Search Results (6)

A new binuclear Gd(III) complex, [Gd₂(L)₆(Phen)₂]·4H₂O, was synthesized via the reaction of gadolinium(III) nitrate hexahydrate, 4-acetylphenoxyacetic acid (HL), NaOH, and 1,10-phenanthroline (Phen) in a solution of water–ethanol (v:v = 1:1). The Gd(III) complex was characterized using IR, UV–vis, TG-DSC, fluorescence, and single-crystal X-ray diffraction analyses. The results showed that the Gd(III) complex crystallizes in the triclinic system, space group P-1, and each Gd(III) ion was coordinated with two nitrogen atoms (N1, N2, or N1a, and N2a) from two Phen ligands and seven oxygen atoms (O1, O2, O7a, O9, O8, O8a, O10a, or O1a, O2a, O7, O8, O8a, O9a, and O10) from six L ligands, respectively, forming a nine-coordinated coordination mode. The Gd(III) complex molecules formed a one-dimensional chained and three-dimensional network structure via benzenering π-π stacking. The Hirschfeld surface analysis and the calculations of the electron density distributions of the frontier molecular orbitals of the Gd(III) complex were performed. The catalytic activities of the photocatalytic CO₂ reduction and benzyl alcohol oxidation using the Gd(III) complex as a catalyst were performed. The results of the photocatalytic CO₂ reduction showed that the yield and the selectivity of CO reached 41.5 μmol/g and more than 99% after four hours, respectively. The results of the benzyl alcohol oxidation showed that the yield of benzaldehyde was 45.7% at 120 °C with THF as the solvent under 0.5 MPa O₂ within 2 h. Full article

The copper-catalyzed cycloaddition of alkynes and azides (CuAAC) to give the corresponding 1,4-disubstituted-1,2,3-triazoles is the most successful and leading reaction within the click chemistry regime. Its heterogenization stands out as the innovative strategy to solve its environmental concerns and toxicity issue. In this report, magnetically retrievable activated carbon produced from biomass Persea Americana Nuts was loaded with a catalytically active copper(I) catalyst, resulting into a heterogeneous nanocatalyst, namely Cu-Fe₃O₄-PAC. This new compound was fully characterized using several techniques such as Powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray diffraction (EDX), Brunauer–Emmett–Teller (BET) analysis, and Raman spectroscopy. Cu-Fe₃O₄-PAC catalyzed the cycloaddition of a variety of substituted terminal alkynes and organic azides in water at room temperature with excellent yields and in a regioselective manner. The hot filtration test demonstrated that no significant leaching of catalytically active copper particles took place during the CuAAC process, a feature that supports the stability of Cu-Fe₃O₄-PAC and its heterogeneous action way. Cu-Fe₃O₄-PAC was magnetically separable by applying an external magnetic field and was recyclable up to five runs, with only an 8% decline in its activity after the 5th catalytic test. The hot filtration experiment heavily suggested that the present catalytic system would proceed in a heterogeneous manner in CuAAC. The electronic characteristics, nature of the intermediate complexes, and type of ligand-to-copper bonding interactions were studied by using quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) calculations, which enabled the confirmation of the proposed binuclear mechanism. Full article

