Palaniswamy Suresh

Per-6-amino-β-cyclodextrin as an Efficient Supramolecular Ligand and Host for Cu(I)-Catalyzed N-Arylation of Imidazole with Aryl Bromides

Per-6-amino-beta-cyclodextrin (per-6-ABCD), acting simultaneously as a supramolecular ligand for CuI and host for aryl bromides, catalyzes N-arylation of imidazole with aryl bromides under mild conditions. This simple method proceeds with excellent yield for the coupling of imidazole with various substituted aryl bromides demonstrating good tolerance of other functionalities.

Per-6-amino-β-cyclodextrin as a reusable promoter and chiral host for enantioselective Henry reaction.

A highly efficient enantioselective Henry reaction has been carried out using per-6-ABCD as a supramolecular chiral host and promoter to give the corresponding adduct with high yield (up to 99%) and enantiomeric excess (up to 99%). Per-6-ABCD also promotes the diastereoselective Henry reaction in a syn-selective manner to give the adduct up to 99% yield with 99:1 syn/anti selectivity. The enantiomeric excess of the syn-adduct is 99%. The catalyst is recovered and reused without loss in its activity.

Aerobic homocoupling of arylboronic acids catalysed by copper terephthalate metal–organic frameworks

Copper terephthalate MOF is utilised as an environmentally benign, efficient and reusable heterogeneous catalyst to effect the aerobic homocoupling of arylboronic acids yielding the corresponding symmetrical biphenyls under mild reaction conditions. This method tolerates various substituents present in arylboronic acids such as halogens, cyano and nitro groups. The catalytic performance has been compared with that of other copper based MOFs namely MOF-101, [Cu(pdc)2]NH2Me2, [Cu2(ndc)2ted]n and [Cu(H2L)]n as well as with other copper salt catalysts. Sheldon test confirmed the heterogeneity of the catalyst, which can be reused under optimized conditions with only a minor loss in its activity. A mechanism for the homocoupling reaction is also proposed. The simplicity of catalyst preparation, its stability, substrate selectivity, easy recovery and regeneration designate possible utilization of this catalytic system in a multitude of catalytic reactions and industrial processes.

Per-6-amino-β-cyclodextrin/CuI catalysed cyanation of aryl halides with K4[Fe(CN)6]

Efficient cyanation of aryl halides is achieved using less toxic K4[Fe(CN)6] as the reagent and amino-β-cyclodextrins as supramolecular ligands for CuI. Four different amino cyclodextrins viz. per-6-amino-β-CD, per-6-methylamino-β-CD, per-6-butyl-amino-β-CD and mono-6-amino-β-CD are prepared and studied. Aryl and heteroaryl nitriles are obtained in good to excellent yield for even bromo derivatives of flavone and 2-aminopyrans. This system uses catalytic amounts (10 mol%) of both copper iodide and per-6-amino-β-cyclodextrin. Easy separation, the absence of nitrogen atmosphere and excellent yield are the other significant outcomes of this protocol.

Palladium nanoparticles embedded on thiourea-modified chitosan: a green and sustainable heterogeneous catalyst for the Suzuki reaction in water

Palladium nanoparticles (PdNPs) embedded on thiourea modified chitosan (TMC) are prepared in spherical and cubical shapes by intercalating palladium(II) acetate in TMC, a natural bio-polymer, and a subsequent reduction using ellagic acid (EA) as a natural and green reducing source in water. The formation of palladium nanoparticles in water is monitored by UV-Vis, spectroscopy and the PdNPs/TMC solid matrix are characterized by FT-IR, powder XRD and HR-TEM. The amount of palladium entrapped on TMC is measured by ICP-OES analysis, and it is found to be 0.00103 mol%. The synthesised PdNPs/TMC reported for the first time, were employed as heterogeneous catalysts for Suzuki cross-coupling reactions of aryl iodide/bromide with various substituted aryl boronic acids in water and showed high catalytic activity under mild reaction conditions. Easy separation, the absence of an inert atmosphere and good to excellent yields are the other significant outcomes of this protocol. In addition, the reactions also work well with various heterocyclic boronic acids. Also the catalyst can be easily recovered and reused for at least five runs without loss in its activity.

