Easy To Synthesize,Robust Organo‐osmium Asymmetric Transfer Hydrogenation Catalysts

Asymmetric transfer hydrogenation (ATH) is an important process in organic synthesis for which the Noyori‐type Ru^II catalysts [(arene)Ru(Tsdiamine)] are now well established and widely used. We now demonstrate for the first time the catalytic activity of the osmium analogues. X‐ray crystal structures of the 16‐electron Os^II catalysts are almost identical to those of Ru^II. Intriguingly the precursor complex was isolated as a dichlorido complex with a monodentate amine ligand. The Os^II catalysts are readily synthesised (within 1 h) and exhibit excellent enantioselectivity in ATH reactions of ketones.     

Photochemical Reduction of Low Concentrations of CO2 in a Porous Coordination Polymer with a Ruthenium(II)–CO Complex

Direct use of low pressures of CO₂ as a C1 source without concentration from gas mixtures is of great interest from an energy‐saving viewpoint. Porous heterogeneous catalysts containing both adsorption and catalytically active sites are promising candidates for such applications. Here, we report a porous coordination polymer (PCP)‐based catalyst, PCP‐Ru^II composite, bearing a Ru^II‐CO complex active for CO₂ reduction. The PCP‐Ru^II composite showed improved CO₂ adsorption behavior at ambient temperature. In the photochemical reduction of CO₂ the PCP‐Ru^II composite produced CO, HCOOH, and H₂. Catalytic activity was comparable with the corresponding homogeneous Ru^II catalyst and ranks among the highest of known PCP‐based catalysts. Furthermore, catalytic activity was maintained even under a 5 % CO₂/Ar gas mixture, revealing a synergistic effect between the adsorption and catalytically active sites within the PCP‐Ru^II composite.     

Immobilization of palladium(II)‐containing bis(imidazolium) ligand on ion‐exchange resins: efficient and reusable catalysts for CC coupling reactions

Suzuki reactions catalysed by a palladium(II) complex of a functionalized bis(imidazolium) ligand, Pd^II(BIM), immobilized on Dowex 50 WX8 and Amberlite IR‐120 ion‐exchange resins as heterogeneous, recyclable and active catalysts are reported. The catalysts, Pd^II(BIM)@Amberlite IR‐120 and Pd^II(BIM)@Dowex 50 WX8, were characterized using Fourier transform infrared and diffuse‐reflectance UV–visible spectroscopies and scanning electron microscopy. These heterogeneous catalysts are oxygen‐insensitive and air‐ and moisture‐stable in C? C coupling reactions, and are reusable several times without significant loss of their catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Catalytic properties of spinel-type complex oxides in oxidation reactions

The catalytic activity of M^IM^II ₂O₃ spinel-type complex oxides (M^I = Cu, Ni, Mn, Zn, Mg, Co, M^II = Co, Cr, Al) in the oxidation of CO and ethylbenzene has been investigated. The Co-containing catalysts were more active than the Cr- and Al-containing catalysts. The nature of the cation influenced the catalytic activity. Higher activities were observed for the catalysts containing two transition elements. A correlation between the catalytic and adsorption properties was established.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1730–1732, October, 1994.     

Synthesis,Characterisation and Catalytic Studies of Iron(III), Cobalt(II), Nickel(II) and Copper(II) Complexes Containing N,O Donor Ligands and Triphenylphosphine

A series of new Schiff base complexes of Fe^III, Co^II, Ni^II and Cu^II containing Ph₃P has been prepared and characterised. The Schiff bases have been prepared by the condensation of salicylaldehyde and naphthaldehyde with the appropriate aniline. The complexes have been characterised by analytical, spectral (i.r., electronic, magnetic, e.p.r., ¹H-n.m.r.) and electrochemical studies. The new complexes have been used as catalysts for aromatic coupling reactions. Higher catalytic activity has been observed for Ni^II compared to the other complexes.     

