Oxygen Reduction by Amide-Ligated Cobalt Complexes: Effect of Hydrogen Bond Acceptor
The ability of earth-abundant metals to serve as catalysts for the oxygen reduction reaction is of increasing importance given the prominence of this reaction in several emerging technologies. It is now recognized that both the primary and secondary coordination environments of these catalysts can b...
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2025-08-01
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| author | Zahra Aghaei Adedamola A. Opalade Victor W. Day Timothy A. Jackson |
| author_facet | Zahra Aghaei Adedamola A. Opalade Victor W. Day Timothy A. Jackson |
| author_sort | Zahra Aghaei |
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| description | The ability of earth-abundant metals to serve as catalysts for the oxygen reduction reaction is of increasing importance given the prominence of this reaction in several emerging technologies. It is now recognized that both the primary and secondary coordination environments of these catalysts can be modulated to optimize their performance. In this present work, we describe two Co<sup>II</sup> complexes [Co<sup>II</sup>(PaPy<sub>2</sub>Q)](OTf) (<b>1</b>) and [Co<sup>II</sup>(PaPy<sub>2</sub>N)](OTf) (<b>2</b>) that catalyze chemical and electrochemical dioxygen reduction. Both <b>1</b> and <b>2</b> contain Co<sup>II</sup> centers in a N<sub>5</sub><sup>−</sup> coordination environment, but <b>2</b> has a naphthyridine group that places a nitrogen atom in the secondary coordination sphere. Solid-state X-ray crystallography and solution-state spectroscopic measurements reveal that, apart from this second-sphere nitrogen in <b>2</b>, complexes <b>1</b> and <b>2</b> have essentially identical properties. Despite these similarities, <b>2</b> performs the chemical reduction of dioxygen ~10-fold more rapidly than <b>1</b>. In addition, <b>2</b> has an enhanced performance in the electrochemical reduction of dioxygen compared to <b>1</b>. Both complexes yield a significant amount of H<sub>2</sub>O<sub>2</sub> in the chemical reduction of dioxygen (>25%). The enhanced catalytic performance of <b>2</b> is attributed to the presence of the second-sphere nitrogen atom, which might enable the efficient protonation of cobalt–oxygen intermediates formed during turnover. |
| format | Article |
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| institution | DOAJ |
| issn | 1420-3049 |
| language | English |
| publishDate | 2025-08-01 |
| publisher | MDPI AG |
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| series | Molecules |
| spelling | doaj-art-24bef2cf2a4b4302bac1fc4b42d1513e2025-08-20T03:04:43ZengMDPI AGMolecules1420-30492025-08-013015327410.3390/molecules30153274Oxygen Reduction by Amide-Ligated Cobalt Complexes: Effect of Hydrogen Bond AcceptorZahra Aghaei0Adedamola A. Opalade1Victor W. Day2Timothy A. Jackson3Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, KS 66045, USADepartment of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, KS 66045, USAX-Ray Crystallography Laboratory, University of Kansas, Lawrence, KS 66045, USADepartment of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, KS 66045, USAThe ability of earth-abundant metals to serve as catalysts for the oxygen reduction reaction is of increasing importance given the prominence of this reaction in several emerging technologies. It is now recognized that both the primary and secondary coordination environments of these catalysts can be modulated to optimize their performance. In this present work, we describe two Co<sup>II</sup> complexes [Co<sup>II</sup>(PaPy<sub>2</sub>Q)](OTf) (<b>1</b>) and [Co<sup>II</sup>(PaPy<sub>2</sub>N)](OTf) (<b>2</b>) that catalyze chemical and electrochemical dioxygen reduction. Both <b>1</b> and <b>2</b> contain Co<sup>II</sup> centers in a N<sub>5</sub><sup>−</sup> coordination environment, but <b>2</b> has a naphthyridine group that places a nitrogen atom in the secondary coordination sphere. Solid-state X-ray crystallography and solution-state spectroscopic measurements reveal that, apart from this second-sphere nitrogen in <b>2</b>, complexes <b>1</b> and <b>2</b> have essentially identical properties. Despite these similarities, <b>2</b> performs the chemical reduction of dioxygen ~10-fold more rapidly than <b>1</b>. In addition, <b>2</b> has an enhanced performance in the electrochemical reduction of dioxygen compared to <b>1</b>. Both complexes yield a significant amount of H<sub>2</sub>O<sub>2</sub> in the chemical reduction of dioxygen (>25%). The enhanced catalytic performance of <b>2</b> is attributed to the presence of the second-sphere nitrogen atom, which might enable the efficient protonation of cobalt–oxygen intermediates formed during turnover.https://www.mdpi.com/1420-3049/30/15/3274oxygen reduction reactioncobalt coordination complexessecondary coordination sphereelectrocatalysis |
| spellingShingle | Zahra Aghaei Adedamola A. Opalade Victor W. Day Timothy A. Jackson Oxygen Reduction by Amide-Ligated Cobalt Complexes: Effect of Hydrogen Bond Acceptor Molecules oxygen reduction reaction cobalt coordination complexes secondary coordination sphere electrocatalysis |
| title | Oxygen Reduction by Amide-Ligated Cobalt Complexes: Effect of Hydrogen Bond Acceptor |
| title_full | Oxygen Reduction by Amide-Ligated Cobalt Complexes: Effect of Hydrogen Bond Acceptor |
| title_fullStr | Oxygen Reduction by Amide-Ligated Cobalt Complexes: Effect of Hydrogen Bond Acceptor |
| title_full_unstemmed | Oxygen Reduction by Amide-Ligated Cobalt Complexes: Effect of Hydrogen Bond Acceptor |
| title_short | Oxygen Reduction by Amide-Ligated Cobalt Complexes: Effect of Hydrogen Bond Acceptor |
| title_sort | oxygen reduction by amide ligated cobalt complexes effect of hydrogen bond acceptor |
| topic | oxygen reduction reaction cobalt coordination complexes secondary coordination sphere electrocatalysis |
| url | https://www.mdpi.com/1420-3049/30/15/3274 |
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