Catalyst 1a Research Articles

Experimental PSA reactor for methanol-enhanced production VIA CO2 hydrogenation

Methanol synthesis via catalytic CO2 hydrogenation has emerged as one of the main ways to valorize CO2. The main problem is that the methanol synthesis reaction is thermodynamically controlled, and there is a parallel endothermic reaction, reverse water gas shift (RWGS), so low methanol production ratios are achieved.In this scenario, process intensification, particularly multifunctional reactors where reaction and separation occur simultaneously, is of great interest. Sorption-enhanced reaction processes (SERP) technologies are widely used in equilibrium-controlled processes to increase reagent conversion through selective product removal.Various authors have proposed SERP processes for CO2 hydrogenation to methanol, but most of them are simulations studies and it is difficult to find experimental data. The aim of the work is the experimental study of the CO2 conversion and selectivity to methanol of a SERP process based on a four-step PSA reactor. The process has been carried out with a commercial Cu/ZnO/Al2O3 catalyst and commercial 3A zeolite as adsorbent.Conversions beyond the equilibrium have been achieved in the SERP process, even complete conversion of CO2 at 50 bar, 250 °C, and 300 °C. In the cyclic process, high CO2 conversions far from equilibrium are achieved in all the range of temperatures, 200–300 °C. The best results of methanol yield are achieved at 250 °C and 50 bar, followed closely by 200 °C. It is worth mentioning that methane is detected in the transitory state at 300 °C and 50 bar. Also, the purge step has been studied, concluding that it is necessary for adsorbent regeneration, improving CO2 conversion in the cyclic steady state.

Design of highly effective organic catalyst for hydrazine electrooxidation: Iodobenzo[b]furan derivatives

In this study, we investigate the electrochemical characteristics of 2-aryl/alkyl-3-iodobenzo[b]furans as anode catalysts for hydrazine (N2H4) fuel cells. Cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) techniques are employed to investigate the performance of these heteroaromatic compounds. The results demonstrate the promising potential of the 2-aryl/alkyl-3-iodobenzo[b]furans in fuel cell technology. Among the tested organic catalysts (2a, 2b, 2c, 2d, and 2e), 2a exhibited the highest electrocatalytic activity, giving a total current density of 26.62 mA/cm2 within the potential range of −0.4 to −0.8 V. 2-aryl/alkyl-3-iodobenzo[b]furans were synthesized by using palladium/copper-catalyzed Sonogashira cross-coupling reactions, followed by electrophilic cyclization with iodine (I2). All products were characterized using 1H and 13C NMR spectroscopy, confirming their structures and providing insights into their chemical properties.

Oxygen-Dependent Ligand-Controlled Iron-Catalyzed Chemoselective Synthesis of Olefins and Vinyl Nitriles.

An oxygen-dependent ligand-controlled chemoselective synthesis of vinyl nitriles and E-olefins by coupling a variety of alcohols and benzyl cyanides, catalyzed by a well-characterized, air-stable, easy-to-prepare Fe(II) catalyst (1a) bearing a redox-active arylazo pincer (L1a) is reported. The azo-moiety of the ligand backbone acts as an electron and hydrogen reservoir, enabling catalyst 1a to efficiently produce a broad spectrum of vinyl nitriles and E-olefins in moderate to good yields selectively under an oxygen and argon atmosphere, respectively.

Ruthenium catalyzed dehydrogenative α-C–H functionalization of β-naphthol using alcohols: a metal–ligand cooperative borrowing hydrogen approach

Chemoselective α-C–H functionalization of β-naphthol is achieved with inexpensive and readily available alcohols using a well-defined, air-stable, and easy-to-prepare Ru(ii)-catalyst (1a) bearing a redox-active tridentate pincer (L1a).

Oxygen Dependent Switchable Selectivity during Ruthenium Catalyzed Selective Synthesis of C3-Alkylated Indoles and Bis(indolyl)methanes.

