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An unambiguous and precise method for the synthesis of 3,1-benzoxathiin-4-ones/1,3-benzodioxin-4-ones by the reaction of propargylic alcohols and salicylic/thiosalicylic acids under a catalyst-free and open-air atmosphere is described. This strategy is found to be quite general using various 2-mercapto and 2-hydroxybenzoic acids providing benzoxathiinones/benzodioxinones in good yields.

The synthesis and characterization of a mixed ligand metal–organic framework (MOF) with good thermal and chemical stability, {[Co(BDC)(L)·2H2O]·xG}n (CoMOF-2), involving an aromatic dicarboxylate (H2BDC = 1,4-benzenedicarboxylic acid) and an acyl-decorated N-donor linker [L = (E)-N′-(pyridin-4-ylmethylene) isonicotinohydrazide] by various physicochemical techniques, including Single crystal X-Ray Diffraction (SXRD), are reported. The MOF showed a good affinity for CO2 capture, and Grand Canonical Monte Carlo simulation studies exposed strong interactions of CO2 with the functionalized N-donor ligand of the framework. CoMOF-2 and KI act as an efficient binary catalyst for the sustainable utilization of CO2 with spiro-epoxy oxindole to spirocyclic carbonate under ambient conditions. Notably, herein we report MOF-based catalysis for the cycloaddition of oxindole-based epoxides with CO2 for harvesting new spirocyclic carbonates. Interestingly, we could isolate and crystallize six of the spirocyclic carbonate ...

The ligand L1 of 4-methyl-2,6-diformylphenol and L2 of 4-tert-butyl-2,6-diformylphenol are synthesized through Schiff base condensation with rac-, (R)-(+), or (S)-(−)-1,1′-binaphthyl-2,2′-diamine (...

A series of mononuclear copper(II) complexes of the type [Cu(L)Cl2] 1–6, where L is a tridentate 3 N ligand such as N-methyl-N′-(pyrid-2-ylmethyl)ethylenediamine (L1), N-ethyl-N′-(pyrid-2-ylmethyl)ethylenediamine (L2), N-phenyl-N′-(pyrid-2-ylmethyl)ethylenediamine (L3), N,N-dimethyl-N′-(pyrid-2-ylmethyl)ethylenediamine (L4), N,N-diethyl-N′-(pyrid-2-ylmethyl)-ethylenediamine (L5) and N-methyl-N′-(pyridin-2-ylmethyl)benzene-1,2-diamine (L6), has been isolated and studied as functional models for catechol oxidase enzymes in different aqueous micellar media. The X-ray crystal structures of 2 and 5 contain a CuN3Cl2 chromophore with a trigonal bipyramidal based coordination geometry. Interestingly, all the complexes form cationic [Cu(L)(DBC)(H2O)]+ adduct species in which DBC2− acts as a monodentate ligand, and the adduct species interacts strongly with anionic SDS micelles. The rates of the oxygenase reaction follow the trend SDS > TX-100 ∼ water > CTAB, revealing that the rate of the reaction in micellar media are higher than those in aqueous solution and that the nature of biomimetic microenvironments of the micellized copper(II) catalyst and also the ligand stereoelectronic factors like donor atom basicity and steric bulk of ligand N-alkyl substituents, determine the catecholase-like activity.

The BF3·Et2O catalyzed reaction of nitrosobenzenes and an excess amount of propargylic alcohols was investigated to synthesize highly-substituted indole-3-carbinols. This reaction involves formal [3 + 2]-cycloaddition and the subsequent 1,3-rearrangement in a tandem manner via 3-alkylidene-3H-indole N-oxides. This methodology involves the sequential addition of propargylic alcohols and inexpensive Lewis acid catalyst, occurs in an open-air environment and is atom economical. The highly-substituted indole-3-carbinols were obtained in short time and the operational simplicity allows for a large scale experiment.

Zn(II)/Cd(II)-based dual ligand Luminescent Metal–Organic Frameworks (LMOFs) {[M(ATA)(L)]}n·xH2O (1) and (2) were synthesized by versatile synthetic routes, viz., diffusion of precursor solutions, conventional reflux, and green mechanochemical (grinding) reactions from bipyridyl-based Schiff base, (E)-N′-(pyridin-4-ylmethylene)isonicotinohydrazide (L) and amino functionalized 2-aminoterephthalic acid (H2ATA) as linkers. Chemical and thermal stability, phase purity, and characterization of both LMOFs were established by various analytical methods. SXRD analysis revealed the 3D framework is composed of two-dimensional [M(ATA)]n nets doubly pillared by L through the terminal nitrogen atom. Selective and sensitive detection of chromate anions (CrO42–/Cr2O72–) and Fe3+/Pd2+ cations in the aqueous phase by fluorescent quenching of the LMOFs 1 and 2 has been established. Competitive experiments in the presence of interfering anions/cations with 1 and 2 revealed no major change in the quenching efficiency. The ob...

A simple, efficient, and general multicomponent reaction involving an enolizable ketone, a primary amine, and an N-protected 3-nitroindole was developed for the synthesis of a range of functionalized pyrrolo[3,2-b]indoles. The methodology was efficaciously utilized for the "pyrroloindoliztion" of natural products, the pyrrolization of 3-nitrobenzo[b]thiophene, and the gram-scale synthesis of pyrroloindole. Furthermore, a "one-pot" approach for accessing indolo[3,2-b]indoles was realized.

An atom-economical synthesis of spiro-indolofurobenzopyrans was developed from diazoamides and O-propargyl salicylaldehydes in the presence of copper(i) thiophene-2-carboxylate in a diastereoselective manner. This methodology involves the preparation of carbonyl ylide intermediates followed by 1,3-dipolar cycloaddition with internal/external alkynes, offering a great potential for constructing biologically significant spiro-indolofurobenzopyrans, as thermodynamically controlled products, in a tandem manner.

