Department of Chemistry

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Start date: 2020Subject: search.filters.subject.Catalysts

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Now showing 1 - 9 of 9
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    Unveiling the dichotomy between cobalt(ii)-exchanged x and y faujasite zeolites via oxidative carboxylation of alkene to cyclic carbonate
    (ACS, 2025-04) Ray, Saumi
    Cobalt(II)-exchanged X and Y zeolites with varying metal loadings were employed to convert CO2 to cyclic carbonates starting from alkenes. The transformation was carried out using O2 as an oxidant in a mixture of O2 and CO2 under atmospheric pressure, and a maximum yield of 35.7% cyclic carbonate was achieved. Studies revealed a stark difference among both the zeolites, primarily arising from a difference in their ion exchange behaviors. Their catalytic and recyclability properties differed as a result of this variation
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    Synthesis of catalyst using bio-benign precursors and its application in one-pot catalytic synthesis of imidazo[1,2-a ]Pyridines
    (Wiley, 2023-03) Sah, Ajay Kumar
    Development of catalysts using natural feedstock is the need of the current era, and accordingly, we have developed a new ligand N-(2-hydroxynapthylidene)-L-leucienyl-4,6-O-ethylidene-β-D-glucopyranosylamine using natural occurring D-glucose and L-amino acid. It interacts with several bio-relevant metal ions like iron, copper, zinc, etc., but its association with cupric ions is immune to pH (4.2–9.1) change. In-situ copper-catalyzed reactions have been proven to be pivotal in many important organic syntheses, including imidazo[1,2-a]pyridines, which is one of the important precursors of many drug molecules. Catalytic synthesis of imidazo[1,2-a]pyridines requires high catalyst loading, hazardous solvent, high temperature, and long reaction time, which are major drawbacks towards green synthetic methodology. Interestingly, our glycoconjugate-derived cupric complex catalyzes the reactions among aldehydes, 2-aminopyridines, and terminal alkynes under the solvent-free condition to afford one-pot synthesis of imidazo[1,2-a]pyridines and 23 derivatives have been reported in good to excellent yields (53–93 %) using lower reaction time, temperature, and catalyst loading compared to other reports on similar reactions. Hence, our approach enhances the green methodology towards the catalytic synthesis of imidazo[1,2-a]pyridine derivatives.
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    Enantioselective Direct Synthesis of C3-Hydroxyalkylated Pyrrole via an Amine-Catalyzed Aldol/Paal–Knorr Reaction Sequence
    (ACS, 2022-10) Kumar, Indresh
    Creating functionality with chirality at position C3 of pyrrole is challenging. An operationally simple organocatalytic method has been developed to generate functionality with a chiral tertiary/quaternary stereocenter at position C3 of pyrrole. The process proceeds through an amine-catalyzed direct aldol reaction of succinaldehyde with various acceptor carbonyls, followed by a Paal–Knorr reaction with a primary amine in the same pot. A series of chiral C3-hydroxyalkylated N-alkyl/Ar/H-pyrroles have been synthesized for the first time with good to high yields and excellent enantioselectivity.
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    Mechanochemical Ruthenium-Catalyzed Ortho-Alkenylation of N-Heteroaryl Arenes with Alkynes under Ball-Milling Conditions
    (ACS, 2022-04) Kumar, Anil
    The mechanochemical, solvent-free Ru(II)-catalyzed alkenylation of N-heteroaryl arenes with alkynes has been successfully described. A wide spectrum of arenes bearing N-heteroaryl moieties such as imidazo[1,2-a]pyridine, imidazo[1,2-a]pyrimidine, benzo[d]imidazo[2,1-b]thiazole, imidazo[2,1-b]thiazole, 2H-indazole, 1H-indazole, 1H-pyrazole, and 1,2,4-oxadiazol-5(4H)-one as a directing group reacted with various substituted alkynes under ball milling in the presence of [Ru(p-cymene)Cl2]2, affording dialkenylated products in moderate to good yields. The reaction of 2,3-dihydrophthalazine-1,4-dione with 1-phenyl-1-propyne afforded a monoalkenylated product. Similarly, reaction of 2-phenylimidazo[1,2-a]pyridine with aliphatic terminal alkynes produced a monoalkenylated derivative as the major product along with minor amount of dialkenylated product. The developed method exhibited excellent functional group compatibility, broad substrate scope, shorter reaction times, and no external heating. Moreover, the method can be readily scaled-up as demonstrated by gram-scale synthesis of 2-(2,6-bis((E)1-phenylprop-1-en-2-yl)phenyl)imidazo[1,2-a]pyridine.
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    Design and Synthesis of a Palladium(II) Complex of a CNHCNN Pincer-Type N-Heterocyclic Carbene Ligand: Application towards the Oxidative Amidation of Aldehydes with 2-Aminopyridines
    (ACS, 2023-08) Kumar, Anil
    This report describes the synthesis of a [CNHCNN]-pincer-type palladium(II) complex bearing a N-heterocyclic carbene (NHC)-derived pincer CNN ligand. The ligand and palladium pincer complex were characterized with the help of 1H, 13C{1H} NMR, Fourier transform infrared (FTIR) spectroscopy, high-resolution mass spectrometry (HRMS), ultraviolet–visible (UV–vis) spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The coordination mode of the ligand with the palladium was confirmed using single-crystal X-ray diffraction studies. The complex possesses a distorted square planar geometry around the palladium center. The Pd(II) pincer complex was used as a catalyst for the oxidative amidation of aldehydes with 2-aminopyridines. Notably, only 1.0 mol % catalyst loading is required to activate a wide range of substrates under mild reaction conditions. The protocol showed excellent tolerance toward a diverse range of functional groups with good to very good yields (up to 88%) of amidation products. A plausible mechanism of the amidation reaction is proposed on the basis of control experiments.
