Redox-active ligand-induced homolytic bond activation

Area of Science:

• Organometallic Chemistry
• Radical Chemistry
• Catalysis

Background:

• Pincer ligands are versatile scaffolds in coordination chemistry.
• Redox-active ligands can enable unique reactivity pathways.
• Palladium complexes are widely used in catalysis and small molecule activation.

Purpose of the Study:

• To synthesize and characterize a novel redox-active phosphine-appended aminophenol pincer ligand (PNO(H2)) coordinated to Pd(II).
• To investigate the electrochemical properties and radical nature of the resulting paramagnetic complex.
• To explore the complex's ability to activate small molecules, specifically diphenyldisulfide, via single-electron transfer.

Main Methods:

• Synthesis and characterization of the Pd(II) complex with the PNO(H2) ligand.
• Electrochemical studies (cyclic voltammetry) to determine redox behavior.
• Reaction of the reduced complex with diphenyldisulfide.
• Spectroscopic and structural analyses to elucidate the reaction products and mechanism.

Main Results:

• A paramagnetic Pd(II) complex featuring a persistent ligand-centered radical was successfully generated.
• The complex exhibited fully reversible single-electron oxidation and reduction.
• Homolytic bond activation of diphenyldisulfide was achieved by the reduced species, forming a dinuclear palladium complex with a bridging thiolate.
• Mechanistic studies revealed an intramolecular ligand-to-disulfide single-electron transfer initiating S-S homolytic cleavage and generating a thiyl radical.

Conclusions:

• The study demonstrates a novel strategy for small molecule activation using a redox-active pincer ligand complex.
• The unprecedented intramolecular single-electron transfer mechanism offers new insights into radical-mediated bond cleavage.
• This work expands the scope of ligand-centered radical chemistry in organometallic complexes and catalysis.