title: Cerium-Complex-Catalyzed Oxidation of Arylmethanols under Atmospheric Pressure of Dioxygen and Its Mechanism through a Side-On μ-Peroxo Dicerium(IV) Complex.
abstract: A new Ce(IV) 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-η(2):η(2)-O2) (3), and the hydroxo-bridged Ce(IV) 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.
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560-8531, Japan.
authors.forename: Mitali
authors.initials: M
authors.lastname: Paul
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560-8531, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Shirase
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka, 565-0871, Japan.
authors.forename: Yuma
authors.initials: Y
authors.lastname: Morimoto
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560-8531, Japan.
authors.forename: Laurent
authors.initials: L
authors.lastname: Mathey
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560-8531, Japan.
authors.forename: Balasubramanian
authors.initials: B
authors.lastname: Murugesapandian
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560-8531, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka, 565-0871, Japan.
authors.forename: Shinobu
authors.initials: S
authors.lastname: Itoh
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560-8531, Japan. mashima@chem.es.osaka-u.ac.jp.
authors.forename: Hayato
authors.initials: H
authors.lastname: Tsurugi
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560-8531, Japan. tsurugi@chem.es.osaka-u.ac.jp.
authors.forename: Kazushi
authors.initials: K
authors.lastname: Mashima
keywords: Schiff bases; alcohol oxidation; catalysis; cerium; dioxygen activation