Cooperativity between the Substrate and Ligand in Palladium-Catalyzed Allylic Alkylation Using 1-Aryl-1-propynes.

A monoprotected amino acid Bz-Gly-OH assists in the allylic alkylation of a variety of ketones, ß-keto esters, aldehydes, etc., during enamine-palladium catalysis. Density functional theory calculations reveal that Bz-Gly-OH assists in the formation of an enamine that attacks the π-allylpalladium complex via an outer sphere mechanism. The preliminary result points to an asymmetric allylic alkylation under a new mode of bifunctional catalysis.

Zn(II)/Cd(II)-Based Metal-Organic Frameworks as Bifunctional Materials for Dye Scavenging and Catalysis of Fructose/Glucose to 5-Hydroxymethylfurfural.

Functional neutral metal-organic frameworks (MOFs) {[M(5OH-IP)(L)]}n [M = Zn(II) for ADES-4; Cd(II) for ADES-5; 5OH-IP = 5-hydroxyisophthalate; L = (E)-N'-(pyridin-3-ylmethylene)nicotinohydrazide) have been synthesized by a diffusion/conventional reflux/mechanochemical method and characterized by various analytical techniques. Crystals were harvested by a diffusion method, and single-crystal X-ray diffraction (SXRD) analysis revealed that an adjacent [M2(COO)2]n ladder chain generates isostructural two-dimensional network motifs by doubly pillaring via L. The bulk-phase purity of ADES-4 and ADES-5 synthesized by a versatile synthetic approach has been recognized by the decent match of powder X-ray diffraction patterns with the simulated one. Both ADES-4 and ADES-5 showed selective adsorption of cationic dyes methylene blue (MB), methyl violet (MV), and rhodamine B (RhB) over anionic dye methyl orange (MO) from water with good uptake and rapid adsorption. Utilization of ADES-4 as a chromatographic column filler for adsorptive removal of individual cationic dyes as well as a mixture of dyes has been demonstrated from the aqueous phase. Interestingly, ADES-4 is reusable with good stability, and it showed a dye desorption phenomenon in methanol. The probable mechanism of cationic dye removal based on insight from structural information and plausible supramolecular interactions has also been explored. Both MOFs also showed efficient catalytic transformation of fructose and glucose into the high-value chemical intermediate 5-hydroxymethylfurfural of industrial significance.

Catalyst-free synthesis of 3,1-benzoxathiin-4-ones/1,3-benzodioxin-4-ones.

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.

Recent advances in metal-organic frameworks as adsorbent materials for hazardous dye molecules.

Water is vital for the sustenance of all forms of life. Hence, water pollution is a universal crisis for the survival for all forms of life and a hurdle in sustainable development. Textile industry is one of the anthropogenic activities that severely pollutes water bodies. Inefficient dyeing processes result in thousands of tons of synthetic dyes being dumped in water bodies every year. Therefore, the efficient removal of synthetic dyes from wastewater has become a challenging research field. Owing to their tuneable structure-property aspects, metal-organic frameworks (MOFs) have emerged as promising adsorbents for the adsorptive removal of dyes from wastewater and textile effluents. In this perspective, we highlight recent studies involving the application of MOFs for the adsorptive removal of hazardous dye molecules. We also classify the developed MOFs into cationic, anionic, and neutral framework categories to comprehend their suitability for the removal of a given class of dyes.

C-H Amidation and Amination of Arenes and Heteroarenes with Amide and Amine using Cu-MnO as a Reusable Catalyst under Mild Conditions.

An atom-economical and efficient route for the direct amidation and amination of aryl C-H bonds using our synthesized recyclable heterogeneous Cu-MnO catalyst is reported here. The direct C-H amidation was carried out using a simple amide without any preactivated coupling partner, and simple air was used as the sole oxidant. The reaction proceeds very smoothly with a broad range of substrates containing numerous functional groups in very good to excellent yields. Direct C-H aminations with a secondary amine were carried out under base-, ligand-, and external oxidant-free conditions in very good to excellent yields in very mild conditions. Both the amidation and amination can be scaled up on a gram scale with similar yields. The major advantage is that our catalyst is recyclable and reused several times without any significant loss of reactivity.

