One-Pot Synthesis of Vinylogous Cyano Aminoaryls (VinCAs) as Benzenic Fluorophores: Tailoring Diverse Emission Colors for White Light Emitting Materials and Cell Imaging.

Donor-acceptor-based organic small molecules with an electronic push-pull effect can demonstrate intramolecular charge transfer to show interesting photoluminescence properties. This is an essential criterion for designing fluorogenic probes for cell imaging studies and the development of organic light-emitting diodes. Now, to design such optical materials sometimes it is necessary to tune the band gap by controlling the energies of the highest occupied molecular orbital and lowest unoccupied molecular orbital. Typically, the band gaps could be modulated by installing unsaturated handles between electron-rich donors and electron-deficient acceptors. However, these methods are often synthetically and economically challenging due to the involvement of expensive catalysts and difficult reaction setups. In our present study, we show a straightforward, cost-effective method for obtaining a series of donor-acceptor-type Vinylogous Cyano Aminoaryls (VinCAs) with diverse emission colors. Further studies reveal that these VinCAs can serve as effective cell imaging agents, showcasing potential use in chemical biology. Additionally, these molecules could be further used to generate white light emission (WLE), showing their potential utility in advanced lighting technologies.

A Multivariate 2D Metal-Organic Framework with Open Metal Sites for Catalytic CO2 Cycloaddition and Cyanosilylation Reactions.

This work reports the synthesis of a dual functional 2D framework, {[Zn2(4-tpom)2(oxdz)2]·4H2O}n (1), at room temperature, where a bent dicarboxylate, oxdz2- (4,4'-(1,3,4-oxadiazole-2,5-diyl)dibenzoate), and a neutral flexible N-donor linker, 4-tpom (tetrakis(4-pyridyloxymethylene)methane), are utilized. Its single-crystal X-ray analysis indicated a 2-fold interpenetrated 2D framework having tetracoordinated Zn(II) centers and dangling pyridyl groups. Its further characterization was carried out with elemental microanalysis, FTIR spectroscopy, TG analysis, and powder X-ray diffraction. The tetracoordinated Zn(II) centers as active Lewis acidic sites and the N atoms of 4-tpom as Lewis basic sites in 1 are explored for its functioning as a heterogeneous catalyst in two important reactions, (i) cycloaddition of CO2 with various epoxides and (ii) cyanosilylation reaction under solvent-free conditions. We could successfully show the cycloaddition of styrene oxide with CO2 (99% conversion) under balloon pressure with low catalyst (0.2-0.3 mol %) and cocatalyst (0.5-0.75 mol %) loadings, which is otherwise difficult to achieve. It was observed that all the substrates (aromatic and aliphatic), irrespective of their sizes, showed conversion percentage >99%. In the cyanosilylation reaction, a conversion of 96% was obtained with 1.5 mol % of 1 at room temperature for 12 h. This framework emerged as an excellent recyclable catalyst for both the reactions.

Strategic Design of Non-d10 Luminescent Metal-Organic Frameworks as Dual-Mode Ultrafast and Selective Sensing Platforms for Aldehydes at the ppb Level.

Utilizing a cautious design of luminescent MOFs of non-d10 divalent transition metals based on two factors (metal nodes in an octahedral geometry to minimize nonradiative energy dissipation and tailored organic chromophores), this work reports {[Ni2(oxdz)2(tpbn)]}n (1), {[Ni2(oxdz)2(tphn)]}n (2), and {[Ni2(oxdz)2(tpon)]}n (3), synthesized at room temperature, varying the spacer length of tpbn/tphn/tpon (four, six, and eight CH2 groups, respectively). This subtle change in 1-3 is correlated to their hydrophobicity and polarizing power via water vapor sorption and selective and sensitive detection of aldehydes at the ppb level, respectively. A decrease in water vapor uptake (14.8, 8.95, and 3.19 mmol g-1 for 1-3, respectively) is observed with an increase in their hydrophobicity. On the other hand, the solution phase detection limits of acetaldehyde and benzaldehyde (2.42 and 6.71 ppb for 1, 2.77 and 4.08 ppb for 2, and 10.35 and 10.4 ppb for 3, respectively) show a similar trend for their polarizing power. The best performance of 1 is expanded to the vapor-phase detection of acetaldehyde (297% luminescence enhancement) under different pH conditions. The second mode of detection of acetaldehyde via the metal-centered electrochemical behavior of 1 provides detection limits of 38.2 and 71.5 ppb at pH 7 and 13, respectively.

