TON Value Research Articles

New mixed ligand oxido-vanadium(V) complexes with O,O-donor and diimine ligands: Synthesis, crystal structure and catalytic activity in eco-friendly oxidation of olefins and phenol

The facile synthesis and structural characterization of a set of three new oxidovanadium(V) complexes of general formula [VO2(L)(diimine)], where L is ethyl-maltol(emal) (1), deferiprone(def) (2) or, maltol(mal) (3), and diimine is 5,6-dimethyl-1,10-phenanthroline(5,6-DMP) are described. The neutral complexes 1–3 have been comprehensively characterized by employing various analytical and spectroscopic techniques including single crystal X-ray diffraction analysis. The coordination geometry around the V(V) in each of the complexes was indicated by XRD-analysis to be distorted octahedral with equatorial plane being occupied by the deprotonated O,O-donor ligands. The complexes 1–3 could be successfully implemented in organic oxidations viz., hydroxylation of phenol (PH) and olefin epoxidation under environmentally clean organic-solvent-free conditions with aqueous H2O2 as oxidant. Phenol was selectively converted into dihydroxybenzene (DHB) products, catechol (CT) and hydroquinone (HQ) (HQ/CT=1.3:1) with aqueous H2O2 as oxidant at room temperature, with a TON value of 266. Moreover, the catalysts showed impressive activity in epoxidation of styrene and a range of cyclic olefins such as cyclohexene, cyclooctene, and norbornene in absence of organic solvent, to provide high conversion (up to 100 %) with excellent epoxide selectivity and good TON values. The catalysts are stable and afford recyclability for multiple cycles of epoxidation with virtually unaltered catalytic activity.

Functionally enhanced polyether-bridged amidopyridinium dicationic ionic liquids for highly efficient and sustainable fixation of CO2 to cyclic carbonates

Task-specific ionic liquids integrated with multi-active sites display promising potential for use in the cycloaddition reaction of CO2 and epoxides. Utilizing the functional enhancement strategy, we successfully synthesized a novel range of polyether-bridged amidopyridinium dicationic ionic liquids (PE-PyDILs) via efficient bisamidation and biquaternization reactions. Under relatively mild reaction conditions, PE-PyDILs can catalyze the coupling of CO2 with various epoxides to produce cyclic carbonates in quantitative yields, demonstrating an enhanced effectiveness and a longer service life compared to previous DILs. At a very low loading of 0.01 mol%, the TON value is as high as 7700. The excellent catalytic performance can be attributed to the intramolecular cooperative activation of epoxides with two amidopyridinium cations bridged by polyether, as supported by the spectroscopic analysis and kinetic studies. This mechanism led to a reduction in activation energy and improved the efficiency of the cycloaddition reaction.

Unveiling the role of proton concentration in dinuclear metal complexes for boosting photocatalytic CO2 reduction

The reaction kinetics of photocatalytic CO2 reduction is highly dependent on the transfer rate of electrons and protons to the CO2 molecules adsorbed on catalytic centers. Studies on uncovering the proton effect in catalysts on photocatalytic activity of CO2 reduction are significant but rarely reported. In this paper, we, from the molecular level, revealed that the photocatalytic activity of CO2 reduction is closely related to the proton availability in catalysts. Specifically, four dinuclear Co(II) complexes based on Robson-type ligands with different number of carboxylic groups (-nCOOH; n = 0, 2, 4, 6) were designed and synthesized. All these complexes show photocatalytic activity for CO2 reduction to CO in a water-containing system upon visible-light illumination. Interestingly, the CO yields increase positively with the increase of the carboxylic-group number in dinuclear Co(II) complexes. The one containing -6COOH shows the best photocatalytic activity for CO2 reduction to CO, with the TON value reaching as high as 10,294. The value is 1.8, 3.4, and 7.8 times higher than those containing -4COOH, -2COOH, and -0COOH, respectively. The high TON value also makes the dinuclear Co(II) complex with -6COOH outstanding among reported homogeneous molecular catalysts for photocatalytic CO2 reduction. Control experiments and density functional theory calculation indicated that more carboxylic groups in the catalyst endow the catalyst with more proton relays, thus accelerating the proton transfer and boosting the photocatalytic CO2 reduction. This study, at a molecular level, elucidates that more carboxylic groups in catalysts are beneficial for boosting the reaction kinetics of photocatalytic CO2 reduction.

