Electronic Coupling and Electrocatalysis in Redox Active Fused Iron Corroles

Amir Mizrahi; Susovan Bhowmik; Arun K Manna; Woormileela Sinha; Amit Kumar; Magal Saphier; Atif Mahammed; Moumita Patra; Natalia Fridman; Israel Zilbermann; Leeor Kronik; Zeev Gross

doi:10.1021/acs.inorgchem.2c01389

Electronic Coupling and Electrocatalysis in Redox Active Fused Iron Corroles

Inorg Chem. 2022 Dec 26;61(51):20725-20733. doi: 10.1021/acs.inorgchem.2c01389. Epub 2022 Dec 13.

Authors

Amir Mizrahi^{1

2}, Susovan Bhowmik^{2

3}, Arun K Manna⁴, Woormileela Sinha^{2

5}, Amit Kumar², Magal Saphier¹, Atif Mahammed², Moumita Patra⁶, Natalia Fridman², Israel Zilbermann^{1

7}, Leeor Kronik⁴, Zeev Gross²

Affiliations

¹ Chemistry Department, Nuclear Research Centre Negev, Beer-Sheva84190, Israel.
² Schulich Faculty of Chemistry, Technion Institute of Technology, Haifa3200003, Israel.
³ Bankura Sammilani College (W.B), Bankura722102, India.
⁴ Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot76100, Israel.
⁵ Department of Chemistry, BITS PilaniK K Birla Goa Campus, NH17B, Zuarinagar, Goa403726, India.
⁶ Kazi Nazrul University (W.B), Asansol713340, India.
⁷ Chemistry Department, Ben-Gurion University of the Negev, Beer-Sheva84105, Israel.

Abstract

Conjugated arrays composed of corrole macrocycles are increasingly more common, but their chemistry still lags behind that of their porphyrin counterparts. Here, we report on the insertion of iron(III) into a β,β-fused corrole dimer and on the electronic effects that this redox active metal center has on the already rich coordination chemistry of [H₃tpfc] COT, where COT = cyclo-octatetraene and tpfc = tris(pentafluorophenyl)corrole. Synthetic manipulations were performed for the isolation and full characterization of both the 5-coordinate [Fe^IIItpfc(py)]₂COT and 6-coordinate [Fe^IIItpfc(py)₂]₂COT, with one and two axial pyridine ligands per metal, respectively. X-Ray crystallography reveals a dome-shaped structure for [Fe^IIItpfc(py)]₂COT and a perfectly planar geometry which (surprisingly at first) is also characterized by shorter Fe-N (corrole) and Fe-N (pyridine) distances. Computational investigations clarify that the structural phenomena are due to a change in the iron(III) spin state from intermediate (S = 3/2) to low (S = 1/2), and that both the 5- and 6-coordinated complexes are enthalpically favored. Yet, in contrast to iron(III) porphyrins, the formation enthalpy for the coordination of the first pyridine to Fe(III) corrole is more negative than that of the second pyridine coordination. Possible interactions between the two corrole subunits and the chelated iron ions were examined by UV-Vis spectroscopy, electrochemical techniques, and density functional theory (DFT). The large differences in the electronic spectra of the dimer relative to the monomer are concluded to be due to a reduced electronic gap, owing to the extensive electron delocalization through the fusing bridge. A cathodic sweep for the dimer discloses two redox processes, separated by 230 mV. The DFT self-consistent charge density for the neutral and cationic states (1- and 2-electron oxidized) reveals that the holes are localized on the macrocycle. A different picture emerges from the reduction process, where both the electrochemistry and the calculated charge density point toward two consecutive electron transfers with similar energetics, indicative of very weak electron communication between the two redox active iron(III) sites. The binuclear complex was determined to be a much better catalyst for the electrochemical hydrogen evolution reaction (HER) than the analogous mononuclear corrole.