Aerobic Oxidation Reactivity of Well-Defined Cobalt(II) and Cobalt(III) Aminophenol Complexes

Abstract

This paper describes the synthesis and reactivity studies of three cobalt complexes bearing aminophenol-derived ligands without nitrogen substitution: 2), and Co III ( tBu2 AP) 3 (3), where tBu2 APH = 2-amino-4,6-di-tert-butylphenol, tBu2 AP = 2amino-4,6-di-tert-butylphenolate, and μ-tBu2 BAP = bridging 2amido-4,6-di-tert-butylphenolate. Stoichiometric reactivity studies of these well-defined complexes demonstrate the catalytic competency of both cobalt(II) and cobalt(III) complexes in the aerobic oxidative cyclization of tBu2 APH with tert-butylisonitrile. Reactions with O 2 reveal the aerobic oxidation of the cobalt(II) complex 1 to generate the cobalt(III) species 2 and 3. UV−visible time-course studies and electron paramagnetic resonance spectroscopy indicate that this oxidation proceeds through a ligand-based radical intermediate. These studies represent the first example of well-defined cobalt aminophenol complexes that participate in catalytic aerobic oxidation reactions and highlight a key role for a ligand radical in the oxidation sequence.

ZnO–TiO2 Nanoparticles Coated by the Dioxomolybdenum (VI) bis-Schiff Base Complex for Catalytic Oxidation of Sulfides

“…However, the effect of ZnO nanoparticles on the oxidation of sulfides was not significant compared to that of the free MoO 2 L 2 catalyst (the homogeneous catalyst) as ZnO lowers the redox activity. ZnO could be considered chemically inert in the redox reaction in such oxidation systems . The MoO 2 2+ ion in MoO 2 OL 2 and MoO 2 L 2 @ZnO–TiO 2 assigned high catalytic reactivity toward the sulfide oxidation (MePhS and Ph 2 S) by H 2 O 2 due to the strong electronegative and Lewis acid character of high valent cis -OMo 6+ O ion modifying the oxygen-transfer pathway. , …”

“…ZnO could be considered chemically inert in the redox reaction in such oxidation systems. 53 The MoO 2 2+ ion in MoO 2 OL 2 and MoO 2 L 2 @ZnO−TiO 2 assigned high catalytic reactivity toward the sulfide oxidation (MePhS and Ph 2 S) by H 2 O 2 due to the strong electronegative and Lewis acid character of high valent cis-O�Mo 6+ �O ion modifying the oxygen-transfer pathway. 54,55 3.3.3.…”

Understanding the Exchange Interaction between Paramagnetic Metal Ions and Radical Ligands: DFT and Ab Initio Study on Semiquinonato Cu(II) Complexes

“…For the copper complexes with catecholate ligands, which are an intermediate in the catalytic oxidation of catechols [ 17 , 18 ], the formation of semiquinonato copper complexes is a crucial step. These natural mechanisms inspired the design of catalytic systems with redox-active/radical ligands, including semiquinones [ 14 , 19 , 20 , 21 , 22 ].…”

Syntheses, characterizations and catalytic properties of three zinc complexes and one lithium compound chelated by β-diketiminate ligands

“…23,24 Recently, they were employed in the hydrosilylation of N-heterocycles 25,26 and aminophenol oxidation. 27,28 The excellent catalytic performance, together with the advantages of low price, easy availability and nontoxicity, enables the chemistry of zinc compounds to be a focus of scientific research.…”