The continuous demand and uneven dispersal of natural mineral resources of lithium with a low recycling rate of lithium commodities have forced researchers to look for alternative resources like geothermal brine, brackish brines, and sea brines. But selective lithium-ion extraction and even lithium-ion binding from these aqueous systems is a recognized challenge due to very high hydration energy and the coexistence of other like metal ions but appealing due to economic benefits. Therefore, the designed synthesis of synthetic ionophores with high lithium selectivity is crucial as they can work on dilute conditions without removal of interfering metal ions. However, most of the lithium selective ionophores known in the literature are mononucleated, and no emphasis is given on designing multinucleating ionophore systems to improve the lithium loading capacity which will open up unexplored paths toward the development of a more sustainable and economical extraction process. Herein, we describe a rare fluorogenic macrocyclic ionophore with two binding pockets for selective lithium recognition and extraction among various major alkali and alkaline earth metal ions of oceanic presence through both solid-state and solution studies. Under solid-liquid extraction conditions, this receptor shows a high lithium loading capacity of 135% with LiClO

Half sandwich cationic mononuclear rhodium(III) and iridium(III) complexes [(η5-C5Me5)M(L)Cl]Cl·2H2O where L = dipyridylamine (dpa) (M = Rh, 1 and Ir, 2) and dipyridylketone (dpk) (M = Rh, 3 and Ir, 4) have been synthesized and characterized. The structure of a representative complex (1) was authenticated by single crystal X-ray diffraction analysis. Complexes 1–4 have been fully characterized by various physicochemical techniques, namely elemental analysis, spectral (IR, 1H, NMR, UV–Vis), electrochemical studies (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)). Notably, the UV absorption spectral titrations of the synthesized complexes with DNA reveal that the complexes bind to calf thymus DNA (CT-DNA) through the intercalation mode. The DNA solution hydrodynamic volume (viscosity) measurements show that the interaction of the compounds with CT-DNA occurs by classical intercalation. A molecular docking study suggested intercalation between the synthesized compounds and nucleotide base pairs. Cyclic voltammetry studies of the complexes indicate irreversible oxidation and reduction potentials. A gel electrophoresis assay demonstrates the ability of the complexes to cleave pUC19 DNA. The antibacterial activities were assayed against selected Gram(−ve) and Gram(+ve) microorganisms. The cytotoxic properties of the metal complexes have been evaluated using a brine shrimp lethality bioassay. The results suggest that the binding affinity of 1–4 lies in the order 1 > 4 > 2 > 3.

An expeditious and convenient method for the generation of 11–21-membered intramolecular macrocyclic sulfonium ylides using catalytic Rh2(OAc)4 is presented. Using this approach, a wide variety of sulfur-macrocycles incorporating the oxindole unit were produced in good yields and with high diastereoselectivity. Interestingly, tetracyclic macrocycles were also attained in good yields and with good regioselectivity using the disclosed sulfonium ylides. Ring-opening reactions of tetracyclic macrocycles were also demonstrated.

A family of calix[4]arene compounds containing crown moieties at both the upper and lower rims of the calix unit with different substituents attached to the nitrogen atom of the aza-crown moiety have been synthesized, characterized and their competitive binding property towards Li+, Na+, K+, Mg2+, Ca2+ and Sr2+ in aqueous media has been investigated. These ionophores exhibit high selectivity towards K+, assessed by two-phase extraction method followed by ion chromatographic assay of the metal ions in the extract. Isothermal calorimetric titration for complex formation with K+ was carried out to evaluate stoichiometry, binding constant and other thermodynamic parameters (ΔH, ΔS and ΔG). For structural elucidation in solution, detail 1H NMR study was carried out and K+ complexes were isolated for solid state characterization. Molecular structures of two of the ionophores and K+-complex of one of the ionophores has been established by single crystal X-ray study. 1H NMR, ITC and single crystal XRD studies suggest 1:1 complex formation with encapsulation of K+ in the crown-6 ring at the upper rim. These ionophores have been applied for extraction of metal ions from bittern.

Two dual ligand isostructural coordination polymers [Co(BrIP)(BIX)]n (1) and [Zn(BrIP)(BIX)]n (2), where BrIP = 5-bromoisophthalate and BIX = 1,4-bis(imidazol-1-ylmethyl)-benzene, have been efficiently synthesized by liquid assisted grinding methods. Single crystals of 1 were harvested by the solvothermal technique and phase pure 1 or 2 can be quantitatively obtained by grinding equimolar amounts of the metal nitrates and the ligands, 5-bromoisophthalic acid (H2BrIP) and 1,4-bis(imidazol-1-ylmethyl)-benzene (BIX) in the presence of a few drops of water or methanol. Use of freshly prepared Co(OH)2 or ZnO also yields the desired end products in an environmentally friendly manner along with the benign by-product water. The structure of 1 was established by single crystal X-ray diffraction studies, in addition to other physicochemical techniques. Morphological aspects of samples of 1 and 2 obtained via different protocols have also been studied.

Isostructural Zn(II)/Cd(II) mixed ligand coordination polymers (CPs) {[M(IPA)(L)]}n (CP1 and CP2) built from isophthalic acid (H2IPA) and 3-pyridylcarboxaldehyde nicotinoylhydrazone (L) were prepared using versatile synthetic routes: viz., diffusion of precursor solutions, conventional reflux methods, and green mechanochemical (grinding) reactions. Both robust CPs synthesized by different routes were characterized by various analytical methods, and their thermal and chemical stability as well as the phase purity was established. Crystallographic studies revealed that CP1 and CP2 are isostructural frameworks and feature a double-lined two-dimensional network composed of Zn2+/Cd2+ nodes connected through IPA and pillared by the Schiff base ligand L with a double-walled edge. The photoluminescent (PL) properties of CP1 and CP2 have been exploited as dual detection fluorosensors for hexavalent chromate anions (CrO42–/Cr2O72–) and 2,4,6-trinitrophenol (TNP) because it was observed that the emission intensity o...

A nucleophilic heterocyclic carbene-mediated intramolecular homoenolate reaction strategy for the efficient synthesis of cyclopentene-fused macrocycles is reported.

The reaction of arynes with indene/benzofurans has been developed. The arynes were generated from 2-(trimethylsilyl)aryl triflates by the fluoride-induced 1,2-elimination react with indene or various benzofurans proceeding via a cascade reaction involving the Diels-Alder reaction and a [2 + 2] cycloaddition reaction. The tandem process afforded functionalized dihydrobenzocyclobutaphenanthrenes in moderate to good yields. Moreover, the method has been utilized for the one-pot synthesis of benzo[b]fluoranthene.