Herein, we report a ligand-centered redox-controlled oxygen-dependent switchable selectivity during ruthenium-catalyzed selective synthesis of C3-alkylated indoles and bis(indolyl)methanes (BIMs). A wide variety of C3-alkylated indoles and BIMs were prepared selectively in moderate to good isolated yields by coupling a wide variety of indoles and alcohols, catalyzed by a well-defined, air-stable, and easy-to-prepare Ru(II)-catalyst (1a) bearing a redox-active tridentate pincer (L1a). Catalyst 1a efficiently catalyzed the C3-alkylation of indoles under an argon atmosphere while, under an oxygen environment, exclusively producing the BIMs. A few drug molecules containing BIMs were also synthesized efficiently. 1a exhibited excellent chemoselectivity with alcohols containing internal carbon-carbon double bonds. Mechanistic investigation revealed that the coordinated azo-aromatic ligand actively participates during the catalysis. During the dehydrogenation of alcohols, the azo-moiety of the ligand stores the hydrogen removed from the alcohols and subsequently transfers the hydrogen to the alkylideneindolenine intermediate, forming the C3-alkylated indoles. While under an oxygen environment, the transfer of hydrogen from the ligand scaffold to the molecular oxygen generates H2O2, leaving no scope for hydrogenation of the alkylideneindolenine intermediate, rather than it undergoing 1,4-Michael-type addition forming the BIMs.

Synthesis of water soluble cobalt(II), copper(II) phthalocyanines and their usage as a catalyst in the photoxidation of benzyl alcohol in biphasic catalysis

In this study, we synthesized and characterized cobalt(II), copper(II) phthalocyanines (2, 3) and their water soluble derivatives (2a, 3a) bearing dimethylamino groups. Then, benzaldehyde selective photoxidation of benzyl alcohol with four different oxygen sources and catalysts (2a, 3a) was carried out by biphasic catalysis. Optimal photocatalytic reaction conditions were determined as benzyl alcohol/ oxidant molar ratio 4.0/1 amount of the catalyst 2.0 mg (9.61 × 10−7 mmol), 25 ◦C and 30 min. 92 % conversion of benzyl alcohol with 1640 turnover number for 2a and 75 % benzaldehyde selectivity for 3a are achieved under the optimal conditions. Both catalysts can be used in three times and 2a can be catalytically active after 5 cycles with giving 72 % product conversion.

Asymmetric Transfer Hydrogenation of Heterocyclic Compounds in Continuous Flow Using an Immobilized Chiral Phosphoric Acid as the Catalyst

AbstractThis manuscript describes transfer hydrogenation of bicyclic nitrogen-containing heterocyclic compounds using the immobilized chiral phosphoric acid catalyst (R)-PS-AdTRIP in batch and continuous flow. A significant improvement in enantioselectivities is achieved in continuous flow with a fluidized bed reactor packed with (R)-PS-AdTRIP when the flow rate is increased from 0.2 mL/min to 2.0–2.5 mL/min. The optimized continuous flow conditions consistently provide 4–6% ee higher selectivity than transfer hydrogenation in batch with 2 mol% of (R)-PS-AdTRIP, and are used to generate multiple chiral products with the same fluidized bed reactor.

Bifunctional metal-organic frameworks as selective turn-on fluorescence sensors for tryptophan and heterogeneous catalysts for Knoevenagel condensation reaction

Two new doubly interpenetrated metal-organic frameworks (MOFs) with formulas [{Zn(L1)(5-nipa)}·DMA]α (1a) and [{Cd(L2)(5-nipa)(H2O)}]α (1b) have been discussed herein, where [L1 = N,N'-(oxybis(4,1-phenylene))diisonicotinamide; L2 = N,N'-(methylenebis(4,1-phenylene)) diisonicotinamide; 5-H2nipa = 5-nitroisophthalic acid; DMA = dimethylacetamide]. A single crystal X-ray analysis reveals that 1a exhibits a 2D-interpenetrated interwoven sheet and finally adapts a 3D framework structure with the help of π···π stacking interactions. Similarly, 1b displays a two-fold interpenetrated 2D sheet-like architecture and is finally adjusted to a 3D structure. Both 1a and 1b feature channels with a cross-section of 25.06 × 25.06 Å2 and 24.01 × 24.01 Å2, respectively, running along the b-axis. Topological analysis of 1a and 1b by ToposPro suggests a (4)-connected uninodal sql topology with point symbol {44.62}. Further, 1a and 1b were exploited as molecular sensors for several amino acids exposing different shapes and sizes and exhibiting selective turn-on fluorescence sensing towards biologically important D/L-tryptophan with the notable limit of detection values of 0.084/0.110 μM and 0.143/0.141 μM, respectively, in aqueous medium. In addition, 1a and 1b were also exploited as heterogeneous catalysts towards several assorted aldehydes having different electronic environments, including sterically demanding aldehydes, under mild reaction conditions and obtained up to 97% of the respective Knoevenagel condensation product. Importantly, sterically hindered aldehydes also worked well with the MOF catalysts 1a and 1b, but showed comparatively low conversion. It is important to mention that in both cases, these MOF materials are recyclable for up to five consecutive runs without displaying any substantial loss in their sensing or catalytic activities. Moreover, the present investigation cultivates a new vision to design novel luminescent MOFs that can be used as multifunctional materials for the turn-on sensing of small organic molecules as well as instigated as heterogeneous catalysts in diverse organic transformation reactions.

