Ruthenium terpyridine Phenol-Substituent supports PCET and semiquinone-like behavior

Katherine L. Moffa, Claire N. Teahan, Charlotte L. Montgomery, Samantha L. Shepherd, John C. Dickenson, Kaitlyn R. Benson, Mark Olsen, Walter J. Boyko, Mark Bezpalko, W. Scott Kassel, Timothy J. Dudley, Daniel P. Harrison, Jared J. Paul

Research output: Contribution to journalArticlepeer-review

Abstract

Ligands play a central role in dictating the electronic properties of metal complexes to which they are coordinated. A fundamental understanding of changes in ligand properties can be used as design principles for more efficient catalysts. Designing ligands that have multiple protonation states that will change the properties of the coordination complex would be useful as potential ways of controlling catalysis, for example, as an on/off switch where one redox state exists below thermodynamic potential and another exists above. Thus, phenol moieties built into strongly coordinating ligands, like that of tpyPhOH (4′-(4-hydroxyphenyl)-2,2′:6′,2′'-terpyridine) may provide such a handle. Herein, we report the electrochemical and spectral characterization, and the crystallographic and computational analysis of two ruthenium analogs: [Ru(tpy)(tpyPhOH)](PF6)2 and [Ru(tpyPhOH)2](PF6)2 (tpy = 2,2′:6′,2′'-terpyridine). Cyclic voltammetry and differential pulse voltammetry indicate that two redox events occur, one of which is pH independent and we hypothesize that these follow an electrochemical-chemical-electrochemical (ECE) mechanism. XRD results of the ruthenium complexes’ protonated forms are generally consistent with expected bond lengths and angles and are in agreement with computational modeling. The properties are compared to a previously reported analog that contains the –OH group directly connected to terpyridine, [Ru(tpyOH)2](PF6)2, where tpyOH is 4′-hydroxy-2,2′:6′,2′'-terpyridine, with some intriguing differences. Overall, these data indicate that the phenyl-substituent decouples the phenol such that it behaves both as an electron withdrawing substituent and a location for a ligand centered oxidation event to occur.

Original languageEnglish (US)
Article number116582
JournalPolyhedron
Volume244
DOIs
StatePublished - Nov 1 2023

Bibliographical note

Funding Information:
Funding for this project comes from a grant from the National Science Foundation – Chemistry Structure, Dynamics & Mechanisms B ( CHE-1900536 ). This work was also supported by Major Research Instrumentation grants from the National Science Foundation ( CHE-1827930 and CHE-2018399 ). Support from the College of Liberal Arts and Sciences at Villanova University is gratefully acknowledged as is the support from the Virginia Military Institute’s Grants-in-Aid of Research supply funds.

Publisher Copyright:
© 2023

Keywords

  • Catalysis
  • Hydroxy-phenyl
  • PCET
  • Ruthenium
  • Semiquinone
  • Terpyridine

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