Photocatalytic Oxygenation Reactions with a Cobalt Porphyrin Complex Using Water as an Oxygen Source and Dioxygen as an Oxidant
2019
Hong, Young Hyun | Han, Ji Won | Jung, Jieun | Nakagawa, Tatsuo | Lee, Yong-Min | Nam, Wonwoo | Fukuzumi, Shunichi
Photocatalytic oxygenation of hexamethylbenzene occurs under visible-light irradiation of an O₂-saturated acetonitrile solution containing a cobalt porphyrin complex Coᴵᴵ(TPP) (TPP²– = tetraphenylporphyrin dianion), water, and triflic acid (HOTf) via a one-photon–two-electron process, affording pentamethylbenzyl alcohol and hydrogen peroxide as products with a turnover number of >6000; in this reaction, H₂O and O₂ were used as an oxygen source and a two-electron oxidant, respectively. The photocatalytic mechanism was clarified by means of electron paramagnetic resonance, time-resolved fluorescence, and transient absorption measurements as well as ¹⁸O-labeling experiments with H₂¹⁸O and ¹⁸O₂. To the best of our knowledge, we report the first example of efficient photocatalytic oxygenation of an organic substrate by a metal complex using H₂O as an oxygen source and O₂ as a two-electron oxidant.
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