Diverse Site-Selective Transformation of Benzylic and Allylic Silyl Ethers via Organocatalytic Oxidation

We herein report nitroxyl-radical catalyst 1a, which recognizes the electronic properties of silyl ethers, thus enabling selective oxidation of benzylic and allylic silyl ethers, despite steric factors. A subsequent one-pot reduction accomplishes the formal deprotection to the corresponding benzylic and allylic alcohols. This catalytic system allows the direct oxidative desymmetrization of bis-benzylic and bis-allylic silyl ethers to access synthetically useful monoprotected conjugated aldehydes, which can be applied to one-pot enantioselective transformations. Mechanistic studies revealed that the highly electron-accepting oxoammonium species from 1a as well as the trifluoroacetate form of phenyl iodonium bis(trifluoroacetate) (PIFA) play key roles for the selectivity-determining hydride transfer step.

Asymmetric Synthesis of Spirooxindole Lactones by Ammonium-tethered Chiral Organocatalysts catalyzed Michael Addition/Cyclization of 3- hydroxyoxindoles with α,β-unsaturated Aldehydes

Abstract: The ammonium-tethered pyrrolidine-based organocatalyst catalyzed asymmetric Michael addition/cyclization reaction of α,β-unsaturated aldehydes with 3-hydroxyoxindole in aqueous media was developed, giving the spirooxidole lactones in high yields with high enantioselectivities. Background: The asymmetric Michael addition/cyclization reaction of 3-hydroxyoxindoles with α,β- unsaturated aldehydes is an important method for the synthesis of chiral spirooxindole derivatives, which are found in a wide range of biologically active natural products and pharmaceutical agents. Objective: Organocatalyzed asymmetric Michael addition/cyclization reactions are one of the most powerful and effective approaches for the construction of complex molecules from relatively simple starting materials. However, a major problem associated with these organocatalytic system is that high catalyst loading and organic solvents are required. In the present work, our objective was to develop a water-compatible organocatalyst that aimed at lowering catalyst loading and being active in an aqueous system. Methods: In a typical experiment, To a solution of catalyst 2a (0.008 mmol) and PhCO2H (0.096 mmol) in 0.5 mL of a mixture solvent iPrOH/H2O (1:3) was added α,β-unsaturated aldehyde (0.4 mmol) and 3-hydroxyoxindole (0.8 mmol). The reaction mixture was proceeded at room temperature for 16 hours, and then was extracted with 10 mL dichloromethane to give the cyclized hemiacetal, which was subjected to the direct oxidation with pyridinium chlorochromate (PCC, 1.2 mmol) for 16 hours to give the desired spirooxindole lactones. Results: The reactions successfully gave spirooxindole lactones in high to excellent yields (81-95%) with moderate to excellent enantioselectivities (up to 99% ee). However, the diastereoselectivities were poor ranging from 1:1.1 to 1:2.3. Conclusion: The asymmetric Michael addition/cyclization reaction of α,β-unsaturated aldehydes with 3-hydroxyoxindole using ammonium-tethered pyrrolidine-based organocatalyst has been developed. The reaction was performed in aqueous media with low catalyst loading (2 mol%) and provided the spirooxidole lactones in high yields (81-95%) with high enantioselectivities (ee: up to 99%).