Four ternary coordination polymers (CPs) namely, {[Ni(SDB)(BITMB)(H2O)]·H2O}n (CP1), {[Cd(SDB)(BITMB) (H2O)]·(THF)(H2O)}n (CP2), {[Zn2(SDB)2(BITMB)]·(THF)2}n (CP3) and {[Co2(SDB)2(BITMB)]·(Dioxane)3}n (CP4) composed of angular dicarboxylate SDB (4,4'-sulfonyldibenzoate) and N-donor BITMB (1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethyl benzene) have been synthesized by solvothermal reactions and characterized by single crystal X-ray diffraction and other physico-chemical techniques. CP1 possesses one-dimensional ribbon type metal–organic motifs glued together by H-bonds and π⋯π interactions, whereas CP2–CP4, exhibit non-interpenetrated sql networks supported by weak supramolecular interactions. Structural diversity of these CPs can be attributed to the coordination geometry adopted by the metal nodes, versatile coordination modes of SDB and conformational flexibility of BITMB. Solid state luminescence properties of CP1–CP4 were explored. Photocatalytic performance of all CPs for the decomposition of metanil yellow by dilute hydrogen peroxide in the presence of visible light was also investigated. 25–83% dye removal from aqueous solutions in the presence of CP1–CP4 was observed.

An unexpected transformation of 1,6-diarylhexa-1,5-diene-3,4-diones (cinnamils) to 2,3,8-triaryl vinyl fulvenes via N-Heterocyclic Carbene (NHC) catalysis is reported. Mechanistic as well as synthetic novelty is the hallmark of this reaction.

A new family of nickel(II) complexes of the type [Ni(PA)(L)(CH3CN)n]BPh4 1–5, where n = 1, 2, H(PA) is 2-picolinic acid and L is N,N′-tetramethylethylenediamine (L1) 1, N,N′,N″-pentamethyldiethylenetriamine (L2) 2, 2,2′-bipyridine (L3) 3, 1,10-phenanthroline (L4) 4 or 2,9-dimethyl-1,10-phenanthroline (L5) 5, has been isolated and characterized using CHN analysis, UV–Vis spectroscopy and ESI-MS. The complex [Ni(PA)(L2)(CH3CN)](BPh4) 2 possesses a distorted octahedral coordination geometry in which Ni(II) is chelated to 2-picolinate anion and L2. DFT calculations show that trans isomers of 3–5 are more stable than cis isomers by ca. 4.0 kJ/mol. In contrast, cis-1 is more stable than trans-1 by 15.8 kJ/mol. The complexes catalyze the hydroxylation of cyclohexane efficiently in presence of m-CPBA as oxidant with 244–569 turnover numbers and good alcohol selectivity (A/K, 3.4–7.0). Adamantane is oxidized to 1-adamantanol, 2-adamantanol and 2-adamantanone with varying bond selectivity (3°/2°, 9.3–14.2) while cumene is selectively oxidized to 2-phenyl-2-propanol. Upon replacing bidentate L1 by tridentate L2 or strongly π-back bonding phen the catalytic activity increases. In contrast, phen is replaced by non-planar bpy or 2,9-dmp with sterically hindering methyl groups the catalytic activity decreases. Thus ligand denticity, Lewis acidity of Ni(II) center and π-back bonding determine the catalytic activity.

An efficient phosphine-mediated diastereoselective synthesis of substituted cyclopentenones from 3-alkyl allenoates and diaryl 1,2-diones is described.

Bola-shaped diester dicarboxylic acid 2-({2-[(2-carboxybenzoyl)-xy]ethoxy}carbonyl)benzoic acid (L1H2) was synthesized by desymmetrizing phthalic anhydride using 1,2-ethane diol. The corresponding dinuclear copper(II)-tetracarboxylate complex [Cu2(L1)2·(DMF)2] (1) has been synthesized. This paddle wheel complex was self-assembled with [15]-membered bis-chelate ring on either sides of the M–M axis. Upon treating with phenanthroline/bipyridine, the symmetrically formed bis-chelate rings in 1 were selectively desymmetrized into monochelate rings. The dinuclear association in 1 rearranged into mononuclear in [Cu(L1)·(bpy)] (2) and [Cu(L1)·(phen)]·(DMF) (3), where bpy = bipyridine and phen = phenanthroline. The paddle wheel arrangement in 1 is very similar to that in dimeric Cu(II) acetate; the symmetric arrangement in 1 rearranged in its corresponding monomeric species on reacting with phen and bpy. The symmetric bis-chelate ring in 1 and the desymmetrized monochelate ring in 2 and 3 are discussed following t...

Employing 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1H-benzimidazole (bpb) as a monodentate ligand, a new greenish-blue copper(II) complex, [Cu(bpb)2(NO3)2] (1a), has been synthesized. 1a has been characterized analytically and spectroscopically. The X-ray crystal structure of 1a reveals that it adopts a cis disposition with respect to the ligands. The solid state structure of 1a is stabilized by intramolecular offset face-to-face π–π stacking. Non-covalent supramolecular edge-to-face C–H⋯π interactions with neighboring molecules give 1-D supramolecular chains that further lead to the formation of an assembled 3-D supramolecular metal-organic framework via hydrogen bonding interactions. 1a shows blue fluorescence most likely due to intramolecular offset face-to-face π–π stacking. At room temperature, 1a is one-electron paramagnetic. It shows a rhombic EPR spectrum with g1 = 2.12, g2 = 2.42, and g3 = 2.52 in the solid state at liquid nitrogen temperature. In cyclic voltammetry, 1a displays a one-electron oxidative Cu(II)/Cu(III) couple. Our DFT calculations, corroborate the observed experimental results of 1a.

A family of calix-crown hybrid molecules incorporating crown-4, crown-5 and crown-6 moieties as ionophore has been synthesized to evaluate their competitive complexing and extracting ability towards different alkali and alkaline earth metal ions. Selectivity of these ionophores towards Li+, Na+, K+, Ca2+, Mg2+ and Sr2+ has been evaluated with aqueous solution containing equimolar mixture of these ions. The concentration of metal ion in the extract (organic phase) has been estimated by ion chromatographic assay. Two of the ionophores show strong complexation with Na+ and K+, whereas the third ionophore exhibits no complexation with any metal ions used in this study. Association constants (Ka) for the binding of Na+ and K+ with two of these ionophores have been determined spectrophotometrically. Molecular structures of the Na+ and K+ complexes of these ionophores have been established by single crystal X-ray study. 1H NMR study of the ionophores and their complexes has also been carried out to investigate conformational behavior of the ionophores and their metal complexes in solution. Results have been discussed in light of various factors contribute to determine ion-selectivity.

