Photoinitiated Dioxygenase‐Type Reactivity of Open‐Shell 3d Divalent Metal Flavonolato Complexes

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Irradiation of 3‐hydroxyflavonolato (3‐Hfl) complexes of MnII, CoII, NiII and CuII (1–4) at 300 nm under aerobic conditions results in dioxygenase‐type reactivity and the formation of the corresponding divalent metal O‐benzoylsalicylato (O‐bs) complexes 8–11 and CO. The latter were characterized by using multiple methods, including elemental analysis, X‐ray crystallography, NMR and/or EPR spectroscopy, mass spectrometry and IR spectroscopy. Compounds 1–4 serve as catalysts for the photoinduced reactivity of 3‐hydroxyflavonol (3‐HflH) to produce O‐benzoylsalicylic acid as the major product. Spectroscopic studies (UV/Vis and 1H NMR) show that each O‐benzoylsalicylato complex 8–11 reacts with one equiv. of 3‐hydroxyflavonol to regenerate 1–4 and enable turnover reactivity. Unlike what is observed for free 3‐HflH, photoinduced reactions involving 1–4 and excess flavonol show only minor amounts of flavonol isomerization reactivity. These results indicate that the presence of a metal ion, whether under stoichiometric or catalytic conditions, facilitates the photoinduced degradation of 3‐HflH to produce a carboxylic acid and CO as products.