Oxidation of CO and hydrocarbons over perovskite-type complex oxides

The catalytic activity of perovskites M^IM^IIO₃ (M^I=La; M^II=Co, Mn, Cr, Al, Ni, and V) and M^ICoO₃ (M=Y, Nd, Sm, and Er) in the oxidation of CO, propylene, and ethylbenzene was investigated. The highest activity was observed for the M^ICoO₃ catalysts with perfect perovskite structure. The nature of the rare-earth element has no influence on the catalytic activity. Deformation of the octahedral coordination of the metal was found for the less active catalysts. The interaction of gases (CO, CO+air) with the catalyst surface was investigated. The more active catalysts adsorb a greater amount of O₂, and the adsorption occurs in the temperature region of the oxidation reaction. The activities of the perovskite- and spinel-type catalysts were compared under similar conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 698–701, April, 1999.     

Uncovering the synergistic photocatalytic behavior of bimetallic molecular catalysts

Bimetallic catalysts usually exhibit better performance than monometallic catalysts due to synergistic effect. However, there is a lack of exploring the synergistic effect on catalytic performance caused by the introduction of inactive metal ion. In this work, we design a molecular model system that can precisely regulate the metal site number and catalytic property. When these molecular metal compounds are used as homogeneous catalysts for photocatalytic CO₂ reduction, the dinuclear heterometallic CuNi-L² shows the highest CO₂-to-CO conversion, which is 2.1 and 3.0 times higher than that of dinuclear homometallic Ni₂-L² and mononuclear Ni-L¹. Density functional theory calculations demonstrate that, in CuNi-L², the introduction of inactive Cu^II is easier to promote the photo-generated electrons transferring to the coupled active Ni^II site to achieve the highest activity. In addition, this work also provides insights to design and construct more efficient bimetallic catalysts in future.     

A comparative screening of the catalytic activity of nanocrystalline M<Superscript>II</Superscript>Zr<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>6</Subscript> ceramics in the one-pot synthesis of 1,6-diamino-4-aryl-2-oxo-1,2-dihydropyridine-3,5-dicarbonitrile derivatives

A four-component reaction of hydrazine hydrate, ethyl cyanoacetate, malononitrile, and aromatic aldehydes was achieved in the presence of nanocrystalline M^IIZr₄(PO₄)₆ ceramics (M^II: Mn, Fe, Co, Ni, Cu, Zn, Cd) as heterogeneous catalysts to produce N-amino-2-pyridones. The reactions were performed in the presence of different catalysts, and it is observed that CdZr₄(PO₄)₆ nanocrystallines are the best catalysts among those examined. Atom economy, excellent yields in short times, high catalytic activity, recycling of catalyst, and environmental benignity are some of the important features of this protocol.     

Oxidation of styrene and cyclohexene with TBHP catalyzed by copper(II) complex encapsulated in zeolite-Y

Reaction of monobasic tridentate Hacpy-oap (Hacpy-oap?=?Schiff base derived from 2-acetylpyridine and o-aminophenol) with Cu^IICl₂ in refluxing methanol results in formation of [Cu^II(acpy-oap)Cl]. DFT calculations have been used to optimize structure of the complex. [Cu^II(acpy-oap)Cl] has also been encapsulated in the nanocavity of zeolite-Y and its encapsulation ensured by various physico-chemical techniques. Neat as well as encapsulated complexes are active catalysts for oxidation of styrene and cyclohexene using tert-butylhydroperoxide. Reaction conditions for oxidation of these substrates have been optimized by concentration of oxidant, amount of catalyst, volume of solvent and temperature of the reaction mixture. [Cu^II(acpy-oap)Cl] does not leach metal ion during catalytic activity and is recyclable.     

Directed C−H Halogenation Reactions Catalysed by PdII Supported on Polymers under Batch and Continuous Flow Conditions

A new generation of N-heterocyclic carbene palladium(II) complexes containing vinyl groups in different positions in the backbone of the N-heterocycle have been developed. The fully characterised monomers were copolymerised with divinylbenzene to fabricate robust polymer supported NHC-Pd^II complexes and these polymers were applied as heterogeneous catalysts in directed C−H halogenation of arenes with a pyridine-type directing group. The catalysts demonstrated medium-high catalytic activity with up to 90 % conversion and 100 % selectivity in chlorination. They are heterogeneous and recyclable (at least six times) with no significant leaching of palladium in batch mode catalysis. The best catalyst was also applied under continuous flow conditions where it disclosed an exceptional activity (90 % conversion) and 100 % selectivity for the mono-halogenated product for at least six days, with no leaching of palladium, no loss of activity and an ability to maintain the original oxidation state of Pd^II.     

