Catalytic Circle Research Articles

Manganese-catalyzed synthesis of 4-CF3-2-phosphinoylquinolines via radical 6-endo-trig cyclization of 1-Isocyano-2-(1-(trifluoromethyl)ethenyl)benzenes

A manganese-catalyzed radical 6-endo-trig cyclization of 1-isocyano-2-(1-(trifluoromethyl) ethenyl)benzenes with arylphosphine oxides which involved a novel Mn(III)/Mn(II) catalytic circle, has been developed. The reaction afforded various 4-CF3-2-phosphinoylquinolines under mild reaction conditions without any external oxidant, ligand or additive.

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO 2 /Epoxide Copolymer

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO ₂ /Epoxide Copolymer

Copper(II)-Catalyzed Direct C-H Trifluoroethylation of Heteroarenes.

Trifluoroethyl (CH2CF3) is an important functional group in many pharmaceutical and agrochemical compounds. Herein, we report an efficient method for the copper-catalyzed direct trifluoroethylation of heteroarenes. The reaction exhibited good compatibility to various substrates, and the desired products were obtained in good yields. Preliminary mechanistic investigations indicate the trifluoroethyl radical is involved in the catalytic circle. Moreover, the late-stage modification of bioactive molecules further confirmed the practical applications of this method.

Copper-catalyzed radical trifluoroethylthiolation of arylboronic acids with PhSO2SCH2CF3

Trifluoroethylthio group (SCH2CF3) is a key functionality in several pharmaceutical and agrochemical compounds, the methods for the installation of the 2,2,2-trifluoroethylthio group are sought after. Herein, we report a copper-catalyzed trifluoroethylthiolation reaction of S-(2,2,2-trifluoroethyl) benzenesulfonothioates and phenylboronic acids at room temperature. The reaction achieved the insertion of trifluoroethylthio moiety to efficiently obtain various substituted aryl 2,2,2-trifluoroethyl thioethers in good yields. Mechanistic investigation indicates the trifluoroethylthiolation radical is involved in the catalytic circle. Moreover, trifluoroethylthiolated clofibrate was synthesized in a particular fashion.

Manganese peroxidase mediated oxidation of sulfamethoxazole: Integrating the computational analysis to reveal the reaction kinetics, mechanistic insights, and oxidation pathway

In this study, manganese peroxidase (MnP) was applied to induce the in vitro oxidation of sulfamethoxazole (SMX). The results indicated that 87.04% of the SMX was transformed and followed first-order kinetics (kobs=0.438 h−1) within 6 h when 40 U L−1 of MnP was added. The reaction kinetics were investigated under different conditions, including pH, MnP activity, and H2O2 concentration. The active species Mn3+ was responsible for the oxidation of SMX, and the Mn3+ production rate was monitored to reveal the interaction among MnP, Mn3+, and SMX. By integrating the characterizations analysis of the MnP/H2O2 system with the density functional theory (DFT) calculations, the proton-coupled electron transfer (PCET) process dominated the catalytic circle of MnP and the transformation of Mn3+. Additionally, possible oxidation pathways of SMX were proposed based on single-electron transfer mechanism, which primarily included the S–N bond cleavage, the C–S bond cleavage, and one electron loss without bond breakage. It was then transformed to hydrolysis, N–H oxidation, self-coupling, and carboxylic acid coupling products. This study provides insights into the atomic-level mechanism of MnP and the transformation pathways of sulfamethoxazole, which lays a significant foundation for the potential of MnP in wastewater treatment applications.

