Catalytic Oxidative Coupling Research Articles

Reusable cobalt-phthalocyanine in water: efficient catalytic aerobic oxidative coupling of thiols to construct S–N/S–S bonds

Reusable Co-catalyzed coupling of thiols to synthesize S–N/S–S bonds in water.

Integrated Experimental and Theoretical Study of Shape-Controlled Catalytic Oxidative Coupling of Aromatic Amines over CuO Nanostructures.

We have synthesized CuO nanostructures with flake, dandelion-microsphere, and short-ribbon shapes using solution-phase methods and have evaluated their structure–performance relationship in the heterogeneous catalysis of liquid-phase oxidative coupling reactions. The formation of nanostructures and the morphological evolution were confirmed by transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, energy-dispersive X-ray spectroscopy, elemental mapping analysis, and Fourier transform infrared spectroscopy. CuO nanostructures with different morphologies were tested for the catalytic oxidative coupling of aromatic amines to imines under solvent-free conditions. We found that the flake-shaped CuO nanostructures exhibited superior catalytic efficiency compared to that of the dandelion- and short-ribbon-shaped CuO nanostructures. We also performed extensive density functional theory (DFT) calculations to gain atomic-level insight into the intriguing reactivity trends observed for the different CuO nanostructures. Our DFT calculations provided for the first time a detailed and comprehensive view of the oxidative coupling reaction of benzylamine over CuO, which yields N-benzylidene-1-phenylmethanamine as the major product. CuO(111) is identified as the reactive surface; the specific arrangement of coordinatively unsaturated Cu and O sites on the most stable CuO(111) surface allows N–H and C–H bond-activation reactions to proceed with low-energy barriers. The high catalytic activity of the flake-shaped CuO nanostructure can be attributed to the greatest exposure of the active CuO(111) facets. Our finding sheds light on the prospective utility of inexpensive CuO nanostructured catalysts with different morphologies in performing solvent-free oxidative coupling of aromatic amines to obtain biologically and pharmaceutically important imine derivatives with high selectivity.

Catalytic Oxidative Carbene Coupling of α-Diazo Carbonyls for the Synthesis of β-Amino Ketones via C(sp(3))-H Functionalization.

A catalytic domino oxidative carbene coupling (OCC) of α-diazo carbonyls has been established by treatment with N,N-dimethylanilines and carboxylic acids (or N-methylaniline) via direct C(sp(3))-H functionalization under convenient conditions. The reaction pathway is proposed to proceed through the sequence of carbene formation, enolization, and nucleophilic addition. The reaction enables de-diazotized carbo-oxygenation and carbo-amination of α-diazo carbonyls and provides practical access to α-(acyloxy)-β-amino ketones and α,β-diamino ketones.

ChemInform Abstract: Catalytic Oxidative Coupling of Primary Amines under Air: A Flexible Route to Benzimidazole Derivatives.

AbstractIn a bioinspired approach, the cooperative action of cupric bromide as electron‐transfer mediator and a topaquinone‐like co‐catalyst is studied.

Low-temperature catalytic oxidative coupling of methane in an electric field over a Ce-W-O catalyst system.

We examined oxidative coupling of methane (OCM) over various Ce–W–O catalysts at 423 K in an electric field. Ce2(WO4)3/CeO2 catalyst showed high OCM activity. In a periodic operation test over Ce2(WO4)3/CeO2 catalyst, C2 selectivity exceeded 60% during three redox cycles. However, Ce2(WO4)3/CeO2 catalyst without the electric field showed low activity, even at 1073 K: CH4 Conv., 6.0%; C2 Sel., 2.1%. A synergetic effect between the Ce2(WO4)3 structure and electric field created the reactive oxygen species for selective oxidation of methane. Results of XAFS, in-situ Raman and periodic operation tests demonstrated that OCM occurred as the lattice oxygen in Ce2(WO4)3 (short W–O bonds in distorted WO4 unit) was consumed. The consumed oxygen was reproduced by a redox mechanism in the electric field.