Zn(II)-Catalyzed Multicomponent Sustainable Synthesis of Pyridines in Air.

Herein, we report a Zn(II)-catalyzed solvent-free sustainable synthesis of tri- and tetra-substituted pyridines using alcohols as the primary feedstock and NH4OAc as the nitrogen source. Using a well-defined air-stable Zn(II)-catalyst, 1a, featuring a redox-active tridentate azo-aromatic pincer, 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (La), a wide variety of unsymmetrical 2,4,6-substituted pyridines were prepared by three-component coupling of primary and secondary alcohols with NH4OAc. Catalyst 1a is equally compatible with the four-component coupling. Unsymmetrical 2,4,6-substituted pyridines were also prepared via a four-component coupling of a primary alcohol with two different secondary alcohols and NH4OAc. A series of tetra-substituted pyridines were prepared up to 67% yield by coupling primary and secondary alcohols with 1-phenylpropan-1-one or 1,2-diphenylethan-1-one and NH4OAc. The 1a-catalyzed reactions also proceeded efficiently upon replacing the secondary alcohols with the corresponding ketones, producing the desired tri- and tetra-substituted pyridines in higher yields in a shorter reaction time. A few control experiments were performed to unveil the mechanistic aspects, which indicates that the active participation of the aryl-azo ligand during catalysis enables the Zn(II)-complex to act as an efficient catalyst for the present multicomponent reactions. Aerial oxygen acts as an oxidant during the Zn(II)-catalyzed dehydrogenation of alcohols, producing H2O and H2O2 as byproducts.

Enantioselective Imine Reduction of Dihydro-β-carbolines by Fe-Thiosquaramide Catalyst.

Enantioselective imine reduction of dihydro-β-carbolines (DHBCs) is a reliable and powerful tool to construct bioactive chiral tetrahydro-β-carbolines (THBCs). Here, we report an efficient enantioselective imine reduction employing in situ generated Fe-thiosquaramides (Fe-TSQs) 3a and 3b as asymmetric organometallic catalysts to produce chiral THBCs (2a-h). The catalyst 3a at 15 mol % was found to be suitable for the substrates with alkyl and aryl groups which afford corresponding chiral THBCs with excellent enantioselectivities (up to ee 99%).

Ruthenium-Catalyzed Dehydrogenative Functionalization of Alcohols to Pyrroles: A Comparison between Metal-Ligand Cooperative and Non-cooperative Approaches.

Herein, we report the synthesis and characterization of two ruthenium-based pincer-type catalysts, [1]X (X = Cl, PF6) and 2, containing two different tridentate pincer ligands, 2-pyrazolyl-(1,10-phenanthroline) (L1) and 2-arylazo-(1,10-phenanthroline) (L2a/2b, L2a = 2-(phenyldiazenyl)-1,10-phenanthroline; L2b = 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline), and their application in the synthesis of substituted pyrroles via dehydrogenative alcohol functionalization reactions. In catalyst [1]X (X = Cl, PF6), the tridentate scaffold 2-pyrazolyl-(1,10-phenanthroline) (L1) is apparently redox innocent, and all the redox events occur at the metal center, and the coordinated ligands remain as spectators. In contrast, in catalysts 2a and 2b, the coordinated azo-aromatic scaffolds are highly redox-active and known to participate actively during the dehydrogenation of alcohols. A comparison between the catalytic activities of these two catalysts was made, starting from the simple dehydrogenation of alcohols to further dehydrogenative functionalization of alcohols to various substituted pyrroles to understand the advantages/disadvantages of the metal-ligand cooperative approach. Various substituted pyrroles were prepared via dehydrogenative coupling of secondary alcohols and amino alcohols, and the N-substituted pyrroles were synthesized via dehydrogenative coupling of aromatic amines with cis-2-butene-1,4-diol and 2-butyne-1,4-diol, respectively. Several control reactions and spectroscopic experiments were performed to characterize the catalysts and establish the reaction mechanism.