Tunable S doping from Co3O4 to Co9S8 for peroxymonosulfate activation: Distinguished Radical/Nonradical species and generation pathways

The introduction of non-metal heteroatoms is an effective way to improve the catalytic properties of heterogeneous catalysts to peroxymonosulfate. Unfortunately, the influence of foreign elements on the catalytic process has not been deeply revealed. Herein, we reported a series of Co9S8 nanorods catalysts from Co3O4 precursor with different S doping ratios. S doping effectively enhanced the catalytic properties, and the catalytic process gradually switched from non-radical (1O2) into radical (SO4−) with the increase of S doping ratio. Moreover, quenching experiments, EPR, XPS, and radicals quantification indicated that the concentration of 1O2 exhibited a linear relationship with ΔOL. Indicating that 1O2 was derived from the reaction between PMS and OL. S doping also altered the valency of cobalt. In Co3O4/PMS, ROS was generated through Co3+/Co2+ catalytic circle. However, in Co9S8/PMS, Co3+/Co2+/Co0 were all involved and accounted for the generation of ROS due to the low redox potential of S2-. Our work may provide some new clues and strategies for studying the influence of foreign elements on the catalytic process in PMS-based heterogeneous catalytic system.

CO2 Activation by Lewis Pairs Generated Under Copper Catalysis Enables Difunctionalization of Imines.

Integration of distinct substrate activation modes in a catalytic circle is critical for the development of new, powerful synthetic methodologies toward complex and value-added chemicals from simple and readily available feedstocks. Here, we describe a highly selective difunctionalization of imines through incorporation of activation of CO2 by intramolecular N/B Lewis pairs into a copper catalytic cycle. Experimental and computational studies on the mechanistic aspect revealed an α-borylalkylamido intermediate, a metal amide-based Lewis pair formed by borylation of a C-N double bond, and enabled an unprecedented CO2 fixation pattern that is in sharp contrast to the traditional CO2 insertion into transition-metal-element bonds. The unique lithium cyclic boracarbamate products could be easily transformed into multifunctional N-carboxylated α-amino boronates. The highly diastereoselective reactions of chiral N-tert-butanesulfinyl aldimines were also achieved. We hope that our findings may inspire further development of selective multicomponent reactions by incorporation of Lewis pair chemistry into transition-metal catalysis.

Monolithic Ag-Cu2O/Ti-foam for the gas phase oxidation of alcohols: Synergistic effect between Ag and Cu2O

The robust Ag-Cu2O/Ti-foam in the gas phase oxidation of alcohols is fabricated by impregnation and calcination method. The best catalyst is Ag-3-Cu2O-5/Ti-foam (3 wt% Ag, 5 wt% Cu), capable of oxidizing benzyl alcohol (95% benzyl alcohol conversion, 98% benzyl aldehyde selectivity) at low temperature of 260 °C. The synergistic effect between Ag and Cu2O in the high alcohol-oxidation performance effectively works in three aspects: Ag promotes the formation of Cu2O from Cu-species with other valences; Ag stabilizes the existence of Cu2O; Ag is beneficial in the dehydrogenation of Cu2O-H intermediates to drive the catalytic circle.

Nickel-Catalyzed Coupling Reaction of α-Bromo-α-fluoroketones with Arylboronic Acids toward the Synthesis of α-Fluoroketones.

A nickel-catalyzed coupling reaction of α-bromo-α-fluoroketones with arylboronic acids was reported, which provides an efficient pathway to access 2-fluoro-1,2-diarylethanones in high yields. We also disclosed the synthesis of the monofluorination agents α-bromo-α-fluoroketones by using a trifluoroacetate release protocol. Mechanistic investigation indicated that a monofluoroalkyl radical is involved in the catalytic circle. Moreover, an important medical intermediate of flindokalner was synthesized via a nickel-catalyzed coupling reaction of α-bromo-α-fluoro-2-indolone and boronic ester.

Synthesis, screening and biological activity of potent thiosemicarbazone compounds as a tyrosinase inhibitor

Inhibitors are designed based on coordination chemistry and catalytic circle of the tyrosinase, coordination atoms binds to copper and blocks enzyme activity, indicated that thiosemicarbazone species possess good potential as tyrosinase inhibitors.