Base-enabled access to diastereoselective spirofuran oxindoles and γ-functionalized allenoates.

Base assisted divergent reactivity of isatins and allenoates has been achieved, which afforded diastereoselective spirofuran oxindoles and γ-functionalized allenoates. The DBU mediated Morita-Baylis-Hillman (MBH) reaction followed by the cascade annulation through the stabilized ß-ammonium enolate intermediate led to the spiro-framework, wherein DABCO furnished the γ-functionalized allenoates. The protocol offers access to biologically relevant functionalized oxindole scaffolds with an excellent substrate scope under mild reaction conditions.

Ring-opening hydrolysis of spiro-epoxyoxindoles using a reusable sulfonic acid functionalized nitrogen rich carbon catalyst.

Controlling the product selectivity of a ring-opening hydrolysis reaction remains a great challenge with mineral acids and to an extent with homogeneous catalysts. In addition, even trace amounts of metal impurities in a bioactive product hinder the reaction progress. This has necessitated the development of robust and metal-free catalysts to offer an alternative sustainable route. We report a nitrogen-rich sulfonated carbon as a catalyst derived from an inexpensive precursor for the synthesis of bioactive vicinal diols of spiro-oxindole derivatives. The well-characterized catalyst shows wide generality with different electronic and steric substituents in the substrates under mild reaction conditions. Hot filtration test confirms no leaching of the acid moiety and the catalyst could be reused for four cycles with retention of activities.

µ-Oxo-bridged diiron(iii) complexes of tripodal 4N ligands as catalysts for alkane hydroxylation reaction using m-CPBA as an oxidant: substrate vs. self hydroxylation.

A series of non-heme µ-oxo-bridged dinuclear iron(iii) complexes of the type [Fe2(µ-O)(L1-L6)2Cl2]Cl21-6 have been isolated and their catalytic activity towards oxidative transformation of alkanes into alcohols has been studied using m-choloroperbenzoic acid (m-CPBA) as an oxidant. All the complexes were characterized by CHN, electrochemical, and UV-visible spectroscopic techniques. The molecular structures of 2 and 5 have been determined successfully by single crystal X-ray diffraction analysis and both possesses octahedral coordination geometry and each iron atom is coordinated by four nitrogen atoms of the 4N ligand and a bridging oxygen. The sixth position of each octahedron is coordinated by a chloride ion. The (µ-oxo)diiron(iii) core is linear in 2 (Fe-O-Fe, 180.0°), whereas it is non-linear (Fe-O-Fe, 161°) in 5. All the diiron(iii) complexes show quasi-reversible one electron transfer in the cyclic voltammagram and catalyze the hydroxylation of alkanes like cyclohexane, adamantane with m-CPBA as an oxidant. In acetonitrile solution, adding excess m-CPBA to the diiron(iii) complex 2 without chloride ions leads to intramolecular hydroxylation reaction of the oxidant. Interestingly, 2 catalyzes alkane hydroxylation in the presence of chloride ions, but intramolecular hydroxylation in the absence of chloride ions. The observed selectivity for cyclohexane (A/K, 5-7) and adamantane (3°/2°, 9-18) suggests the involvement of high-valent iron-oxo species rather than freely diffusing radicals in the catalytic reaction. Moreover, 4 oxidizes (A/K, 7) cyclohexane very efficiently up to 513 TON while 5 oxidizes adamantane with good selectivity (3°/2°, 18) using m-CPBA as an oxidant. The electronic effects of ligand donors dictate the efficiency and selectivity of catalytic hydroxylation of alkanes.

Controlled assembly of cobalt embedded N-doped graphene nanosheets (Co@NGr) by pyrolysis of a mixed ligand Co(ii) MOF as a sacrificial template for high-performance electrocatalysts.

