Supported monocationic copper(II) complexes obtained by coordination with dialkylphosphonate groups on styrene–divinylbenzene copolymer as catalysts for oxidation of organic compounds

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.

1-Butanol absorption in poly(styrene-divinylbenzene) ion exchange resins for catalysis

The swelling behaviour of poly(styrene-co-divinylbenzene), P(S-DVB), ion exchange resins in 1-butanol (BuOH) has been studied by means of atomistic classical molecular dynamics simulations (MD). The topological characteristics reported for the resin in the dry state, which exhibited complex internal loops (macropores), were considered for the starting models used to examine the swelling induced by BuOH contents ranging from 10% to 50% w/w. Experimental measurements using a laser diffraction particle size analyzer indicate that swelling causes a volume variation with respect to the dry resin of 21%. According to MD simulations, such a volume increment corresponds to a BuOH absorption of 31-32% w/w, which is in excellent agreement with the indirect experimental estimation (i.e. 31% w/w). Simulations reveal that, independently of the content of BuOH, the density of the swelled resin is higher than that of the dry resin, evidencing that the alcohol provokes important structural changes in the polymeric matrix. Thus, BuOH molecules cause a collapse of the resin macropores when the content of alcohol is ≤20% w/w. In contrast, when the concentration of BuOH is close to the experimental value (∼30% w/w), P(S-DVB) chains remain separated by pores faciliting the access of the reactants to the reaction centers. On the other hand, evaluation of both bonding and non-bonding interactions indicates that the mixing energy is the most important contribution to the absorption of BuOH into the P(S-DVB) resin. Overall, the results displayed in this work represent a starting point for the theoretical study of the catalytic conversion of BuOH into di-n-butyl ether in P(S-DVB) ion exchange resins using sophisticated electronic methods.

Atomistic simulations of the structure of highly crosslinked sulfonated poly(styrene-co-divinylbenzene) ion exchange resins

The microscopic structures of highly crosslinked sulfonated poly(styrene-co-divinylbenzene) resins have been modeled by generating atomistic microstructures using stochastic-like algorithms, which are subsequently relaxed using molecular dynamics. Two different generation algorithms have been tested. The relaxation of the microstructures generated by the first algorithm, which is based on a homogeneous construction of the resin, leads to a significant overestimation of the experimental density as well as to an unsatisfactory description of the porosity. In contrast, the generation approach that combines algorithms for the heterogeneous growing and branching of the chains enables the formation of crosslinks with different topologies. In particular, the intrinsic heterogeneity observed in these resins is efficiently reproduced when the topological loops, which are defined by two or more crosslinks closing a cycle, are present in their microscopic description. Thus, the apparent density, porosity and pore volume estimated using microstructures with these topological loops, called super-crosslinks, are in very good agreement with the experimental results. Although the backbone dihedral angle distribution of the generated and relaxed models is not influenced by the topology, the number and type of crosslinks affect the medium- and long-range atomic disposition of the backbone atoms and the distribution of sulfonic groups. An analysis of the distribution of the local density indicates that super-crosslinks are responsible for the heterogeneous homogenization observed during the MD relaxation. Finally the π-π stacking interactions have been analyzed. Results indicate that those in which the two rings adopt a T-shaped disposition are considerably more abundant as compared to those with the co-facially oriented rings, independently of the resin topology.

Magnetic nanoparticles entrapped in the cross-linked poly(imidazole/imidazolium) immobilized Cu(ii): an effective heterogeneous copper catalyst

Anchoring of copper sulfate in layered poly(imidazole-imidazolium) coated magnetic nanoparticles provided a highly stable, active, reusable, high loading, and green catalyst for the click synthesis of 1,2,3-triazoles via a one-pot cycloaddition of alkyl halide, azide, and alkyne (Cu-A³C).