Natural Abundance 15N NMR by Dynamic Nuclear Polarization: Fast Analysis of Binding Sites of a Novel Amine‐Carboxyl‐Linked Immobilized Dirhodium Catalyst

A novel heterogeneous dirhodium catalyst has been synthesized. This stable catalyst is constructed from dirhodium acetate dimer (Rh₂(OAc)₄) units, which are covalently linked to amine‐ and carboxyl‐bifunctionalized mesoporous silica (SBA‐15?NH₂?COOH). It shows good efficiency in catalyzing the cyclopropanation reaction of styrene and ethyl diazoacetate (EDA) forming cis‐ and trans‐1‐ethoxycarbonyl‐2‐phenylcyclopropane. To characterize the structure of this catalyst and to confirm the successful immobilization, heteronuclear solid‐state NMR experiments have been performed. The high application potential of dynamic nuclear polarization (DNP) NMR for the analysis of binding sites in this novel catalyst is demonstrated. Signal‐enhanced ¹³C CP MAS and ¹⁵N CP MAS techniques have been employed to detect different carboxyl and amine binding sites in natural abundance on a fast time scale. The interpretation of the experimental chemical shift values for different binding sites has been corroborated by quantum chemical calculations on dirhodium model complexes.     

Highly Efficient Ruthenium‐Catalyzed N‐Formylation of Amines with H2 and CO2

A highly efficient catalyst system based on ruthenium‐pincer‐type complexes has been discovered for N‐formylation of various amines with CO₂ and H₂, thus affording the corresponding formamides with excellent productivity (turnover numbers of up to 1 940 000 in a single batch) and selectivity. Using a simple catalyst recycling protocol, the catalyst was reused for 12 runs in N,N‐dimethylformamide production without significant loss of activity, thus demonstrating the potential for practical utilization of this cost‐effective process. A one‐pot two‐step procedure for hydrogenation of CO₂ to methanol via the intermediacy of formamide formation has also been developed.     

Synthesis and characterisation of a polymer-bound rhodium-benzimidazole complex as catalyst for the hydrogenation of nitroarenes

A polymer-anchored rhodium complex was synthesised by sequential attachment of benzimidazole (BzlH) and RhCl₃ to chloromethylated poly(styrene–divinylbenzene) co-polymer (PSDVB) with 6.5% cross-linking. The catalyst was characterised by X-ray photoelectron spectroscopy, far-IR, UV–Vis, FTIR, SEM and thermogravimetric analysis. Various physico-chemical properties such as bulk density, surface area and swelling behaviour in different solvents were also studied. The polymer-anchored complex was tested as a catalyst for reduction of nitroarenes, namely o,m,p-nitrobenzoic acid, nitroaniline, nitrophenol and nitrotoluene. Kinetic measurements were carried for o-nitroaniline and p-nitrophenol by varying temperature, catalyst concentration and concentration of substrates. The rate of the reaction was found to be first order with respect to catalyst concentration and also with substrate concentration at low concentrations, becoming independent of substrate at higher concentrations. A plausible mechanism for the reaction is proposed. The energy and entropy of activation calculated from Arrhenius plots indicate high activity of the catalyst on the support. The recycling efficiency of the catalyst has been studied and there was no leaching of metal from the catalyst surface.     

Evaluation of the catocene/graphene oxide nanocomposite catalytic activity on ammonium perchlorate thermal decomposition

A novel nanocomposite catalyst for thermal degradation of the ammonium perchlorate (AP) has been synthesized, and its effect on the thermal behavior of AP has been investigated. Preparation of the catalyst was carried out via functionalization of the graphene oxide with phenyl isocyanate and its noncovalent bonding to catocene. The catalytic activity of the catalyst was studied by thermal gravimetric analysis/differential scanning calorimetry at various heating rates. In addition, the effect of the catalyst on the AP thermal decomposition has been investigated by Kissinger and Friedman methods as two model-free methods for calculation of the activation energy parameter. According to the Kissinger method calculations, the E_a of AP decomposition reduced about 151 kJ⋅mol⁻¹ lower than the reported value for pure AP in the presence of the catalyst. Calculation of the E_a value for various reaction conversion rates by the Friedman method also confirmed the Kissinger method results.     