Self‐assembly aryl cyclopalladated imine film supported on the silicon surface—Fabrication, formation of active PdPd/PdO sites, and catalytic properties for Sonogashira cross‐coupling reaction

Tailoring the structure and arrangement of the organometallic catalyst are essential for the fundamental investigating and applications, and the impacting challenges, such as the size, active species distribution, and composition, as well as the orientation of catalyst, are critical for determining their activities and efficiencies. Herein, a series of aryl cyclopalladated catalysts containing different alkane chains were synthesized, and their self‐assembly films covalent binding to the silicon surface were fabricated and characterized with water drop contact angle, Raman, atomic force microscopy, scanning electron microscopy, and X‐ray photoelectron spectroscopy. The catalytic performances of these catalytic films were explored using Sonogashira cross‐coupling reaction as a template. One of these catalytic films exhibited a higher catalytic activity with a TON value of up to 68,333 h−1, which was 20 times higher than that of homogeneous catalyst due to the ordered arrangement of this catalyst on the silicon surface, and could be reused at least seven times. The catalytic mechanism was heterogeneous catalysis occurred at interface confirmed by hot filtration tests, poisoning tests, and ReactIR. The real active site was PdPd/PdO, and the synergistic effect between Pd and PdO in the active sites (PdPd/PdO) made the key initial oxidation step easily proceed, improving its catalytic activity. The loss of active sites and residues absorbed on the surface of catalytic film were the main reason for deactivation.

Immobilization of Pd(0) nanoparticles on polyaza-ligand-functionalized polyacrylonitrile fiber as highly active catalyst for the Heck reaction

An novel aza-ligand functionalized polyacrylonitrile fiber (PANPALF) with amino groups and quaternary ammonium salt moieties was synthesized, and then a highly active catalyst for the Heck reaction was obtained by immobilizing Pd(0) nanoparticles on PANPALF through chelation and in situ reduction. The functionalized fibers were characterized by appropriate instruments, such as inductively coupled plasma atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), etc., in order to further confirm that the modification process has been successfully carried out. The catalytic properties of the prepared fiber were evaluated in Heck reaction. The experimental results show that PANPALF-Pd(0) can catalyze Heck reactions and achieving 42 kinds of products with yields ranging from 43% to 99% under solvent-free condition, and verifies that the reactive activation of iodized aromatics is better than that of brominated aromatics. Noteworthily, the TON value of the reaction catalyzed by PANPALF-Pd(0) can reach up to 89000, showing that the fiber catalyst has excellent catalytic activity. Moreover, after PANPALF-Pd(0) reused 11 times, the isolated yield was still as high as 93%, and the average single Pd(0) leaching is only 0.075%, indicating that PANPALF-Pd(0) has satisfactory recyclability. Finally, a rational reaction mechanism was proposed to explain the role of fiber catalyst in the reaction.

Reductive functionalization of CO2 under mild reaction conditions for the catalytic synthesis of N-formamides by Mannich base based Cobalt (III) complex

Reductive functionalization of carbon dioxide is an important approach which not only reduces CO2 concentration but also functionalized it for the formation of value added chemicals. In this perspective, a hexadentate mononuclear cobalt (III) complex [CoIIIL] of Mannich base ligand (H4L) was synthesized and structurally characterized by single crystal X-ray diffraction. The electronic spectra of the complex showed two bands at 448 and 561 nm corresponds to the LMCT and d-d transitions respectively. The derived inexpensive [CoIIIL] complex was very much effective as catalyst in carbon dioxide functionalization reaction. The catalytic synthesis of mono selective N-formamide product from amines was produced through diagonal transformation of carbon dioxide in presence of polymethylhydrosiloxane (PMHS) as reducing agent and [CoIIIL] complex as catalyst. The effects of various reaction parameters were examined. Broad range of substrates (aromatic as well as aliphatic amines) smoothly produced good percentage of respective N-formamides product (72–94%) under mild reaction condition utilizing 1 atmospheric CO2. The high TON (1540–2000) and TOF value (192.5–400.0 h−1) for the catalytic reactions strongly depicted the productive nature of the [CoIII(L)] catalyst. The probable mechanestics studies clearly reveals that the [CoIIIL] complex activated the Si−H bond of PMHS to react with carbon dioxide in order to form the silyl formates intermediate for activation of N–H bonds in amines, thus leading to the excellent performance of the catalytic reaction.

