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      Volume 123, Issue 2

      March 2011,   pages  95-242

    • Foreword

      S Vasudevan G U Kulkarni

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    • Silver complexes of 1,2,4-triazole derived N-heterocyclic carbenes: Synthesis, structure and reactivity studies

      Chandrakanta Dash Mobin M Shaikh Prasenjit Ghosh

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      Two silver(I) complexes {[1-R-4-($N$-t4-butylacetamido)-1,2,4-triazol-5-ylidene]2Ag}+ Cl [R = Et (1b), 𝑖-Pr (2b)] of $N/O$-functionalized N-heterocyclic carbenes derived from 1,2,4-triazoles are reported. The silver complexes, 1b and 2b, have been synthesized from the reaction of the $N/O$-functionalized triazolium chloride salts namely, 1-R-4-(N-t-butylacetamido)-1,2,4-triazolium chloride [R = Et (1a), 𝑖-Pr (2a)] by treatment with Ag2O in 53-56% yield. The 1,2,4-triazolium chloride salts 1a and 2a were prepared by the alkylation reaction of 1-R-1,2,4-triazole (R = Et, 𝑖-Pr) with $N-t$-butyl-2-chloro acetamide in 47-63% yield. The molecular structures of the silver(I) complexes, 1b and 2b, have been determined by X-ray diffraction studies. The density functional theory studies on the silver 1b and 2b complexes suggest that the 1,2,4-triazole derived N-heterocyclic carbenes to be strong 𝜎−donating ligands similar to the now much recognized imidazolebased N-heterocyclic carbenes. The reactivity studies with (SMe2)AuCl and (SMe2)CuBr indicated the silver complexes, 1b and 2b, to be good transmetallating agents.

    • Organo-gallium and indium complexes with dithiolate and oxo ligands: Synthesis, structures and applications

      Vimal K Jain Amey Wadawale Nisha P Kushwah Manoj K Pal

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      The chemistry of organo-gallium and indium complexes with dithiolate and internally functionalised oxo ligands has been explored. With 1,1-dithiolate ligands both classical and organometallic complexes of gallium and indium, [M(S$^\cap$S)3], [RM(S$^\cap$S)2] and [R2M(S$^\cap$S)] (where R = Me or Et; M = Ga or In; S$^\cap$S = RCS2, ROCS2, R2NCS2 and (RO)2PS2) have been isolated. Reactions of internally functionalised oxo ligands with R3MR$\cdot$OEt2 afforded diorganometal complexes [R2ML]$_n$. Molecular structures of several of these complexes have been established by single crystal X-ray diffraction analyses. Complexes derived from oxo ligands showed photoluminescence. They have been used as alkylating agents for C-C coupling reactions of aryl bromides in the presence of PdCl2(PPh3)2. Indium dithiolate complexes have been used as molecular precursors for the preparation of mono dispersed ẞ-In2S3 nanoparticles.

    • Aspects of secondary bonding intramolecular interaction in organomercury and organochalcogen derivatives

      Sagar Sharma Tapash Chakraborty Kriti Srivastava Harkesh B Singh

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      Recent trends in the area of intramolecularly coordinated organomercury and organochalcogens derivatives are reviewed. Intramolecular coordination in organomercury derivatives facilitates the formation of mercurametallamacrocycle and leads to novel metal-metal interaction with closed shell ions. It also plays a key role in stabilizing telluroxanes as well as in the activation of chalcogen-carbon bonds.

    • Synthesis of first row transition metal carboxylate complexes by ring opening reactions of cyclic anhydrides

      Jubaraj Bikash Baruah

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      Hydrolytic and solvolytic ring opening reactions of phthalic anhydride, pyromellitic dianhydride and 2,3-pyridine dicarboxylic anhydride in the presence of various transition metal salts with or without a ancillary ligands were studied. The reactions were found to be dependent on stoichiometry of ligand and types of anhydride used. In the case of pyromellitic dianhydride selective ring opening reaction by cobalt(II) ions gave 1,3-benzene dicarboxylate derivatives, whereas use of copper(II) ions gave 1,4-benzene dicarboxylate derivatives. Preference for methanolysis was seen in the case of copper (II) promoted reactions of pyromellitic dianhydride in the presence of 1:1 metal to 1,10-phenanthroline ratio.

