Spectroelectrochemical studies of a ruthenium complex containing the pH sensitive 4,4′-dihydroxy-2,2′-bipyridine ligand

Erin J. Viere; Ashley E. Kuhn; Margaret H. Roeder; Nicholas A. Piro; W. Scott Kassel; Timothy J. Dudley; Jared J. Paul

doi:10.1039/c7dt04554a

Spectroelectrochemical studies of a ruthenium complex containing the pH sensitive 4,4′-dihydroxy-2,2′-bipyridine ligand

Erin J. Viere, Ashley E. Kuhn, Margaret H. Roeder, Nicholas A. Piro, W. Scott Kassel, Timothy J. Dudley, Jared J. Paul

Research output: Contribution to journal › Article › peer-review

14 Scopus citations

Abstract

Attaining high oxidation states at the metal center of transition metal complexes is a key design principle for many catalytic processes. One way to support high oxidation state chemistry is to utilize ligands that are electron-donating in nature. Understanding the structural and electronic changes of metal complexes as higher oxidation states are reached is critical towards designing more robust catalysts that are able to turn over at high rates without decomposing. To this end, we report herein the changes in structural and electronic properties as [Ru(bpy)₂(44′bpy(OH)₂)]²⁺ is oxidized to [Ru(bpy)₂(44′bpy(OH)₂)]³⁺ (bpy = 2,2′-bipyridine; 44′bpy(OH)₂ = 4,4′-dihydroxy-2,2′-bipyridine). The 44′bpy(OH)₂ ligand is a pH-dependent ligand where deprotonation of the hydroxyl groups leads to significant electronic donation to the metal center. A Pourbaix Diagram of the complex reveals a pH independent reduction potential below pH = 2.0 for the Ru^3+/2+ process at 0.91 V vs. Ag/AgCl. Above pH = 2.0, pH dependence is observed with a decrease in reduction potential until pH = 6.8 where the complex is completely deprotonated, resulting in a reduction potential of 0.62 V vs. Ag/AgCl. Spectroelectrochemical studies as a function of pH reveal the disappearance of the Metal to Ligand Charge Transfer (MLCT) or Mixed Metal-Ligand to Charge Transfer bands upon oxidation and the appearance of a new low energy band. DFT calculations for this low energy band were carried out using both B3LYP and M06-L functionals for all protonation states and suggest that numerous new transition types occur upon oxidation to Ru³⁺.

Original language	English (US)
Pages (from-to)	4149-4161
Number of pages	13
Journal	Dalton Transactions
Volume	47
Issue number	12
DOIs	https://doi.org/10.1039/c7dt04554a
State	Published - 2018

Bibliographical note

Funding Information:
JJP thanks the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research and support from the College of Liberal Arts and Sciences at Villanova University is gratefully acknowledged. We would like to acknowledge Dr Eric Schelter from the University of Pennsylvania for helpful suggestions.

Publisher Copyright:
© 2018 The Royal Society of Chemistry.

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title = "Spectroelectrochemical studies of a ruthenium complex containing the pH sensitive 4,4′-dihydroxy-2,2′-bipyridine ligand",

abstract = "Attaining high oxidation states at the metal center of transition metal complexes is a key design principle for many catalytic processes. One way to support high oxidation state chemistry is to utilize ligands that are electron-donating in nature. Understanding the structural and electronic changes of metal complexes as higher oxidation states are reached is critical towards designing more robust catalysts that are able to turn over at high rates without decomposing. To this end, we report herein the changes in structural and electronic properties as [Ru(bpy)2(44′bpy(OH)2)]2+ is oxidized to [Ru(bpy)2(44′bpy(OH)2)]3+ (bpy = 2,2′-bipyridine; 44′bpy(OH)2 = 4,4′-dihydroxy-2,2′-bipyridine). The 44′bpy(OH)2 ligand is a pH-dependent ligand where deprotonation of the hydroxyl groups leads to significant electronic donation to the metal center. A Pourbaix Diagram of the complex reveals a pH independent reduction potential below pH = 2.0 for the Ru3+/2+ process at 0.91 V vs. Ag/AgCl. Above pH = 2.0, pH dependence is observed with a decrease in reduction potential until pH = 6.8 where the complex is completely deprotonated, resulting in a reduction potential of 0.62 V vs. Ag/AgCl. Spectroelectrochemical studies as a function of pH reveal the disappearance of the Metal to Ligand Charge Transfer (MLCT) or Mixed Metal-Ligand to Charge Transfer bands upon oxidation and the appearance of a new low energy band. DFT calculations for this low energy band were carried out using both B3LYP and M06-L functionals for all protonation states and suggest that numerous new transition types occur upon oxidation to Ru3+.",

author = "Viere, {Erin J.} and Kuhn, {Ashley E.} and Roeder, {Margaret H.} and Piro, {Nicholas A.} and Kassel, {W. Scott} and Dudley, {Timothy J.} and Paul, {Jared J.}",

note = "Funding Information: JJP thanks the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research and support from the College of Liberal Arts and Sciences at Villanova University is gratefully acknowledged. We would like to acknowledge Dr Eric Schelter from the University of Pennsylvania for helpful suggestions. Publisher Copyright: {\textcopyright} 2018 The Royal Society of Chemistry.",

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AU - Viere, Erin J.

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AU - Roeder, Margaret H.

AU - Piro, Nicholas A.

AU - Kassel, W. Scott

AU - Dudley, Timothy J.

AU - Paul, Jared J.

N1 - Funding Information: JJP thanks the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research and support from the College of Liberal Arts and Sciences at Villanova University is gratefully acknowledged. We would like to acknowledge Dr Eric Schelter from the University of Pennsylvania for helpful suggestions. Publisher Copyright: © 2018 The Royal Society of Chemistry.

PY - 2018

Y1 - 2018

N2 - Attaining high oxidation states at the metal center of transition metal complexes is a key design principle for many catalytic processes. One way to support high oxidation state chemistry is to utilize ligands that are electron-donating in nature. Understanding the structural and electronic changes of metal complexes as higher oxidation states are reached is critical towards designing more robust catalysts that are able to turn over at high rates without decomposing. To this end, we report herein the changes in structural and electronic properties as [Ru(bpy)2(44′bpy(OH)2)]2+ is oxidized to [Ru(bpy)2(44′bpy(OH)2)]3+ (bpy = 2,2′-bipyridine; 44′bpy(OH)2 = 4,4′-dihydroxy-2,2′-bipyridine). The 44′bpy(OH)2 ligand is a pH-dependent ligand where deprotonation of the hydroxyl groups leads to significant electronic donation to the metal center. A Pourbaix Diagram of the complex reveals a pH independent reduction potential below pH = 2.0 for the Ru3+/2+ process at 0.91 V vs. Ag/AgCl. Above pH = 2.0, pH dependence is observed with a decrease in reduction potential until pH = 6.8 where the complex is completely deprotonated, resulting in a reduction potential of 0.62 V vs. Ag/AgCl. Spectroelectrochemical studies as a function of pH reveal the disappearance of the Metal to Ligand Charge Transfer (MLCT) or Mixed Metal-Ligand to Charge Transfer bands upon oxidation and the appearance of a new low energy band. DFT calculations for this low energy band were carried out using both B3LYP and M06-L functionals for all protonation states and suggest that numerous new transition types occur upon oxidation to Ru3+.

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Spectroelectrochemical studies of a ruthenium complex containing the pH sensitive 4,4′-dihydroxy-2,2′-bipyridine ligand

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