Europium (symbol Eu, atomic number 63) is a lanthanide rare-earth metal, and europium ion is known as a key element in luminophore development. Although 15 elements exist from lanthanum (La, atomic number 57) to lutetium (Lu, atomic number 71), catalytic applications of these elements in organic transformation are relatively less common than transition metal catalysis. In traditional organic synthesis, several lanthanide-based molecules (e.g., SmI2 and (NH4)2Ce(NO3)5), are widely applied as oxidizing or reducing reagents for stoichiometric usage. Since Eu has two relatively stable oxidation states, Eu(II) and Eu(III), which is due to the half-filled d orbital and exceptional among the various lanthanide elements, we have successfully applied redox cycle of europium (Eu(II)/Eu(III)) to catalytic organic transformation. The aerobic oxidation was efficiently performed with catalytic europium salts and external oxidants. The Eu-catalyzed aerobic oxidation showed wide substrate ranges and good functional group tolerances. In addition, the photoluminescence spectra was applied to follow the oxidation state changes of europium. Since Eu(III) has a significant peaks on PL spectra than Eu(II) salt, the reaction progress could be monitored in situ manner using PL spectra, and it was revealed that either Eu(II) or Eu(III) could initiate the catalytic cycle. The efficient application of the redox cycle of europium to organic transformation opens up the new possibility of catalytic reaction using some lanthanide salts and provides important insight into lanthanide chemistry in organic reactions.

Catalytic application of Eu(II)/Eu(III) redox cycles and photoluminescence tracking

2019 Fall National Meeting

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