Construction of Pyridazine Analogues via Rhodium‐mediated C‐H Activation

AbstractHerein a rhodium (III)‐mediated catalysis was demonstrated for approaching the structurally divergent N,N‐bicyclic pyridazine analogues. The pyrazolidinone moiety was used to direct the ortho C−H activation and this led to a general synthesis of benzopyridazine analogues with satisfactory yields. The crucial effect of the base was illustrated in the sequential dehydration process. For mechanistic insight, control experiments were performed for illustration of the catalytic circle. Gram scale synthesis and several practical transformations were conducted for further applications.magnified image

Influence of alkali metal amides on the catalytic activity of manganese nitride for ammonia decomposition

Strong promoting effect of alkali metal amides, i.e., LiNH2, NaNH2 and KNH2, on the catalytic activity of manganese nitride (MnN) for ammonia decomposition has been demonstrated, which is evidenced by ca. 100K drop in onset temperature and by ca. 50–60kJmol−1 reduction in apparent activation energy as compared with the neat MnN. The order of promotion capability of alkali metal amides can be ranked as LiNH2>KNH2≥NaNH2, either in term of NH3 conversion rate or turnover frequency (TOF), which is distinctly different from that of conventional alkali metal oxides or hydroxides, i.e., K>Na>Li. This phenomenon suggests that the promoting mechanism of alkalis depends on their chemical forms. When alkalis are in the form of amide or imide, they may function as co-catalysts by participating in the catalytic circle directly rather than by executing electronic promotion influence on transition metals.

Au25 Clusters as Electron-Transfer Catalysts Induced the Intramolecular Cascade Reaction of 2-nitrobenzonitrile

Design of atomically precise metal nanocluster catalysts is of great importance in understanding the essence of the catalytic reactions at the atomic level. Here, for the first time, Au25z nanoslusters were employed as electron transfer catalysts to induce an intramolecular cascade reaction at ambient conditions and gave rise to high conversion (87%) and selectivity (96%). Electron spin-resonance spectra indeed confirmed the consecutive electron transfer process and the formation of N radical. UV-vis absorption spectra also verified Au25z was intact after the catalytic circle. Our research may open up wide opportunities for extensive organic reactions catalyzed by Au25z.

Dimerization of 1-Phenyl-1<i>H</i>-Tetrazole-5-Thiol over Metalloporphyrin Catalysts

In an alkaline methanol solution, dimerization of 1-phenyl-1H-tetrazole-5-thiol (HL) was carried out over metalloporphyrin catalysts under mild conditions. The dimer product, 1,2-bis (1-phenyl-1H-tetrazol-5-yl) disulfane (L-L), was characterized by determinations of infrared (IR), HPLC, NMR and elementary analysis respectively. In situ UV-Vis spectroscopic analysis and cyclic voltammetric (CV) determinations suggested that the active intermediate for L-L formation is an axially ligated complex, RS-MnⅢTHPP, which decomposes into a MnⅡTHPP molecule and a stable radical (SR) for coupling to form the disulfane. Meanwhile MnIITHPP molecule can be oxidized easily to form MnⅢTHPP species again by oxygen from the air for using in next catalytic circle.

Promoting behaviors of alkali compounds in low temperature methanol synthesis over copper-based catalyst

Hybrid catalyst systems comprised of Na compounds (HCOONa, NaOH, Na2CO3 and NaHCO3) and Cu/MgO catalysts have contributed to a novel high-performance methanol synthesis in ethanol solvent from syngas (CO/H2=1/2) at a low temperature of 433K and 5MPa. It is found that Na2CO3 dopant is more beneficial to enhance hydrogenolysis ability of Cu/MgO catalyst than NaOH and HCOONa. Whereas, all the starting Na compounds in ethanol solvent are reversibly converted to HCOONa in alcohol solvent by ex situ observations, revealing that formate alone is the essential species in the catalytic circle. The results unambiguously elucidate that the essence of alkali component in promoting the low temperature methanol synthesis is virtually attributed to the formation of highly reactive alkali-participated active site. It is also proposed that solid Cu/MgO catalyst should play binary roles in successive carbonylation and hydrogenolysis reactions.