Strategic design of a rare trigonal symmetric luminescent covalent organic framework by linker modification.

We designed a trigonal symmetric imine-linked covalent organic framework (COF), TFPC-DAB, with control over the angularity of the building units, where a bent C2-symmetric diamine, such as 1,3-diaminobenzene (1,3-DAB or DAB), with an exo-angle of 120° was used instead of those with an exo-angle of 180°, in combination with a C3-symmetric trialdehyde, such as tri(4-formylphenoxy)cyanurate (TFPC). Its synthesis was accomplished by reacting the building units in a mixture of mesitylene/dioxane/6 M acetic acid under solvothermal conditions. The phase purity, thermal stability, and porosity of TFPC-DAB were established by various analytical techniques. Utilizing the Density Functional Tight Binding (DFTB+) simulation and Pawley refinement, the best fit of the small angle x-ray pattern was found to have an AA stacking of TFPC-DAB in the trigonal space group P3 with low refinement parameters. Such smart materials are in huge demand to detect hazardous corrosive chemicals, such as HCl and NH3. The dual features of electron deficient π-acidic triazine moiety and heteroatoms (N/O) from TFPC and electron rich phenyl units from DAB embodied in the framework enhance its luminescent property and thereby make it suitable for solvent-based HCl and NH3 sensing. The detection limits for HCl and NH3 in methanol were found to be 14 and 82 ppb, respectively. The effect of solvent polarity on the sensing studies was observed with much lower detection limits in dioxane: 2.5 and 11 ppb for HCl and NH3, respectively. A detailed theoretical calculation using density functional theory and configurational bias Monte Carlo modules was conducted for understanding interactions between the COF and HCl or NH3 analytes.

Tandem Transformation of Indazolones to Quinazolinones through Pd-Catalyzed Carbene Insertion into an N-N Bond.

Serendipitous and expedite transformation of 1-aryl- and 2-aryl-1,2-dihydro-3H-indazol-3-ones to 1,2-di(hetero)aryl- and 2,3-di(hetero)aryl-2,3-dihydroquinazolin-4(1H)-ones, respectively, was achieved in high efficiency by reacting them with aldehydic N-tosylhydrazones. The protocol proceeded through a cascade process involving base-mediated Pd-carbenoid generation by the decomposition of N-tosylhydrazones, nucleophilic attack of indazolone on the Pd-carbenoid complex, and intramolecular ring expansion via N-N bond cleavage. The utility of the strategy is demonstrated toward the synthesis of bioactive NPS 53574, a calcium receptor antagonist.

Two Zn(II)/Cd(II) Coordination Polymers as Recyclable Heterogeneous Catalysts for an Efficient Room-Temperature Synthesis of α-Aminonitriles via the Solvent-Free Strecker Reaction.

The α-aminonitriles are versatile building blocks in the synthesis of natural or artificial amino acids as well as important intermediates in organic synthesis. For their synthesis, the three-component Strecker reaction involving an aldehyde or a ketone together with amines and trimethylsilyl cyanide is used. In the literature, hydrothermally produced metal-based heterogeneous Lewis acid catalysts have been utilized in various solvents. In this work, we aimed at a greener approach toward such catalysis by (a) making two precatalysts with d10 metal centers, {[Zn(hipamifba)(H2O)]·2H2O}n (1) and {[Cd(hipamifba)(H2O)2]·2H2O}n (2) (where H2hipamifba = 4-(((4-((carboxymethyl) carbamoyl)phenyl)amino)methyl)benzoic acid), via an easy and scalable room-temperature method, and (b) showcasing the use of these coordination polymers (CPs) as very efficient, recyclable, and heterogeneous catalysts for the Strecker reaction to form α-aminonitriles in high yields under solvent-free reaction at ambient conditions. This has also allowed us to demonstrate the importance of open metal sites in such catalysis through an efficiency comparison between activated 1 and 2. In addition, activated 2 exhibited a wide substrate scope including a natural product Girgensohnine, providing an example of a natural product synthesis by a CP catalyst via an organic transformation such as the Strecker reaction.

