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Room Temperature Chemoselective Deoxygenation of Aromatic Ketones and Aldehydes Promoted by a Tandem Pd/TiO₂ + FeCl₃ Catalyst

Dong, Zhenhua, Yuan, Jinwei, Xiao, Yongmei, Mao, Pu, Wang, Wentao
Journal of organic chemistry 2018 v.83 no.18 pp. 11067-11073
acetophenones, aldehydes, ambient temperature, catalysts, catalytic activity, chemical reactions, chemical structure, chemoselectivity, ethylbenzene, ferric chloride, gas chromatography-mass spectrometry, hydrogen, leaching, nuclear magnetic resonance spectroscopy, palladium, protocols, reaction mechanisms
A rapid and practical protocol for the chemoselective deoxygenation of various aromatic ketones and aldehydes was described, which used a tandem catalyst composed of heterogeneous Pd/TiO₂ + homogeneous FeCl₃ with the green hydrogen source, polymethylhydrosiloxane (PMHS). The developed catalytic system was robust and scalable, as exemplified by the deoxygenation of acetophenone, which was performed on a gram scale in an atmospheric environment utilizing only 0.4 mol % Pd/TiO₂ + 10 mol % FeCl₃ catalyst to give the corresponding ethylbenzene in 96% yield within 10 min at room temperature. Furthermore, the Pd/TiO₂ catalyst was shown to be recyclable up to three times without an observable decrease in efficiency and it exhibited low metal leaching under the reaction conditions. Insights toward the reaction mechanism of Pd-catalyzed reductive deoxygenation for aromatic ketones and aldehydes were investigated through operando IR, NMR, and GC-MS techniques.