The development of high-efficiency and durable bifunctional electrocatalysts is an important and challenging topic in the area of energy storage/conversion. Herein, we prepared metallic cobalt nanoparticle decorated N-doped graphitic sheets (Co@NGr) by adopting facile pyrolysis of a mixed ligand cobalt-based MOF (CoMOF-2) as a sacrificial template displaying good OER and HER activity. The catalytic material harvested at three different pyrolytic temperatures was characterized by various analytical methods such as PXRD, SEM, TEM, Raman, and XPS analyses. The catalytic activity of the obtained hybrid composite materials towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) was studied. Co@NGr-900 was found to be an efficient bifunctional electrocatalyst and 10 mA cm-2 current density was afforded at an overpotential of 390 mV for OER and 340 mV for HER respectively. This study provides insight for the development of cost-effective nonprecious element-based electrocatalysts for water splitting which has relevance in energy storage and conversion. Catalytic performance is governed by the synergistic compositional effect of metallic cobalt/nitrogen-doping in the graphitic carbon increasing the electrical conductivity/active sites of the composite material.

Crystalline Free-Standing Two-Dimensional Zwitterionic Organic Nanosheets for Efficient Conduction of Lithium Ions.

Crystalline two-dimensional organic nanosheets (2D-ONs) having atomic or near-atomic thickness with infinite lateral dimensions are of crucial significance for their possible application as a material for energy storage. The presence of nanofluidic channels with a designed array of molecular interlayers in such 2D-ONs, for a favorable lithium-ion transport, has special significance for improving the efficacy of lithium-ion batteries. However, the rational design of crystalline 2D-ONs remains a challenge because of the lack of appropriate monomers and convenient preparation methods. Herein, we report a unique lithium-ion conducting behavior of zwitterionic 2D-ONs, formed through self-assembly of a small organic molecule AM-1. Different microscopic studies confirm the near-atomic thickness (∼3.5 nm) of these 2D-ONs. Results of the single-crystal X-ray diffraction studies confirm the presence of a one-dimensional (1D) channel in crystalline 2D-ONs, which was generated during the self-assembly process of the zwitterionic monomer scaffold. The presence of immobilized ionic centers with well-defined directional channels in the 2D-ONs favors the transportation of lithium ions with a room-temperature lithium-ion conductivity of 5.14 × 10-5 S cm-1, which is rather unique for self-assembled 2D-ONs.

Catalytic Direct α-Amination of Arylacetic Acid Synthons with Anilines.

A unique α-amination approach using various anilines has been developed for arylacetic acids via adaptation as benzazoles. The reaction proceeds through a single electron transfer mechanism utilizing an iron-based catalyst system to access α-(N-arylamino)acetic acid equivalents. Modification of approved drugs, facile cleavage of the benzazole auxiliary, and tolerance of amide linkage forming conditions constitute the potential applicability of this strategy.

Catalytic Conversion of Carbon Dioxide Using Binuclear Double-Stranded Helicates: Cyclic Carbonate from Epoxides and Diol.

