Issue 12, 2018

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+.

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

Supplementary files

Article information

Article type
Paper
Submitted
03 Dec 2017
Accepted
15 Feb 2018
First published
16 Feb 2018

Dalton Trans., 2018,47, 4149-4161

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

E. J. Peterson, A. E. Kuhn, M. H. Roeder, N. A. Piro, W. S. Kassel, T. J. Dudley and J. J. Paul, Dalton Trans., 2018, 47, 4149 DOI: 10.1039/C7DT04554A

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