Ln-substituted polytungstates as efficient hetergeneous catalysts for Knoevenagel condensation reaction

Three isomorphic polytungstates, Cs9K18H10{[Sm2(H2O)4W4O10(AsW9O33)3]2(N(CH2PO3)2)}·46.5H2O (1), Cs10K9H18{[Eu2(H2O)4W4O10(AsW9O33)3]2(N(CH2PO3)2)}·41.5H2O (2), Cs10K9H18{[Gd2(H2O)4W4O10 (AsW9O33)3]2(N(CH2PO3)2)}·46H2O (3), have been successfully synthesized and characterized by routine methods, and demonstrated excellent catalytic activities in Knoevenagel condensation reaction as heterogeneous catalysts. Notably, catalyst 1 achieved higher reaction activity than catalysts 2 and 3, where a satisfactory reaction yield (95%) and high TON value (6380) could be obtained at moderate reaction condition. In addition, in the scale-up experiment, with the help of catalyst 1, 7.8 g benzaldehyde and 5.7 g ethyl cyanoacetate could transform into corresponding condensation product with a satisfactory yield (83%) and impressive TON value (13,883).

One-step DMC synthesis from CO2 under catalysis of ionic liquids prepared with 1,2-propylene glycol

Three quaternary ammonium ionic liquids with strong nucleophilicity and distinctive structures were synthesized with high yield and purity based on the 1,2-propylene glycol anion (CH3CH2OHCH2O-) derived from transesterification products. Dimethyl carbonate (DMC) was in turn produced via a one-step reaction among propylene oxide (PO), CO2, and methanol (MeOH) by using the synthesized ionic liquids. The involved two-stage catalytic reaction of PO-CO2 cycloaddition and PC-MeOH transesterification was implemented without catalyst separation. Under mild conditions, the PO conversion reached 99.0%, with a PC yield of 99.0%, and a TON value of 119.5. Following the cycloaddition, MeOH was immediately introduced to achieve a PC conversion of 71.2%, a selectivity to DMC above 99%, and a TON value of 57.4 for the transesterification reaction. The influences of temperature as well as time for cycloaddition and transesterification were investigated. Cycloaddition of CO2 with various epoxides was also examined and all showed good performance. By taking advantage of the decomposability of as-prepared ionic liquids and the recyclability of decomposition products, a new catalyst circulation process was designed to complete the full cycle without introduction of any impurities into the product system.

Organic-solvent-free oxidation of styrene, phenol and sulfides with H2O2 over eco-friendly niobium and tantalum based heterogeneous catalysts

Immobilization of triperoxido derivatives of Nb(V) and Ta(V) on chitosan, an abundant and renewable support material, afforded a pair of stable heterogeneous catalysts, which could be successfully implemented in a variety of organic oxidations under ecologically sustainable organic-solvent-free conditions. The catalysts were extensively characterized by elemental analysis, SEM-EDX, powder XRD, XPS, BET, TG-DTG, FT-IR, Raman and NMR analysis. The supported catalysts showed excellent activity in the non-solvent epoxidation of styrene with H2O2 to provide 96% conversion with nearly 100% selectivity of the desired epoxide and a high TON value of 260 at room temperature. Moreover, phenol was selectively converted into 100% dihydroxybenzene (HQ:CT = 2:1) at ambient temperature, in absence of organic solvent, with a TON value of 80. In addition, both the catalysts were highly active towards the oxidation of a diverse range of sulfides such as aromatic, aliphatic, vinylic, allylic, and alcoholic sulfides to chemoselectively produce the desired sulfoxides in an aqueous medium with a TON value as high as 1900. The heterogeneous nature of the insoluble catalysts was confirmed by a hot filtration test. The catalysts are stable, water tolerant and easily recyclable at least up to five successive cycles of epoxidation and sulfoxidation with undiminished activity and selectivity.

