A silica-supported, switchable, and recyclable hydroformylation-hydrogenation catalyst

A homogeneous hydroformylation catalyst, designed to produce selectively linear aldehydes, was covalently tethered to a polysilicate support. The immobilized transition-metal complex [Rh(A)CO]+(1+)), in which A is N-(3-trimethoxysilane-n-propyl)-4,5-bis(diphenylphosphino)phenoxazine, was prepared both via the sol-gel process and by covalent anchoring to silica. 1+ was characterized by means of (31)P and (29)Si MAS NMR, FT-IR, and X-ray photoelectron spectroscopy. Polysilicate immobilized Rh(A) performed as a selective hydroformylation catalyst showing an overall selectivity for the linear aldehyde of 94.6% (linear to branched aldehyde ratio of 65). In addition 1-nonanol, obtained via the hydrogenation of the corresponding aldehyde, was formed as an unexpected secondary product (3.6% at 20% conversion). Under standard hydroformylation conditions, 1+ and HRh(A)(CO)(2)(1) coexist on the support. This dual catalyst system performed as a hydroformylation/hydrogenation sequence catalyst (Z), giving selectively 1-nonanol from 1-octene; ultimately, 98% of 1-octene was converted to mainly 1-nonanal and 97% of the nonanal was hydrogenated to 1-nonanol. The addition of 1-propanol completely changes Z in a hydroformylation catalyst (X), which produces 1-nonanal with an overall selectivity of 93%, and completely suppresses the reduction reaction. If the atmosphere is changed from CO/H(2) to H(2) the catalyst system is switched to the hydrogenation mode (Y), which shows a clean and complete hydrogenation of 1-octene and 1-nonanal within 24 h. The immobilized catalyst can be recycled and the system can be switched reversibly between the three "catalyst modes" X, Y, and Z, completely retaining the catalyst performance in each mode.     

Catalytic ring expansion, contraction, and metathesis-polymerization of cycloalkanes

Tandem dehydrogenation-olefin-metathesis catalyst systems, comprising a pincer-ligated iridium-based alkane dehydrogenation catalyst and a molybdenum-based olefin-metathesis catalyst, are reported to effect the metathesis-cyclooligomerization of cyclooctane and cyclodecane to give cycloalkanes with various carbon numbers, predominantly multiples of the substrate carbon number, and polymers.     

Catalytic,theoretical, and biological investigation of an enzyme mimic model

Artificial catalyst studies were always stayed at the kinetics investigation level, in this work bioactivity of designed catalyst were shown by the induction of biomineralization of the cells, indicating the possible use of enzyme mimics for biological applications. The development of artificial enzymes is a continuous quest for the development of tailored catalysts with improved activity and stability. Understanding the catalytic mechanism is a replaceable step for catalytic studies and artificial enzyme mimics provide an alternative way for catalysis and a better understanding of catalytic pathways at the same time. Here we designed an artificial catalyst model by decorating peptide nanofibers with a covalently conjugated catalytic triad sequence. Owing to the self-assembling nature of the peptide amphiphiles, multiple action units can be presented on the surface for enhanced catalytic performance. The designed catalyst has shown an enzyme-like kinetics profile with a significant substrate affinity. The cooperative action in between catalytic triad amino acids has shown improved catalytic activity in comparison to only the histidine-containing control group. Histidine is an irreplaceable contributor to catalytic action and this is an additional reason for control group selection. This new method based on the self-assembly of covalently conjugated action units offers a new platform for enzyme investigations and their further applications. Artificial catalyst studies always stayed at the kinetics investigation level, in this work bioactivity of the designed catalyst was shown by the induction of biomineralization of the cells, indicating the possible use of enzyme mimics for biological applications.     

A Manganese Pre‐Catalyst: Mild Reduction of Amides,Ketones, Aldehydes,and Esters

A new (N ‐phosphinoamidinate)manganese complex is shown to be a useful pre‐catalyst for the hydrosilative reduction of carbonyl compounds, and in most cases at room temperature. The Mn‐catalyzed reduction of tertiary amides to tertiary amines, with a useful scope, is demonstrated for the first time by use of this catalyst, and is competitive with the most effective transition‐metal catalysts known for such transformations. Ketones, aldehydes, and esters were also successfully reduced under mild conditions by using this new Mn catalyst.     

