Acid-responsive rhenium(I) NHC complexes: pyrazine vs. pyridine.

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Materials Science

Background:

• N-heterocyclic carbenes (NHCs) are versatile ligands in organometallic chemistry.
• Rhenium(I) tricarbonyl complexes are of interest for their photophysical and electrochemical properties.
• Understanding the influence of ligand structure on metal complex properties is crucial for designing new materials.

Purpose of the Study:

• To synthesize and characterize novel rhenium(I) tricarbonyl complexes functionalized with pyridine and pyrazine NHCs.
• To investigate the impact of Brønsted and Lewis acids on the electronic properties of these isosteric complexes.
• To compare the electronic behavior of pyridine- versus pyrazine-functionalized complexes.

Main Methods:

• Synthesis of four rhenium(I) tricarbonyl complexes.
• Full characterization including single-crystal X-ray diffraction.
• Electrochemical and spectroelectrochemical measurements.

Main Results:

• Molecular structures of the complexes were determined.
• Pyridine-containing complexes showed no significant electronic changes upon acid addition.
• Pyrazine-containing complexes exhibited notable shifts in redox potentials due to the extra nitrogen atom's interaction with acids.
• Brønsted acids induced larger electronic perturbations than alkali salts.

Conclusions:

• The electronic properties of rhenium(I) NHC complexes are sensitive to the ligand's heterocyclic core.
• The presence of an additional nitrogen atom in the pyrazine ring facilitates acid interactions, leading to significant electronic perturbations.
• This work provides insights into the design of functional organometallic materials sensitive to acidic environments.