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Published August 21, 2007 | Published + Supplemental Material
Journal Article Open

Mixed-valence states formation in conformationally flexible metal-free 5,10,15,20-tetraferrocenylporphyrin and 5,10-bisferrocenyl-15,20-bisphenylporphyrin

Abstract

Metal-free 5,10,15,20-tetraferrocenylporphyrin and 5,10-bisferrocenyl-15,20-bisphenylporphyrin have been prepared and characterized by UV-Vis, MCD, ^1H, ^(13)C, and variable-temperature NMR, APCI- and ESI-MS, and Mössbauer spectroscopy, while their redox properties were investigated using electrochemical (cyclic voltammetry and differential pulse voltammetry), spectroelectrochemical, and chemical oxidation approaches. The electronic structure calculations at Density Functional Theory level reveal that both compounds adopt saddle conformations and the HOMOs in both complexes are predominantly metal-centered, while the LUMOs predominantly consist of porphyrin π* orbitals. In spite of the rotational freedom of ferrocenyl substituents at room temperature, both metal-free 5,10,15,20-tetraferrocenylporphyrin and 5,10-bisferrocenyl-15,20-bisphenylporphyrin are able to form mixed-valence states upon the successive ferrocene-based two- and one-electron oxidations, respectively, as confirmed by UV-Vis, MCD, Mössbauer, electro-, and spectroelectrochemical methods, and thus, the earlier suggested (Boyd et al. Chem. Commun., 1999, 637) requirements for the formation of mixed-valence states in ferrocene-containing porphyrins should be revised.

Additional Information

© The Royal Society of Chemistry 2007. Received 9th March 2007, Accepted 11th May 2007. First published on 4th June 2007. Generous support from the Research Corporation (Cottrell College Science Award CC6766), University of Minnesota Grant-in-Aid (Grant 20209) and Minnesota Supercomputing Institute to VN as well as University of Minnesota Duluth Undergraduate Research Opportunity Grants to CB and RH is greatly appreciated. We also wish to acknowledge Dr N. M. Loim for the preliminary discussion and synthetic details for the preparation of TFcPH_2 and Dr N. Kobayashi for the possibility to collect preliminary electrochemical and MCD data on TFcPH_2.

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August 19, 2023
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