title: Mechanistic insight into aerobic alcohol oxidation using NOx-nitroxide catalysis based on catalyst structure-activity relationships.
abstract: The mechanism of an NOx-assisted, nitroxide(nitroxyl radical)-catalyzed aerobic oxidation of alcohols was investigated using a set of sterically and electronically modified nitroxides (i.e., TEMPO, AZADO (1), 5-F-AZADO (2), 5,7-DiF-AZADO (3), 5-MeO-AZADO (4), 5,7-DiMeO-AZADO (5), oxa-AZADO (6), TsN-AZADO (7), and DiAZADO (8)). The motivation for the present study stemmed from our previous observation that the introduction of an F atom at a remote position from the nitroxyl radical moiety on the azaadamantane nucleus effectively enhanced the catalytic activity under typical NOx-mediated aerobic-oxidation conditions. The kinetic profiles of the azaadamantane-N-oxyl-[AZADO (1)-, 5-F-AZADO (2)-, and 5,7-DiF-AZADO (3)]-catalyzed aerobic oxidations were closely investigated, revealing that AZADO (1) showed a high initial reaction rate compared to 5-F-AZADO (2) and 5,7-DiF-AZADO (3); however, AZADO-catalyzed oxidation exhibited a marked slowdown, resulting in ∼90% conversion, whereas 5-F-AZADO-catalyzed oxidation smoothly reached completion without a marked slowdown. The reasons for the marked slowdown and the role of the fluoro group are discussed. Oxa-AZADO (6), TsN-AZADO (7), and DiAZADO (8) were designed and synthesized to confirm their comparable catalytic efficiency to that of 5-F-AZADO (2), providing supporting evidence for the electronic effect on the catalytic efficiency of the heteroatoms under NOx-assisted aerobic-oxidation conditions.
authors.affiliation: Department of Basic Medicinal Sciences, Graduate School of Pharmaceutical Sciences, Nagoya University , Chikusa, Nagoya 464-8601, Japan.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Shibuya
authors.forename: Shota
authors.initials: S
authors.lastname: Nagasawa
authors.forename: Yuji
authors.initials: Y
authors.lastname: Osada
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Iwabuchi
mesh_terms: D000218:Adamantane / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry; D000438:Alcohols / Q000737:chemistry*; D002384:Catalysis; D003497:Cyclic N-Oxides / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D009589:Nitrogen Oxides / Q000737:chemistry*; D010084:Oxidation-Reduction; D013329:Structure-Activity Relationship
chemical_list: C522607:2-azaadamantane N-oxyl; D000438:Alcohols; D003497:Cyclic N-Oxides; D009589:Nitrogen Oxides; C039900:nitroxyl; D000218:Adamantane