The syntheses and spectral/structural characterization of ansa-ferrocene-incorporated normal calixphyrins and core-modified calixpyrroles and calixphyrins are reported. Acid-promoted dehydrative condensation of 1,1′-bis(dimethylpyrrolylmethyl)ferrocene and 2,5-bis(dimethylhydroxymethyl)thiophene/furan yielded ansa-ferrocene-based core-modified calixpyrroles, while acid-catalyzed dehydrative condensation of 1,1′-bis(diphenylpyrrolylmethyl)ferrocene with the aryl aldehydes and 2,5-bis(phenylhydroxymethyl)thiophene followed by DDQ oxidation resulted in the formation of ansa-ferrocene-appended normal and core-modified calixphyrins, respectively. The newly synthesized macrocycles were characterized by FAB-MS, NMR, and UV–vis spectral analyses and finally confirmed by single-crystal X-ray structural analysis. All these studies clearly revealed the introduction of ferrocene in the main framework of the corresponding macrocycles in an ansa-type way. The core-modified calixpyrroles adopt a 1,3-alternate conformati...

One new binuclear chloride bridged copper(II) complex [L′(Cl)Cu-(μ-Cl)-Cu(pz)L′](PF6)2 (1) and two mononuclear cobalt(II) complexes [Co(Cl)L]BF4·1/2CH3OH (2) and [Co(Cl)L]PF6 (3) where L = {N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)}(2-aminomethyl)pyridine, L′ = {N-(3,5-dimethylpyrazol-1-ylmethyl)}(2-aminomethyl)pyridine and pz = 3,5-dimethyl-pyrazole have been synthesized and characterized by physico-chemical methods and single crystal X-ray diffraction studies. The crystal structure of the binuclear copper(II) complex [L′(Cl)Cu-(μ-Cl)-Cu(pz)L′](PF6)2 shows that the two square plane copper(II) moieties are joined through a single chloride (μ-Cl) bridge and the coordination environment around the two copper atoms are different, whereas the cobalt ion in [Co(Cl)L]BF4·1/2CH3OH has a trigonal bipyramidal geometry. The cytotoxic activity of the ligand, and the copper and cobalt complexes 1 and 2 were measured in vitro against the human lymphocyte HL-60 and it shows that the metal complexes have different cytotoxic activities to the organic ligand.

A series of diester-dicarboxylic acids, L1H2, L2H2, L3H2, L4H2, and L5H2 and their dinuclear Cu2 complexes [Cu(L1)CH3CN]2 (1), [Cu(L2)H2O]2 (2), [Cu(L3)CH3CN]2 (3), [Cu(L4)EtOH]2 (4), and [Cu(L5)CH3CN]2 (5), were synthesized. The crystal structures obtained for 1, 2, and 4 and the density functional theory optimized structures for 2, 3, and 5 illustrated the formation of tetracarboxylate “paddle wheel” complexes. The phthalyl and diphenyl head groups and the spacer moieties were appropriately altered and the size of the chelate ring expanded from 15-membered in 1 to 21-membered in 5. The dinuclear units have strong Cu–Cu interaction with EPR spectra exploring spin coupled features.

Binuclear cyanate bridged nickel(II) complex [Ni(L)(NCO)] 2 (PF 6 ) 2 ( 1 ) and copper(II) complex [Cu(L)(NCO)] 2 (PF 6 ) 2 ( 2 ), where L is N , N -bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine, a tetradentate N 4 -coordinated ligand have been synthesized and characterized by physicochemical method. The structures of complexes 1 and 2 have been studied by single crystal X-ray diffraction analysis. The structure analysis reveals that both nickel(II) and copper(II) center are coordinated in distorted octahedral fashion and coordination mode of cyanate ligand is end-to-end (μ-1,3) for complex 1 but it is double end-on (μ-1,1) mode for complex 2 . The variable temperature magnetic susceptibility data, measured from 2 to 300 K, show weak antiferromagnetic interaction with J value −6.2(1) cm −1 for complex 1 , whereas complex 2 has very weak ferromagnetic interaction with J value +0.5(1) cm −1 .

When the complexes [Cu(L1)(H2O)](ClO4)2 1, where L1 = 4-methyl-1-(pyrid-2-ylmethyl)-1,4-diazacycloheptane, and [Cu(L2)Cl2] 2, where L2 = 4-methyl-1-(quinol-2-ylmethyl)-1,4-diazacycloheptane are interacted with one/two equivalents of bis(p-nitrophenylphosphate, (p-NO2Ph)2PO2, BNP), no hydrolysis of BNP is observed. From the solution the adducts of copper(II) complexes [Cu2(L1)2((p-NO2Ph)2PO2)2]-(ClO4)2 3 and [Cu(L2)((p-NO2Ph)2PO2)2]·H2O 4 have been isolated and structurally characterised. The X-ray crystal structure of 3 contains two Cu(L1) units bridged by two BNP molecules. The Cu···Cu distance (5.1 A) reveals no Cu–Cu interaction. On the other hand, the complex 4 is mononuclear with Cu(II) coordinated to the 3N ligand as well as BNP molecules through phosphate oxygen. The trigonality index (τ, 0.37) observed for 4 is high suggesting the presence of significant trigonal distortion in the coordination geometry around copper(II). The complexes are further characterized by spectral and electrochemical studies.

Mononuclear NCS− containing complexes, [M(NCS)2L] (L = N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine), [Cu(NCS)2L′] (L′ = N-(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine), and NCSe− containing complexes [ML(NCSe)(H2O)]ClO4 (M = Ni+2, Co+2) have been synthesized and characterized by elemental analysis, spectroscopic, and physico-chemical methods. Structural studies of [Cu(NCS)2L′] show copper is five coordinate with distorted trigonal bipyramidal geometry with two cis NCS−. [M(NCS)2L] and [ML(NCSe)(H2O)]ClO4 (M = Ni+2 and Co+2) are expected to be octahedral.