A study on the influence of WEDM parameters on surface roughness, kerf width, and corrosion behavior of AZ31B Mg alloy

Wire electric discharge machining (WEDM) is a nontraditional machining process where the material is removed by the spark erosion technique. This technique is used to machine AZ31B, a biodegradable Magnesium alloy. In the present work impact of WEDM input parameters, namely pulse on time (Ton), pulse off time (Toff), servo voltage (SV), and wire feed (WF) on response characteristics is studied. The response characteristics considered are kerf width (KW), surface roughness (SR), and corrosion rate (CR). L9 orthogonal array by Taguchi’s is employed as the design of experimentation. Taguchi’s analysis implied that TON is the most influencing input parameter on the response characteristics. At a relatively lower TON setting (105 µs), comparatively lesser kerf width (335.894 µm), lower surface roughness (3.069 µm), and lower corrosion rate (0.95 mm/year) are exhibited by the machined specimens. From the main effects plots using signal-to-noise ratios, it is understood that the values of response characteristics increased with an increase in TON value. It is due to the increase in discharge at the more pulse on time duration. It is also understood that a surface with relatively better surface finish exhibited better corrosion resistance. With the help of regression equations, the relation between response characteristics and input parameters is built.

Synthesis and Catalytic Application of Ru-Deposited Magnetic Nanoparticles for the Selective Hydrogenation of CO2 Gas

: In this report, a hybrid terpyridine (tpy) ligand functionalize with magnetic support was synthesized to obtain well-dispersed Ru NPs with a 2.0±0.5 nm mean size. This material was further analyzed using different analytical techniques before utilizing it as a catalyst for the CO2 hydrogenation reaction. A noticeable application of Ru-deposited magnetic nanoparticles as catalysts was observed during the CO2 hydrogenation. We successfully synthesized the formic acid with a high TON value under high-pressure reaction conditions. Easy recovery of the catalyst under the applied magnetic field helped us to reuse the catalyst up to 6 times with good TON and TOV value.

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation

Synthesis, structure and catalytic activity of new oxovanadium(V) complexes with deferiprone and N,N-donor ligands

A pair of new water-soluble oxovanadium(V) complexes comprising of deferiprone (def) and N,N-donor ligands, 2,2ʹ-bipyridine (bpy) or 1,10-phenanthroline (phen), [VO2(def)(bpy)]⋅H2O (1) and [VO2(def)(phen)]⋅4H2O (2) were synthesized. The complexes were characterized by elemental analysis, spectral studies and single crystal X-ray diffraction analysis. The X-ray crystal structures of 1 and 2 reveal that both the complexes possess distorted octahedral coordination geometries with O4N2 coordination sphere around the vanadium center, and the deprotonated deferiprone occupying the equatorial plane. The complexes 1 and 2 efficiently catalyzed selective epoxidation of styrene with 30% H2O2 under ecologically sustainable organic solvent-free conditions, at ambient temperature. The catalysts afforded good styrene conversion and high TON value along with excellent epoxide selectivity (>99%). Recyclability of the catalysts at least up to three consecutive cycles without significant alteration in activity or selectivity, is an additional remarkable feature of the developed catalytic protocol.

Controllable Cyclopalladated Polythiophene Imine Monolayer by Self-Assembly, Hybrid Doping and Electrochemical Polymerization: A Simple Way to Enhance Activity and Stability

In this article, an approach to generate self-assembly cyclopalladated polythiophene imine monolayers (denoted as ITO@Pd-CPTIMs) is described. The monolayers were fabricated by combining self-assembly (SA), hybrid doping (HD), and electrochemical polymerization (ECP) called SA-HD-ECP. The catalytic activity and stability of the polymerized monolayers in the Suzuki coupling reaction were improved by modulating the structure and morphology in hybrid doping using different thiophene derivatives, concentrations, and scanning numbers during electrochemical polymerization. Morphological changes in the catalytic surface associated with catalytic activity were investigated. ITO@Pd-PTF could improve catalytic activity with a higher TON value (45000 mol/molcat) and attain recycling ability at least 10 times.