Oxidative coupling of 2-naphthol catalyzed by a new methoxido bridged dinuclear oxidovanadium(V) complex

A new dinuclear oxidovanadium(V) complex, [(VO)2(μ-L-κ4O,N,N,O)(μ-OCH3)2(OMe)2]·CH3OH (1), is synthesized by the reaction of V2O5 with 1,1′-((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene))bis(naphthalen-2-ol) (H2L) in methanol. H2L is synthesized by two different methods: (i) from the reaction of hydrazine hydrate with 2-hydroxy-1-naphthaldehyde and (ii) from the reaction of hydrazine hydrate with 2-naphthol in the presence of formaldehyde (Mannich condensation). The ligand and its vanadium complex are characterized by elemental analysis, spectroscopic methods (FT-IR, NMR and UV–Vis) and their structures are determined by single crystal X-ray analysis. X-ray studies show that 1 is a neutral dinuclear complex of oxidovanadium(V) in which two vanadium(V) ions are connected by two methoxido bridging groups. The Schiff base ligand is coordinated to both vanadium centers by two NO-donor sets. Complex 1 is employed as initiator for oxidative coupling of 2-naphthol to produce BINOL. The effect of temperature, reaction atmosphere and solvent in catalytic reaction is studied. According to the obtained results, a mechanism is proposed for catalytic oxidative coupling reaction in the presence of complex 1.

Catalytic Oxidative Coupling of Primary Amines under Air: A Flexible Route to Benzimidazole Derivatives

AbstractBenzimidazoles are of fundamental importance in chemistry and biology, and the development of efficient, environmentally benign methods for their preparation remains a key challenge for organic chemists. In a biomimetic approach inspired by copper amine oxidases, we disclose herein the scope and factors influencing the success of the cooperative action of CuBr2 as electron‐transfer mediator and a topaquinone‐like substrate‐selective catalyst in the oxidative cyclocondensation of primary amines with o‐aminoanilines. This one‐pot atom‐economic multistep process, which works under green conditions with ambient air as the terminal oxidant, low loadings of catalyst, and equimolar amounts of commercially available amine substrates, is particularly suitable for the preparation of 1,2‐disubstituted benzimidazoles. Furthermore, it allows the functionalization of nonactivated primary aliphatic amines, which are known to be challenging substrates for non‐enzymatic catalytic aerobic systems.

Kinetics of Oxidation of 2,6-Dimethylphenol (DMP) Using Novel μ-Carbonato [(Pip)<sub>4n</sub>Cu<sub>4</sub>X<sub>4</sub>(CO<sub>3</sub>)<sub>2</sub>] Complexes

This paper reports the kinetics of the oxidation of 2,6-dimethylphenol (DMP) to get 3,3’,5,5’-tetra- methyl-4,4’-diphenoquinone (DPQ) using novel oxidative coupling complexes [(Pip)4nCu4X4-(CO3)2] (n = 1 or 2, X = Cl or Br, Pip = piperidine). The new prepared tetranuclear complexes were characterized using cryoscopic measurements, electronic spectra, FTIR, EPR and cyclic voltammetry techniques. These complexes are catalytically active. The proposed mechanism of the catalytic oxidative coupling can be illustrated as a pre-equilibrium, K, between the catalyst and DMP to form a complex intermediate which is converted to activated complex through the rate determining step, k2, to form the final product. The inverse of the observed rate constants kobsd versus 1/[DMP]2 gives a straight line with intercept. From the slope and the intercept, both K and k2 are obtained. At different temperatures, thermodynamic and kinetic parameters are evaluated. It is worth to mention that, the dependence of kobsd on [DMP]2 indicates that the coordination number for every copper center in both n = 1 or 2 in [(Pip)4nCu4X4(CO3)2] is equal to six. Therefore, carbonato bridging centers in n = 1 acts as a tridentate ligand, while for n = 2 acts as a bidentate ligand.