Two new chiral Mn(III) macrocyclic salen complexes 1a and 1b were prepared for the enantioselective epoxidation of non-functionalized alkenes. A 5 mol% loading of these catalysts in the presence of pyridine N-oxide as an axial base and sodium hypochlorite or urea hydrogen peroxide adduct as oxidant worked well to give respective epoxides in high yields and ee (up to >95% in selected cases). The catalyst 1b with urea hydrogen peroxide adduct as an oxidant was recovered by precipitation with hexane and was reused up to four times with retention of enantioselectivity.

A series of new copper(II) complexes of four sterically hindering linear tridentate 3N ligands N′-ethyl-N′-(pyrid-2-ylmethyl)-N,N-dimethylethylenediamine (L1), N′-benzyl-N′-(pyrid-2-ylmethyl)-N,N-dimethylethylenediamine (L2), N′-benzyl-N′-(6-methylpyrid-2-yl-methyl)-N,N-dimethylethylenediamine (L3) and N′-benzyl-N′-(quinol-2-ylmethyl)-N,N-dimethylethylenediamine (L4) have been isolated and examined as catalysts for olefin aziridination. The complexes [Cu(L1)Cl2]·CH3OH 1, [Cu(L2)Cl2]·CH3OH 2, [Cu(L3)Cl2]·0.5 H2O 3 and [Cu(L4)Cl2] 4 have been structurally characterized by X-ray crystallography. In all of them copper(II) adopts a slightly distorted square pyramidal geometry as inferred from the values of trigonality index (τ) for them (τ: 1, 0.02; 2, 0.01; 3, 0.07; 4, 0.01). Electronic and EPR spectral studies reveal that the complexes retain square-based geometry in solution also. The complexes undergo quasireversible Cu(II)/Cu(I) redox behavior (E1/2, −0.272 − −0.454 V) in acetonitrile solution. The ability of the complexes to mediate nitrene transfer from PhINTs and chloramine-T trihydrate to olefins to form N-tosylaziridines has been studied. The complexes 3 and 4 catalyze the aziridination of styrene very slowly yielding above 80% of the desired product. They also catalyze the aziridination of the less reactive olefins like cyclooctene and n-hexene but with lower yields (30–50%). In contrast to these two complexes, 1 and 2 fail to catalyze the aziridination of olefins in the presence of both the nitrene sources. All these observations have been rationalized based on the Cu(II)/Cu(I) redox potentials of the catalysts.

Two chiral coordination polymers involving amino acid backbone l -cysteic acid (H2 l -cys) and N-donor ligand 4,4′-bipyridine (4,4′-bpy) [{Cd( l -cys)(4,4′-bpy)(H2O)}3.5H2O]n 1, [{Zn2( l -cys)2(4,4′-bpy)2(H2O)4}·(H2O)·(4,4′-bpy)]n 2 with rectangular grids have been synthesized. Both compounds are insoluble in common polar/non-polar solvents and well characterized by various physico-chemical techniques such as CHN, IR, TGA, NMR, solid state CD and single crystal X-ray diffraction methods. Complexes 1 and 2 comprise l -cysteate dianions self assembled into chiral coordination polymers by bridging the adjacent metal centres through the carboxylate oxygen generating one-dimensional helical chains. The helical chains are pillared by 4,4′-bpy generating two dimensional network. Complex 1 generates two dimensional (4,4) rectangular grid network with dimension 4.77 A × 11.74 A (based on dCd···Cd) involving with the edge sharing l -cys and 4,4′-bpy ligands, respectively. Complex 2 possesses a brick-wall type (6,3) network topology with edge lengths of the grids 11.42 A × 10.11 A based on dZn···Zn. Lattice water molecules are encapsulated between the adjacent rectangular grids via hydrogen bonding interactions. One 4,4′-bpy moiety is stacked between the adjacent layers of brick-wall network via weak π···π interaction with the edge sharing N-donor ligand. Even though both the complexes are rigid and stable, N2 adsorption studies by these complexes revealed not much promising results. The terminal protruding sulphonate groups, angular orientation of the grids within the two-dimensional network and interpenetration of the adjacent offset sheets concomitantly prevent the formation of through tubular channels. Flexible coordination geometry around the metal centre and the versatile coordination mode of the amino carboxylate group from the l -cys moiety are accountable for the variation of the appealing network topology in these complexes. Chiral nature is established by solid state CD spectrum which shows a positive cotton effect for both complexes.

An interesting series of nine new copper(II) complexes [Cu2L2(OAc)2]� H2 O( 1), [CuLNCS]� ½H2 O( 2), [CuLNO3]� ½H2 O( 3), [Cu(HL)Cl2]� H2 O( 4), [Cu2(HL)2(SO4)2]� 4H2 O( 5), [CuLClO4]� ½H2 O( 6), [CuLBr]� 2H2 O( 7), [CuL2]� H2 O( 8) and [CuLN3]� CH3OH (9) of 2-benzoylpyridine-N(4)-phenyl semicarbazone (HL) have been synthesized and physico-chemically characterized. The tridentate character of the semicarbazone is inferred from IR spectra. Based on the EPR studies, spin Hamiltonian and bonding parameters have been calculated. The g values, calculated for all the complexes in frozen DMF, indicate the presence of the unpaired electron in the dx2� y2 orbital. The structure of the compound, [Cu2L2(OAc)2 ]( 1a) has been resolved using single crystal X-ray diffraction studies. The crystal structure revealed monoclinic space group P21/n. The coordination geometry about the copper(II) in 1a is distorted square pyramidal with one pyridine nitrogen atom, the imino nitrogen, enolate oxygen and acetate oxygen in the basal plane, an acetate oxygen form adjacent moiety occupies the apical position, serving as a bridge to form a centrosymmetric dimeric structure.

A family of fluoroionophores have been synthesized incorporating Ru(II)-bipyridine moiety as fluorogenic unit and amino/benzenesulphonamido functionalized 1,10-phenanthroline moiety, attached to Ru(II), as binding sites. Two of the ligands and one of the complexes have been characterized crystallographically. Anion recognition property, studied by luminescence, UV–vis and 1H NMR spectroscopy, with a large number of anions exhibit strong complexation with F−, H2PO4− and AcO−. Binding constants have been determined from luminescence titration and 1H NMR study gave insight about binding site of anions. Bidentate chelating nature of the H2PO4− and AcO− anions and steric crowding created by benzenesulphonamide moiety has significantly influenced binding constants and selectivity.

