Nanocomposite‐based inorganic‐organocatalyst Cu(II) complex and SiO₂‐ and Fe₃O₄ nanoparticles as low‐cost and efficient catalysts for aniline and 2‐aminopyridine oxidation

Abstract

Bis‐imino Cu(II) complex (CuLAn2), in which the imine ligand (HLAn) acts as a bidentate chelating ligand, was synthesized. The catalytic potential of the inorganic‐organocatalyst was studied homogeneously and heterogeneously in the oxidation of aniline and 2‐aminopyridine by H2O2 or tBuOOH. Two heterogeneous inorganic‐organocatalysts, CuLAn2@Fe3O4 and CuLAn2@SiO2@Fe3O4, were synthesized by the successful immobilization of CuLAn2 on the Fe3O4 surface and the composited Fe3O4 with SiO2, respectively. The heterogeneous structure of those inorganic‐organocatalysts was confirmed using Fourier‐transform infrared, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, transmission electron microscopy, and magnetic properties. The adsorption–desorption isotherms revealed respectable adsorption parameters (SBET, Vp, and rp). All catalysts exhibited high potential in the oxidation of aniline (with phenylhydroxylamine as the main product) and good potential in the oxidation of 2‐aminopyridine, in the first attempt (with 2‐nitropyridine‐N‐oxide and 2‐nitrosopyridine‐N‐oxide as main products), at room temperature. Acetonitrile was found to be the best solvent compared to ethanol, dimethyl sulfoxide, chloroform, and water. The homogeneous catalyst exhibited reusability for three times. The heterogeneous catalysts, CuLAn2@Fe3O4 and CuLAn2@SiO2@Fe3O4, were active for five and seven times, respectively. A mechanism was proposed within electron and oxygen transfer processes.

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

“…These findings support our results that ZnO–TiO 2 nanoparticles do not enhance the catalytic efficacy of the MoO 2 L 2 catalyst, likely due to their lower redox reactivity. Therefore, we are motivated further to explore immobilization of our MoO 2 L 2 catalyst on various other nanoparticles, e.g., Fe 3 O 4 , Fe 3 O 4 –TiO 2 , or Fe 3 O 4 –SiO 2 , as developed previously by our working group for Cu–Schiff base complexes Table S3. ,, …”

“…In the visible area, a broad band was observed at 434 nm, which is due to the ligand charge transfer, i.e., L-ct, for HL interpreting the electron charging through the whole ligand molecule. 38 In a similar manner, the diluted solution of MoO 2 L 2 represented an observed band at 440 nm referring to the charge transfer from the coordinated ligand to cis-MoO 2 2+ ion, i.e., L-mct (Figure S6).…”

“…Synthesis of HL and MoO 2 L 2 . Based on the previously reported procedure for the synthesis of similar Schiff base derivatives, 38 our desired 4-hydroxyiminophenol ligand (HL) was synthesized by direct condensation of 4-hydroxybenzaldehyde with 2aminophenol in methanol and provided 94% yield as a yellow solid. The respective complex MoO 2 L 2 was prepared by coordinating ligand (HL) with cis-MoO 2 2+ ion in a 2:1 molar ratio using the water/ethanol mixture providing 74% yield.…”

“…3 O 4 , Fe 3 O 4 − TiO 2 , or Fe 3 O 4 −SiO 2 , as developed previously by our working group for Cu−Schiff base complexes TableS3 6,7,38. Scheme 2.…”

Immobilized transition metal (II) bis–imine chelate on ZnO@TiO2 nanoparticles as sufficient catalysts for alcohol oxidation and for α,β‐cinnamic acid decarboxylative bromination

“…Directly, in methanol, 4-hydroxybenzadlehyde was condensed with 2-aminophenol to give HL, as reported for various similar derivatives. 46 HL was coordinated with the Cu 2+ ion in a water-ethanol mixture in 2:1 equivalent amounts, respectively, to form CuL 2 , in which HL behaved as a monobasic bidentate pincer chelating ligand, as shown in Scheme 1. HL and CuL 2 gave respectable yields of 94% and 75% with 0.18 and 0.12 g, respectively.…”