Infrared Spectroelectrochemistry of Iron-Nitrosyl Triarylcorroles. Implications for Ligand Noninnocence

Md Hafizur Rahman; Michael D Ryan; Hugo Vazquez-Lima; Abraham Alemayehu; Abhik Ghosh

doi:10.1021/acs.inorgchem.9b03613

Infrared Spectroelectrochemistry of Iron-Nitrosyl Triarylcorroles. Implications for Ligand Noninnocence

Inorg Chem. 2020 Mar 2;59(5):3232-3238. doi: 10.1021/acs.inorgchem.9b03613. Epub 2020 Feb 13.

Authors

Md Hafizur Rahman¹, Michael D Ryan¹, Hugo Vazquez-Lima^{2

3}, Abraham Alemayehu², Abhik Ghosh²

Affiliations

¹ Department of Chemistry, Marquette University, 1414 West Clybourn Street, Milwaukee, Wisconsin 53233, United States.
² Department of Chemistry, UiT-The Arctic University of Tromsø, 9037 Tromsø, Norway.
³ Centro de Química, Instituto de Ciencias, Universidad Autónoma de Puebla, Edif. IC9, CU, San Manuel, 72570 Puebla, Puebla, Mexico.

Abstract

Recent DFT calculations have suggested that iron nitrosyl triarylcorrole complexes have substantial {FeNO}⁷-corrole^•2- character. With this formulation, reduction of Fe(C)(NO) complexes, where C = triarylcorrole, should be centered on the corrole macrocycle rather than on the {FeNO}⁷ moiety. To verify this proposition, visible and infrared spectroelectrochemical studies of Fe(C)(NO) were carried out and the results were interpreted using DFT (B3LYP/STO-TZP) calculations. The first reduction of Fe(C)(NO) led to significant changes in the Soret and Q-band regions of the visible spectrum as well as to a significant downshift in the ν_NO and changes in the corrole vibrational frequencies. DFT calculations, which showed that the electron was mostly added to the corrole ligand (85%), were also able to predict the observed shifts in the ν_NO and corrole bands upon reduction. These results underscore the importance of monitoring both the corrole and nitrosyl vibrations in ascertaining the site of reduction. By contrast, the visible spectroelectrochemistry of the second reduction revealed only minor changes in the Soret band upon reduction, consistent with the reduction of the FeNO moiety.