The iron(III) complexes of the tridentate N 3 ligands pyrazol-1-ylmethyl(pyrid-2-ylmethyl)amine (L1), 3,5-dimethylpyrazol-1-ylmethyl(pyrid-2-ylmethyl)amine (L2), 3- iso -propylpyrazol-1-ylmethyl(pyrid-2-ylmethyl)amine (L3) and (1-methyl-1 H -imidazol-2-ylmethyl)pyrid-2-ylmethylamine (L4) have been isolated and studied as functional models for catechol dioxygenases. They have been characterized by elemental analysis and spectral and electrochemical methods. The X-ray crystal structure of the complex [Fe(L1)Cl 3 ] 1 has been successfully determined. The complex possesses a distorted octahedral coordination geometry in which the tridentate ligand facially engages iron(III) and the Cl − ions occupy the remaining coordination sites. The Fe–N pz bond distance (2.126(5) A) is shorter than the Fe–N py bond (2.199(5) A). The systematic variation in the ligand donor substituent significantly influences the Lewis acidity of the iron(III) center and hence the interaction of the present complexes with a series of catechols. The catecholate adducts [Fe(L)(DBC)Cl], where H 2 DBC = 3,5-di- tert -butylcatechol, have been generated in situ and their spectral and redox properties and dioxygenase activities have been studied in N , N -dimethylformamide solution. The adducts [Fe(L)(DBC)Cl] undergo cleavage of DBC 2− in the presence of dioxygen to afford major amounts of intradiol and smaller amounts extradiol cleavage products. In dichloromethane solution the [Fe(L)(DBC)Cl] adducts afford higher amounts of extradiol products (64.1–22.2%; extradiol-to-intradiol product selectivity E / I , 2.6:1–4.5:1) than in DMF (2.5–6.6%; E / I , 0.1:1–0.4:1). The results are in line with the recent understanding of the function of intra- and extradiol-cleaving catechol dioxygenases.

Five new transition metal complexes [MnL(OAc)]·H 2 O ( 1 ), [FeLCl 2 ] ( 2 ), [NiL 2 ]·H 2 O ( 3 ), [CuLCl] ( 4 ) and [ZnL 2 ]·2H 2 O ( 5 ) have been synthesized using a tridentate Schiff base ligand, HL (quinoxaline-2-carboxalidine-2-amino-5-methylphenol) and the complexes have been characterized by physicochemical and spectroscopic techniques. The spectral analyses reveal an octahedral geometry for 3, square pyramidal structure for 2 and square planar structure for 4 . Analytical and physicochemical data indicate tetrahedral structure for 1 and octahedral structure for 5 . The crystallographic study reveals that [NiL 2 ]·H 2 O shows distorted octahedral geometry with a cis arrangement of N 4 O 2 donor set of the bis Schiff base and exhibits a two-dimensional polymeric structure parallel to [0 1 0] plane. The complexes were screened for catalytic phenol hydroxylation reaction. Coordinatively unsaturated manganese(II), iron(III) and copper(II) complexes were found to be active catalysts. The poor catalytic activity of the nickel(II) complex is due to coordinatively saturated octahedral nature of the complex. Maximum conversion of phenol was observed for the copper(II) complex and the major product was catechol.

Specific recognition of CN(-) in sodium cyanide solution was achieved using two imidazole-based receptors (A and B). Visually detectable color changes were associated with the formation of hydrogen bonded adducts, A.CN(-) and B.CN(-). Ratiometric fluorescence response was achieved for receptor A on binding to CN(-), and this reagent was used for imaging bacterial cells pre-exposed to 1.42 microM CN(-) solution.

Two copper/cobalt metal complexes, [Cu( l -cys)(2,2′-bpy)(H2O)] (1) and {[Co( l -cys)(4,4′-bpy)(H2O)]·H2O}n (2), with the N-donor ligands 2,2′-bipyridyl/4,4′-bipyridyl and the l -cysteate dianion ( l -cys) have been synthesized by different reaction methods and structurally characterized. Compound 1 exists as a discrete monomeric unit in which the metal ions possess a distorted square-pyramidal coordination environment provided by nitrogen atoms from the 2,2′-bpy ligand and the amino-carboxylate group of l -cys in a chelated coordination, constituting the square base, and with a water molecule occupying the axial coordination site to complete the penta coordination. Packing and hydrogen bonding interactions of 1 reveal that the screw related monomeric units are involved in intermolecular hydrogen bonding with the formation of helical bilayers via O–H⋯O and N–H⋯O interactions. These hydrogen bonded bilayered helical nets are involved in stacking and C–H⋯O interactions which generate a two dimensional hydrogen bonded network in the bc-plane. Complex 2 is a two dimensional coordination polymer which is insoluble in common polar and non-polar solvents. The coordination around the metal center possesses a distorted octahedral geometry. The adjacent metal centers are bridged via the carboxylate group of the l -cys moiety in a syn–anti fashion, generating a one dimensional helical network along the b-axis. Adjacent helical chains are further pillared by the 4,4′-bpy ligand through the terminal nitrogen atoms, generating a two dimensional square grid type coordination network. Both the complexes are characterized well by various physico-chemical techniques such as CHN analysis, IR spectroscopy, PXRD and CD analysis.

Metalloreceptors containing ruthenium(II) bipyridine unit as fluorophore and pendant macrocyclic units as ionophore have been synthesized and their luminescence and electrochemical properties have been investigated. Ion-binding study of these fluoroionophore with the anions F − , Cl − , Br − , I − , H 2 PO 4 - , ClO 4 - , NO 3 - , BF 4 - , CH 3 COO − , and HSO 4 - and cations Na + , K + , Mg 2+ , Ca 2+ , Zn 2+ , Ba 2+ , Sr 2+ Cd 2+ , Hg 2+ , Pb 2+ and Cu 2+ , monitored by luminescence and 1 H NMR spectral changes, reveal strong interactions of H 2 PO 4 - and F − for 2 and 3 and of Cu 2+ only for 3 . Luminescence titrations for 2 and 3 have been carried out to determine binding constants ( K s ), and the calculated values are in the range 2.85 × 10 2 to 4.48 × 10 4 M −1 . The 1 H NMR spectral changes for 2 and 3 with the addition of increasing concentration of F − and H 2 PO 4 - exhibit substantial low-field shift of the CO NH proton indicating its involvement in complex formation with the anions. The H 2 PO 4 - adduct of 2 and 3 have been isolated and characterized by 1 H and 31 P NMR, mass and IR spectroscopy. The results are discussed in light of selectivity, structures of the anion bound complexes and their luminescence property.

