Ruthenium Nitrosyl Porphyrins Coordinated with Aryloxides Containing Internal Hydrogen Bonds

Abstract The synthesis, characterization, and redox behavior of aryloxide complexes containing an increasing number of internal hydrogen bonds (OEP)Ru(NO)(OAr xH ) (OEP=octaethylporphyrinato dianion; x=0, 1, 2) are reported. These nitrosyl aryloxide compounds were characterized by X‐ray crystallography, IR and 1 H NMR spectroscopy. The IR spectra displayed υ NO frequencies in the 1823–1843 cm −1 range with compounds possessing more internal hydrogen bonds demonstrating higher υ NO frequencies due to diminished π‐backdonation to the Ru−NO fragment. Comparison of the distinct υ NH and δ N−H signals in the IR and 1 H NMR spectra of the free and complexed OAr 1H /OAr 2H ligands support the notion of additional electron density being removed via intramolecular hydrogen bonding. Results of DFT calculations on the (porphine)Ru(NO)(OAr xH ) models (porphine=unsubstituted porphyrin) reveal that the HOMOs of these complexes have significant axial ligand contributions, whereas the HOMOs of the five‐coordinate [(porphine)RuNO)] + cation resides mostly on the equatorial porphyrin macrocycle. The electrochemical results of these (OEP)Ru(NO)(OAr xH ) complexes in CH 2 Cl 2 reveal first oxidations that occur at increasingly positive potentials when more internal hydrogen bonds are present. Based on the DFT and preliminary IR spectroelectrochemical results, we propose that the electrooxidations result in eventual dissociation of the axial aryloxide ligands.