Amino acid-assisted synthesis of TS-1 zeolites containing highly catalytically active TiO6 species

Tailoring the Ti coordination states in titanosilicate zeolites to simultaneously improve feedstock conversion and maximize the target product selectivity remains a challenge in the pursuit of high-performance catalysts for selective oxidation reactions. Herein, we provide a facile strategy to synthesize hierarchical anatase-free TS-1 (MFI-type) zeolites with tetrahedrally coordinated (TiO4) and octahedrally coordinated Ti species (TiO6). The TiO4 species provide high epoxide selectivity, while the TiO6 species afford improved alkene conversion. This strategy is achieved by synergistically using an L-lysine-assisted approach and a two-step crystallization; the two-step crystallization approach prevents the formation of anatase TiO2, while L-lysine stabilizes the TiO6 species and ensures efficient incorporation of TiO6 into the anatase-free TS-1 zeolites. Compared with their conventional counterparts, which only contain TiO4 species, the as-prepared TS-1 zeolites (Si/Ti = 36.9) result in a higher 1-hexene conversion (33%), higher TON value (153), and comparable epoxide selectivity (95%). This synthetic strategy provides avenues to tailor the amount and distribution of Ti species in titanosilicate zeolites to achieve high catalytic performances in various processes.

A Robust Photocatalytic Hybrid Material Composed of Metal-Organic Cages and TiO2 for Efficient Visible-Light-Driven Hydrogen Evolution.

The design of photochemical molecular devices (PMDs) for photocatalytic H2 production from water is a meaningful but challenging subject currently. Herein, a Pd2 L4 type metal-organic cage (denoted as MOC-Q2) is designed as a PMD, which consists of two catalytic centers (Pd2+ ) and four photosensitive ligands (L-2) with four pyridine anchoring groups. Subsequently, the MOC-Q2 is combined with TiO2 to form TiO2 -MOC-Q2 hybrid materials with different MOC-Q2 contents by a facile sol-gel method, which have micro/mesoporous structures and large surface areas. The optimized TiO2 -MOC-Q2 (6.5 wt%) exhibits high H2 production activity (7.9 mmol g-1 h-1 within 5 h) and excellent durability, giving a TON value of 23477 or 11739 (based on MOC-Q2 or Pd moles) after recycling for 7 rounds. By contrast, the pure MOC-Q2 only shows an ordinary photocatalytic H2 production rate (0.84 mmol g-1 h-1 within 5 h) in the homogeneous system. It can be deduced that TiO2 drives the photocatalysis and simultaneously acts as the structure promoter. This study presents a meaningful and distinctive attempt of a new approach for the design and development of MOC-based heterogeneous photocatalysts.

Ultrafine Copper Oxide Particles Dispersed on Nitrogen-Doped Hollow Carbon Nanospheres for Oxidative Esterification of Biomass-Derived 5-Hydroxymethylfurfural.

One-pot synthesis of furan-2,5-dimethylcarboxylate (FDMC) from 5-hydroxymethylfurfural (HMF) is highly demanding for the commercial production of polyethylene furanoate (PEF). Herein, a direct synthesis of FDMC is reported from oxidative esterification of HMF using ultrafine CuO particles dispersed on nitrogen-doped hollow carbon nanospheres (CuO/N-C-HNSs) as a catalyst and tert-butyl hydroperoxide (TBHP) as an oxidizing and methylating reagent. The CuO/N-C-HNSs was prepared through a template protection-sacrifice strategy using SiO2 as a sacrificial template and histidine as the precursor for N and C. N-doping facilitated a strong interaction between the support and copper species, affording formation of CuO nanoparticles of less than 10 nm in size. By virtue of the highly dispersed CuO nanoparticles and a high BET surface area 373 m2 /g, the CuO/N-C-HNSsshows excellent catalytic performance in the selective conversion of HMF into FDMC affording 93 % yield of the desired product with a TON value of 49. Furthermore, the oxidative esterification involving SP3 C-H bond functionalization is also demonstrated using the same catalyst.