N-Isocyaniminotriphenylphosphorane (Ph3PNNC) as a metal-free catalyst for the synthesis of functionalized isoindoline-1-ones

A novel application in the field of N-isocyaniminotriphenylphosphorane (Ph₃PNNC) chemistry has been introduced in this work. A series of substituted isoindolin-1-one ring systems has been successfully synthesized through a novel and efficient multicomponent reaction of methyl 2-formylbenzoate and primary amines in the presence of N-isocyaniminotriphenylphosphorane (Ph₃PNNC) as a catalyst. This one-pot three component reaction (3-CR) gives high yield using N-isocyaniminotriphenylphosphorane (Ph₃PNNC) as a metal-free catalyst under mild conditions.     

Molybdenum(VI)–oxodiperoxo complex containing an oxazine ligand: synthesis,X-ray studies,and catalytic activity

A new mononuclear molybdenum(VI)–oxodiperoxo complex [MoO(O₂)₂(phox)] with a simple bidentate ligand, 2-(2′-hydroxyphenyl)-5,6-dihydro-1,3-oxazine (Hphox), has been synthesized and characterized by X-ray structure analysis, elemental analysis, infrared, and ¹H NMR spectroscopy. A triclinic space group P-1 was determined by X-ray crystallography from single-crystal data of this complex. The resulting complex functioned as a facile sulfide oxidation catalyst with urea hydrogen peroxide as terminal oxidant at room temperature. The catalyst showed efficient reactivity in oxidation of sulfides giving high yield and selectivity.     

Preparation,characterization and application of silica‐supported palladium complex as a new and heterogeneous catalyst for Suzuki and Sonogashira reactions

An efficient heterogeneous Pd catalytic system has been developed, based on immobilization of Pd nanoparticles (PNPs) on a silica‐bonded propylamine–cyanuric–cysteine (SiO₂–pA–Cyan–Cys) substrate. The synthesized catalyst was characterized by transmission electron microscopy, scanning electron microscopy, FT‐IR, N₂ adsorption analysis (BET), TGA and inductively coupled plasma/atomic emission spectroscopy, and catalytic activity of this catalyst was investigated in the Suzuki and Sonogashira cross‐coupling reactions. The catalysts showed excellent performance in these two reactions, including various aryl halide derivatives (except aryl chloride derivatives) with phenylboronic acid and phenylacetylene under green conditions. Moreover, the catalyst was recycled for several runs without any significant loss of catalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

First sonochemical,simple and solvent-free synthesis of chiral tert-butanesulfinimines using silica supported p-toluenesulfonic acid

A solvent-free, versatile procedure has been developed for the effective synthesis of tert-butanesulfinylimines of a variety of aldehydes using chiral tert-butanesulfinamides under green, sonochemical conditions. This method utilizes silica supported p-toluenesulfonic acid (pTSA·SiO₂) as an efficient, safer and inexpensive catalyst under aerobic conditions. The practicable simplicity, easy preparation of the catalyst from readily available substances, high substrate scope, excellent yields of products in short reaction times and environmentally benign (solvent-free sonochemical) conditions are the exceptional assets of this finding.     

Enantioselective Alkynylation of Isatins: A Combination of Metal Catalysis and Organocatalysis

An efficient and catalytic asymmetric alkynylation of isatins has been developed using a bifunctional amidophosphine-urea/AgBF₄ complex as the catalyst. By a combination of metal catalysis and organocatalysis, excellent enantioselectivities (up to 99 % ee) and good yields are achieved. A wide range of both terminal alkynes and isatins are tolerated by this new catalyst system, providing access to structurally diverse propargylic alcohols with tetrasubstituted stereogenic centers in high efficiency.     

