Cerium‐Complex‐Catalyzed Oxidation of Arylmethanols under Atmospheric Pressure of Dioxygen and Its Mechanism through a Side‐On μ‐Peroxo Dicerium(IV) Complex |
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| Authors: | Mitali Paul Satoru Shirase Dr Yuma Morimoto Dr Laurent Mathey Dr Balasubramanian Murugesapandian Dr Shinji Tanaka Prof?Dr Shinobu Itoh Prof?Dr Hayato Tsurugi Prof?Dr Kazushi Mashima |
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| Institution: | 1. Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan;2. Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan |
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| Abstract: | A new CeIV complex Ce{NH(CH2CH2N=CHC6H2‐3,5‐(tBu)2‐2‐O)2}(NO3)2] ( 1 ), bearing a dianionic pentadentate ligand with an N3O2 donor set, has been prepared by treating (NH4)2Ce(NO3)6 with the sodium salt of ligand L1 . Complex 1 in the presence of TEMPO and 4 Å molecular sieves (MS4 A) has been found to serve as a catalyst for the oxidation of arylmethanols using dioxygen as an oxidant. We propose an oxidation mechanism based on the isolation and reactivity study of a trivalent cerium complex Ce{NH(CH2CH2N=CHC6H2‐3,5‐(tBu)2‐2‐O)2}(NO3)(THF)] ( 2 ), its side‐on μ‐O2 adduct Ce{NH(CH2CH2N=CHC6H2‐3,5‐(tBu)2‐2‐O)2}(NO3)]2(μ‐η2:η2‐O2) ( 3 ), and the hydroxo‐bridged CeIV complex Ce{NH(CH2CH2N=CHC6H2‐3,5‐(tBu)2‐2‐O)2}(NO3)]2(μ‐OH)2 ( 4 ) as key intermediates during the catalytic cycle. Complex 2 was synthesized by reduction of 1 with 2,5‐dimethyl‐1,4‐bis(trimethylsilyl)‐1,4‐diazacyclohexadiene. Bubbling O2 into a solution of 2 resulted in formation of the peroxo complex 3 . This provides the first direct evidence for cerium‐catalyzed oxidation of alcohols under an O2 atmosphere. |
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| Keywords: | alcohol oxidation catalysis cerium dioxygen activation Schiff bases |
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