The construction of sophisticated molecular architectures from chemical subunits requires careful selection of the spacers, precise synthetic strategies, and substantial efforts. Here, we report a series of binuclear double-stranded helicates synthesized from different combinations of pyridyl hydrazone-based multidentate ligands (H2 1, H2 2, H2 3) by increasing the methylene spacer and transition metals (Co, Ni, and Zn). The ligands H2 1 (N'1,N'3-bis((E)-pyridin-2-ylmethylene)malonohydrazide), H2 2 (N'1,N'4-bis((E)-pyridin-2-ylmethylene)succinohydrazide), and H2 3 (N'1,N'5-bis((E)-pyridin-2-ylmethylene)glutarohydrazide) and their respective complexes with Co, Ni, and Zn were obtained. Single-crystal X-ray diffraction studies of these binuclear metallohelicates confirm the double-stranded helical structure of the complexes derived from H2 2. The set of helicates Co-1, Co-2, and Co-3; Ni-1, Ni-2, and Ni-3; and Zn-1, Zn-2, and Zn-3 were investigated for its catalytic activity in the cyclic carbonate formation reaction. Intriguingly, among the synthesized catalyst, Co-1 was found to be better in terms of conversions with the calculated TOF (turnover frequency) of 128/h. The catalytic performance was significantly improved by adding 0.2 mmol of tetrabutylammonium bromide by achieving 76% conversion in 30 min, with the observed TOF of 15,934 h-1/molecule and 7967 h-1/Co center. The results obtained herein show that the double-stranded helicates are effective catalysts for converting both terminal and non-terminal epoxides into their corresponding cyclic carbonates. The striking feature of this catalytic protocol lies in demonstrating the catalytic activity for the conversion of diol to cyclic carbonate, and the detailed kinetic experiments tempted us to propose a tentative reaction mechanism for this conversion.

Colorimetric dual sensor for Cu(II) and tyrosine and its application as paper strips for detection in water and human saliva as real samples.

A calix[4]arene based compound incorporating amide and morpholine moieties has been synthesized and its ion recognition property towards metal ions and application of its metal complex towards sensing of amino acids has been investigated. The synthesized compound interacts with Cu2+ with high selectivity and sensitivity (LOD, 0.1 ppb) in aqueous media with instant color change from colorless to yellow without interference from any other metal ions used in this study. The molecular structure of the calix compound (1) has been determined by single crystal X-ray study and the structure of its Cu2+ complex has been established by DFT calculation. The Cu2+ complex of 1 selectively detects tyrosine (LOD, 1.2 ppm) in water with distinct color change and without any interference from other 22 amino acids used in this study. The mechanism for detection of tyrosine with color change is also presented. For easy field application, paper based sensor strips have been prepared by coating compound 1 and its Cu2+ complex on filter paper, which have been used for semi-quantitative measurement of Cu2+ and tyrosine. Compound 1 and its Cu2+ complex have also been used for detection of Cu2+ and tyrosine, respectively in water and human saliva as real samples and satisfactory results are obtained.

Copper-catalyzed synthesis of spiro-indolofurobenzopyrans: tandem reactions of diazoamides and O-propargyl salicylaldehydes.

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.

Pd-Catalyzed regioselective synthesis of 2,6-disubstituted pyridines through denitrogenation of pyridotriazoles and 3,8-diarylation of imidazo[1,2-a]pyridines.

Synthesis of 2,6-disubstituted pyridines from pyridotriazoles through palladium-catalyzed aerobic oxidative denitrogenative reactions has been described. Denitrogenation of arylated pyridotriazoles generates metal-carbene intermediates in situ and provides selectively 6-aryl-2-benzoylpyridines. The same conditions have been extended to regioselective C-3 and C-8 diarylation of several imidazo[1,2-a]pyridines.

Adenine-Based Zn(II)/Cd(II) Metal-Organic Frameworks as Efficient Heterogeneous Catalysts for Facile CO2 Fixation into Cyclic Carbonates: A DFT-Supported Study of the Reaction Mechanism.

