Cobalt Schiff Base Complex-Catalyzed Oxidation of Anilines with tert-Butyl Hydroperoxide

Abstract

Cobalt Schiff base complexes [Co(SB)] catalyze the oxidation of anilines (1) with tert-butyl hydroperoxide to give nitrobenzenes 2 and 4-(tert-butylperoxy)-2,5-cyclohexadien-1-imine derivatives 3 in yield distributions depending on the substitution mode of the substrate. 4-Alkyl- and 4-aryl-2,6-di-tert-butylanilines gave mixtures of 2 and 3, where the higher the bulkiness of the 4-substituent, the higher the yield of 2. With 2,4,6-trimethylaniline, the ratio of oxidations of the nitrogen and C-4 atoms was almost the same; but a hydrolyzed product 5 of the imine was obtained. 2,4,6-Triphenylaniline gave only 2. Nitrobenzene derivatives were also obtained from 2,6-dialkylanilines and 4-substituted anilines. The catalytic activity of Co(SB) depended on the nature of the SB ligand: the formal potential E° and steric factors seem to affect the reaction rate. Kinetic studies showed that the key step may involve hydrogen abstraction from the aniline, presumably by t-BuO• generated from homolytic decomposition of initially formed CoIII(SB)(OO-t-Bu). A precursor of 2 was found to be the nitrosobenzene derivative.

Spectroscopic studies and determination of the formation constants and thermodynamic parameters for a new water-soluble Co(II) Schiff-base complex and some imidazole derivatives

“…The ability of certain cobalt(II) complexes to bind dioxygen reversibly, discovered decades ago [6], is being studied [7]. Cobalt(II) Schiff-base complexes are of considerable importance because of their catalytic activities in the synthesis of important compounds [8][9][10]. Cobalt complexes have also shown their role in the development of charge-transfer (CT) complexes.…”

Nickel(II) and copper(II) complexes of Schiff base ligands containing N4O2 and N4S2 donors with pyrrole terminal binding groups: Synthesis, characterization, X-ray structures, DFT and electrochemical studies

“…Schiff base ligands and their complexes have been studied extensively with the aim of shedding light on various aspects of catalytic activity [1][2][3][4][5], magnetic, spectroscopic and anticancer properties [6][7][8][9][10][11] as well as the role of metal ions in biological systems [12][13][14]. The active sites of many metalloenzymes contain nickel and copper, and the transition metals play important roles in controlling the catalytic function [15][16][17][18].…”

“…Herein, we report the synthesis and characterization of copper(II) and nickel(II) complexes of the new ligands H 2 L 1 , H 2 L 2 , H 2 L 3 and H 2 L 4 (Scheme 2) which are structurally related to those in Scheme 1 [34] but with different donor sets of atoms, N 4 (4), respectively. We report the crystal structures of NiL 3 and CuL 2 and discuss the effects of different donor atom type, chelate size and the nature of the terminal binding groups on the coordination chemistry of the ligands.…”

“…In each case the precipitate was filtered and recrystallized from CH3 CH 2 OH/CH 2 Cl 2 for NiL 1 , NiL 2 , NiL 3 , CuL 1 , CuL 2 and CuL 3 and from THF/(C 2 H 5 ) 2 O for NiL 4 and CuL 4 . 2.4.3.1.…”

Solvent-free oxidation of cumene by molecular oxygen catalyzed by cobalt salen-type complexes

“…1) [8,9] is a tetradentate, planar Schiff's base complex which is classified as an oxygen carrier [10]. It has been used as a catalyst for the preparative oxygenation of phenols [11][12][13], indoles [14,15], flavonols [16], amines [17,18], anilines [19,20] and other substrates [11,21] with both dioxygen or hydroperoxides as the oxygen source. It is most likely that the ROOH formed initially reacts with the cobalt catalyst to form the intermediate of cobalt alkylperoxy [22].…”