Determination of the equilibrium constant for the reaction between bisphenol A and diphenyl carbonate

Despite the industrial significance of poly(bisphenol A carbonate), there is a scarcity of open literature on the equilibrium of the melt‐phase process. In fact, the equilibrium constant (K_eq) for this reaction has never been measured directly. This article describes a process on the basis of NMR for the measurement of K_eq for the reaction between bisphenol A and diphenyl carbonate in the presence and absence of a catalyst. The apparent enthalpy and entropy were calculated using a van't Hoff plot. Decomposition of bisphenol A is a common side reaction in the melt‐phase reaction performed at high temperatures in the presence of catalyst. The effect of these side reactions on the K_eq in the presence of catalyst is determined. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 171–178, 2002     

Kombucha SCOBY Waste as a Catalyst Support

It is established that food waste can be repurposed to extend its lifecycle and decrease its carbon footprint. In this work, SCOBY (symbiotic culture of bacteria and yeast) waste from kombucha tea production has been repurposed as a catalyst support. Copper nanoparticles (Cu NPs) have been embedded in a piece of treated SCOBY via an in-situ method which enabled the catalyst, inCu/t-SCOBY, to be easily recycled. In addition, inCu/t-SCOBY catalyzed the full reduction of 4-nitrophenol in an excess of sodium borohydride (NaBH₄) within 20 minutes. After 6 additional catalytic cycles, the catalyst maintained up to 50% of its performance in the first cycle. Characterization of the catalyst has also been done to understand the mechanism of action and interactions occurring between t-SCOBY and Cu NPs. The results of this work clearly present a proof-of-concept in utilizing porous wastes materials such as SCOBY as catalyst supports, allowing metallic NPs to be efficacious and practical heterogenous catalysts.     

Reaction of benzoxazine-based phenolic resins with strong and weak carboxylic acids and phenols as catalysts

The reaction of 3,4-dihydro-3,6-dimethyl-2H-1,3-benzoxazine using strong and weak carboxylic acids and phenols as catalysts has been studied using Fourier transform infrared (FTIR) spectroscopy. The auto-accelerated curing using sebacic acid as catalyst is further documented using ¹H-nuclear magnetic resonance (NMR) and dielectric analysis. Termination of curing, using strong acids or no catalyst, are discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1913–1921, 1999     

Olefin epoxidation with tert-butyl hydroperoxide catalyzed by functionalized polymer-supported copper(II) Schiff base complex

Abstract  

A new polymer-supported Cu(II) Schiff base complex has been synthesized and characterized by elemental (including metal) analysis, FT-IR spectroscopy, UV–Vis diffuse reflectance spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The catalytic performance of this complex was evaluated in the epoxidation of styrene in acetonitrile/N,N-dimethylformamide (9:1) mixture with 70% tert-butyl hydroperoxide as an oxidizing agent under liquid phase reaction conditions for selective synthesis of styrene oxide. Suitable reaction conditions have been optimized by considering the effects of various reaction parameters such as temperature, reaction time, solvent, oxidant, catalyst amount, and styrene to hydroperoxide molar ratio for the maximum conversion of styrene as well as selectivity of styrene oxide. We have also investigated the epoxidation reaction of various olefins under the optimized reaction conditions. Comparison between catalytic activities of the polymer-supported Cu(II) Schiff base complex and its homogeneous analogue showed that the polymer-supported catalyst was more active. This heterogeneous complex was reused for five times. The selectivity of the heterogeneous catalyst does not change even after five times of reusing.     

MWCNTs-ZrO2 as a reusable heterogeneous catalyst for the synthesis of N-heterocyclic scaffolds under green reaction medium

A simple, efficient, and facile heterogeneous multi-walled carbon nanotubes-zirconia nanocomposite (MWCNTs-ZrO₂) has been synthesized using natural feedstock coconut juice (água-de-coco do Ceará). The synthesized catalyst was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy analysis. The heterogeneous nanocomposite has been used for one-pot synthesis of various N-heterocyclic compounds like pyrazoles, 1,2-disubstituted benzimidazoles, 2-arylbenzazoles, and 2,3-dihydroquinazolin-4(1H)-ones under green reaction medium at room temperature. This novel method has several advantages, such as short reaction time, simple work-up, excellent yield, and green reaction conditions. The catalyst was recycled up to four times without significant loss in catalytic activity.     

Discovery and Optimization of Heterogeneous Catalysts by Using Combinatorial Chemistry

A novel ceramic array microreactor system has been designed and, in conjunction with resonance-enhanced multiphoton ionization (REMPI), used for the discovery of an optimum ternary catalyst composition for the dehydrogenation of cyclohexane to benzene. The catalyst library consisted of 66 ternary combinations of Pt, Pd, and In loaded on γ-Al₂O₃ pellets. The optimum catalyst for the production of benzene had the composition 0.8 % Pt, 0.1 % Pd, and 0.1 % In (see diagram). The preparation and screening of the library of 66 catalysts took about 2.5 days to complete—with conventional methods this would have taken several months!     