A Manganese Pre‐Catalyst: Mild Reduction of Amides,Ketones, Aldehydes,and Esters

A new (N ‐phosphinoamidinate)manganese complex is shown to be a useful pre‐catalyst for the hydrosilative reduction of carbonyl compounds, and in most cases at room temperature. The Mn‐catalyzed reduction of tertiary amides to tertiary amines, with a useful scope, is demonstrated for the first time by use of this catalyst, and is competitive with the most effective transition‐metal catalysts known for such transformations. Ketones, aldehydes, and esters were also successfully reduced under mild conditions by using this new Mn catalyst.     

Highly reactive, general and long-lived catalysts for palladium-catalyzed amination of heteroaryl and aryl chlorides, bromides, and iodides: scope and structure-activity relationships

We describe a systematic study of the scope and relationship between ligand structure and activity for a highly efficient and selective class of catalysts containing sterically hindered chelating alkylphosphines for the amination of heteroaryl and aryl chlorides, bromides, and iodides. In the presence of this catalyst, aryl and heteroaryl chlorides, bromides, and iodides react with many primary amines in high yields with part-per-million quantities of palladium precursor and ligand. Many reactions of primary amines with both heteroaryl and aryl chlorides, bromides, and iodides occur to completion with 0.0005-0.05 mol % catalyst. A comparison of the reactivity of this catalyst for the coupling of primary amines at these loadings is made with catalysts generated from hindered monophosphines and carbenes, and these data illustrate the benefits of chelation. Studies on structural variants of the most active catalyst indicate that a rigid backbone in the bidentate structure, strong electron donation, and severe hindrance all contribute to its high reactivity. Thus, these complexes constitute a fourth-generation catalyst for the amination of aryl halides, whose activity complements catalysts based on monophosphines and carbenes.     

Activation processes and polyethylene formation on a phillips model catalyst studied by laser ablation, laser desorption, and static secondary ion mass spectrometry

Since the discovery of the Phillips catalysts, there still is much uncertainty concerning their activation, their molecular structure, the nature of the active chromium sites, and the polymerization mechanisms. Surface techniques are not easy to be used for such study according to the nonconductive behavior of the support. Therefore, model Phillips catalyst is elaborated by spin coating a trivalent chromium precursor on a silicon wafer. The surface characterization of this model catalyst is conducted by laser ablation mass spectrometry (LA-MS), laser desorption/ionization mass spectrometry (LDI-MS), and static secondary ion mass spectrometry (s-SIMS), at different steps of its preparation. To validate our approach, a comparison is also made between the model and the real Philips catalyst. Moreover, the model catalyst efficiency for polyethylene synthesis is evaluated and allows us to discuss the validity of the mechanisms previously proposed to explain the catalytic process. The characterization of Phillips model catalyst by mass spectrometry allows us to better understand the activation processes of such catalyst. Depending on the activation temperature, chromium oxide species are formed and anchored at the support surface. They consist mainly in mono-chromium sites at high temperature. The chromium valence is hexavalent. This model catalyst is active for the polymerization of ethylene. A pseudo-oligomer molecular weight distribution is observed by LA-MS, whereas s-SIMS allows us to elucidate the anchorage of the polymer at activate chromium surface sites.     

Synthesis,characterization, and application of hollow ceramic microsphere based Pd catalyst for hydrogenation of 2-ethylanthraquinone

Palladium metal has been used extensively in the hydrogenation reactions due to their great affinity towards hydrogen atoms. In the present study, the catalyst preparation attempted with Pd supported Hollow Ceramic Microspheres using wet impregnation method and its use as catalysts is explored in the hydrogenation of 2-ethylanthraquinone studing the effect of the reaction time, temperature, volume of working solution and the catalyst dosages on the conversion of 2-ethylanthraquinone and yield of hydrogen peroxide. The hydrogenation reaction of 2-ethylanthraquinone is the key step in the anthraquinone method for the industrial production of the hydrogen peroxide. The Pd supported catalyst was characterized by XRF, FTIR, and BET to confirm the composition of the prepared catalyst, Pd deposition, and the surface area. The highest catalyst activity was found to be 9.42 ​g/L with the maximum conversion of 96% at 70°C, 0.3 ​MPa. The kinetics of the heterogeneous hydrogenation reaction of 2-ethylanthraquinone with Pd supported on Hollow Ceramic Microspheres as catalyst was also investigated. This paper is in contribution of our earlier publication.     

