Accessing Unusual Reactivity through Chelation-Promoted Bond Weakening

Area of Science:

• Organometallic Chemistry
• Synthetic Chemistry
• Redox Chemistry

Background:

• Proton-coupled electron transfer (PCET) is crucial for many chemical transformations.
• Developing potent PCET reductants requires understanding metal-ligand interactions and X-H bond weakening.
• Low-valent metal reductants offer unique reactivity profiles.

Purpose of the Study:

• To investigate the relationship between low-valent metal-protic ligand affinity and X-H bond weakening.
• To develop potent proton-coupled electron transfer (PCET) reductants.
• To explore the reactivity of samarium(II) complexes with protic ligands.

Main Methods:

• Systematic investigation of various samarium(II)-protic ligand reductant systems.
• Characterization of metal-ligand affinity and stability against H2 evolution.
• Testing the reductive capabilities of the optimized SmBr2-NMEA system on diverse substrates.

Main Results:

• Samarium dibromide N-methylethanolamine (SmBr2-NMEA) demonstrated superior metal-ligand affinity and stability.
• SmBr2-NMEA effectively reduced recalcitrant substrates like alkynes, lactones, and arenes.
• NMEA's chelating role enabled unique reductive cyclizations, and the system reduced nitrogen fixation intermediates.

Conclusions:

• SmBr2-NMEA is a powerful and versatile reductant for challenging organic transformations.
• The study highlights the potential for rational design of PCET reagents with weakened X-H bonds.
• This work advances the development of novel synthetic methodologies using low-valent metal reductants.