    • Studies on bismuth carboxylates—synthesis and characterization of a new structural form of bismuth(III) dipicolinate

      O Anjaneyulu K C Kumara Swamy

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      Synthesis and X-ray structure of a new bismuth dipicolinate cooordination polymer, {[Bi((2,6-O2C)2C5H3N)((2-HO2C-6-O2C)C5H3N)(H2O)]2.5H2O}$_n$ (7) are presented. Compound 7 has dimeric units with a Bi2O2 skeleton that are linked by additional weak Bi-O interactions leading to a polymeric structure. The overall coordination number at bismuth is 9 [two Bi-N and seven Bi-O bonds]. New routes to a second crystalline modification (4′) of the previously reported coordination polymer, bismuth tris(picolinate), [Bi(2-O2C-C5H4N)3]$_n$ (4), are described; bond parameters in the two crystalline forms (4 and 4′) are compared. In both the compounds 4′ and 7, bismuth has a distorted tricapped trigonal prismatic geometry.

    • Phenalenyl-based ligand for transition metal chemistry: Application in Henry reaction

      Arup Mukherjee Tamal K Sen Swadhin K Mandal Daniel Kratzert Dietmar Stalke Alexander Döring Carola Schulzke

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      We report the synthesis and characterization of the first transition metal complex of a phenalenylbased ligand. The reaction of Cu(OAc)2.H2O with 9-𝑁-methylamino-1-𝑁'$-methylimino-phenalene (LH) in 1:1 stoichiometric ratio results in the formation of a mononuclear copper complex [LCu(OAc)] (1). The molecular structure of 1 was established by X-ray crystallography. The electrochemistry of 1 indicates the formation of an anionic radical by one electron reduction into the non-bonding molecular orbital of the phenalenyl system. The complex 1 efficiently catalyses the C-C bond forming Henry reaction.

    • Mononuclear non-heme iron(III) complexes of linear and tripodal tridentate ligands as functional models for catechol dioxygenases: Effect of 𝑁-alkyl substitution on regioselectivity and reaction rate

      Mallayan Palaniandavar Kusalendiran Visvaganesan

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      Catechol dioxygenases are responsible for the last step in the biodegradation of aromatic molecules in the environment. The iron(II) active site in the extradiol-cleaving enzymes cleaves the C-C bond adjacent to the hydroxyl group, while the iron(III) active site in the intradiol-cleaving enzymes cleaves the C-C bond in between two hydroxyl groups. A series of mononuclear iron(III) complexes of the type [Fe(L)Cl3], where L is the linear 𝑁-alkyl substituted bis(pyrid-2-ylmethyl)amine, 𝑁-alkyl substituted 𝑁-(pyrid-2-ylmethyl)ethylenediamine, linear tridentate 3N ligands containing imidazolyl moieties and tripodal ligands containing pyrazolyl moieties have been isolated and studied as structural and functional models for catechol dioxygenase enzymes. All the complexes catalyse the cleavage of catechols using molecular oxygen to afford both intra- and extradiol cleavage products. The rate of oxygenation depends on the solvent and the Lewis acidity of iron(III) center as modified by the sterically demanding 𝑁-alkyl groups. Also, our studies reveal that stereo-electronic factors like the Lewis acidity of the iron(III) center and the steric demand of ligands, as regulated by the 𝑁-alkyl substituents, determine the regioselectivity and the rate of dioxygenation. In sharp contrast to all these complexes, the pyrazole-containing tripodal ligand complexes yield mainly the oxidized product benzoquinone.

    • Cobalt(III)-oxo cubane clusters as catalysts for oxidation of organic substrates

      Birinchi Kumar Das Rajesh Chakrabarty

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      Transition metal coordination complexes play a vital role as catalysts in the oxidation of organic substrates including renewable chemicals in an economically viable and environmentally friendly way. Here we highlight the preparation, characterization and application of oxo-cubane complexes of cobalt(III) as oxidation catalysts using air and water as oxidants. Cobalt(III)-oxo complexes of the type Co4O4(O2CR)4L4 have been prepared by a general method and these have been characterized by analytical, spectroscopic, electrochemical and crystallographic methods. These soluble complexes have shown promising utility as catalysts in the aerobic oxidation of side chains of alkylaromatic hydrocarbon compounds. Oxidation of neat ethylbenzene has shown very high conversion and selectivity for acetophenone formation. On the other hand, oxidation of 𝑝-xylene has been found to yield both 𝑝-toluic acid and terephthalic acid. It is also possible to oxidize 𝑝-xylene in an aqueous medium under moderate applied O2 pressure. Selective epoxidation of 𝛼-pinene with air as the oxidant also takes place with the cobalt(III)-based homogeneous catalysts.

