Structure-Activity and Stability Relationships for Cobalt Polypyridyl-Based Hydrogen-Evolving Catalysts in Water.
ChemSusChem
; 10(22): 4570-4580, 2017 11 23.
Article
em En
| MEDLINE
| ID: mdl-29052339
ABSTRACT
A series of eight new and three known cobalt polypyridyl-based hydrogen-evolving catalysts (HECs) with distinct electronic and structural differences are benchmarked in photocatalytic runs in water. Methylene-bridged bis-bipyridyl is the preferred scaffold, both in terms of stability and rate. For a cobalt complex of the tetradentate methanol-bridged bispyridyl-bipyridyl complex [CoII Br(tpy)]Br, a detailed mechanistic picture is obtained by combining electrochemistry, spectroscopy, and photocatalysis. In the acidic branch, a proton-coupled electron transfer, assigned to formation of CoIII -H, is found upon reduction of CoII , in line with a pKa (CoIII -H) of approximately 7.25. Subsequent reduction (-0.94â
V vs. NHE) and protonation close the catalytic cycle. Methoxy substitution on the bipyridyl scaffold results in the expected cathodic shift of the reduction, but fails to change the pKa (CoIII -H). An analysis of the outcome of the benchmarking in view of this postulated mechanism is given along with an outlook for design criteria for new generations of catalysts.
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Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Piridinas
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Água
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Cobalto
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Hidrogênio
Idioma:
En
Ano de publicação:
2017
Tipo de documento:
Article