Chiral Sulfide/Phosphoric Acid Cocatalyzed Enantioselective Intermolecular Oxysulfenylation of Alkenes with Phenol and Alcohol O -Nucleophiles

Chiral Sulfide/Phosphoric Acid Cocatalyzed Enantioselective Intermolecular Oxysulfenylation of Alkenes with Phenol and Alcohol <i>O</i> -Nucleophiles

Synthesis, structural elucidation, and catalytic activity of bimetallic rhenium-tin complexes containing Schiff base ligand

Novel bimetallic systems with Re and Sn metals, containing Schiff base linker were designed and explored for their cooperative effect in the catalysis. ReSn bimetallic complexes were prepared by adopting a two-step synthesis procedure, which includes covalent binding of Sn with the Schiff base and then with the Re(CO)5Br. The Schiff base, (E)- N’-(2, 3-dihydroxybenzylidene)isonicotinohydrazide (H2L,1) was used in the preparation of three Schiff base diorganotin (IV) complexes; Diphenyltin(IV) Schiff base complex (DPTC, (2a)), Dimethyltin(IV) Schiff base complex (DMTC, (2b)); and Dioctyltin(IV) Schiff base complex (DOTC, (2c)). The Schiff base organotin (IV) complexes, 2a-2c were used as precursors to synthesize bimetallic ReSn complexes. The ReSn bimetallic complexes; ReDPTC (3a), ReDMTC (3b) and ReDOTC (3c) were prepared by treating respective organotin(IV) Schiff base complex, DPTC (2a), DMTC (2b), DOTC (2c) with the rhenium pentacarbonyl bromide (Re(CO)5Br). All the three ReSn bimetallic complexes 3a, 3b and 3c were characterized by FTIR, HRMS, EDX, and UV-Vis spectroscopy. DFT studies were employed to rationalize the ground state structure of the synthesized bimetallic complexes. The catalytic activity of compounds 3a, 3b, 3c were investigated for selective oxidation of anthracene to 9,10 anthraquinone under mild reaction conditions by employing H2O2 as an oxidizing agent. The catalyst 3a (ReDPTC) with the phenyl substituent on the Sn has shown excellent catalytic activity (96.9 % conversion with 100% selectivity) in comparison to 3b (with methyl substituent) and 3c (with octyl substituent).

Benzylnickel(II) Complexes of 2-Iminopyrrolyl Chelating Ligands: Synthesis, Structure, and Catalytic Oligo-/Polymerization of Ethylene to Hyperbranched Polyethylene

A family of benzyl nickel(II) complexes of 5-aryl-2-iminopyrrolyl ligands has been synthesized and characterized, and their behavior as aluminum-free catalysts for the oligo-/polymerization of ethylene is discussed. η1-Benzyl Ni(II) complexes of the type [Ni{κ2N,N′-5-R-NC4H2-2-C(H)═N(2,6-iPr2C6H3)}(η1-CH2C6H5)(PMe3)] (R = 3,5-(CF3)2C6H3 (1a), 2,4,6-iPr3C6H2 (1b)) were synthesized by the reaction of [NiCl(η3-CH2C6H5)(PMe3)] with 1 equiv of the respective 5-R-2-[N-(2,6-diisopropylphenyl)formimino]pyrrolyl potassium salt (KLa,b) in good yields. Complexes 1a,b, upon treatment with B(C6F5)3, yielded η3-benzyl Ni(II) complexes of the type [Ni{κ2N,N′-5-R-NC4H2-2-C(H)═N(2,6-iPr2C6H3)}(η3-CH2C6H5)] (R = 3,5-(CF3)2C6H3 (2a), 2,4,6-iPr3C6H2 (2b)). All complexes were characterized by 1H and 13C{1H} NMR spectroscopy and elemental analysis and 1b and 2a by X-ray diffraction. All complexes were further tested in the oligo-/polymerization of ethylene. Complexes 1a,b in the presence of 2 equiv of [Ni(COD)2] showed activities from 2.06 to 61.81 kg mol–1 h–1 bar–1, whereas complexes 2a,b alone showed activities from 0.67 to 14.44 kg mol –1 h–1 bar–1. The polyethylene products obtained with catalyst systems 1a and 2a are low-viscosity oils with molecular weights in the range 900–1200 g mol–1, and those obtained with catalyst systems 1b and 2b are high-viscosity oils with molecular weights between 10900 and 17700 g mol–1, all showing very high branching degrees (100–115 branches/1000C atoms), characteristic of hyperbranched polyethylene products.