Six new coordination polymers namely [{Cu(μ- L1 )(CH 3 COO) 2 }] ∝ 1a , [{Cu(μ- L1 ) 2 (CH 3 COO) 2 ] ∝ 1b , [{Cu(μ- L1 ) 2 (H 2 O) 2 }(NO 3 ) 2 ] ∝ 2 , [{Cu(μ- L1 ) 2 (H 2 O) 2 }(ClO 4 ) 2 ] ∝ 3 , [{Cu(μ- L1 )(H 2 O) 2 (μ-SO 4 )}·3H 2 O] ∝ 4a and [{Cu(μ- L1 ) 2 SO 4 }·X] ∝ 4b ( L1 = N,N ′-bis-(3-pyridyl)terephthalamide) have been synthesized. Single crystal structures of five coordination polymers namely 1a , 2–4b and the free ligand L1 are discussed in the context of the effect of conformation dependent ligating topology of the ligands, hydrogen bonding backbone, counter anions on the resultant supramolecular structures observed in these coordination polymers. It was revealed from the single crystal X-ray structure analysis that conformation dependent ligating topology of the bis-amide ligand L1 , counter anion’s ligating strength dependent metal: ligand ratio, hydrogen bonding ability of the ligand as well as counter anions are responsible for the formation of 1D zigzag, 1D looped chain, 2D corrugated sheet in 1a , 2–3 , 4a − 4b , respectively. By following in situ coordination polymer crystallization technique, anion binding and separation studies have also been performed; nitrate anion has been separated as neat coordination polymer crystals from a complex mixture of anions.

Three metal complexes containing malonate as primary ligand and 4-aminopyridine as secondary ligand (counter ion) namely, {(ampyH)2[Cu(mal)2]}n (1), (ampyH)2[Ni(mal)2(H2O)2] (2) and (ampyH)2[Co(mal)2(H2O)2] (3) [ampyH = protonated 4-aminopyridine, malH2 = malonic acid] have been synthesized from purely aqueous media and their crystal structures have been determined by single crystal X-ray diffraction. The copper complex is polymeric, whereas the nickel and cobalt complexes are monomeric in nature. The most striking feature of the present study is the observed ligand induced topological variations of the [Cu(mal)2]2− unit, which is the building block not only for 1, but for several other copper–malonate complexes previously synthesized by us. It is also observed that this influence of the ligand is not reflected in the primary coordination of the analogs Ni(II) and Co(II) complexes, as the same monomeric unit [M(II)(mal)2(H2O)2]2−, [M = Ni/Co] exists not only in 2 and 3, but also in other Ni and Co complexes prepared by us, although there are subtle differences in the overall supramolecular arrangements in the solid state of these complexes (Ni and Co). Starting with 2-amino-4-picoline molecule as an auxiliary ligand [S. Ray Choudhury, A.D. Jana, E. Colacio, H.M. Lee, G. Mostafa, S. Mukhopadhyay, Cryst. Growth Des. 7 (2007) 212], we have found that protonated heterocyclic bases (2-amino-4-picoline and 2-aminopyridine) have a preferred hydrogen bonded recognition motif R 2 2 ( 8 ) with metal carboxylate frameworks, which has an important role in guiding the crystal packing in the solid state. In the present study, we have extended our investigation by choosing 4-aminopyridine as an auxiliary ligand and discuss its effect in the overall self-assembly. A comprehensive comparison of the present complexes with our previously reported related complexes revealed the delicate nature of the self-assembly process.

Four new coordination polymers of cadmium(II) with hexamethylenetetramine (htm) have been synthesized and characterized by routine physicochemical techniques as well as by X-ray single crystal structure analysis. They are [CdBr(htm)(SCN)(H2O)2·CH3OH]n (1), [CdI(htm)(SCN)(H2O)2·0.5(CH3OH)]n (2), [Cd2(htm)3(SCN)4(H2O)]n·nH2O (3) and [Cd3Br6(htm)2(H2O)5·(htm)(H2O)6]n (4). Complexes 1, 2 and 3 exhibit 1D polymeric structure and complex 4 shows a 2D undulated layered arrangement, containing Cd6(htm)6 hexagonal units as building block, which extended to a 3D supramolecular architecture through hydrogen bonding. Thorough thermal investigation suggest that as far as the thermal stability of Cd(II)-htm bond is concerned it attains the maximum in complex 1 and minimum in complex 4. In case of complex 3 the thermal study inferred that CdS end product was obtained at ∼730 °C, whereas in case of other complexes the thermally stable end product remained unidentified. Solid state fluorescence study shows that all the complexes are luminescent at room temperature except complex 3.

A stereoselective Michael addition of homoenolate, generated from enals by nucleophilic heterocyclic carbene (NHC) catalysis, to beta-nitrostyrenes is reported for the first time. The products of this reaction obtained in good yields are of potential value in the synthesis of a variety of acyclic and heterocyclic compounds.

