Ruthenium complexes with asymmetric hydroxy- and methoxy-substituted bipyridine ligands

Kaitlyn R. Benson, Jaqueline Stash, Katherine L. Moffa, Russell H. Schmehl, Timothy J. Dudley, Jared J. Paul

    Research output: Contribution to journalArticlepeer-review

    Abstract

    The development of metal complexes with ligands capable of proton transfer can result in significant advances in Proton Coupled Electron Transfer (PCET) chemistry, specifically understanding how these reactions occur mechanistically in the excited state. The synthesis of three ruthenium complexes containing asymmetric bipyridine ligands: [Ru(bpy)2(4bpyOH)]2+, [Ru(bpy)2(4bpyOMe)]2+, and [Ru(bpy)2(44′bpy(OH)(OMe))]2+ (bpy = 2,2′-bipyridine; 4bpyOH = 4-hydroxy-2,2′-bipyridine; 4bpyOMe = 4-methoxy-2,2′-bipyridine; 44′bpy(OH)(OMe) = 4-hydroxy-4′-methoxy-2,2′-bipyridine) are reported. These complexes were studied using both experimental and computational methods. These studies indicate that the methoxy-substitution gives similar electron-donating properties to the hydroxy-substitution, meaning that the methoxy-substitution is a good control when examining electron transfer in the absence of proton transfer. Potential versus pH diagrams show that [Ru(bpy)2(4bpyOH)]2+ has a RuIII/II reduction potential of 0.97 V vs. Ag/AgCl in aqueous acidic solution that decreases to 0.76 V vs. Ag/AgCl when deprotonated. The [Ru(bpy)2(44′bpy(OH)(OMe))]2+, with an additional methoxy-substituent, has a RuIII/II reduction potential that is slightly lower with a potential of 0.92 V vs. Ag/AgCl in acidic aqueous solution that decreases to 0.74 V vs. Ag/AgCl when deprotonated. These complexes are comparable to other hydroxy- and methoxy-substituted polypyridyl ruthenium complexes reported previously, showing the additive effects of hydroxy- and methoxy-substitutions on the reduction potential of the RuIII/II wave and spectroscopic shifts that occur as the ligand scaffold is altered.

    Original languageEnglish (US)
    Article number115300
    JournalPolyhedron
    Volume205
    DOIs
    StatePublished - Sep 1 2021

    Bibliographical note

    Funding Information:
    Funding for this project comes from a grant from the National Science Foundation ? Chemical Structure, Dynamics & Mechanisms B (CHE-1900536). This work was also supported by two 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. Thank you to Mark Olson for running mass spectrometry samples. This work is dedicated to Robert L. Paul.

    Funding Information:
    Funding for this project comes from a grant from the National Science Foundation – Chemical Structure, Dynamics & Mechanisms B (CHE-1900536). This work was also supported by two 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. Thank you to Mark Olson for running mass spectrometry samples. This work is dedicated to Robert L. Paul.

    Publisher Copyright:
    © 2021 Elsevier Ltd

    Keywords

    • Bipyridine
    • Hydroxy
    • Methoxy
    • PCET
    • Ruthenium

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