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In Situ FT-IR Spectroelectrochemistry Reveals Mechanistic Insights into Nitric Oxide Release from Ruthenium(II) Nitrosyl Complexes

Year: 2024

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide Ruthenium(II) tetraamine nitrosyl complexes with N-heterocyclic ligands are known for their potential as nitric oxide (NO • ) donors, capable of releasing NO • through either direct photodissociation or one-electron reduction of the Ru(II)NO + center. This study delivers a novel insight into the one-electron reduction mechanism for the model complex trans -[Ru II (NO)(NH 3 ) 4 (py)] 3+ (RuNOpy, py = pyridine) in phosphate buffer solution (pH 7.4). In situ FT-IR spectroelectrochemistry reveals that the pyridine ligand is readily released upon one-electron reduction of the nitrosyl complex, a finding supported by nuclear magnetic resonance spectroscopy ( 1 H NMR) and electrochemistry coupled to mass spectrometry (EC-MS), which detect free pyridine in solution. However, direct evidence of NO • release from RuNOpy as the primary step following reduction was not observed. Interestingly, FT-IR results indicate that the isomers of the nitrosyl complex, cis -[Ru(NO)(NH 3 ) 4 (OH)] + and trans -[Ru(NO)(NH 3 ) 4 (OH)] +, are formed following reduction and pyridine labilization, initiating an outer-sphere electron transfer process that triggers a chain electron transfer reaction. Finally, nitric oxide is liberated as an end product, arising from the reduction of the hydroxyl isomer complexes cis -[Ru(NO)(NH 3 ) 4 (OH)] 2+ and trans -[Ru(NO)(NH 3 ) 4 (OH)] 2+ . This study provides new insights into the reduction mechanism and transformation pathways of ruthenium nitrosyl complexes, contributing to our understanding of their potential as NO • donors.

Source: Inorganic Chemistry

DOI: 10.1021/acs.inorgchem.4c03185