Framework-Copper-Catalyzed C−N Cross-Coupling of Arylboronic Acids with Imidazole: Convenient and Ligand-Free Synthesis of N-Arylimidazoles

A convenient and environmentally benign synthesis of N‐arylimidazoles has been demonstrated by a straightforward reaction catalyzed by the unsaturated coordination sites of Cu in the copper terephthalate metal–organic framework (Cu(tpa)‐MOF). A series of N‐arylimidazoles has been synthesized in excellent yields by the C−N cross‐coupling reaction of arylboronic acids and imidazoles catalyzed by the Cu(tpa)‐MOF using ethanol as a benign solvent. The present ligand‐free catalytic system proceeds smoothly under mild conditions, avoids stoichiometric Cu reagents, tolerates many functional groups, has a wide substrate scope, and is feasible with other nitrogen heterocycles. The stability and heterogeneity of the catalyst is evidenced by the results of a heterogeneity test, and the catalyst can be reused several times without a loss of activity. The easy preparation of the catalyst, its stability, recovery by simple filtration, and reusability reveal Cu(tpa) MOF as a versatile catalyst for academic and industrial applications.

Copper-catalyzed oxidative coupling of arylboronic acids with aryl carboxylic acids: Cu3(BTC)2 MOF as a sustainable catalyst to access aryl esters

A convenient and sustainable method is demonstrated for the oxidative coupling of arylboronic acids with aryl carboxylic acids via C–O cross-coupling reaction catalyzed by the unsaturated coordination sites of copper present in the Cu3(BTC)2 MOF. Using air as an environment-friendly oxidant, the as-prepared Cu3(BTC)2 was employed in a MOF-based catalysis reaction with high efficiency and high chemoselectivity without the use of any external oxidants, ligands or additives. The present methodology avoids stoichiometric reagents and special reaction conditions, and shows excellent functional group tolerance with decent to excellent yields of aryl esters. The catalyst was found to exhibit high stability and reusability, without loss in activity even after several cycles, which was evident from the FT-IR, PXRD, and SEM characterizations of the reused catalyst.

The electrochemical 4-chlorophenol sensing properties of a plasma-treated multilayer graphene modified photolithography patterned platinum electrode

The present work describes the electrochemical 4-chlorophenol (4-CP) sensing properties of multilayer graphene samples (MLG). In order to enhance the presence of oxygen functional groups and to increase the edge plane defects, oxygen plasma treatment is adopted. Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) characterizations are used to investigate the effect of plasma treatment on MLG. Compared to pristine MLG, the oxygen plasma treated one shows increased oxidation current towards 4-CP. The sensor data exhibit high sensitivity and stability with high anti-interference property in the presence of other phenolic compounds including phenol, bisphenol, 2,3-chlorophenol, 2,3,4-nitrophenol and inorganic ions.

Brønsted acidic reduced graphene oxide as a sustainable carbocatalyst: a selective method for the synthesis of C-2-substituted benzimidazole

Bronsted acidic reduced graphene acts as an efficient and sustainable carbocatalyst for the selective synthesis of C-2-substituted benzimidazoles under ambient conditions. A massive influx of sulphonic acid group on reduced graphene oxide surface gives graphene sulfonic acid (G-SO3H), which acts as a Bronsted acidic catalyst for the synthesis of a series of benzimidazoles under mild conditions. The present methodology is a revamp of the benzimidazole synthesis with broad functional group tolerance in shorter time. G-SO3H provides an operationally simple, metal-free condition and is amenable to gram-scale production. Pyridine adsorption studies prove the catalytically responsible Bronsted acidity of the catalyst. The catalyst is highly stable for several cycles without any loss of activity, which is evidenced by the FT-IR, PXRD and TEM characterization of the reused catalyst.