Synthesis of modified bile acids via palladium-catalyzed C(sp3)-H (hetero)arylation.

A Pd(II)-catalyzed strategy for the diastereo- and regioselective (hetero)arylation of unactivated C(sp3)-H bonds in bile acids is accomplished with aryl and heteroaryl iodides under solvent-free conditions using the 8-aminoquinoline auxiliary as a directing group. This methodology demonstrated excellent functional group tolerance with respect to aryl/heteroaryl iodides on O-protected N-(quinolin-8-yl)cholyl/deoxycholyl amides to afford ß-C(sp3)-H (hetero)arylated products in good-to-excellent yields. Moreover, the 8-aminoquinoline (AQ) auxiliary can easily be removed to obtain modified bile acids.

Regiodivergent Synthesis of Cinnoline-Fused Indazolones through Pd-Catalyzed Annulation of 1-Arylindazolones with Allenoates.

A tender-hearted Pd(II)-catalyzed C-H activation of 1-arylindazolones followed by an oxidative [4 + 2] annulation reaction has been accomplished, engaging allenoates as annulating partners. Using this strategy, two different regioisomeric forms of cinnoline-fused indazolones possessing internal and exocyclic double bonds were synthesized in acetic acid and dioxane, respectively. Mild and aerobic conditions, avoiding the use of any metal-oxidant, highlights the rewards of this oxidative annulation protocol.

Effect of Unsaturated Metal Site Modulation in Highly Stable Microporous Materials on CO2 Capture and Fixation.

We have designed and synthesized two unprecedented microporous three-dimensional metal-organic frameworks, {[Cd6(TPOM)3(L)6]·12DMF·3H2O}n (1) and {[Zn2(TPOM)(L)2]·2DMF·H2O}n (2), based on a flexible quadritopic ligand, tetrakis(4-pyridyloxymethylene)methane (TPOM), and a bent dicarboxylic acid, 4,4'-(dimethylsilanediyl)bis-benzoic acid (H2L). The networks of 1 and 2 share a 4-c uninodal net NbO topology but exhibit different metal environments due to coordination preferences of Cd(II) and Zn(II). The Cd(II) center in 1 is six-coordinated, whereas the Zn(II) center in 2 is only four-coordinated, making the latter an unsaturated metal center. Such modulation of coordination atmosphere of metal centers in MOFs with the same topology is possible due to diverse binding of the carboxylate groups of L2-. Both 1 and 2 have relatively high thermal stability and exhibit permanent porosity after the removal of guest solvent molecules based on variable temperature powder X-ray diffraction and gas adsorption analysis. These materials exhibit similar gas adsorption properties, especially highly selective CO2 uptake/capture over other gases (N2 and CH4). However, because of the presence of an unsaturated Lewis acidic metal site, 2 acts as a very efficient heterogeneous catalyst toward the chemical conversion of CO2 to cyclic carbonates under mild conditions, whereas 1 shows very less activity. This work provides experimental evidence for the postulate that an unsaturated metal site in MOFs enhances adsoprtion of CO2 and promotes its conversion via the Lewis-acid catalysis.

Ruthenium-catalyzed (spiro)annulation of N-aryl-2,3-dihydrophthalazine-1,4-diones with quinones to access pentacyclic spiro-indazolones and fused-cinnolines.

Ru(II)-catalyzed strategies were developed for the [4 + 1] and [4 + 2] oxidative coupling between N-aryl-2,3-dihydrophthalazine-1,4-diones and 1,4-benzoquinones, achieving spiro-indazolones and fused-cinnolines, respectively. Mild, aerobic and external oxidant-free conditions, as well as the use of a ruthenium catalyst for such (spiro)annulative strategies with quinones over reported Rh/Ir-catalyts, underline the rewards of the disclosed protocols.

Amorphous Salts Solid Dispersions of Celecoxib: Enhanced Biopharmaceutical Performance and Physical Stability.

