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.

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.

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.

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.

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.

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.

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.

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.

Sustainable Heterogeneous Catalysts for CO2 Utilization by Using Dual Ligand ZnII /CdII Metal-Organic Frameworks.

Two-dimensional ZnII /CdII -based dual ligand metal-organic frameworks (MOFs) {[M(CHDC)(L)]⋅H2 O}n involving 4-pyridyl carboxaldehyde isonicotinoylhydrazone (L) in combination with flexible 1,4-cyclohexanedicarboxylic acid (H2 CHDC) as linkers have been synthesized by adaptable synthetic protocols including a green mechanochemical (grinding) method. Characterization, chemical/thermal stability, phase purity, and solid-state luminescent properties of both MOFs have been established by various analytical methods. Structural analysis revealed dimeric metal clusters composed of [M2 (CHDC)2 ]n loops doubly pillared with L, generating a 2D framework. Both MOFs can be used as highly active solvent-free binary catalysts for CO2 cycloaddition with epoxides in the presence of the co-catalyst tetrabutylammonium bromide (TBAB) with good catalytic conversion in up to six catalytic cycles without significant loss of activity. The present investigation demonstrates the application of MOFs as efficient heterogeneous catalysts for CO2 utilization under moderate reaction conditions. Based on the single-crystal X-ray data, a probable mechanism for the cycloaddition reaction has also been proposed.

Nanoemulsions with All Ionic Liquid Components as Recyclable Nanoreactors.

Nanoemulsions (NEs) comprising ionic liquids (ILs); ethanolammonium formate (HO-EOAF), proliniumisopropylester dioctylsulfosuccinate ([ProC3][AOT]), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, ([Bmim][NTf2]) as insoluble hydrophilic, surface active, and hydrophobic components have been constructed. This novel class of colloidal formulations exhibited several contrasting properties vis-à-vis conventional water-in-oil or water-in-ionic liquid or nonaqueous NEs such as (i) spontaneous formation, (ii) thermodynamic stability and isotropic nature, (iii) decrease of droplet size with increase in polar medium concentration, and (iv) high thermal and kinetic stability. Mechanisms and characteristics for such anomalies have been investigated by physical, spectroscopic, and imaging techniques. NEs have been demonstrated as versatile recyclable nanoreactors for user-friendly synthesis of materials such as metal-organic frameworks/light harvesting hybrid systems. We anticipate that this development will lead to the construction of several other need-based "all ionic-liquid nanoemulsions" in view of the flexibility provided by the tailoring nature of ILs.

A BF3·Et2O catalyzed atom-economical approach to highly substituted indole-3-carbinols from nitrosobenzenes and propargylic alcohols.

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.

Phenothiazinyl Boranes: A New Class of AIE Luminogens with Mega Stokes Shift, Mechanochromism, and Mechanoluminescence.

Phenothiazines with a dimesityl boron moiety, a new class of aminoboranes with B-N linkage, were synthesized. These aminoboranes exhibited interesting photophysical behavior including aggregation-induced emission (AIE), mechanochromism (MC), mechanoluminescence (ML), and a mega Stokes shift (up to 312 nm in hexane). The solid-state emission of the aminoboranes could be switched reversibly by grinding-fuming processes. Furthermore, the phenothiazine derivative with a bromo and an arylborane group at 3- and 7-positions exhibited bright mechanoluminescence.

Mixed-Ligand LMOF Fluorosensors for Detection of Cr(VI) Oxyanions and Fe3+/Pd2+ Cations in Aqueous Media.

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 observed limits of detection (LOD) values by 1 for CrO42-/Cr2O72- were 0.25 µM (48 ppb)/0.43 µM (126 ppb) and for Fe3+/Pd2+ were 3.76 µM (0.61 ppm)/0.20 µM (35 ppb), whereas LOD values by 2 were 0.18 µM (35 ppb)/0.19 µM (55 ppb) and 1.77 µM (0.29 ppm)/0.10 µM (18 ppb), respectively. Simple fluorescent-based test paper strips have been developed for reliable and visual detection of the mentioned analytes in practical applications. The present investigation clearly demonstrates selective detection of CrO42-/Cr2O72- and Fe3+/Pd2+ in aqueous media, and the probable mechanism for the quenching phenomena based on structural aspects has also been discussed.

Mechanochemical and Conventional Synthesis of Zn(II)/Cd(II) Luminescent Coordination Polymers: Dual Sensing Probe for Selective Detection of Chromate Anions and TNP in Aqueous Phase.

