Development
of nanocatalysts for a chemical reaction with ideal
values in green chemistry metrics is considered to be a challenging
task to achieve sustainable chemistry. With this aim, we herein report
a hierarchically porous sphere-like copper oxide (HS-CuO) nanocatalyst
to afford benzofuranamine and dihydro-benzofuranamine isomers with
anomalous selectivity via O-annulated A3 coupling among salicylaldehydes,
secondary amines, and alkynes followed by cycloisomerization in the
absence of base and solvent. The anomalous selectivity of benzofuran
isomers was dependent on the electronic factors of substituents on
salicylaldehyde and the type of secondary amines used in the coupling
reaction. The HS-CuO nanocatalyst was recycled five times without
significant loss in its catalytic activity. The present method offers
several advantages over the reported methods such as wide substrate
scope with anomalous selectivity in the products, high yields in short
reaction time, avoided the usage of extra reagents such as additives/bases,
and showed ideal values of green chemistry metrics such as low E-factor
and process mass intensity (PMI), high atom economy (AE), reaction
mass efficiency (RME), and carbon efficiency (CE).
CuI/CSP
nanocomposites were found to be efficient and recyclable
nanocatalysts for one-pot synthesis of aminoindolizines via A3 coupling
reaction in the presence of ethylene glycol (EG) as a recyclable solvent.
In contrast, chalcones were isolated when the reaction was performed
in the presence of secondary amines such as piperidine, 3-methylpiperidine,
pyrrolidine, and piperazine under solvent free conditions. The CuI/CSP
was recycled for five times without significant loss in its catalytic
activity. The anomalous selectivity in the formation of aminoindolizines
and chalcones was dependent on solvents and secondary amines used
for the reaction. The present methodology is facile and follows green
principles with higher atom economy (94%) and smaller E-factor (0.06).
Palladium nanoparticles were impregnated on porous silica shell carbon‐coated cobalt nanoparticles, resulting in a magnetically retrievable material that was evaluated in the catalytic hydrogenation of nitroarenes, alkenes and alkynes. The prepared material was characterized by HR‐XRD, HR‐TEM, elemental mapping EDX, ICP‐OES and XPS analyses, revealing highly dispersed palladium nanoparticles within the porous platform that could account for the high activity observed. Mild reaction conditions, easy retrievability of the catalyst with the aid of an external magnet, recycling in four runs with a total leaching of 19 ppm (1.2 % of the initially employed Pd amount), and high stability makes this material attractive for sustainable and environmentally benign applications.
Recently, the development of hybrid nanocatalysts involving Earth-abundant transition metals for photosensitization and multicomponent reactions in industry and academia has been a matter of intense study. Such hybridized catalytic systems minimize the production cost and act as a bridged system by diversifying the application in different areas. In the present study, copper indium ethylxanthate was used as a versatile precursor for the synthesis of colloidal chalcopyrite phase copper indium sulfide nanoparticles (C-CIS NPs) in photosensitization of graphene quantum dots and reusable powdered wurzite phased copper indium sulfide nanoparticles (PW-CIS500 NPs) for selective and efficient single-pot sustainable synthesis of substituted imidazopyridines via an A3 coupling strategy of an aldehyde, amine, and alkyne. The material was characterized by various spectroscopic techniques viz. high-resolution transmission electron microscopy, powder X-ray diffraction, field emission scanning electron microscopy, elemental mapping studies, UV visible spectroscopy, photoluminescence, Xray photoelectron spectroscopy, Brunauer−Emmett−Teller analysis, inductively coupled plasma optical emission spectroscopy/mass spectrometry, etc. Quenching of photoluminescence intensity of colloidal CuInS 2 on anchoring the graphene quantum dots (GQDs) was confirmed by photosensitization of GQDs via efficient charge transfer in the CIS-GQD interface. On the other hand, the PW-CIS500 nanocomposites (NCs) catalyzed A3 coupling strategy demonstrates the high catalytic efficiency for the A3 coupling reaction giving substituted imidazopyridines without losing its activity and could be recycled with a total turnover (TOF) number of >210, good E-factor of 0.13, and high RME of 88%.
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