Preparation of 1,2,4,5-tetrasubstituted imidazoles over magnetic core-shell titanium dioxide nanoparticles

Magnetic polyborate nanoparticles as a green and efficient catalyst for one-pot four-component synthesis of highly substituted imidazole derivatives

In this study, magnetic polyborate nanoparticles (MPBNPs) were prepared via a simple procedure from boric acid by using ball-milling and then characterized by various spectroscopic, microscopic and analytical methods including FT-IR, EDX, XRD, FESEM, VSM and TGA analysis. The obtained MPBNPs were further explored, as a green and highly efficient catalyst, in the multi-component synthesis of a wide range of tetra-substituted imidazoles from cascade cyclocondensation as well as in situ air oxidation of benzil or benzoin, aromatic aldehydes, primary amine and ammonium acetate in EtOH, as a green solvent, under reflux conditions. Additionally, environmentally friendly conditions for the preparation of the catalyst by the use of non-toxic reactants, facile procedure and high to excellent yields of the desired products as well as the use of a green solvent are some advantages of this new protocol.

Catalytic application of sulfamic acid-functionalized magnetic Fe3O4 nanoparticles (SA-MNPs) for protection of aromatic carbonyl compounds and alcohols: experimental and theoretical studies

Protection techniques of functional groups within the structure of organic compounds are important synthetic methods against unwanted attacks from various reagents during synthetic sequences. Acetal and thioacetal groups are well known as protective functional groups in organic reactions. In this study, acetalization of carbonyl compounds with diols and dithiols and methoxymethylation of alcohols with formaldehyde dimethyl acetal (FDMA) have been carried out using sulfamic acid-functionalized magnetic Fe3O4 nanoparticles (SA-MNPs) as a heterogeneous solid acid catalyst. Products were characterized by FT-IR and NMR spectroscopies. The structural and electronic properties of some products were computed by quantum mechanical (QM) methods. Depending on the stereochemistry and electronic properties that were obtained by computational results, we have suggested that hyperconjugation plays a key role in the structural properties of 2-phenyl-1,3-dioxolane derivatives, and also the electron transfer between π-electrons of the aromatic ring with the 3d orbital of S-atoms influences the 2-phenyl-1,3-dithiane derivatives' structure.

Fe3O4@nano-cellulose/Cu(ii): a bio-based and magnetically recoverable nano-catalyst for the synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives

Fe₃O₄@nano-cellulose/Cu(ii) as a green bio-based magnetic catalyst was prepared through in situ co-precipitation of Fe²⁺ and Fe³⁺ ions in an aqueous suspension of nano-cellulose. The mentioned magnetically heterogeneous catalyst was characterized by FT-IR, XRD, VSM, FESEM, TEM, XRF, EDS and TGA. In this research, the synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives was developed via a three component reaction of aromatic aldehyde, 2-aminobenzothiazole and ethyl acetoacetate using Fe₃O₄@nano-cellulose/Cu(ii) under solvent-free condition at 80 °C. Some advantages of this protocol are good yields, environmentally benign, easy work-up and moderate reusability of the catalyst. The product structures were confirmed by FT-IR, ¹H NMR, and ¹³C NMR spectra.

Fe₃O₄@nano-cellulose/Cu(ii) as a green bio-based magnetic catalyst are prepared, characterized and applied for synthesis of 4H-pyrimido[2,1-b]benzothiazoles with good to excellent yields.

The recent development of efficient Earth-abundant transition-metal nanocatalysts

Whereas noble metal compounds have long been central in catalysis, Earth-abundant metal-based catalysts have in the same time remained undeveloped. Yet the efficacy of Earth-abundant metal catalysts was already shown at the very beginning of the 20th century with the Fe-catalyzed Haber-Bosch process of ammonia synthesis and later in the Fischer-Tropsch reaction. Nanoscience has revolutionized the world of catalysis since it was observed that very small Au nanoparticles (NPs) and other noble metal NPs are extraordinarily efficient. Therefore the development of Earth-abundant metals NPs is more recent, but it has appeared necessary due to their "greenness". This review highlights catalysis by NPs of Earth-abundant transition metals that include Mn, Fe, Co, Ni, Cu, early transition metals (Ti, V, Cr, Zr, Nb and W) and their nanocomposites with emphasis on basic principles and literature reported during the last 5 years. A very large spectrum of catalytic reactions has been successfully disclosed, and catalysis has been examined for each metal starting with zero-valent metal NPs followed by oxides and other nanocomposites. The last section highlights the catalytic activities of bi- and trimetallic NPs. Indeed this later family is very promising and simultaneously benefits from increased stability, efficiency and selectivity, compared to monometallic NPs, due to synergistic substrate activation.

The recent development of efficient Earth-abundant transition-metal nanocatalysts

This review presents the recent remarkable developments of efficient Earth-abundant transition-metal nanocatalysts.