The promoter effect of alkali in Fischer-Tropsch iron and cobalt catalysts

Abstract The promoter effect of alkali on Fischer-Tropsch iron catalysts causes an increased 1-alkene selectivity, a slightly increased reaction rate, an increased growth probability of hydrocarbon chains and also an increased resistance against oxidation of iron by the reaction product water. Experiments are presented which show that for cobalt catalysts alkali addition also leads to increased 1-alkene selectivity. However, the reaction rate is markedly reduced. The effect on the 1-alkene selectivity is without doubt due to increased adsorption strength of carbon monoxide causing an enhanced displacement of 1-alkenes while the propensity towards hydrogenation is hardly reduced. For iron catalysts the 1-alkene selectivity increases in the turn of Li, Na, K, Cs. With respect to the bimodal Anderson-Schulz-Flory (ASF) distribution the strong effect on the growth probability α 2 is independent of the nature of the alkali cation while the fraction f 2 of the distribution that is characterized by α 2 increases in the turn Li, Na, K, and Cs. These strong promoter effects are interpreted on the basis of a novel mechanism of Fischer-Tropsch synthesis whereby the alkali cation takes part in the catalytic circle. Finally an analogy of the promoter effect of alkali on iron for the ammonia synthesis and the Fischer-Tropsch synthesis is suggested.

Alumina-Supported Copper Chloride: 4. Effect of Exposure to O2 and HCl

A complete catalytic cycle was performed on CuCl2/Al2O3 catalyst for ethylene oxychlorination at 500 K. X-ray absorption near-edge spectroscopy, extended X-ray absorption fine structure, electron paramagnetic resonance, and IR of adsorbed CO were used to demonstrate that the ethylene oxychlorination reaction, C2H4+2HCl+1/2 O2→C2H4Cl2+H2O, follows a three-step mechanism: (i) reduction of CuCl2 to CuCl (2CuCl2+C2H4→C2H4Cl2+2CuCl), (ii) oxidation of CuCl to give an oxychloride (2CuCl+1/2 O2→Cu2OCl2), and (iii) closure of the catalytic circle by rechlorination with HCl, restoring the original CuCl2 (Cu2OCl2+2HCl→2CuCl2+H2O). The dispersing/sintering effect of the different reagents on the active phase has been also investigated.

The CuCl2/Al2O3 Catalyst Investigated in Interaction with Reagents

Alumina supported CuCl2, the basic catalyst for ethylene oxychlorination, has been investigated by UV-Vis spectroscopy, EPR, EXAFS and XANES in a wide range (0.25-9.0 wt%) of Cu concentration. We have evidenced that, at low Cu content, the formation of a surface aluminate species takes place. The formation of this surface copper aluminate stops at 0.95 wt% Cu / 100 m2; at higher Cu concentrations excess copper chloride precipitates directly from solution during the drying step forming an highly dispersed CuCl2.H2O, phase, overlapping progressively the surface aluminate. Depletion tests and IR spectroscopy of adsorbed NO have demonstrated that the latter is the only active phase. A complete catalytic cycle has then been performed on CuCl2/Al2O3 catalyst. EPR, XANES and EXAFS, have been used to demonstrate that the ethylene oxychlorination reaction: C2H4 + 2HCl + ½ O2 --> C2H4Cl2 + H2O follows a three steps mechanism: (i) reduction of CuCl2 to CuCl (2CuCl2 + C2H4 --> C2H4Cl2 + 2CuCl), (ii) oxidation of CuCl to give an oxychloride (2CuCl + ½ O2 --> Cu2OCl2) and (iii) closure of the catalytic circle by rechlorination with HCl, restoring the original CuCl2 (Cu2OCl2 + 2HCl --> 2CuCl2 + H2O). Finally, we have shown that time resolved, in situ, spectroscopy is a very promising technique to investigate the interplay between catalyst activity and oxidation state of copper.