A recyclable polymer anchored copper(II) catalyst for oxidation reaction of olefins and alcohols with tert-butylhydroperoxide in aqueous medium

Cu(II) and Mn(II) Anchored on Functionalized Mesoporous Silica with Schiff Bases: Effects of Supports and Metal-Ligand Interactions on Catalytic Activity

New series of Cu(II) and Mn(II) complexes with Schiff base ligands derived from 2-furylmethylketone (Met), 2-furaldehyde (Fur), and 2-hydroxyacetopheneone (Hyd) have been synthesized in situ on SBA-15-NH₂, MCM-48-NH₂, and MCM-41-NH₂ functionalized supports. The hybrid materials were characterized by X-ray diffraction, nitrogen adsorption-desorption, SEM and TEM microscopy, TG analysis, and AAS, FTIR, EPR, and XPS spectroscopies. Catalytic performances were tested in oxidation with the hydrogen peroxide of cyclohexene and of different aromatic and aliphatic alcohols (benzyl alcohol, 2-methylpropan-1-ol, and 1-buten-3-ol). The catalytic activity was correlated with the type of mesoporous silica support, ligand, and metal-ligand interactions. The best catalytic activity of all tested hybrid materials was obtained in the oxidation of cyclohexene on SBA-15-NH₂-MetMn as a heterogeneous catalyst. No leaching was evidenced for Cu and Mn complexes, and the Cu catalysts were more stable due to a more covalent interaction of the metallic ions with the immobilized ligands.

Constructing a metal-free 2D covalent organic framework for visible-light-driven photocatalytic reduction of CO2: a sustainable strategy for atmospheric CO2 utilization

A 2D polyimide-linked covalent organic framework (COF) with band gap energy of 2.2 eV is developed as a stable and efficient porous photocatalyst which shows CO2 reduction to formic acid, formaldehyde and methanol.

Selective Styrene Oxidation to Benzaldehyde over Recently Developed Heterogeneous Catalysts

The selective oxidation of styrene under heterogeneous catalyzed conditions delivers environmentally friendly paths for the production of benzaldehyde, an important intermediate for the synthesis of several products. The present review explores heterogeneous catalysts for styrene oxidation using a variety of metal catalysts over the last decade. The use of several classes of supports is discussed, including metal-organic frameworks, zeolites, carbon materials and silicas, among others. The studied catalytic systems propose as most used oxidants tert-butyl hydroperoxide, and hydrogen peroxide and mild reaction conditions. The reaction mechanism proceeds through the generation of an intermediate reactive metal-oxygen species by catalyst-oxidant interactions. Overall, most of the studies highlight the synergetic effects among the metal and support for the activity and selectivity enhancement.

Nickel(II), Copper(II) and Palladium(II) Complexes with Bis-Semicarbazide Hexaazamacrocycles: Redox-Noninnocent Behavior and Catalytic Activity in Oxidation and C-C Coupling Reactions

Nickel(II), copper(II), and palladium(II) complexes ML^H, where M = Ni (1), Cu (2), Pd (3), and ML^OMe, where M = Ni (4), Cu (5), Pd (6), have been prepared by reactions of NiCl₂·6H₂O, Cu(OAc)₂·H₂O, and PdCl₂(MeCN)₂ with 14-membered bis-semicarbazide hexaazamacrocycles H₂L^H and H₂L^OMe in dimethylformamide (DMF). The compounds were characterized by elemental analysis, ESI mass spectrometry, IR, UV-vis, and 1D (¹H, ¹³C) and 2D (¹H-¹H COSY, ¹H-¹H TOCSY, ¹H-¹H NOESY, ¹H-¹³C HSQC, ¹H-¹³C HMBC) NMR spectra (1, 3, 4, and 6), and X-ray diffraction (2, 4-6). The complexes with M^IIN₄ coordination environment have S = 0, 1/2, 0 ground states for Ni, Cu, and Pd, respectively. The electrochemical behavior of 1-6 was investigated in detail. The electronic structures of 1e-oxidized species were studied by EPR, UV-vis-NIR spectroelectrochemistry, and DFT calculations, indicating the redox-noninnocent behavior of the ligands. Compounds 1-6 were tested in the oxidation of styrene and C-C coupling (Henry and Knoevenagel condensations). Compounds 2 and 5 selectively catalyze the microwave-assisted oxidation of neat styrene to benzaldehyde (up to 88% yield), whereas the 1 and 4 catalytic systems afforded up to 99% β-nitroethanol yield with an appreciable diastereoselectivity toward the formation of the anti isomer.

Two-Dimensional Imine-Linked Covalent Organic Frameworks as a Platform for Selective Oxidation of Olefins

Two-dimensional imine-linked covalent organic frameworks with hydroxyl groups, TAPT-DHTA-COF_HX and TAPT-DHTA-COF_DMF, were respectively constructed by the condensation of 1,3,5-tris-(4-aminophenyl)triazine and 2,5-dihydroxyl-terephthalaldehyde under solvothermal and reflux conditions. Both COFs possess excellent thermal stability and a similar eclipsed stacking structure verified by XRD patterns. However, TAPT-DHTA-COF_HX presented a larger surface area (2238 m²/g) and higher crystallinity than TAPT-DHTA-COF_DMF. Significantly, copper ions are efficiently incorporated into the pores of these two COFs via the coordination interaction with hydroxyl groups and imine linkers. The obtained copper-containing COFs (Cu-COF_HX and Cu-COF_DMF) were employed in the selective oxidation of styrene to benzaldehyde. Cu-COF_HX with superior surface area (1886 m²/g) and pore volume (1.11 cm³/g) exhibited excellent catalytic performance and recyclability. This strategy not only provides a convenient approach to design imine-linked 2D COFs with hydroxyl groups, but also develops their novel application for catalysis.