N‐Heterocyclic Carbene Catalyzed Oxidative Coupling of Alkenes/ α‐Bromoacetophenones with Aldehydes: A Facile Entry to α,β‐Epoxy Ketones

AbstractA novel, N‐heterocyclic carbene (NHC) catalyzed direct oxidative coupling of styrenes with aldehydes has been described for the synthesis of α,β‐epoxy ketones in good yields. This unprecedented regioselective oxidative coupling employs NBS/DBU/DMSO (DBU=1,8‐diazabicyclo [5.4. 0] undec‐7‐ene, DMSO=dimethylsulfoxide, NBS=N‐bromosuccinimide) as an oxidative system at ambient conditions. Additionally, first NHC‐catalyzed Darzens reaction of α‐bromoketones and aldehydes under mild reaction conditions has also been described. Interestingly, mechanistic studies have revealed the preferred reactivity of NHC with alkene/α‐bromoketone rather than aldehydes, thus proceeding via the ketodeoxy Breslow intermediate.

N-Heterocyclic Carbene Catalyzed Oxidative Coupling of Alkenes/α-Bromoacetophenones with Aldehydes: A Facile Entry to α,β-Epoxy Ketones.

A novel, N-heterocyclic carbene (NHC) catalyzed direct oxidative coupling of styrenes with aldehydes has been described for the synthesis of α,β-epoxy ketones in good yields. This unprecedented regioselective oxidative coupling employs NBS/DBU/DMSO (DBU=1,8-diazabicyclo [5.4. 0] undec-7-ene, DMSO=dimethylsulfoxide, NBS=N-bromosuccinimide) as an oxidative system at ambient conditions. Additionally, first NHC-catalyzed Darzens reaction of α-bromoketones and aldehydes under mild reaction conditions has also been described. Interestingly, mechanistic studies have revealed the preferred reactivity of NHC with alkene/α-bromoketone rather than aldehydes, thus proceeding via the ketodeoxy Breslow intermediate.

ChemInform Abstract: Synthesis of Polycyclic Amines Through Mild Metal‐Free Tandem Cross‐Dehydrogenative Coupling/Intramolecular Hydroarylation of N‐Aryltetrahydroisoquinolines and Crotonaldehyde.

A [4+2] cycloaddition reaction proceeding through tandem cross-dehydrogenative coupling/intramolecular hydroarylation between N-aryltetrahydroisoquinolines and crotonaldehyde was developed by virtue of enamine–iminium catalysis, which enabled the rapid construction of ring-fused tetrahydroquinolines. The first metal-free catalytic oxidative coupling of γ-selective C(sp3)–H bonds of crotonaldehyde was realized by using a secondary amine catalyst and 2,3-dichloro-5,6-dicyanoquinone.

Phase states of Li/W/Mn/SiO2 composites in catalytic oxidative coupling of methane

Phase diagrams of the Li2O-WO3-MnO-Mn2O3 and Li2O-WO3-Mn2O3-SiO2 systems have been mapped out and Li/W/Mn/SiO2 composite catalysts have been shown to be in melt-Mn2O3-quartz (cristobalite) equilibrium at temperatures of oxidative coupling of methane.

ChemInform Abstract: Aerobic Oxidative Homocoupling of Aryl Amines Using Heterogeneous Rhodium Catalysts.

The first heterogeneous catalyzed oxidative coupling of aryl amines is reported. Aryl amines were dimerized at room temperature under air using a heterogeneous Rh/C catalyst in the presence of acids. By choosing a suitable acidic solvent, biaryl compounds and carbazoles were selectively prepared in good yields. This reaction is operationally simple and provides an efficient synthetic methodology for the preparation of biaryl diamines via oxidative C–H activation.

