Enhanced hydrogen evolution in neutral water catalyzed by a cobalt complex with a softer polypyridyl ligand

P Wang, G Liang, N Smith, K Hill… - Angewandte Chemie …, 2020 - Wiley Online Library
P Wang, G Liang, N Smith, K Hill, B Donnadieu, CE Webster, X Zhao
Angewandte Chemie International Edition, 2020Wiley Online Library
To explore the structure–function relationships of cobalt complexes in the catalytic hydrogen
evolution reaction (HER), we studied the substitution of a tertiary amine with a softer pyridine
group and the inclusion of a conjugated bpy unit in a Co complex with a new pentadentate
ligand, 6‐[6‐(1, 1‐di‐pyridin‐2‐yl‐ethyl)‐pyridin‐2‐ylmethyl]‐[2, 2′] bipyridinyl (Py3Me‐
Bpy). These modifications resulted in significantly improved stability and activity in both
electro‐and photocatalytic HER in neutral water.[Co (Py3Me‐Bpy)(OH2)](PF6) 2 catalyzes …
Abstract
To explore the structure–function relationships of cobalt complexes in the catalytic hydrogen evolution reaction (HER), we studied the substitution of a tertiary amine with a softer pyridine group and the inclusion of a conjugated bpy unit in a Co complex with a new pentadentate ligand, 6‐[6‐(1,1‐di‐pyridin‐2‐yl‐ethyl)‐pyridin‐2‐ylmethyl]‐[2,2′]bipyridinyl (Py3Me‐Bpy). These modifications resulted in significantly improved stability and activity in both electro‐ and photocatalytic HER in neutral water. [Co(Py3Me‐Bpy)(OH2)](PF6)2 catalyzes the electrolytic HER at −1.3 V (vs. SHE) for 20 hours with a turnover number (TON) of 266 300, and photolytic HER for two days with a TON of 15 000 in pH 7 aqueous solutions. The softer ligand scaffold possibly provides increased stability towards the intermediate CoI species. DFT calculations demonstrate that HER occurs through a general electron transfer/proton transfer/electron transfer/proton transfer pathway, with H2 released from the protonation of CoII−H species.
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