Numerous amorphous solid dispersion (ASD) formulations of celecoxib (CEL) have been attempted for enhancing the solubility, dissolution rate, and in vivo pharmacokinetics via high drug loading, polymer combination, or by surfactant addition. However, physical stability for long-term shelf life and desired in vivo pharmacokinetics remains elusive. Therefore, newer formulation strategies are always warranted to address poor aqueous solubility and oral bioavailability with extended shelf life. The present investigation elaborates a combined strategy of amorphization and salt formation for CEL, providing the benefits of enhanced solubility, dissolution rate, in vivo pharmacokinetics, and physical stability. We generated amorphous salts solid dispersion (ASSD) formulations of CEL via an in situ acid-base reaction involving counterions (Na+ and K+) and a polymer (Soluplus) using the spray-drying technique. The generated CEL-Na and CEL-K salts were homogeneously and molecularly dispersed in the matrix of Soluplus polymer. The characterization of generated ASSDs by differential scanning calorimetry revealed a much higher glass-transition temperature (Tg) than the pure amorphous CEL, confirming the salt formation of CEL in solid dispersions. The micro-Raman and proton nuclear magnetic resonance spectroscopy further confirmed the formation of salt at the -S═O position in the CEL molecules. CEL-Na-Soluplus ASSD exhibited a synergistic enhancement in the aqueous solubility (332.82-fold) and in vivo pharmacokinetics (9.83-fold enhancement in the blood plasma concentration) than the crystalline CEL. Furthermore, ASSD formulations were physically stable for nearly 1 year (352 days) in long-term stability studies at ambient conditions. Hence, we concluded that the ASSD is a promising strategy for CEL in improving the physicochemical properties and biopharmaceutical performance.

Reducing-Agent-Free Convergent Synthesis of Hydroxyimino-Decorated Tetracyclic Fused Cinnolines via RhIII-Catalyzed Annulation Using Nitroolefins.

A mild Rh-catalyzed method was developed for the synthesis of hydroxyimino functionalized indazolo[1,2-a]cinnolines and phthalazino[2,3-a]cinnolines by reductive [4 + 2] annulation between 1-arylindazolones and 2-aryl-2,3-dihydrophthalazine-1,4-diones with varied nitroolefins. The targeted oxime decorated tetracyclic fused cinnolines were synthesized via sequential C-H activation/olefin insertion/reduction under reducing-agent-free conditions.

Efficient and Highly Selective CO2 Capture, Separation, and Chemical Conversion under Ambient Conditions by a Polar-Group-Appended Copper(II) Metal-Organic Framework.

A polar sulfone-appended copper(II) metal-organic framework (MOF; 1) has been synthesized from the dual-ligand approach comprised of tetrakis(4-pyridyloxymethylene)methane and dibenzothiophene-5,5'-dioxide-3,7-dicarboxylic acid under solvothermal conditions. This has been studied by different techniques that included single-crystal X-ray diffractometry, based on which the presence of Lewis acidic open-metal sites as well as polar sulfone groups aligned on the pore walls is identified. MOF 1 displays a high uptake of CO2 over N2 and CH4 with an excellent selectivity (S = 883) for CO2/N2 (15:85) at 298 K under flue gas combustion conditions. Additionally, the presence of Lewis acidic metal centers facilitates an efficient size-selective catalytic performance at ambient conditions for the conversion of CO2 into industrially valuable cyclic carbonates. The experimental investigations for this functional solvent-free heterogeneous catalyst are also found to be in good correlation with the computational studies provided by configurational bias Monte Carlo simulation for both CO2 capture and its conversion.

A Highly Stable Triazole-Functionalized Metal-Organic Framework Integrated with Exposed Metal Sites for Selective CO2 Capture and Conversion.

A new triazole-functionalized tetracarboxylic acid ligand (H4 L) has been synthesized and utilized for the fabrication of a 3D ZnII organic framework with a Zn4 (-COO)6 cluster as the secondary building unit. The framework exhibits very good thermal stability and consists of dual functionalities of exposed Lewis acidic metal sites and accessible nitrogen-donor Lewis basic sites. The Lewis basic nitrogen sites in the framework serve as CO2 binding sites for highly selective CO2 capture and the presence of exposed Lewis acidic metal sites in the framework make it an efficient heterogeneous catalyst for the chemical fixation of CO2 into value-added cyclic carbonates under ambient conditions.

A Microporous Metal-Organic Framework Catalyst for Solvent-free Strecker Reaction and CO2 Fixation at Ambient Conditions.

