Structure-Activity and Stability Relationships for Cobalt Polypyridyl-Based Hydrogen-Evolving Catalysts in Water.

摘要: A series of eight new and three known cobalt polypyridyl-based hydrogen-evolving catalysts (HECs) with distinct electronic structural differences are benchmarked in photocatalytic runs water. Methylene-bridged bis-bipyridyl is the preferred scaffold, both terms stability rate. For a complex tetradentate methanol-bridged bispyridyl–bipyridyl [CoIIBr(tpy)]Br, detailed mechanistic picture obtained by combining electrochemistry, spectroscopy, photocatalysis. In acidic branch, proton-coupled electron transfer, assigned to formation CoIII−H, found upon reduction CoII, line pKa(CoIII−H) approximately 7.25. Subsequent (−0.94 V vs. NHE) protonation close catalytic cycle. Methoxy substitution on bipyridyl scaffold results expected cathodic shift reduction, but fails change pKa(CoIII−H). An analysis outcome benchmarking view this postulated mechanism given along an outlook for design criteria generations catalysts.