Replacing Pyridine with Pyrazine in Molecular Cobalt Catalysts: Effects on Electrochemical Properties and Aqueous H<sub>2</sub> Generation
Four new molecular Co(II)tetrapyridyl complexes were synthesized and evaluated for their activity as catalysts for proton reduction in aqueous environments. The pyridine groups around the macrocycle were substituted for either one or two pyrazine groups. Single crystal X-ray analysis shows that the...
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| Format: | Article |
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MDPI AG
2021-01-01
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| Series: | Catalysts |
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| Online Access: | https://www.mdpi.com/2073-4344/11/1/75 |
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| author | Lars Kohler Andrea M. Potocny Jens Niklas Matthias Zeller Oleg G. Poluektov Karen L. Mulfort |
| author_facet | Lars Kohler Andrea M. Potocny Jens Niklas Matthias Zeller Oleg G. Poluektov Karen L. Mulfort |
| author_sort | Lars Kohler |
| collection | DOAJ |
| description | Four new molecular Co(II)tetrapyridyl complexes were synthesized and evaluated for their activity as catalysts for proton reduction in aqueous environments. The pyridine groups around the macrocycle were substituted for either one or two pyrazine groups. Single crystal X-ray analysis shows that the pyrazine groups have minimal impact on the Co(II)–N bond lengths and molecular geometry in general. X-band EPR spectroscopy confirms the Co(II) oxidation state and the electronic environment of the Co(II) center are only very slightly perturbed by the substitution of pyrazine groups around the macrocycle. The substitution of pyrazine groups has a substantial impact on the observed metal- and ligand-centered reduction potentials as well as the overall H<sub>2</sub> catalytic activity in a multimolecular system using the [Ru(2,2′-bipyridine)<sub>3</sub>]Cl<sub>2</sub> photosensitizer and ascorbic acid as a sacrificial electron donor. The results reveal interesting trends between the H<sub>2</sub> catalytic activity for each catalyst and the driving force for electron transfer between either the reduced photosensitizer to catalyst step or the catalyst to proton reduction step. The work presented here showcases how even the difference of a single atom in a molecular catalyst can have an important impact on activity and suggests a pathway to optimize the photocatalytic activity and stability of molecular systems. |
| first_indexed | 2024-03-09T05:43:51Z |
| format | Article |
| id | doaj.art-1ca85bef3a4e4634b5040e19ec86e9e4 |
| institution | Directory Open Access Journal |
| issn | 2073-4344 |
| language | English |
| last_indexed | 2024-03-09T05:43:51Z |
| publishDate | 2021-01-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Catalysts |
| spelling | doaj.art-1ca85bef3a4e4634b5040e19ec86e9e42023-12-03T12:22:18ZengMDPI AGCatalysts2073-43442021-01-011117510.3390/catal11010075Replacing Pyridine with Pyrazine in Molecular Cobalt Catalysts: Effects on Electrochemical Properties and Aqueous H<sub>2</sub> GenerationLars Kohler0Andrea M. Potocny1Jens Niklas2Matthias Zeller3Oleg G. Poluektov4Karen L. Mulfort5Division of Chemical Sciences and Engineering, Argonne National Laboratory, Lemont, IL 60439, USADivision of Chemical Sciences and Engineering, Argonne National Laboratory, Lemont, IL 60439, USADivision of Chemical Sciences and Engineering, Argonne National Laboratory, Lemont, IL 60439, USADepartment of Chemistry, Purdue University, West Lafayette, IN 47907, USADivision of Chemical Sciences and Engineering, Argonne National Laboratory, Lemont, IL 60439, USADivision of Chemical Sciences and Engineering, Argonne National Laboratory, Lemont, IL 60439, USAFour new molecular Co(II)tetrapyridyl complexes were synthesized and evaluated for their activity as catalysts for proton reduction in aqueous environments. The pyridine groups around the macrocycle were substituted for either one or two pyrazine groups. Single crystal X-ray analysis shows that the pyrazine groups have minimal impact on the Co(II)–N bond lengths and molecular geometry in general. X-band EPR spectroscopy confirms the Co(II) oxidation state and the electronic environment of the Co(II) center are only very slightly perturbed by the substitution of pyrazine groups around the macrocycle. The substitution of pyrazine groups has a substantial impact on the observed metal- and ligand-centered reduction potentials as well as the overall H<sub>2</sub> catalytic activity in a multimolecular system using the [Ru(2,2′-bipyridine)<sub>3</sub>]Cl<sub>2</sub> photosensitizer and ascorbic acid as a sacrificial electron donor. The results reveal interesting trends between the H<sub>2</sub> catalytic activity for each catalyst and the driving force for electron transfer between either the reduced photosensitizer to catalyst step or the catalyst to proton reduction step. The work presented here showcases how even the difference of a single atom in a molecular catalyst can have an important impact on activity and suggests a pathway to optimize the photocatalytic activity and stability of molecular systems.https://www.mdpi.com/2073-4344/11/1/75photocatalysishydrogenaqueouscobaltmacrocyclepyrazine |
| spellingShingle | Lars Kohler Andrea M. Potocny Jens Niklas Matthias Zeller Oleg G. Poluektov Karen L. Mulfort Replacing Pyridine with Pyrazine in Molecular Cobalt Catalysts: Effects on Electrochemical Properties and Aqueous H<sub>2</sub> Generation Catalysts photocatalysis hydrogen aqueous cobalt macrocycle pyrazine |
| title | Replacing Pyridine with Pyrazine in Molecular Cobalt Catalysts: Effects on Electrochemical Properties and Aqueous H<sub>2</sub> Generation |
| title_full | Replacing Pyridine with Pyrazine in Molecular Cobalt Catalysts: Effects on Electrochemical Properties and Aqueous H<sub>2</sub> Generation |
| title_fullStr | Replacing Pyridine with Pyrazine in Molecular Cobalt Catalysts: Effects on Electrochemical Properties and Aqueous H<sub>2</sub> Generation |
| title_full_unstemmed | Replacing Pyridine with Pyrazine in Molecular Cobalt Catalysts: Effects on Electrochemical Properties and Aqueous H<sub>2</sub> Generation |
| title_short | Replacing Pyridine with Pyrazine in Molecular Cobalt Catalysts: Effects on Electrochemical Properties and Aqueous H<sub>2</sub> Generation |
| title_sort | replacing pyridine with pyrazine in molecular cobalt catalysts effects on electrochemical properties and aqueous h sub 2 sub generation |
| topic | photocatalysis hydrogen aqueous cobalt macrocycle pyrazine |
| url | https://www.mdpi.com/2073-4344/11/1/75 |
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