Air-stable,storable, and highly selective chiral Lewis acid catalyst

An air-stable, storable, and highly selective chiral Lewis acid catalyst for asymmetric Mannich-type reactions has been developed. The catalyst can be stored for more than three months in air at room temperature without loss of activity. Moreover, it has also been demonstrated that the catalyst can be recovered and reused. [structure: see text]     

An immobilized homogeneous catalyst for efficient and selective hydrogenation of functionalized aldehydes, alkenes, and alkynes

An immobilized cationic rhodium(I) catalyst bearing the diphosphine 1,1'-bis(diisopropylphosphino)ferrocene (DiPFc, 1) allows efficient and chemoselective hydrogenation of a range of functionalized aldehydes, as well as alkenes and alkynes, under mild conditions. This heterogenized catalyst system is convenient to prepare, is stable to air and moisture over extended periods, and is readily recycled.     

Acid and catalytic properties of MnOm?ZrO2 (M=Ca, Ba, Sm, Yb) compositions

The volume stages of ethylene glycol oxidation to glyoxal on silver have been studied by varying the catalyst grain size. Temperature oscillations have been detected in the catalyst layer. The nature of the oscillations and the range of their generation were investigated by varying the oxygen, ethylene glycol and water vapor contents in the reaction mixture. Glyoxal formation was shown to occur on the silver catalyst surface. The generation of oscillations is responsible for the CO to CO₂ oxidation in the volume between the catalyst grains.     

Hydrolysis of cellulose by amorphous carbon bearing SO3H, COOH, and OH groups

The hydrolysis of cellulose into saccharides using a range of solid catalysts is investigated for potential application in the environmentally benign saccharification of cellulose. Crystalline pure cellulose is not hydrolyzed by conventional strong solid Br?nsted acid catalysts such as niobic acid, H-mordenite, Nafion and Amberlyst-15, whereas amorphous carbon bearing SO 3H, COOH, and OH function as an efficient catalyst for the reaction. The apparent activation energy for the hydrolysis of cellulose into glucose using the carbon catalyst is estimated to be 110 kJ mol (-1), smaller than that for sulfuric acid under optimal conditions (170 kJ mol (-1)). The carbon catalyst can be readily separated from the saccharide solution after reaction for reuse in the reaction without loss of activity. The catalytic performance of the carbon catalyst is attributed to the ability of the material to adsorb beta-1,4 glucan, which does not adsorb to other solid acids.     

Quaterpolymerization of Ethylene,Propylene, Dicyclopentadiene,and Methylcyclopentadienyl-5-endo-norborn-2-enyl-methane

Abstract

The quaterpolymerization of methylcyclopentadienyl-5-endo-norborn-2-enyl-methane with ethylene, propylene, and either endo- or exo-dicyclopentadiene was studied by using the catalyst system VAcac₃-Et₂AlCl. The influence of catalyst and polyenes concentrations, catalyst modifiers, and other polymerization parameters on the general properties of quaterpolymers was investigated. The polymers obtained showed a random distribution of the comonomeric units and the ability to covulcanize with 1,4-cis-polyisoprene.     

The composition of catalysts prepared from tri-n-propylaluminum,anisole, and titanium tetrachloride

Catalysts were prepared from titanium tetrachloride and tri-n-propylaluminum or tri-n-propylaluminum anisole at [Al]/[Ti] molar ratios of 0.20–1.10. They were aged and filtered, and the solid and liquid portions were analyzed for aluminum, titanium, chlorine, and certain organic constituents. The analyses indicate that the solid of the nonetherate catalyst is predominantly TiCl₃, some AlCl₃ or aluminum alkyl chlorides being included. Only at [Al]/[Ti] = 1.10 was any alkyl group found in the solid. The same general results were found for the etherate catalyst, but the solid had a somewhat lower [Cl]/[Ti] ratio, indicating greater reduction or alkylation, or both, of the titanium species than in the nonetherate catalyst. The solid also contained some anisole at the higher [Al]/[Ti] ratios. The results lend general support to proposed reactions for the catalyst formation. The main differences in the etherate catalysts relative to the non-etherate system, particularly at the higher [Al]/[Ti] ratios, are the apparently greater reduction or alkylation of the titanium in the solids, the presence of anisole in the liquid and solid portions, and the presence of phenol in the liquid portion. The phenol presumably comes from cleavage of the anisole during the catalyst formation. Not all of the anisole has been accounted for in a materials balance, nor has all of the chlorine in the etherate catalysts. No propyl or isopropyl chloride was found in the catalysts; there is no significant amount of polypropylene in any of the catalyst solids. Hence the fate of the alkyl groups remains undetermined at present.     