The self-assembly of zinc(II) acetate tetrahydrate, a flexible tetrapyridyl ligand, tetrakis(3-pyridyloxymethylene)methane (3-tpom), a bent dicarboxylic acid, and 4,4'-(dimethylsilanediyl)bis- benzoic acid (H2L) under solvothermal conditions has resulted in the formation of a microporous zinc(II)-organic framework, {[Zn2(3-tpom)(L)2]·2H2O}n (1). The framework exhibits very good thermal stability as evident from the thermogravimetric analysis, which is further supported by variable temperature powder X-ray diffraction analysis. The microporous nature of the framework has been established by the gas adsorption analysis. The framework exhibits exceptionally selective carbon dioxide adsorption in contrast with other gases having comparatively larger kinetic diameters (3.64 Å for N2 and 3.8 Å for CH4) under ambient conditions (298 K and 1 bar pressure). Further, the framework decorated with catalytically active unsaturated metal sites acts as a good catalyst toward the cycloaddition reaction of CO2 with epoxides and the three-component Strecker reaction at ambient conditions and without the requirement of any solvent. The heterogeneous nature along with good catalytic activity at ambient and solvent-free conditions entitles 1 as an excellent catalyst for these organic transformations.

A Primary Amide-Functionalized Heterogeneous Catalyst for the Synthesis of Coumarin-3-carboxylic Acids via a Tandem Reaction.

A crystalline primary amide-based bifunctional heterogeneous catalyst, {[Cd2(2-BPXG)(Fum)2(H2O)2]·2H2O}n (1) (where, 2-BPXG = 2,2'-((1,4-phenylenebis(methylene))bis((pyridin-2-ylmethyl)azanediyl)) diacetamide and Fum = fumarate), has been developed for the one-pot synthesis of a series of potentially biologically active coumarin-3-carboxylic acids at room temperature via a Knoevenagel-intramolecular cyclization tandem reaction. Catalyst 1 is prepared at room temperature from a one-pot self-assembly process in 81% yield and high purity within a few hours and has a ladder-like polymeric architecture based on single-crystal X-ray diffraction. Additional characterization of 1 includes elemental analysis, infrared spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. Based on the optimized conditions, it is determined that 1 is highly efficient (conditions: 2 mol % catalyst, 3 h, and 26-28 °C in methanol) for this reaction. Its recyclability up to five cycles without significant loss of activity and structural integrity is also demonstrated. Using both electron-donating and electron-withdrawing substituents on the salicylaldehyde substrate, seven different derivatives of coumarin-3-carboxylic acid were made. Additionally, the monoamine oxidase (MAO) inhibitor, coumarin-3-phenylcarboxamide, has also been synthesized from coumarin-3-carboxylic acid obtained in the catalysis process. A detailed mechanism of action is also provided.

Design and Construction of a Luminescent and Highly Stable 3D Metal-Organic Framework with a [Zn4(µ3-OH)2]6+ Core.

A highly stable and luminescent 3D metal-organic framework (MOF), {[Zn4(µ3-OH)2(BTC)2(BBI4PY)2]·10H2O}n (Zn-MOF), with a rare [Zn4(µ3-OH)2]6+ core has been synthesized using a new rigid and functionalized pillar linker, 2,6-bis(pyridin-4-yl)-1,7-dihydrobenzo[1,2-d:4,5-d']diimidazole (BBI4PY) in combination with Zn(OAc)2·2H2O and 1,3,5-benzenetricarboxylic acid (H3BTC) under solvothermal conditions. Unlike other MOFs with the [Zn4(µ3-OH)2]6+ core, Zn-MOF was synthesized without using an external base, as the intrinsic basicity of BBI4PY served the purpose. Furthermore, it retains crystallinity and phase purity up to 350 °C on the basis of TGA and in situ variable temperature PXRD, correlating with its solid-state structure. Using the dehydrated Zn-MOF, water sorption studies show uptake of 220 cm3 g-1 (corresponds to 10 water molecules). A large hysteresis in desorption isotherm signifies strong interactions between adsorbed water and Lewis basic sites present in the framework. The reversible nature of water sorption was further manifested by TGA and PXRD studies. As an example of its application, the highly fluorescent and electron-rich nature of Zn-MOF has been utilized for the selective sensing of Fe3+ and 2,4,6-trinitrophenol (TNP) in water with detection limits of 3.7 and 1.8 ppm, respectively. The mechanistic details for the turn-off quenching have been elucidated with the help of Stern-Volmer plots, spectral overlap, lifetime studies, and density functional theory calculations. This mechanistic evidence reveals that a combination of strong hydrogen bonding with resonance energy transfer and photoinduced electron transfer (PET) processes is synchronously responsible for the quenching of the fluorescence intensity of Zn-MOF.

