Cerium(IV)
Carboxylate Photocatalyst for Catalytic
Radical Formation from Carboxylic Acids: Decarboxylative Oxygenation
of Aliphatic Carboxylic Acids and Lactonization of Aromatic Carboxylic
Acids
posted on 2020-03-10, 20:46authored bySatoru Shirase, Sota Tamaki, Koichi Shinohara, Keishi Hirosawa, Hayato Tsurugi, Tetsuya Satoh, Kazushi Mashima
We
found that in situ generated cerium(IV) carboxylate
generated by mixing the precursor Ce(OtBu)4 with the corresponding carboxylic acids served as
efficient photocatalysts for the direct formation of carboxyl radicals
from carboxylic acids under blue light-emitting diodes (blue LEDs)
irradiation and air, resulting in catalytic decarboxylative oxygenation
of aliphatic carboxylic acids to give C–O bond-forming products
such as aldehydes and ketones. Control experiments revealed that hexanuclear
Ce(IV) carboxylate clusters initially formed in the reaction mixture
and the ligand-to-metal charge transfer nature of the Ce(IV) carboxylate
clusters was responsible for the high catalytic performance to transform
the carboxylate ligands to the carboxyl radical. In addition, the
Ce(IV) carboxylate cluster catalyzed direct lactonization of 2-isopropylbenzoic
acid to produce the corresponding peroxy lactone and γ-lactone
via intramolecular 1,5-hydrogen atom transfer (1,5-HAT).