Enantioselective Synthesis of α‐Hydroxy Amides and β‐Amino Alcohols from α‐Keto Amides

Synthesis of enantiomerically enriched α‐hydroxy amides and β‐amino alcohols has been accomplished by enantioselective reduction of α‐keto amides with hydrosilanes. A series of α‐keto amides were reduced in the presence of chiral Cu^II/(S)‐DTBM‐SEGPHOS catalyst to give the corresponding optically active α‐hydroxy amides with excellent enantioselectivities by using (EtO)₃SiH as a reducing agent. Furthermore, a one‐pot complete reduction of both ketone and amide groups of α‐keto amides has been achieved using the same chiral copper catalyst followed by tetra‐n‐butylammonium fluoride (TBAF) catalyst in presence of (EtO)₃SiH to afford the corresponding chiral β‐amino alcohol derivatives.     

Synthesis of 1H-isochromenes, 4H-chromenes,and ortho-aminocarbonitrile tetrahydronaphthalenes from the same reactants by using metal-free catalyst

A facile and rapid multicomponent synthesis of pharmaceutically diverse 1H-isochromenes, 4H-chromenes, and ortho-aminocarbonitrile tetrahydronaphthalenes has been developed from benzaldehyde, malononitrile, and cyclohexanone. Three different methods from the same reactants, solvent, temperature, and catalyst lead to three products with excellent yields. All the reactions were followed with the Michael addition and cyclization. In this study, morpholine was used as an active metal-free base catalyst that increases the yields of products and decreases the time of reactions.     

Selective Oxidation of Linear Alkanes by a Schiff Base Ligand [1,4-bis(Salicylidene Amino)-Phenylene] Vanadium (VO2+) Complex Bonded on Modified Silica Gel Support1

A Schiff base complex from vanadium (VO²⁺) has been successfully immobilized by chemical reaction on an isocyanate modified silica gel support. This catalyst proves to be an active heterogeneous catalyst for the selective oxidation of n-pentane and n-hexane in the presence of molecular oxygen at moderate temperatures (150°C) and pressures (20 atm). The products were identified by GC/MS analysis, and the product distribution was found to be entirely different from that reported in the literature. The oxygenated compounds formed from n-pentane are mostly mesaconic acid (COOH(CH₃)C=CHCOOH) while those from n-hexane are alcohols (2-methyl-2,4-pentanediol, 1-hexanol, and 1,6-hexanediol), ketones (2-hexanone), and acids. As analyzed by thermogravimetric analysis, the catalyst was seen to be stable up to 393°C and the atomic absorption study shows a negligible leaching of the catalyst.     

Polymerization of vinyl chloride by use of modified Ziegler–Natta catalysts. I. Overall kinetic features

Vinyl chloride has been polymerized by a modified Ziegler-Natta type catalyst VOCl₂ · 2THF–Al(i-Bu)₃–THF, and the kinetics of the polymerization reaction have been investigated in some detail. The present kinetic analysis has demonstrated that the generation of active centers is directly proportional to the catalyst concentration, and that their depletion is by a second-order decay process. Triisobutylaluminum has been found to contribute to the effective removal of active centers through complex formation.     

Atactic polymerization of propylene catalyzed by mono(η5-cyclopentadienyl)titanium tribenzyloxide combined with methylaluminoxane

Propylene has been polymerized with mono(η⁵-cyclopentadienyl)titanium tribenzyloxide activated with methylaluminoxane (MAO). It was found that the content of residual trimethylaluminium (TMA) in MAO has a determinative effect on the polymerization. An excess of TMA in the catalyst system reduces the Ti species to inactive lower valent states. The catalyst system gives medium molecular-weight atactic polypropylene (M_v = 2–7 × 10⁴) with narrow molecular weight distribution (M_w/M_n = 1.4–1.8). The polymer has a stereoirregular structure described by Bernoullian statistics. Statistical analysis of the regiotriad distribution of the polypropylene chains indicates a regioblock microstructure. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2051–2057, 1998