Department of Chemistry

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Start date: 2000Subject: search.filters.subject.Catalysts

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Now showing 1 - 10 of 23
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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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    Sustained Solar H2 Evolution from a Thiazolo[5,4-d]thiazole-Bridged Covalent Organic Framework and Nickel-Thiolate Cluster in Water
    (ACS, 2019-06-20) Banerjee, Tanmay
    Solar hydrogen (H2) evolution from water utilizing covalent organic frameworks (COFs) as heterogeneous photosensitizers has gathered significant momentum by virtue of the COFs’ predictive structural design, long-range ordering, tunable porosity, and excellent light-harvesting ability. However, most photocatalytic systems involve rare and expensive platinum as the co-catalyst for water reduction, which appears to be the bottleneck in the development of economical and environmentally benign solar H2 production systems. Herein, we report a simple, efficient, and low-cost all-in-one photocatalytic H2 evolution system composed of a thiazolo[5,4-d]thiazole-linked COF (TpDTz) as the photoabsorber and an earth-abundant, noble-metal-free nickel-thiolate hexameric cluster co-catalyst assembled in situ in water, together with triethanolamine (TEoA) as the sacrificial electron donor. The high crystallinity, porosity, photochemical stability, and light absorption ability of the TpDTz COF enables excellent long-term H2 production over 70 h with a maximum rate of 941 μmol h–1 g–1, turnover number TONNi > 103, and total projected TONNi > 443 until complete catalyst depletion. The high H2 evolution rate and TON, coupled with long-term photocatalytic operation of this hybrid system in water, surpass those of many previously known organic dyes, carbon nitride, and COF-sensitized photocatalytic H2O reduction systems. Furthermore, we gather unique insights into the reaction mechanism, enabled by a specifically designed continuous-flow system for non-invasive, direct H2 production rate monitoring, providing higher accuracy in quantification compared to the existing batch measurement methods. Overall, the results presented here open the door toward the rational design of robust and efficient earth-abundant COF–molecular co-catalyst hybrid systems for sustainable solar H2 production in water.
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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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    Resin-Immobilized CuO and Cu Nanocomposites for Alcohol Oxidation
    (ACS, 2008-10-31) Pande, Surojit
    Resin immobilized stable, spherical CuO nanoparticles prepared in the presence of cyclodextrin (CD) act as catalysts for liquid phase alcohol oxidation in air. The catalytic activity of the CuO nanocomposites and its green chemistry approach make it superior to the related resin-bound Cu(0) nanocomposite. The effect of alcohol chain length and electron-donating or -withdrawing groups influence product yield. The nanocomposites exhibit good reusability, simple workup procedure, and a straightforward approach to aldehyde formation.
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    Tuning of Catalytic Property Controlled by the Molecular Dimension of Palladium–Schiff Base Complexes Encapsulated in Zeolite Y
    (ACS, 2017) Ray, Saumi
    Planar palladium–Schiff base complexes are synthesized, maintaining the order of their molecular dimensions as PdL1 < PdL2 < PdL3 < PdL4 < PdL5 in free state, as well as encapsulated in zeolite Y, where L1: N,N′-bis(salicylidene)ethylenediamine and L2, L3, L4, and L5 are derivatives of L1. All encapsulated complexes have shown better catalytic activity for the sulfoxidation of methyl phenyl sulfide in comparison to their homogeneous counter parts. These hybrid systems are characterized with the help of different characterization techniques such as X-ray diffraction analysis, scanning electron microscopy–energy-dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared, and UV–visible spectroscopy; all of these studies have suggested that the largest complex deviates by the maximum from its free-state properties, and a radical change in the reactivity of the complex is observed.