An efficient catalyst based on a water-soluble cobalt(II) complex of S,S′-bis(2-pyridylmethyl)-1,2-thiobenzene for electrochemical- and photochemical-driven hydrogen evolution

The reaction of S,S′-bis(2-pyridylmethyl)-1,2-thiobenzene and CoCl₂ affords a water-soluble cobalt(II) complex, (bptb)CoCl₂], which has been characterized using various methods. Under blue light, together with CdS nanorods as a photosensitizer and ascorbic acid as a sacrificial electron donor, (bptb)CoCl₂] can catalyze hydrogen generation from water and can work for 90 h. Under optimal conditions, this photocatalytic system achieves a turnover number (TON) of 22 900 moles of H₂ per mole of catalyst during 60 h of irradiation, and the highest apparent quantum yield is ca 26.63% at 469 nm. Moreover, (bptb)CoCl₂] exhibits much higher activity than (bpte)CoCl₂] (bpte = S,S′-bis(2-pyridylmethyl)-1,2-thioethane; TON = 6740 moles of H₂ per mole of catalyst during 60 h of irradiation), indicating that bptb can constitute a better catalyst for hydrogen production than bpte. This result can be attributed to the electronic properties of the ligands (bptb and bpte). The introduction of phenyl makes the electron distribution more uniform in the cobalt complex, allowing easier formation of the Co(III)–H species, further promoting the formation of hydrogen.