The Schiff base ligands 2-(2,6-diisopropylphenyliminomethyl)phenol H(L1), 5-diethylamino-2-(2,6-diisopropylphenyliminomethyl)phenol H(L2), 2,4-di-tert-butyl-6-(2,6-diisopropylphenyliminomethyl)phenol H(L3), 3-(2,6-diisopropylphenyliminomethyl)naphthalen-2-ol H(L4) and 4-(2,6-diisopropylphenyliminomethyl)-5-hydroxymethyl-2-methylpyridin-3-ol H(L5) have been synthesized by the condensation, respectively, of salicylaldehyde, 4-(diethylamino)salicylaldehyde, 3,5-di-tert-butylsalicylaldehyde, 2-hydroxy-1-napthaldehyde and pyridoxal with 2,6-diisopropylaniline. The copper(II) bis-ligand complexes [Cu(L1)2] 1, [Cu(L2)2] 2, [Cu(L3)2] 3, [Cu(L4)2] 4 and [Cu(L5)2] · CH3OH 5 of these ligands have been isolated and characterized. The X-ray crystal structures of two of the complexes [Cu(L1)2] 1 and [Cu(L5)2] · CH3OH 5 have been successfully determined, and the centrosymmetric complexes possess a CuN2O2 chromophore with square planar coordination geometry. The frozen solution EPR spectra of the complexes reveal a square-based CuN2O2 chromophore, and the values of g‖ and g‖/A‖ index reveal enhanced electron delocalization by incorporating the strongly electron-releasing –NEt2 group (2) and fusing a benzene ring on sal-ring (4). The Cu(II)/Cu(I) redox potentials of the Cu(II) complexes reveal that the incorporation of electron-releasing –NEt2 group and fusion of a benzene ring lead to enhanced stabilization of Cu(II) oxidation state supporting the EPR spectral results. The hydrogen bonding interactions between the two molecules present in the unit cell of 5a generate an interesting two-dimensional hydrogen-bonded network topology.

meso-Tetraarylporphycenes, structural isomers of meso-tetraarylporphyrins, were synthesized by the acid-catalyzed oxidative coupling reaction for the first time which is an alternative synthetic methodology to the traditional McMurry coupling reaction. The structure of the macrocycle and Ni(II) complex are characterized by single-crystal X-ray diffraction analyses where both form 1-D supramolecular assembly.

A series of mixed halide–dicyanamide and halide complexes of cadmium(II) mediated by 2-aminoalkylpyridine ligands [2-aminomethylpyridine (ampy) and 2-aminoethylpyridine (aepy)] have been synthesized. Five of them, $[CdCl(dca)(aepy)]_n$ (1), $[CdBr(dca)(ampy)]_n$ (2), $[CdCl(dca)(ampy)]_n$ (3)(dca = dicyanamide); $[CdI_2(aepy)]_n$ (4), and $[CdI_2(ampy)]_n$ (5), (dca = dicyanamide) have been characterized by X-ray single crystal structure analysis. The structural determination shows that the compounds are 1D coordination polymers, with the exception of 3 that gives origin to a 2D sheet-like network. The ampy and aepy ligands (also with the occurrence of dca anions in 1–3) reveal to be useful ancillary fragments for the construction of unprecedented Cd–halide polymeric species. The crystal packing shows that the dimensionality of all compounds is enlarged to 2D, and 3D in the case of complex 3, through \pi – \pi interactions occurring between the pyridine rings. All the species exhibit interesting luminescence property in solution as well in solid state which is originated from ligand-centered \pi – \pi* transitions.The fluorescence band maxima and fluorescence efficiency (in methanol) are found to be dependent not only on the pyridine ligand but also on the type of halide, and the co-ligand. Solid state luminescent study implies that p–p interactions occurring between pyridine rings are also important in controlling the fluorescence intensity. Amongst the synthesized complexes reported, complex 5 exhibits the highest fluorescence efficiency in methanol.

A series of dinuclear copper(II) complexes has been synthesized with the aim to investigate their applicability as potential structure and function models for the active site of catechol oxidase enzyme. They have been characterized by routine physicochemical techniques as well as by X-ray single-crystal structure analysis: [Cu 2(H 2L2 (2))(OH)(H 2O)(NO 3)](NO 3) 3.2H 2O ( 1), [Cu(HL1 (4))(H 2O)(NO 3)] 2(NO 3) 2.2H 2O ( 2), [Cu(L1 (1))(H 2O)(NO 3)] 2 ( 3), [Cu 2(L2 (3))(OH)(H 2O) 2](NO 3) 2, ( 4) and [Cu 2(L2 (1))(N 3) 3] ( 5) [L1 = 2-formyl-4-methyl-6R-iminomethyl-phenolato and L2 = 2,6-bis(R-iminomethyl)-4-methyl-phenolato; for L1 (1) and L2 (1), R = N-propylmorpholine; for L2 (2), R = N-ethylpiperazine; for L2 (3), R = N-ethylpyrrolidine, and for L1 (4), R = N-ethylmorpholine]. Dinuclear 1 and 4 possess two "end-off" compartmental ligands with exogenous mu-hydroxido and endogenous mu-phenoxido groups leading to intermetallic distances of 2.9794(15) and 2.9435(9) A, respectively; 2 and 3 are formed by two tridentate compartmental ligands where the copper centers are connected by endogenous phenoxido bridges with Cu-Cu separations of 3.0213(13) and 3.0152(15) A, respectively; 5 is built by an end-off compartmental ligand having exogenous mu-azido and endogenous mu-phenoxido groups with a Cu-Cu distance of 3.133(2) A (mean of two independent molecules). The catecholase activity of all of the complexes has been investigated in acetonitrile and methanol medium by UV-vis spectrophotometric study using 3,5-di- tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) as substrates. In acetonitrile medium, the conversion of 3,5-DTBC to 3,5-di- tert-butylbenzoquinone (3,5-DTBQ) catalyzed by 1- 5 is observed to proceed via the formation of two enzyme-substrate adducts, ES1 and ES2, detected spectroscopically for the first time. In methanol medium no such enzyme-substrate adduct has been detected, and the 3,5-DTBC to 3,5-DTBQ conversion is observed to be catalyzed by 1- 5 very efficiently. The substrate TCC forms an adduct with 2- 5 without performing further oxidation to TCQ due to the high reduction potential of TCC (in comparison with 3,5-DTBC). But most interestingly, 1 is observed to be effective even in TCC oxidation, a process never reported earlier. Kinetic experiments have been performed to determine initial rate of reactions (3,5-DTBC as substrate, in methanol medium) and the activity sequence is 152 = 43. A treatment on the basis of Michaelis-Menten model has been applied for kinetic study, suggesting that all five complexes exhibit very high turnover number, especially 1, which exhibits turnover number or K cat of 3.24 x 10 (4) (h (-1)), which is approximately 3.5 times higher than the most efficient catalyst reported to date for catecholase activity in methanol medium.