Adsorption of Pd, Ni, and Cu ions on anode-oxidized carbon fiber materials

The anodic oxidation of the carbon felt Carbonetcalon results in the formation of surface defects which serve as centers of strong adsorption of Pd^II, Ni^II, and Cu^II ions. The electrochemical reduction of adsorbed ions makes it possible to obtain metallic catalysts, which undergo multiple redox cycles without loss of metal. The catalysts are characterized by high dispersity of the reduced phase, high adsorption capacity with respect to hydrogen, and 100% selectivity in hydrogenation of acetophenone. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 81–85, January 1997     

Asymmetric 1,3‐Dipolar Cycloadditions of 2‐Diazocyclohexane‐1,3‐diones and Alkyl Diazopyruvates

The 1,3‐dipolar cycloaddition reactions of 2‐diazocyclohexane‐1,3‐dione ( 7a ; Table 1) and of alkyl diazopyruvates ( 11a – e ; Table 3) to 2,3‐dihydrofuran and other enol ethers have been investigated in the presence of chiral transition metal catalysts. With Rh^II catalysts, the cycloadditions were not enantioselective, but those catalyzed by [Ru^IICl₂( 1a )] and [Ru^IICl₂( 1b )] proceeded with enantioselectivities of up to 58% and 74% ee, respectively, when diazopyruvates 11 were used as substrates. The phenyliodonium ylide 7c yielded the adduct 8a in lower yield and poorer selectivity than the corresponding diazo precursor 7a (Table 2) upon decomposition with [Ru(pybox)] catalysts. This suggests that ylide decomposition by Ru^II catalysts, contrary to that of the corresponding diazo precursors, does not lead to Ru‐carbene complexes as reactive intermediates. Our method represents the first reproducible, enantioselective 1,3‐cycloaddition of these types of substrates.     

Heterogeneous catalytic oxidation of chromotrope 2B with H2O2 and metal complexes supported on aluminum oxide hydroxide as catalyst

The heterogeneous catalytic oxidation of Chromotrope 2B (C2B) dye with H₂O₂ and the aluminum oxide hydroxide (AlOOH) modified with ammonia complexes of Cu^II, Co^II, Ni^II, and Cr^III (AlOOH/[Mⁿ⁺(amm)_m]) as catalysts were studied. The AlOOH/[Cu^II(amm)₄] is the most efficient catalyst and therefore it was chosen as the potential catalyst for the oxidative degradation of C2B in an aqueous solution. The AlOOH/[Cu^II(amm)₄] was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and transmission electron microscopy (TEM), techniques. The rate of reaction was dependent on the type of the metal complex supported on the AlOOH, initial concentration of the dye and H₂O₂, catalyst dose, pH, the concentration of NaCl, and temperature. The catalytic activity of the AlOOH/[Mⁿ⁺(amm)_m] according to the kind of metal ion decreased in the order: Cu^II > Co^II > Cr^III > Ni^II. Other catalysts consisting of the AlOOH supported with Cu^II complexed with ethylenediamine, ethanolamine, 1,3 propanediamine, and 1,4 butanediamine, (AlOOH/[Cu^II(amine)_m]), were also investigated. The activity of the (AlOOH/[Cu^II(amine)_m]) as catalyst according to the type of ligand followed the order: 1,4 butanediamine > 1,3 propanediamine > ethanolamine > ethylenediamine > ammonia. The reaction rate increased with increasing the catalyst dose, concentration of H₂O_2, C2B, and NaCl, pH, and temperature. Since the reusability results for the AlOOH/[Cu^II(amm)₄] revealed good stability over seven cycles, it can thus be considered a promising and cost-effective catalyst for the removal of harmful dyes from wastewater.     

Catalytic oxidation of CO,hydrocarbons, and ethyl acetate over perovskite-type complex oxides

The catalytic activity of M^IM^IIO₃] perovskite-type complex oxides (M^I = La, Y, Nd, Yb; M^II = Co, Mn, Ni) in the oxidation of CO, propylene, benzene, ethylbenzene,o-xylene, and ethyl acetate was investigated. The Co-containing catalysts were shown to be more active in the oxidation than the Mn-containing catalysts. A relationship between the catalytic and adsorption properties was established.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 602–605, April, 1994.     