Design and Construction of a Chiral Cd(II)-MOF from Achiral Precursors: Synthesis, Crystal Structure and Catalytic Activity toward C-C and C-N Bond Forming Reactions.

Using achiral components, a V-shaped dicarboxylic acid (H2L) and a conformationally flexible bidentate linker (bpp), a thermally stable chiral metal organic framework {[Cd(bpp)(L)(H2O)]·DMF} n (1), where H2L = 4,4'-(dimethylsilanediyl)bis-benzoic acid, bpp = 1,3-bis(4-pyridyl)propane and DMF = N,N-dimethylformamide, has been solvothermally synthesized and crystallographically characterized. It consists of 1D helical chains linked at the cadmium centers resulting in an overall 2D framework. Its microporous nature was confirmed by gas-sorption measurements. Upon thermal activation of 1, where both guest DMF molecules present in the 1D open channels and the coordinated H2O molecules are removed, its active metal site shows Lewis acid character to be an excellent heterogeneous catalyst for the C-C (Knoevenagel condensation reaction) and C-N (Strecker) bond forming reactions.

Design and Development of a Heterogeneous Catalyst for the Michael Addition of Malononitrile to 2-Enoylpyridines: Influence of the Primary Amide Decorated Framework on Catalytic Activity and Selectivity.

For the Michael addition of malononitrile to 2-enoylpyridines, we report the first heterogeneous catalyst, {[Zn2(2-bpbg)(fum)2]·4H2O·EtOH}n (1) (where 2-bpbg = N,N'-bis(2-pyridylmethyl)-1,4-diaminobutane-N,N'-diacetamide and where fum = fumarate), which is decorated with primary amide side arms. It is prepared from the self-assembly of starting materials in methanol at room temperature (27 °C). Using 3 mol % of 1, greater than 99% conversion of substrates to the desired product is achieved within 1 h at 27 °C. Moreover, the catalyst is recyclable up to five consecutive cycles without significant loss of activity and structural integrity. In order to show the uniqueness of 1, the reaction under the same conditions was catalyzed by a fully pyridyl-based (i.e., having no primary amide group) and isostructural analogue, {[Zn2(tpbn)(fum)2]·6H2O}n (2) (where tpbn = N',N',N″,N''-tetrakis(pyridin-2-ylmethyl)butane-1,4-diamine), but resulting only in 7% conversion. This demonstrates the selective catalytic activity of 1 over 2 due to the presence of the primary amide side arms, where it acts as a bifunctional catalyst through the excellent hydrogen bond donating (HBD) ability in this reaction. For providing an insight into its mechanism of action involving a cyclic seven-membered hydrogen bonding motif, the reaction was performed with freshly synthesized (E)-chalcone, 3-enoylpyridine, and 4-enoylpyridine instead of 2-enoylpyridine under the same conditions. In the case of (E)-chalcone no product formation was observed, whereas for 3-enoylpyridine and 4-enoylpyridine the conversions were only 29% and 25%, respectively. Both 1 and 2 were fully characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, and single-crystal and powder X-ray diffraction.

Can Remote N-Heterocyclic Carbenes Coordinate with Main Group Elements? Synthesis, Structure, and Quantum Chemical Analysis of N+ -Centered Complexes.

Remote N-heterocyclic carbenes (rNHCs), such as N-methyl-4-pyridylidene, are known to form coordination complexes with TMs. Herein, it is established that rNHCs can also coordinate to the N+ centre. Synthesis of some novel divalent NI complexes with the general formula (rNHC)→N+ ←(NHC) and (rNHC)→N+ ←(rNHC) was achieved, and X-ray diffraction studies supported the coordination bond character between the rNHCs and the N+ centre. Quantum chemical analysis established the presence of divalent NI character at the central nitrogen in these systems.