Elaboration of a convenient route towards donor-substituted pyrazoles from heteropropargyl precursors is challenging due to a number of thermodynamically favorable side reactions (e.g., acetylene–allene isomerization and Glaser homocoupling). In this work, Sonogashira cross-coupling conditions of 4-tert-butylphenyl propargyl ether with benzoyl chloride followed by tandem Michael addition/cyclocondensation with hydrazine into 3,5-disubstituted pyrazole (kinetic control), as well as cycloisomerization conditions of ketoacetylene intermediate into 2,5-disubstituted furan (thermodynamic control), were established through a variation of the catalyst loading, solvent polarity, excess of triethylamine, and time of reaction. During the optimization of process parameters, a number of by-products represented by a monophosphine binuclear complex (PPh₃PdI₂)₂ with two bridging iodine atoms and diyne were identified and isolated in the pure form. The quantum-chemical calculations and solution-state ¹H/¹³C NMR spectroscopy suggested that the 5(3)-(4-tert-butylphenyloxy)methoxy-3(5)-phenyl-1H-pyrazole exists in the tautomeric equilibrium in a polar methanol solvent and that individual tautomers could be characterized in case aprotic solvents employed. The pyrazole features a unique tetramer motif in the crystal phase formed by alternating 3(5)-phenyl-1H-pyrazole tautomers, which was stabilized by N–H···N bonds and stacking interactions of pyrazole rings, whereas pyrazole dimers were identified in the gas phase. Full article

Inspired by the advantages of bi-atom catalysts and recent exciting progresses of nanozymes, by means of density functional theory (DFT) computations, we explored the potential of metal dimers embedded in phthalocyanine monolayers (M₂-Pc), which mimics the binuclear centers of methane monooxygenase, as catalysts for methane conversion using H₂O₂ as an oxidant. In total, 26 transition metal (from group IB to VIIIB) and four main group metal (M = Al, Ga, Sn and Bi) dimers were considered, and two methane conversion routes, namely *O-assisted and *OH-assisted mechanisms were systematically studied. The results show that methane conversion proceeds via an *OH-assisted mechanism on the Ti₂-Pc, Zr₂-Pc and Ta₂-Pc, a combination of *O- and *OH-assisted mechanism on the surface of Sc₂-Pc, respectively. Our theoretical work may provide impetus to developing new catalysts for methane conversion and help stimulate further studies on metal dimer catalysts for other catalytic reactions. Full article

Exploration of efficient catalysts is a priority for the electrochemical nitrogen reduction reaction (NRR) in order to receive a high product yield rate and faradaic efficiency of NH₃, under ambient conditions. In the present contribution, the binding free energy of N₂, NNH, and NH₂ were used as descriptors to screen the potential NRR electrocatalyst among different single or binuclear transition metal atoms on N-doped nanoporous graphene. Results showed that the binuclear Mo catalyst might exhibit the highest catalytic activity. Further free energy profiles confirmed that binuclear Mo catalysts possess the lowest potential determining step (hydrogenation of NH₂* to NH₃). The improved activities could be ascribed to a down-shift of the density of states for Mo atoms. This investigation could contribute to the design of a highly active NRR electrocatalyst. Full article

Chiral alkyl aryl sulfoxides were obtained by molybdenum-catalyzed oxidation of alkyl aryl sulfides with hydrogen peroxide as oxidant in mild conditions with high yields and moderate enantioselectivities. The asymmetry is generated by the use of imidazolium-based dicarboxylic compounds, HL^R. The in-situ-generated catalyst, a mixture of aqueous [Mo(O)(O₂)₂(H₂O)_n] with HL^R as chirality inductors, in the presence of [PPh₄]Br, was identified as the anionic binuclear complex [PPh₄]{[Mo(O)(O₂)₂(H₂O)]₂(μ-L^R)}, according to spectroscopic data and Density Functional Theory (DFT) calculations. A nonclassical hydrogen bond between one C–H bond of the alkyl R group of coordinated (L^R)⁻ and one oxygen atom of the peroxido ligand was identified as the interaction responsible for the asymmetry in the process. Additionally, the step that governs the enantioselectivity was theoretically analyzed by locating the transition states of the oxido-transfer to PhMeS of model complexes [Mo(O)(O₂)₂(H₂O)(κ¹-O-L^R)]⁻ (R = H, ⁱPr). The ∆∆G^≠ is ca. 0 kcal∙mol⁻¹ for R = H, racemic sulfoxide, meanwhile for chiral species the ∆∆G^≠ of ca. 2 kcal∙mol⁻¹ favors the formation of (R)-sulfoxide. Full article