A versatile and efficient ligand for copper-catalyzed formation of C-N, C-O, and P-C bonds: pyrrolidine-2-phosphonic acid phenyl monoester

A new and readily available bidentate ligand, namely, pyrrolidine-2-phosphonic acid phenyl monoester (PPAPM), has been developed for the copper-catalyzed formation of C-N, C-O, and P-C bonds, and various N-, O-, and P-arylation products were synthesized in good to excellent yields by using the CuI/PPAPM catalyst system. Addition of the PPAPM ligand greatly increases the reactivity of the copper catalyst, and the resulting versatile and efficient catalyst system is of widespread and practical application in cross-coupling reactions.     

A novel multi-component reaction of indole, formaldehyde, and tertiary aromatic amines

A novel multi-component reaction of indoles, formaldehydes, and tertiary aromatic amines is described for the synthesis of dialkylaminoarylated indoles using silica-supported perchloric acid (HClO₄-SiO₂) as an inexpensive and highly efficient catalyst. The key features of this multi-component reactions are operational simplicity, mild reaction conditions, regioselectivity, and recycling of catalyst.     

丙烯、氧气和环氧丙烷在Cu-NaCl/SiO2催化剂上吸附的红外光谱研究

 用红外光谱法研究了丙烯、丙烯/氧气混合气以及环氧丙烷(PO)在Cu-NaCl/SiO2催化剂上的吸附. 结果表明,丙烯在载体和催化剂上的吸附是完全可逆的. 丙烯和氧气在催化剂上共吸附后生成了丙烯醛,未观察到环氧丙烷(PO)生成. PO在载体和未还原催化剂上的吸附行为表明,PO与载体的硅羟基有强相互作用,PO发生开环反应生成开环物种. 而PO在还原态催化剂上的吸附行为较复杂,可能生成了酮类化合物.     

Facile and rapid immobilization of copper(II) bis(oxazoline) catalysts on silica: application to Diels-Alder reactions, recycling, and unexpected effects on enantioselectivity

Two chiral copper(II) bis(oxazoline) complexes have been immobilized on silica via electrostatic interactions using a remarkably straightforward procedure. The immobilized catalysts were tested in a standard Diels-Alder reaction and gave surprising results. Where the immobilized Cu((S,S)-phenyl-box)(OTf)₂ catalyst was used, the predominant enantiomer formed was the opposite of that produced using the same catalyst in a homogeneous reaction. This is a startling result given that the only difference is the electrostatic immobilization of the catalyst on amorphous silica. The activity of the catalyst in a hetero Diels-Alder reaction was also tested. This catalyst was also recycled, successfully maintaining a similar activity to the homogeneous analogue through a number of cycles.     

A Dynamic Kinetic Model for Methanol to Light Olefins Reactions over a Nanohierarchical SAPO‐34 Catalyst: Catalyst Synthesis,Model Presentation,and Validation at the Bench Scale

This study includes three main parts: synthesizing the hierarchical silicoaluminophosphate (SAPO‐34) catalyst, evaluating the performance of this modified catalyst in the methanol to light olefins (MTO) process, and providing a new dynamic kinetic model for the modified catalyst. At first, a carbon nanotube (CNT) was used as a mesopore template in the sonochemical synthesis of SAPO‐34 hierarchical catalyst. By comparing the performance of this hierarchical catalyst and the common catalyst in the MTO process, it is observed that better performance is obtained on a modified catalysts for a longer period of time. Then, nine process tests were performed in differential fixed bed reactors at different temperatures and space velocities to obtain the kinetic model of the desired catalyst in the MTO process. Finally, the dynamic kinetic model of the modified SAPO‐34 catalyst was considered for main reactions in the MTO process. In this model, the rate equations were assumed elementary and lumped, and the decreasing of the catalyst activity over time on stream was also considered. The reactions constant and catalyst activity coefficient for different reactions were obtained by simultaneous connection of the code related to the reactor model and the genetic algorithm and genetic programming codes. The results obtained from the kinetic model were consistent with the experimental results.     

Synthesis of flavanones, azaflavanones, and thioflavanones catalyzed by PMA-SiO2 as a mild, efficient, and reusable catalyst

Abstract  

Cyclization of a variety of chalcones to flavanones catalyzed by 1 mol% phosphomolybdic acid (PMA) supported on silica as a mild, efficient, and reusable catalyst was carried out in high yields. PMA-SiO₂ is an efficient, inexpensive, and green catalyst which gave high conversion yields and could be recycled up to three times without significant loss in activity.