Synthesis of Polycyclic Amines through Mild Metal‐Free Tandem Cross‐Dehydrogenative Coupling/Intramolecular Hydroarylation of N‐Aryltetrahydroisoquinolines and Crotonaldehyde

AbstractA [4+2] cycloaddition reaction proceeding through tandem cross‐dehydrogenative coupling/intramolecular hydroarylation between N‐aryltetrahydroisoquinolines and crotonaldehyde was developed by virtue of enamine–iminium catalysis, which enabled the rapid construction of ring‐fused tetrahydroquinolines. The first metal‐free catalytic oxidative coupling of γ‐selective C(sp3)–H bonds of crotonaldehyde was realized by using a secondary amine catalyst and 2,3‐dichloro‐5,6‐dicyanoquinone.

Aerobic oxidative homocoupling of aryl amines using heterogeneous rhodium catalysts.

The first heterogeneous catalyzed oxidative coupling of aryl amines is reported. Aryl amines were dimerized at room temperature under air using a heterogeneous Rh/C catalyst in the presence of acids. By choosing a suitable acidic solvent, biaryl compounds and carbazoles were selectively prepared in good yields. This reaction is operationally simple and provides an efficient synthetic methodology for the preparation of biaryl diamines via oxidative C-H activation.

Phase states of Na/W/Mn/SiO2 composites at temperatures of catalytic oxidative coupling of methane

This paper analyzes phase states in the Na2O-WO3-MnO-Mn2O3 and Na2O-WO3-Mn2O3-SiO2 systems at temperatures of oxidative coupling of methane (OCM). The results indicate that, in the case of effective OCM, Na/W/Mn/SiO2 composite catalysts are in melt-Mn2O3 -tridymite (cristobalite) equilibrium.

Catalytic formation of acrylate from carbon dioxide and ethene.

With regard to sustainability, carbon dioxide (CO2) is an attractive C1 building block. However, due to thermodynamic restrictions, reactions incorporating CO2 are relatively limited so far. One of the so-called "dream reactions" in this field is the catalytic oxidative coupling of CO2 and ethene and subsequent β-H elimination to form acrylic acid. This reaction has been studied intensely for decades. However up to this date no suitable catalytic process has been established. Here we show that the catalytic conversion of ethene and CO2 to acrylate is possible in the presence of a homogeneous nickel catalyst in combination with a "hard" Lewis acid. For the first time, catalytic conversion of CO2 and ethene to acrylate with turnover numbers (TON) of up to 21 was demonstrated.

Transition metal-doped TiO2 nanowire catalysts for the oxidative coupling of methane

The catalytic oxidative coupling of methane (OCM) on transition metal-doped TiO2 nanowire catalysts was performed and the effects of metal dopants were studied. With transition metal doping, the electric and optical properties of nanowires were adjusted, which seemed to improve the catalytic activity and selectivity of the OCM reaction. A Mn-doped TiO2 nanowire catalyst exhibited the highest C2 yield with the highest (ethylene)/(ethane) ratio because of its moderate oxidation activity, while a highly active Rh-doped TiO2 nanowire catalyst converted methane into fully oxidized CO and CO2. The electric conductivity assessed by UV–vis absorption represented the oxidation activity of the nanowire catalysts.

Catalytic oxidative coupling of dimethyl ether under supercritical conditions

Catalytic oxidative coupling of dimethyl ether (DME) is studied for the first time under supercritical conditions. The oxidation of DME with molecular oxygen of air in the presence of the CaO-SnO2 catalyst is carried out in a substrate (DME) medium and in its mixtures with CO2 under the supercritical conditions (100 atm, 250–300°C). At 255°C, the maximum conversion of DME (≈40% at the ratio of the yields of monoglim and diglim about 2: 1) is achieved at a 20-fold (by volume) dilution of DME with supercritical CO2.

ChemInform Abstract: N‐Heterocyclic Carbene Catalyzed Oxidative Coupling of Aldehydes with Carbodiimides under Aerobic Conditions: Efficient Synthesis of N‐Acylureas.

AbstractFor the first time the oxidative coupling reaction of N,N‐disubstituted carbodiimides with aldehydes catalyzed by a N‐heterocyclic carbene (NHC) precatalyst under aerobic conditions is achieved.