Mechanistic Study of the N-Quaternized Pyridoxal-Catalyzed Biomimetic Asymmetric Mannich Reaction: Insights into the Origins of Enantioselectivity and Diastereoselectivity.

Density functional theory calculations have been performed to gain insights into the catalytic mechanism of the N-quaternized pyridoxal (i.e., 1a)-mediated biomimetic asymmetric Mannich reaction of tert-butyl glycinate 3 with N-diphenylphosphinyl imine 2a to give the diamino acid ester 4a in high yield with excellent enantiomeric and diastereomeric selectivity (Science 2018, 360, 1438). The study reveals that the whole catalysis can be characterized via three stages: (i) the catalyst 1a reacts with the tert-butyl glycinate 3 to generate the active carbanion complex IM3. (ii) IM3 then reacts with the N-diphenylphosphinyl imine 2a giving the imine intermediate IM8. (iii) IM8 undergoes hydrolysis to give the final product anti-4a and regenerate the catalyst 1a for the next catalytic cycle. Each stage is kinetically and thermodynamically feasible for experimental realization. The hydrolysis step in the stage III is predicted to be the rate-determining step during the whole catalytic cycle. Furthermore, the origins of the enantioselectivity and diastereoselectivity for the target reaction, as well as the deactivation of the catalyst 1b, are also discussed.

A porous Co-MOF for CO2 conversion and protective activity on infectious fever by reducing bacterial inflammatory response

By applying a mixed-ligand approach based on an amino functionalized ligand 1-aminobenzene-3,4,5-tricarboxylic acid (H3abta), a novel metal-organic framework (MOF) containing Co(II) ion {[Co2.5(abta)(trz)2 (H2O)]·3H2O}n (1, Htrz = 1H-1,2,4-triazole) were produced via Co(NO3)2·6H2O reacting with H3abta with the existence of Htrz as the co-ligand. The prepared catalyst 1a (activated 1) is abundant in the amino groups and open metal sites (OMSs), which is helpful to obtain high CO2 capacity of adsorption around room temperature and effectively convert CO2 to pentacyclic carbamate with the help of Bu4NBr as the cocatalyst. For the treatment of infectious fever, the colony-forming unit (CFU) was performed and the E. coli number in the mice was counted. Next, the inflammatory cytokines level in the infected mice was measured after the compound treatment.

Retracted: A new porous Co(II)‐coordination polymer for the chemical fixation of CO2 and treatment effect against tuberculosis by reducing the pckA expression in Mycobacterium tuberculosis

Using the mixed‐ligand method, a novel coordination polymer containing Co(II) of [Co(ditb)(tdc)]n·5nH2O (1) was prepared by reacting rigid 2,5‐thiophenedicarboxylic acid with flexible 1,4‐di(1H‐1,2,4‐triazol‐1‐yl)butane using the slow evaporation method. Active samples of 1 (1a for short) showed good stability and the ability to capture CO2. It can be used as a potential heterogeneous catalyst for chemical immobilization of epoxide and CO2 to form cyclic carbonates. In addition, catalyst 1a retained its original structure after four times of reuse. Its biological properties were assessed against Mycobacterium tuberculosis (M.TB) both in vivo and in vitro. First, the bactericidal ability of the compound against M.TB was measured by a sterilization curve. Then, the expression of pckA gene related to M.TB survival was detected using reverse transcription‐polymerase chain reaction. For the in vivo study, the colony‐forming unit determination was performed for evaluating the anti‐bacterial effect of the compound, and the enzyme‐linked immunosorbent assay was used for the inflammatory cytokine measurement in vivo. Through molecular docking simulations, all three types of polar atoms on the complex were confirmed to have chances of interacting with the protein.

Rational Design of New Dihydrobenzooxophosphole-Based Lewis Base Organocatalysts.

A series of new dihydrobenzooxophosphole-based Lewis Base organocatalysts were designed and synthesized. They are demonstrated effective in trichlorosilane-mediated stereoselective conjugate reductions of C=C bonds. DFT calculations reveal that the strong hydrogen bond between the amide linker and the chloride on silicon in the transition state contributes to the high reactivity of the catalyst 3a.