• Organic Synthesis
• Supramolecular Chemistry
• Photochemistry

Background:

• Direct and selective chemical bond activation under mild conditions is a key challenge in organic synthesis.
• Elemental σ/π-hole interactions offer novel noncovalent molecular activation strategies.
• Pnictogen σ/π-hole interactions are underexplored in photoinduced radical processes.

Purpose of the Study:

• To leverage pnictogen σ/π-hole interactions for visible-light-induced organic radical generation.
• To develop general strategies for visible-light-driven radical transformations.
• To explore the application of N-heterocyclic nitrenium (NHN) and carbene (NHC) systems in these photoreactions.

Main Methods:

• Tuning pnictogen σ/π-hole properties through element selection, substituents, and acceptors.
• Assembling charge-transfer complexes (CTCs) that undergo visible-light-induced single-electron transfer (SET).
• Utilizing NHN and NHC systems to promote photoactive CTC formation and mediate radical transformations.

Main Results:

• Developed a transition-metal-free, photocatalyst-free strategy for generating various radicals (P(III)-centered, alkyl, carboranyl, etc.) via pnictogen σ-hole interactions.
• Expanded scope using NHNs for metal-free reductive radical transformations, activating C-I, C-Br, and C-Cl bonds, and enabling controlled radical polymerizations.
• Extended the concept to NHC-based systems, generating NHC radical anions that activate inert bonds like C_aryl-F, C_aryl-N, C_aryl-S, C_aryl-Se, and C_aryl-O.

Conclusions:

• Pnictogen σ/π-hole interactions are powerful tools for visible-light-induced radical generation and organic transformations.
• The developed strategies offer efficient, metal-free pathways for synthesizing diverse radical species and activating challenging bonds.
• These findings provide a foundation for designing new reagents and catalysts based on pnictogen interactions in radical chemistry.