Papu Biswas

A mononuclear copper(II) complex immobilized in mesoporous silica: an efficient heterogeneous catalyst for the aerobic oxidation of benzylic alcohols

The diamide ligand 2,6-bis[(N-phenyl)amido]-4-methylphenol (HL) has been used to synthesize a mononuclear copper(II) complex, [CuL2(DMF)2] (1). The X-ray crystal structure of this complex reveals that the copper(II) center is coordinated to the two phenoxides and two amide carbonyl oxygens of the HL ligand and additionally to the amide carbonyl oxygens of two dimethylformamide molecules. This complex was also characterized using UV-Vis and EPR spectroscopy, along with thermal and electrochemical analysis. Complex 1 was then immobilized in a 2-D mesoporous silica matrix. This immobilized complex, 1a, has been characterized using UV-Vis and FT-IR spectroscopy, as well as small angle X-ray diffraction, N2 sorption and TEM. The immobilized complex was found to heterogeneously catalyze the aerobic oxidation of benzylic alcohols to the corresponding aldehydes in the presence of TEMPO, with high turnover numbers and good recyclability for up to four cycles.

3,6-Di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz) mediated metal-free mild oxidation of thiols to disulfides in aqueous medium

Thiols are efficiently oxidized to disulfides (RSSR) in the presence of 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz) in aqueous medium, as well as in the absence of a solvent under mild and metal-free conditions. A broad range of alkyl, aryl and heterocyclic symmetrical disulfides can be easily obtained in almost quantitative yields. The X-ray single crystal structure of 2-aminocyclopent-1-ene-1-carbothioic dithioperoxyanhydride (disulfide obtained from 2-aminocyclopentene-1-dithiocarboxylic acid, ACDA) is reported. The reaction mechanism has been studied thoroughly. It is shown that the reaction proceeds through the formation of an organosulphur radical. Pytz interacts with thiol to accept one electron and produces an organosulphur radical. Pytz ultimately accepts two electrons to form H2pytz and is capable of oxidizing 2 equivalents of thiols.

Metal free visible light driven oxidation of alcohols to carbonyl derivatives using 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz) as catalyst

3,6-Di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz) catalyzed oxidation of alcohols to the corresponding carbonyl compounds under visible light irradiation is described. This reaction occurs smoothly at room temperature and shows good tolerance of functional groups. It provides an alternative approach for the synthesis of alkyl and aryl aldehydes and ketones.

An abiotic receptor and its Cu(II) complex as selective 'turn-off' chemosensor for bisulfate ion.

The ligand 2,6-bis[(N-phenyl)amido]-4-methylphenol (receptor 1) and its copper(II) complex (receptor 2) having amide moiety have been designed and synthesized for selective sensing of anions. The anion recognition behavior of the receptor 1 and its copper complex (receptor 2) has been studied in acetonitrile. Quenching of fluorescence was observed for both receptors in presence of HSO4(-) anion whereas other physiologically and environmentally important anions such as F(-), Cl(-), Br(-), I(-), CN(-), OAc(-), HCO₃(-), H₂PO₄(-), NO₃(-), NO₂(-) and SO₄(2-) show fluorescence enhancement behavior. The sensing protocol has been studied both spectrophotometrically as well as spectrofluorometrically. Fluorescence quenching is suggested to proceed via both dynamic and static processes.

3,6-Di(pyridin-2-yl)-1,2,4,5-tetrazine capped Pd(0) nanoparticles: a catalyst for copper-free Sonogashira coupling of aryl halides in aqueous medium

3,6-Di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz) capped Pd(0) nanoparticles (TzPdNPs) as a catalyst in the Sonogashira coupling of aryl halides in aqueous medium with diminished homocoupling is reported. The methodology provides a facile route to obtain polyfunctional alkynes under ligand- and copper-free conditions. The procedure is also efficient for aryl chlorides.

Mesoporous silica supported samarium as recyclable heterogeneous catalyst for synthesis of 5-substituted tetrazole and 2-substituted benzothiazole

Synthesis of nitrogen-containing heterocycles such as tetrazoles and benzothiazoles gains immense importance as they are omnipresent structural modules often utilized in pharmaceuticals. In the present study, well ordered MCM-41 type mesoporous silica with large pore (l-MSN) was synthesized and impregnated with samarium nitrate (Sm@l-MSN). Due to high abundance of samarium relative to many catalytically active transition metals (e.g. Ru, Ir, Pt), it may offer an opportunity to develop sustainable catalysts for organic conversions. The synthesized materials were characterized using nitrogen sorption, scanning electron microscopy, energy-dispersive X-ray, elemental mapping and transmission electron microscopy. The catalytic efficiency of the materials was explored for the synthesis of tetrazoles and benzothiazoles, two very important heterocyclic moieties in medicinal chemistry and biology. The catalyst was readily recovered and recycled up to five consecutive runs without noteworthy loss of activity or leaching.