Catalytic activity of a zirconium(IV) oxide surface supported with transition metal ions

The kinetics of H₂O₂ decomposition have been investigated using ZrO₂ supported with transition metal ions including Cu^II, Ag^I, Hg^II, Co^II, Mn^II, Ni^II and Fe^III. At pH = 6.8, the reaction rate exhibits a first order dependence on the initial H₂O₂ concentration at low concentrations. The order of activity of the different catalysts is strongly dependent on the [H₂O₂]₀ used. The reaction proceed via the formation of the peroxo-intermediate which has an inhibiting effect on the reaction rate. The rate increases with increasing pH, and attains a limiting rate at higher pH's. A reaction mechanism is proposed involving liberation of HO₂ radicals from the peroxo-intermediate as the rate-determining step.     

Selective Synthesis of Six Products from a Single Indolyl α‐Diazocarbonyl Precursor

Indolyl α‐diazocarbonyls can be selectively cyclized to give six distinct products through the careful choice of catalyst and reaction conditions. A range of catalysts were used, including complexes of Rh^II, Pd^II, and Cu^II, as well as SiO₂, to promote diazo decomposition and subsequent cyclization/rearrangement through a range of mechanistic pathways.     

Kinetics and mechanism of the color removal from congo red with hydrogen peroxide catalyzed by supported zirconium oxide

The kinetics of the oxidative color removal from congo red dye using H₂O₂ in conjunction with transition metal ions supported on ZrO₂ were studied. The rate of reaction is first order on H₂O₂, the catalyst, and in congo red. It attains a limiting rate at higher concentrations of reagent. Also, the rate of reaction decreases with increasing [H⁺], due to protonation of the substrate amino groups, as well as to the low deprotonation constant of H₂O₂ in acid medium. Addition of KCl to the mixture increased the rate of reaction. The catalytic activity of the catalysts lies in the following order: Ag^I > Cu^II > Hg^II > Co^II > Mn^II > Fe^III > Ni^II > ZrO₂ which is correlated with the redox potential, mg loading and % surface content of the supported metal ions. A probable mechanism for the oxidation processes has been suggested, which is consistent with the experimental results.     

Discovery of Highly Selective Alkyne Semihydrogenation Catalysts Based on First‐Row Transition‐Metallated Porous Organic Polymers

Five different first‐row transition metal precursors (V^III, Cr^III, Mn^II, Co^II, Ni^II) were successfully incorporated into a catechol porous organic polymer (POP) and characterized using ATR‐IR and XAS analysis. The resulting metallated POPs were then evaluated for catalytic alkyne hydrogenation using high‐throughput screening techniques. All POPs were unexpectedly found to be active and selective catalysts for alkyne semihydrogenation. Three of the metallated POPs (V, Cr, Mn) are the first of their kind to be active single‐site hydrogenation catalysts. These results highlight the advantages of using a POP platform to develop new catalysts which are otherwise difficult to achieve through traditional heterogeneous and homogeneous routes.     

The Baeyer–Villiger oxidation of ketones: A paradigm for the role of soft Lewis acidity in homogeneous catalysis

The Baeyer–Villiger oxidation of ketones to the corresponding esters or lactones is a valuable transformation that has been upgraded several times over the last century, from the original use of monopersulfuric acid as oxidant to more atom efficient and environmentally friendly oxidants such as hydrogen peroxide. The latter requires activation with organometallic complexes to explicate its oxidizing power. The catalytic version of the reaction can be achieved with several transition metal catalysts, but major differences are present among the various catalysts proposed in terms of scope of the reaction. In particular, most of the catalytic systems are active towards four-membered ring ketones leading to the corresponding substituted γ-butyro-lactones. Pt^II complexes characterized by the employment of chelating diphosphines turned out to be the most efficient in catalyzing the BV oxidation of a wider range of substrates, in particular cyclohexanones are suitable substrates and acyclic ketones can be converted into the corresponding esters, albeit with low turnover. As long as organometallic catalyzed BV reaction is concerned, Pt^II catalysts show the most versatile activity and selectivity. Such peculiar features are the result of the unique electronic properties of such metal combined with an easily tailored soft Lewis acid character modulated by the proper choice of the ancillary ligands. The enantioselective version of the reaction benefits from these properties and the compatibility of Pt^II species with water enabled the development of asymmetric catalytic BV reactions in water aided by the presence of micelles as dynamic self-assembled environments.