A chiral Schiff base complex has been prepared by treating (R)-1,2-diaminopropane with 3,5-dichlorosalicylaldehyde in ethanol, followed by addition of manganese chloride hexahydrate to generate a homogeneous catalyst, [MnL(Cl)(H 2 O)] (HMN). Crystal structure of the complex reveals its mononuclear nature. Circular dichroism (CD) studies indicate that the ligand and its corresponding complex contain an asymmetric center. The catalytic activity of HMN toward epoxidation of alkenes, oxidation of alcohols and oxidation of alkanes has been investigated in the presence of iodosylbenzenediacetate (PhI(OAc) 2 ), in acetonitrile. In the present work we found yields to be much higher compared to our previous approaches. For further adaptation, we attached our efficient homogeneous catalyst with surface modified magnetic nanoparticles (Fe 3 O 4 @dopa) and thereby obtained a new magnetically separable nanocatalyst Fe 3 O 4 @dopa@MnLCl (FDM). This catalyst has been characterized and its oxidation ability assessed in similar conditions as those used for the homogeneous catalyst. Enantiomeric excess in epoxide yield reveals retention of chirality of the active site of Fe 3 O 4 @dopa@MnLCl. The catalyst can be recovered by magnetic separation and recycled several times without significant loss of catalytic activity. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

A CHAKRABORTY

T CHATTOPADHYAY

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Fe3O4@dopa (dopa = dopamine hydrochloride) functionalized Mn(III) Schiff base complex: A promising magnetically separable heterogeneous catalyst for oxidative transformations

Journal of Coordination Chemistry

A copper(II) macrocyclic Schiff base complex (ML) was synthesized by condensation between 2,2-dimethylpropane-1,3-diammine and 2,6-diformyl-4-butylphenol with the aim to modify the surface of widely used magnetically separable nanocatalyst Fe 3 O 4 @dopa. ML was characterized by physicochemical techniques and single crystal X-ray diffraction. The newly synthesized heterogeneous catalyst Fe 3 O 4 @dopa@ML was characterized by SEM, TEM, PXRD, EDX, TGA, etc. ML showed stability in aqueous medium and utilizing this unique property, the heterogeneous catalyst Fe 3 O 4 @dopa@ML was used for catalyzing epoxidation, nitroarene reduction and C–C coupling (Henry reaction) in aqueous medium. The separation method of the prepared nano-catalyst is very easy and can be done with an external magnetic field. The experimental findings suggest that Fe 3 O 4 @dopa@ML is a versatile “green catalyst.”. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.

Designing of a magnetically separable Fe 3 O 4 @dopa@ML nano-catalyst for multiple organic transformations (epoxidation, reduction, and coupling) in aqueous medium

Cetrimonium bromide (CTAB)-coated water disperse magnetically separable nanocatalysts CTAB/Fe3O4@dopa@ML (M = Fe or Mn, L = cyclohexane-1,2-diylbis(azanylylidene)bis(methanylylidene)bis(2,4-diXphenol; X = Cl, Br, and I) have been synthesized using a simple synthetic strategy. This approach provides a new fruitful strategy to reduce the leaching of the active metal complex from the catalyst surface to the aqueous media. The synthesized catalysts have been found to be excellent for oxidation of alcohols in aqueous medium at room temperature. A probable catalytic pathway involving the generation of hydroperoxo intermediates has been assumed, and these intermediates have been characterized using density functional theory and several spectroscopic techniques. It is worthy of mention that the synthesized CTAB-coated magnetically separable nanocatalysts can be magnetically recovered from the aqueous reaction mixture after more than five cycles, which renders this approach as a sustainable and accessible one. © 2019 American Chemical Society

Fulltext

ACS Omega

Surfactant-mediated solubilization of magnetically separable nanocatalysts for the oxidation of alcohols

We have prepared two chiral Schiff base ligands, H2L1 and H2L2, and one achiral Schiff base ligand, H2L3, by treating 2,6-diformyl-4-methylphenol separately with (R)-1,2-diaminopropane, (R)-1,2-diaminocyclohexane and 1,1′-dimethylethylenediamine, in ethanolic medium, respectively. The complexes MnL1ClO4 (1), MnL2ClO4 (2), MnL3ClO4 (3), FeL1ClO4 (4), FeL2ClO4 (5) and FeL3ClO4 (6) have been obtained by reacting the ligands H2L1, H2L2 and H2L3 with manganese(III) perchlorate or iron(III) perchlorate in methanol. Circular dichroism studies suggest that ligands H2L1 and H2L2 and their corresponding complexes have asymmetric character. Complexes 1–6 have been used as homogeneous catalysts for epoxidation of alkenes. Manganese systems have been found to be much better than iron counterparts for alkene epoxidation, with 3 as the best catalyst among manganese systems and 6 as the best among iron systems. The order of their experimental catalytic efficiency has also been rationalized by theoretical calculations. We have observed higher enantiomeric excess product with catalysts 1 and 4, so they were attached to surface-modified magnetic nanoparticles to obtain two new magnetically separable nanocatalysts, Fe3O4@dopa@MnL1 and Fe3O4@dopa@FeL4. They have been characterized and their alkene epoxidation ability has been investigated. These catalysts can be easily recovered by magnetic separation and recycled several times without significant loss of catalytic activity. Hence our study focuses on the synthesis of a magnetically recoverable asymmetric nanocatalyst that finds applications in epoxidation of alkenes and at the same time can be recycled and reused. Copyright © 2016 John Wiley & Sons, Ltd.