    • Urea/thiourea derivatives and Zn(II)-DPA complex as receptors for anionic recognition—A brief account

      Priyadip Das Prasenjit Mahato Amrita Ghosh Amal K Mandal Tanmay Banerjee Sukdeb Saha Amitava Das

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      This review covers few examples of anion complexation chemistry, with a special focus on urea/thiourea-based receptors and Zn(II)-dipicolyl amine-based receptors. This article specially focuses on structural aspects of the receptors and the anions for obtaining the desire specificity along with an efficient receptor-anion interaction. Two types of receptors have been described in this brief account; first one being the strong hydrogen bond donor urea/thiourea derivatives, which binds the anionic analytes through hydrogen bonded interactions; while, the second type of receptors are coordination complexes, where the coordination of the anion to the metal centre. In both the cases the anion binding modulate the energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and thereby the spectroscopic response. Appropriate choice of the signalling unit may allow probing the anion binding phenomena through visual detection.

    • Synthesis, structure and applications of [cis-dioxomolybdenum(VI)-(ONO)] type complexes

      Rajan Deepan Chakravarthy Dillip Kumar Chand

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      Oxo-molybdenum chemistry is of great interest since such units are found in the active sites of a majority of molybdo-enzymes. In order to mimic the biological systems, a number of oxo-molybdenum complexes have been synthesised and studied. This review describes synthesis, structure and applications of oxomolybdenum complexes particularly cis-MoO2(L)(D) where L stands for a dianionic tridentate ONO ligand and D for a donor solvent molecule/monodentate ligand. The ligand moieties are derived from Schiff base, hydrazide Schiff base and other related tridentate ligands L(H)2. The coordination geometry around the Mo center in these complexes can be best described as a distorted octahedron in which the ONO-tridentate ligand occupies meridional position with two anionic oxygen donors mutually trans and are cis to the oxygen centers of the cis-dioxo group. Mostly the applications of cis-MoO2-(ONO) type complexes seen in literature are oxo transfer reactions like epoxidation, sulfoxidation and phosphine oxidation reactions.

    • Re(I) bridged porphyrin dyads, triads and tetrads

      M Yedukondalu M Ravikanth

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      Porphyrin rings containing two meso-pyridyl groups either in cis or trans fashion can be used to construct Re(I) bridged multiporphyrin assemblies. The cis-dipyridyl porphyrins with various porphyrin cores such as N4, N3O, N3S, N2S2 have been used to react with Re(CO)5Cl in THF at refluxing temperature and constructed planar Re(I) bridged porphyrin dyads containing either one type of porphyrin subunit or two types of porphyrin subunits. The trans-dipyridyl porphyrins have been used to construct Re(I) bridged porphyrin squares. The porphyrin dyads have been explored for singlet-singlet energy transfer studies and porphyrin squares have been used for catalysis, chemical sensing, molecular sieving and photocurrent production studies. An overview of synthesis of Re(I) bridged porphyrin dyads, triads and tetrads and their interesting photophysical properties are highlighted in this paper.

    • Structural models of vanadate-dependent haloperoxidases, their reactivity, immobilization on polymer support and catalytic activities

      Mannar R Maurya

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      The design of structural and functional models of enzymes vanadate-dependent haloperoxidases (VHPO) and the isolation and/or generation of species having {VO(H2O)}, {VO2}, {VO(OH)} and {VO(O2)} cores, proposed as intermediate(s) during catalytic action, in solution have been studied. Catalytic potential of these complexes have been tested for oxo-transfer as well as oxidative bromination and sulfide oxidation reactions. Some of the oxidovanadium(IV) and dioxidovanadium(V) complexes have been immobilized on polymer support in order to improve their recycle ability during catalytic activities and turn over number. The formulations of the polymer-anchored complexes are based on the respective neat complexes and conclusions drawn from the various characterization studies. These catalysts have successfully been used for all catalytic reactions mentioned above. These catalysts are stable and recyclable.

    • Polyoxometalates: Toward new materials

      A Srinivasa Rao T Arumuganathan Vaddypally Shivaiah Samar K Das

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      This article describes an account of some of our polyoxometalate (POM)-based research, we have been doing in our laboratory last several years. There are several well-defined POM cluster anions, that are structurally characterized. We have chosen Anderson-type of heteropolyanion [Al(OH)6Mo6O18]$^{3−}$ and explored its linking propensity in different dimensions using `s', `d' and `f' block elements as linkers.We have demonstrated how a lanthanide linker provides a new pathway in forming a two-dimensional linked {As8V14} system [{Ln(H2O)6}2As8V14O42(SO3)]$_n$.8nH2O, that is derived from discrete {As8V14} cluster containing compound (NH4)6[As8V14O42(SO3)]. A polyoxometalate compound has been described in which a reduced tungstovanadate-heteropolyanion clusters get linked via capped V = O groups into one-dimensional chains. All these systems have already been reported elsewhere. The last portion of this article will be described by a new system [3-ampH]6[V10O28]$\cdot$2H2O having discrete molecular structure and extended supramolecular structure.

    • Editor’s Note

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