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    Catalyst-Controlled Regiodivergent Oxidative Annulation of 2-Arylimidazo[1,2-a]pyridines with Cinnamaldehyde Derivatives for Construction of Fused N-Heterocyclic Framework
    (ACS, 2023-09) Kumar, Anil
    Catalyst-dependent regioselective oxidative annulation of 2-arylimidazo[1,2-a]pyridines with cinnamaldehyde derivatives to construct fused N-heterocyclic frameworks has been described. The annulation reaction afforded 5-arylnaphtho[1′,2′:4,5]imidazo[1,2-a]pyridine-6-carbaldehydes in the presence of [RhCp*Cl2]2 as catalyst while 1,7-diarylimidazo[5,1,2-cd]indolizine-6-carbaldehydes were obtained using Pd(OAc)2 as catalyst. The reaction produced annulated products in good yields and exhibited broad substrate scope and excellent functional group tolerance. The method provides two different isomeric annulated products bearing an aldehyde functionality which can be elaborated into an array of functionalities leading to valuable compounds.
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    Rational Design of Covalent Cobaloxime–Covalent Organic Framework Hybrids for Enhanced Photocatalytic Hydrogen Evolution
    (ACS, 2020-06-20) Banerjee, Tanmay
    Covalent organic frameworks (COFs) display a unique combination of chemical tunability, structural diversity, high porosity, nanoscale regularity, and thermal stability. Recent efforts are directed at using such frameworks as tunable scaffolds for chemical reactions. In particular, COFs have emerged as viable platforms for mimicking natural photosynthesis. However, there is an indisputable need for efficient, stable, and economical alternatives for the traditional platinum-based cocatalysts for light-driven hydrogen evolution. Here, we present azide-functionalized chloro(pyridine)cobaloxime hydrogen-evolution cocatalysts immobilized on a hydrazone-based COF-42 backbone that show improved and prolonged photocatalytic activity with respect to equivalent physisorbed systems. Advanced solid-state NMR and quantum-chemical methods allow us to elucidate details of the improved photoreactivity and the structural composition of the involved active site. We found that a genuine interaction between the COF backbone and the cobaloxime facilitates recoordination of the cocatalyst during the photoreaction, thereby improving the reactivity and hindering degradation of the catalyst. The excellent stability and prolonged reactivity make the herein reported cobaloxime-tethered COF materials promising hydrogen evolution catalysts for future solar fuel technologies.
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    Design and Syntheses of Palladium Complexes of NNN/CNN Pincer Ligands: Catalyst for Cross Dehydrogenative Coupling Reaction of Heteroarenes
    (ACS, 2020) Kumar, Anil
    This report describes simple syntheses of a new class of palladium(II) pincer complexes having NNN and CNN coordination modes. The new complexes were fully characterized with the help of 1H and 13C{1H} NMR, HRMS, and IR spectroscopy. The structure and bonding modes of complexes were further authenticated with the help of single-crystal X-ray diffraction. Thermally robust and moisture-/air-insensitive palladium pincer complexes C1–C4 have been used as catalysts for cross dehydrogenative coupling (CDC) reactions of two heteroarenes and found to be very efficient. The catalyst was successful in activating the C–H bond of a variety of heteroarenes, including benzimidazole, imidazole, benzothiazole, imidazopyridine, thiophene, and furan, with only 1.0 mol % of catalyst, achieving excellent yields of the coupled products. The catalyst showed excellent tolerance toward functional groups such as CHO, COMe, COOMe, COOEt, CONHPh, Me, CN, Br, and Cl. Further, the catalyst is reusable up to four reaction cycles with only a minor loss in its efficiency. The mechanism of the CDC reaction was investigated through control experiments, and it has been suggested that a palladium acetate analogue of the NNN pincer ligand (C5) is the active catalyst.
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    Rhodium(III)-Catalyzed Dehydrogenative Annulation and Spirocyclization of 2-Arylindoles and 2-(1H-Pyrazol-1-yl)-1H-indoles with Maleimides: A Facile Access to Isogranulatimide Alkaloid Analogues
    (ACS, 2021) Kumar, Anil; Kumar, Dalip
    A Rh(III)-catalyzed dehydrogenative annulation and spirocyclization of 2-arylindoles and 2-(1H-pyrazol-1-yl)-1H-indole with maleimides is described. The cascade protocol provided highly functionalized benzo[a]pyrrolo[3,4-c]carbazole-1,3(2H,8H)-diones and spiro[isoindolo[2,1-a]indole-6,3′-pyrrolidine]-2′,5′-diones in good to excellent. The developed reaction methodology exhibited broad substrate scope with good functional group tolerance and is operationally simple and scalable. Photophysical properties of the annulated products were investigated. The annulated product of 2-(1H-pyrazol-1-yl)-1H-indole showed high absorption and emission values with a large red-shift as compared to that of 2-phenylindole.