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 of aqueous suspensions of CPs selectively quenches by chromate anions or TNP among large pools of different anions or nitro compounds, respectively. Competitive experiments in the presence of interfering anions/other nitro compounds also revealed no major effect in the quenching efficiency, suggesting the selective detection of hexavalent chromate anions as well as TNP by the LCPs. The limits of detection by CP1 for CrO42-/Cr2O72- and TNP are 4 ppm/4 ppm and 28 ppb, respectively, whereas the limits of detection by CP2 for the same analytes are 1 ppm/1 ppm and 14 ppb, respectively. A probable mechanism for the quenching phenomena is also discussed.

Coordinatively Unsaturated Lanthanide(III) Helicates: Luminescence Sensors for Adenosine Monophosphate in Aqueous Media.

Coordinatively unsaturated double-stranded helicates [(H2 L)2 Eu2 (NO3 )2 (H2 O)4 ](NO3 )4 , [(H2 L)2 Tb2 (H2 O)6 ](NO3 )6 , and [(H2 L)2 Tb2 (H2 O)6 ]Cl6 (H2 L=butanedioicacid-1,4-bis[2-(2-pyridinylmethylene)hydrazide]) are easily obtained by self-assembly from the ligand and the corresponding lanthanide(III) salts. The complexes are characterized by X-ray crystallography showing the helical arrangement of the ligands. Co-ligands at the metal ions can be easily substituted by appropriate anions. A specific luminescence response of AMP in presence of ADP, ATP, and other anions is observed. Specificity is assigned to the perfect size match of AMP to bridge the two metal centers and to replace quenching co-ligands in the coordination sphere.

A mechanochemically synthesized Schiff-base engineered 2D mixed-linker MOF for CO2 capture and cationic dye removal.

Developing synthetic strategies for smart materials for the adsorption and separation of toxic chemicals is of great importance. Metal-organic frameworks (MOFs) have been proven to be outstanding adsorbent materials that possess excellent pollutant removal performances in wastewater treatment, including dye recycling. In this work, a neutral Cd(II) based 2D framework with a dual ligand strategy involving -OH functionalized 5-hydroxyisophthalic acid (5-OH-H2IPA) and the amide decorated Schiff base ligand (E)-N'-(pyridin-4-ylmethylene)isonicotinohydrazide (L) has been synthesized by different synthetic routes and characterized by various analytical methods. Thus, crystals of {[Cd(5-OH-IPA)(L)]·CH3OH}n synthesized via diffusion (ADES-7D) and the phase pure bulk product synthesized by conventional reflux (ADES-7C) and the mechanochemical grinding method (ADES-7M) have been established using PXRD data of the respective product showing identical simulated SXRD data to those of ADES-7D. The mechanochemically synthesized ADES-7M possesses a better surface area and CO2 adsorption capability compared to ADES-7C, which is also supported by electron microscopy and particle size measurements. Furthermore, ADES-7 can be used as an efficient adsorbent material for the reversible, selective adsorption (42-99%) and separation of the cationic dyes malachite green (MG), methyl violet (MV), methylene blue (MB), and rhodamine B (RhB) from the mixture of cationic/anionic dyes (methyl orange (MO) and bromocresol green (BCG)) in the aqueous phase. Specifically, ADES-7M possesses better dye capture capability compared to ADES-7C, even in the case of the bigger dye RhB with adsorption differences of 2.38 to 1.01 mg g-1, respectively. The dye adsorption kinetics follows pseudo-second-order kinetics, and the dye adsorption isotherm fits well with the Langmuir/Freundlich adsorption isotherm models. The probable mechanism of adsorption involving the supramolecular interaction between the host MOF and the guest dye has also been proposed.

Spontaneous resolution to absolute chiral induction: pseudo-Kagomé type homochiral Zn(II)/Co(II) coordination polymers with achiral precursors.

It is observed that conglomerate crystallization of achiral precursors yielding racemate metal organic frameworks/coordination polymers (MOFs/CPs) can be driven to absolute homochiral crystallization of the desired enantiomorph by utilizing a suitable chiral induction agent. In a series of crystallization experiments isostructural Zn and Co homochiral CPs (1P, 1M and 2P, 2M) are prepared using the achiral precursors. In the presence of enantiopure camphoric acid, the crystallization process prefers absolute chiral induction over conglomerate formation which is established by single crystal X-ray diffraction and CD spectroscopy.