Ligand substituent effects on the light-driven hydrogen evolution by Cobalt(II) tripodal iminopyridine catalysts under precious-metal free conditions

Cobalt tripodal iminopyridine complexes [Co(L)] 2+ ( 1 – 4 ), where L = cis,cis ,-1,3,5-tris(pyridine-2-carboxaldimino)-cyclohexane ( 1 ) and its derivatives, bearing substituents of varying electronic properties at the pyridine moieties, act as water reduction catalysts (WRCs) under visible light ( λ> 420 nm) in aqueous acetonitrile (2.5%, v/v), using tris( n -butyl)triazatriagulenium ( TATA + ) as the organic photosensitizer and triethylamine (TEA) as the sacrificial donor. In the presence of added acetic acid, enhanced turnover numbers (TONs) of 1430 – 2810 were recorded with the substituted catalysts ( 2 – 4 ), which are attributed to the varied catalytic potential ( E cat ) upon the introduction of the substituents. Copyright © 2022 Wiley-VCH GmbH.