Hydrogen evolution reaction highly electrocatalyzed by MWCNT/N-octylpyridinum hexafluorophosphate metal-free system

A mixed electrocatalyst that consists of multi walled carbon nanotubes (MWCNTs) and the ionic liquid (IL) N-octylpyridinum hexafluorophosphate (OPyPF6) as binder (MWCNT/IL system) was used in the study of hydrogen evolution reaction. This electrocatalyst was compared to graphite/mineral oil (Gr), graphite/OPyPF6 (Gr/IL), MWCNT/mineral oil (MWCNT) systems. All systems were characterized by cyclic voltammetry determining that MWCNT/IL system is highly electrocatalytic (E onset = -0.3 V vs Ag/AgCl) in relation to the other systems studied containing MWCNT or IL separately. The presence of each of the components that form the electrodic surface is corroborated by XRD, Raman, and FESEM-EDX, and it is demonstrated by chronoamperometric analysis that MWCNT/IL system is highly stable. The efficiency of the electrode, determined by its electrocatalytic activity, is confirmed by the quantification by gas chromatography of the hydrogen produced. Moreover, an elevated TON value (16274) and faradaic efficiency close to 60% are calculated, in comparison to other electrocatalysts found in literature. All these attractive properties are complemented by the fact that the MWCNT/IL system is simple, novel and easy to prepare.

C(acyl)-C(sp2) and C(sp2)-C(sp2) Suzuki-Miyaura cross-coupling reactions using nitrile-functionalized NHC palladium complexes.

Application of N-heterocyclic carbene (NHC) palladium complexes has been successful for the modulation of C–C coupling reactions. For this purpose, a series of azolium salts (1a–f) including benzothiazolium, benzimidazolium, and imidazolium, bearing a CN-substituted benzyl moiety, and their (NHC)2PdBr2 (2a–c) and PEPPSI-type palladium (3b–f) complexes have been systematically prepared to catalyse acylative Suzuki–Miyaura coupling reaction of acyl chlorides with arylboronic acids to form benzophenone derivatives in the presence of potassium carbonate as a base and to catalyse the traditional Suzuki–Miyaura coupling reaction of bromobenzene with arylboronic acids to form biaryls. All the synthesized compounds were fully characterized by Fourier Transform Infrared (FTIR), and 1H and 13C NMR spectroscopies. X-ray diffraction studies on single crystals of 3c, 3e and 3f prove the square planar geometry. Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), metal mapping analyses and thermal gravimetric analysis (TGA) were performed to get further insights into the mechanism of the Suzuki–Miyaura cross coupling reactions. Mechanistic studies have revealed that the stability and coordination of the complexes by the CN group are achieved by the removal of pyridine from the complex in catalytic cycles. The presence of the CN group in the (NHC)Pd complexes significantly increased the catalytic activities for both reactions.

Polyoxomolybdates as efficient catalysts for Knoevenagel condensation reaction of benzaldehyde and ethyl cyanoacetate under mild condition

The development of new heterogeneous catalysts for Knoevenagel condensation reaction is critical for practical applications. Herein, we prepared three organophosphonate-functionalized polyoxomolybdates, Cs2Na9H9[{Co(H2O)4}(TeMo6O21)2{Co(OOCCH2NCH2PO3)2}3]·41H2O (1), Cs2Na8[H6{Co(H2O)4}3(SeMo6O21)2{Co(OOCCH2NCH2PO3)2}3]·31H2O (2) and Cs2Na9H3[H6{Ni(H2O)4}(SeMo6O21)2{Ni(OOCCH2NCH2PO3)2}3]·28H2O (3), which exhibit high catalytic activity for gram-scale Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate. Especially, under the optimal conditions, compound 1 can achieve a satisfactory yield (98%) and show high TON value (1960), which is superior to that of compounds 2 and 3. Notably, the TON value is much higher than that of previously reported catalysts. Such high catalytic performance could be attributed to the co-existence of Lewis acid and Lewis base sites in catalysts. In addition, based on substrates screening and recyclability tests, 1 has exhibited broad catalytic generality and good recyclability.