We synthesized two new adenine-based Zn(II)/Cd(II) metal-organic frameworks (MOFs), namely, [Zn2(H2O)(stdb)2(5H-Ade)(9H-Ade)2]n (PNU-21) and [Cd2(Hstdb)(stdb)(8H-Ade)(Ade)]n (PNU-22), containing auxiliary dicarboxylate ligand (stdb = 4,4'-stilbenedicarboxylate). Both MOFs were characterized by multiple analytical techniques such as single-crystal X-ray diffraction (SXRD), powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscopy, as well as temperature program desorption and Brunauer-Emmett-Teller measurements. Both MOFs were structurally robust and possessed unsaturated Lewis acidic metal centers [Zn(II) and Cd(II)] and free basic N atoms of adenine molecules. They were used as heterogeneous catalysts for the fixation of CO2 into five-membered cyclic carbonates. Significant conversion of epichlorohydrin (ECH) was attained at a low CO2 pressure (0.4 MPa) and moderate catalyst (0.6 mol %)/cocatalyst (0.3 mol %) amounts, with over 99% selectivity toward the ECH carbonate. They showed comparable or even higher catalytic activity than other previously reported MOFs. Because of high thermal stability and robust architecture of PNU-21/PNU-22, both catalysts could be reused with simple separation up to five successive cycles without any considerable loss of their catalytic activity. Densely populated acidic and basic sites in both Zn(II)/Cd(II) MOFs facilitated the conversion of ECH to ECH carbonate in high yields. The reaction mechanism of the cycloaddition reaction between ECH and CO2 is described by possible intermediates, transition states, and pathways, from the density functional theory calculation in correlation with the SXRD structure of PNU-21.

Cycloaddition of CO2 with an Epoxide-Bearing Oxindole Scaffold by a Metal-Organic Framework-Based Heterogeneous Catalyst under Ambient Conditions.

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 products, and the structure of the newly synthesized molecules has been established by SXRD analysis. We present a plausible proposed catalytic mechanism through activation of the epoxide ring by the Lewis acidic/basic sites present on the framework surface that is validated by molecular modeling.

Visible Light-Promoted Photocatalytic C-5 Carboxylation of 8-Aminoquinoline Amides and Sulfonamides via a Single Electron Transfer Pathway.

An efficient photocatalytic method was developed for the remote C5-H bond carboxylation of 8-aminoquinoline amide and sulfonamide derivatives. This methodology uses in situ generated •CBr3 radical as a carboxylation agent with alcohol and is further extended to a variety of arenes and heteroarenes to synthesize the desired carboxylated product in moderate-to-good yields. The reaction proceeding through a single electron transfer pathway was established by a control experiment, and a butylated hydroxytoluene-trapped aryl radical cation intermediate in high-resolution mass spectrometry was identified.

An Ionophore for High Lithium Loading and Selective Capture from Brine.

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 LiClO4 and 69.16% with LiCl salt with exclusive selectivity. Under liquid-liquid extraction conditions, this ionophore shows a loading capacity of 27% with 1 M LiCl and 48.57% with 1 M LiClO4 source phase concentration. This new ionophore, therefore, inspiring further to modify and develop a better multinucleating extractant with high lithium loading capacity which is rare in the literature.

Binuclear Double-Stranded Helicates and Their Catalytic Applications in Desymmetrization of Mesodiols.

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 (BNDA). As a result, the racemic L1rac, L2rac, and enantiopure L1RR, L1SS, L2RR, and L2SS ligands are obtained incorporating Cu(II) and Zn(II) salts by a simple one-pot metal template method. The series of dinuclear complexes of [M2LX2] (here, M = Cu2+, Zn2+; X = acetate ion, chloride ion; L = L1RR, L1SS, L1rac, L2RR, L2SS, L2rac) formulas are obtained in common. Among them, the single crystal X-ray structures for [Zn2L1rac(OAc)2] and [Zn2L1SSCl2] complexes are obtained. The detailed crystal structure and the chiroptical studies performed on these complexes dictates a self-sorting behavior in their self-assembly process and illustrate a chirality transfer from the ligand to the metal center on the complexes. The enantiopure dinuclear complexes [M2LRRX2] and [M2LSSX2] generate enantiopure ΛΛ and ΔΔ isomers, respectively, but the racemic complexes produce only homochiral ΛΛ and ΔΔ assemblies. The detailed studies based on UFLC (Ultra Fast Liquid Chromatography), CD, and single crystal X-ray structure together show the absence of heterochiral ΛΔ mesocate. All these complexes are adapted as catalysts for desymmetrization of various mesodiols, and the enantiopure complexes are found to give efficient enantioselectivity in desymmetrization of mesodiols with benzoyl chloride to monobenzoylated ester providing 98% yield and 92% ee.