Applied Organometallic Chemistry

A route to magnetically separable nanocatalysts: Combined experimental and theoretical investigation of alkyl substituent role in ligand backbone towards epoxidation ability

Three chiral Schiff base ligands H2L1, H2L2, H2L3 have been synthesized by treating (R)-1,2-diaminopropane separately with 3,5-dichlorosalicylaldehyde, 3,5-dibromosalicylaldehyde and 3,5-diiodosalicylaldehyde, respectively. Three new asymmetric FeIII complexes, namely, FeL1Cl (1), FeL2Cl (2), FeL3Cl (3) have been prepared from their corresponding ligands. The crystal structure of 2 reveals that the complexes are mononuclear in nature. Circular dichroism (CD) studies suggest that the ligands and their corresponding complexes contain an asymmetric center. The catalytic activity of these complexes toward the epoxidation of alkenes has been investigated in the presence of iodosylbenzene (PhIO), in two solvents CH3CN and CH2Cl2. The epoxide yield suggests that the order of their catalytic efficiency is 3 &gt; 2 &gt; 1. This trend as well as the role of substitution on the ligand backbone on alkene epoxidation has also been confirmed by density functional theory (DFT) calculations. For further adaptation, we attached our most efficient homogeneous catalyst, 3, with surface modified magnetic nanoparticles (Fe3O4@dopa) and thereby obtained the new magnetically separable nanocatalyst Fe3O4@dopa@FeL3Cl. This catalyst has been characterized and its olefin epoxidation ability investigated in similar conditions to those used for homogeneous catalysts. The enantiomeric excess of the epoxide yield reveals the retention of chirality of the active site of Fe3O4@dopa@FeL3Cl. The catalyst can be easily recovered by magnetic separation and recycled several times without significant loss of its catalytic activity. © 2015 The Royal Society of Chemistry.

RSC Advances

Development of an efficient magnetically separable nanocatalyst: Theoretical approach on the role of the ligand backbone on epoxidation capability

A coordination polymer, Na2Cd2I6L2(H2O)6 [L= Urotropine] has been employed as sole precursor to synthesize CdO particles. Two different preparation methods viz (i) pyrolysis of the title compound at 700 °C for 2 h and (ii) forming cadmium hydroxide from the title compound followed by pyrolysis at 700 °C for 2 h have been used for the synthesis of nano sized CdO-I and CdO-II, respectively. From powder XRD data the lattice parameters (0.4701 and 0.4696 nm respectively for the two samples) and particle size (~77 and 30 nm for CdO-I and CdO-II) have been evaluated. Morphology of the two varieties of CdO is widely different as is evident from their SEM images. The estimated values of the band gap of 2.53 eV and 2.59 eV for CdO-I and CdO-II respectively are obtained from the optical spectral analysis.

Materials Letters

Na2Cd2I6L2(H2O)6 [L=Urotropine]: An interesting precursor for synthesizing CdO particles

Four side-off compartmental ligands L1 –L4 [L1 = N,N¢-ethylenebis(3-formyl-5-methyl-salicylaldimine), L2 = N,N¢-1-methylethylenebis(3-formyl-5-methylsalicylaldimine), L3 = N,N¢-1,1-dimethylethylenebis(3-formyl-5-methylsalicylaldimine) and L4 = N,N¢-cyclohexenebis(3-formyl-5- methylsalicylaldimine)] having two binding sites, N2O2 and O4, have been chosen to synthesize mononuclear and dinuclear manganese(III) complexes with the aim to study their catecholase activity using 3,5-di-tert-butylcatechol (3,5-DTBC) as substrate in the presence of molecular oxygen. In all cases only mononuclear manganese complexes (1–4) were obtained, with manganese coordination taking place at the N2O2 binding site only, irrespective of the amount of manganese salt used. All these complexes have been characterized by routine physico-chemical techniques. Complex MnL2 Cl·4H2O (2) has further been structurally characterized by X-ray single crystal structure analysis. Four dinuclear manganese complexes, 5–8, were obtained after condensing the two pending formyl groups on each ligand (L1 –L4 ) with aniline followed by reaction with MnCl2 to put the second Mn atom onto another N2O2 site. The catalytic activity of all complexes 1–8 has been investigated following the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) with molecular oxygen in two different solvents, methanol and acetonitrile. The study reveals that the catalytic activity is influenced by the solvent and to a significant extent by the backbone of the diamine and the behavior seems to be related mainly to steric rather than electronic factors. Experimental data suggest that a correlation, the lower the E1/2 value the higher the catalytic activity, can be drawn between E1/2 and V max of the complexes in a particular solvent. The EPR measurements suggest that the catalytic property of the complexes is related to the metal center(s) participation rather than to a radical mechanism.

Dalton Transactions

Mono- and dinuclear manganese(III) complexes showing efficient catechol oxidase activity: syntheses, characterization and spectroscopic studies

Synthesis, characterization, and catalytic activity of supported molybdenum Schiff base complex as a magnetically recoverable nanocatalyst in epoxidation reaction

Fe 3 O 4 @dopa (dopa = dopamine hydrochloride) functionalized Mn(III) Schiff base complex: A promising magnetically separable heterogeneous catalyst for oxidative transformations

Journal	Data powered by TypesetJournal of Coordination Chemistry
Publisher	Data powered by TypesetTaylor and Francis Ltd.
ISSN	0095-8972