Homogeneous Analogues Research Articles

Green oxidation of alkenes in ionic liquid solvent by hydrogen peroxide over high performance Fe(III) Schiff base complexes immobilized on MCM-41

A series of Fe(III) Schiff base complexes immobilized on MCM-41 were prepared and characterized by various physicochemical and spectroscopic methods. The complexes were used for oxidation of cyclohexene by 30% hydrogen peroxide in the presence and absence of ethylmethyl imidazolium chloride (EMIM) ionic liquid as solvent. The immobilized complexes proved to be effective catalysts and generally exhibited much higher catalytic performance than their homogeneous analogue. Catalytic performance of the complexes was also found to be closely related to the Schiff base ligands used. Additionally, ion liquid solvent efficiently improved all the catalytic performances. Finally, the reaction was extended to different alkenes using the heterogeneous complex 2-L4. Among all the alkenes, those containing π-electron-withdrawing groups and trans-orientations exhibited lower tendency for oxidation. A series of Fe(III) Schiff base complexes immobilized on MCM-41 were prepared and used for oxidation of cyclohexene by 30% hydrogen peroxide. The immobilized complexes proved to be effective catalysts and generally exhibited much higher catalytic performance.

Mixed-grained CMOS field programmable analog array for smart sensory applications

The drive towards shorter design cycles for analog integrated circuits has given impetus to the development of Field Programmable Analog Arrays (FPAAs), which are the analogue counterparts of Field Programmable Gate Arrays (FPGAs). In this paper, we present a new design methodology which using FPAA as a powerful analog front-end processing platform in the smart sensory microsystem. The proposed FPAA contains 16 homogeneous mixed-grained Configurable Analog Blocks (CABs) which house a variety of processing elements especially the proposed fine-grained Core Configurable Amplifiers (CCAs). The high flexible CABs allow the FPAA operating in both continuous-time and discrete-time approaches suitable to support variety of sensors. To reduce the nonideal parasitic effects and save area, the fat-tree interconnection network is adopted in this FPAA. The functionality of this FPAA is demonstrated through embedding of voltage and capacitive sensor signal readout circuits and a configurable band pass filter. The minimal detectable voltage and capacitor achieves 38 uV and 8.3 aF respectively within 100 Hz sensor bandwidth. The power consumption comparison of CCA in three applications shows that the FPAA has high power efficiency. And the simulation results also show that the FPAA has good tolerance with wide PVT variations.

Dioxomolybdenum(VI) complex covalently attached to amino‐modified graphene oxide: heterogeneous catalyst for the epoxidation of alkenes

Transition metal salen complex MoO2–salen was successfully tethered onto amino‐functionalized graphene oxide (designated as MoO2–salen–GO), which was tested in the epoxidation of various alkenes using tert‐butylhydroperoxide or H2O2 as oxidant. Characterization results showed that dioxomolybdenum(VI) complex was successfully grafted onto the amino‐functionalized graphene oxide and the structure of the graphene oxide was well preserved after several stepwise synthesis procedures. Catalytic tests showed that heterogeneous catalyst MoO2–salen–GO was more active than its homogeneous analogue MoO2–salen in the epoxidation of cyclooctene due to site isolation. In addition, the MoO2–salen–GO catalyst could be reused three times without significant loss of activity. Copyright © 2014 John Wiley & Sons, Ltd.

Grafting of a chiral Mn(iii) complex on graphene oxide nanosheets and its catalytic activity for alkene epoxidation

A chiral Mn(III) complex supported by a covalent grafting method on modified graphene oxide was synthesized using 3-chloropropyltrimethoxysilane as a reactive surface modifier. The heterogeneous catalyst was characterized by X-ray diffraction, Fourier transform infrared spectra, thermogravimetric analysis, ultraviolet-visible spectra, nitrogen adsorption–desorption isotherms, transmission electron microscopy and atomic absorption spectroscopy. The catalytic potential of the heterogeneous catalyst and comparison with its homogeneous counterpart were studied for enantioselective epoxidation of various alkenes using m-chloroperbenzoic acid as an oxidant and it showed high selectivity and comparable catalytic reactivity with its homogeneous analogue. In addition, higher enantioselectivity and higher yield were observed in the presence of 4-methylmorpholine N-oxide and pyridine N-oxide, respectively. The catalyst was reused for several runs without significant loss of activity and selectivity.

Environmental Benign Oxidation of Benzyl Alcohol Catalyzed by Sulphonato-Salphen–Chromium(III) Complexes Immobilized on MCM-41

Three amphiphilic sulphonato-salen–chromium(III) complexes immobilized on MCM-41 were prepared for the solvent-free selective oxidation of benzyl alcohol with 30 % hydrogen peroxide. The immobilized complexes were effective catalysts and exhibited much higher catalytic performance than their corresponding homogeneous analogues and immobilized lipophilic complexes. Under the optimum reaction conditions, benzyl alcohol conversion could reach 60.3 % with 100 % of the selectivity to benzaldehyde. In addition, the catalysts could be recycled at least five times. The immobilized amphiphilic sulphonato-salen–chromium(III) complexes were effective in the selective oxidation of benzyl alcohol due to the increased accessibility of oxidant to catalyst and reactant. The best benzyl alcohol conversion reached 60.3% with 100% of the selectivity to benzaldehyde.

Aluminum- and calcium-incorporated MCM-41-type silica as supports for the immobilization of titanium(IV) isopropoxide in ring-opening polymerization of l-lactide and ε-caprolactone

Aluminum- and calcium-incorporated MCM-41-type silica with various Al/Si and Ca/Si ratios were evaluated as catalytic supports for ring-opening polymerization (ROP) of l-lactide and ε-caprolactone. The catalytic centers were generated by grafting titanium(IV) isopropoxide onto the support. All prepared heterogeneous catalysts better restrained the ROP of lactide than the homogeneous analog, titanium(IV) isopropoxide. Compared to siliceous MCM-41, the incorporation of aluminum or calcium in MCM-41 framework improved the molecular weight of the polymers although it lessened the polymerization rate. The more acidic Al-MCM-41 support appeared to be more favorable than the more basic Ca-MCM-41 support for the ROP reactions.

Solid Supported Ruthenium Complexes for Olefin Metathesis

Immobilization of ruthenium metathesis catalysts on solid supports has attracted much attention in recent years since it opens up the possibility for easy catalyst–product separation and catalyst reuse as well as reduction of the residual ruthenium content in the organic product. The state of the art on immobilization of ruthenium based metathesis initiators on solid supports is surveyed in this review. In addition, a comparison of the performance of the heterogenized catalysts with homogeneous analogues is made. Keywords: Alkylidene, Immobilization, Inorganic supports, Heterogeneous catalysis, Olefin Metathesis, polymeric supports, ruthenium carbenes, ruthenium.

Illuminating Photoswitchable Catalysis

Through the realization of conceptually new approaches aimed at controlling chemical reactions using light, the field of photoswitchable catalysis has seen rapid development over the past three decades. Although many photoswitchable catalysts are heterogeneous and utilize photosensitive surfaces, such as TiO2 and CdSe, significant attention has also been directed toward homogeneous analogues, primarily by capitalizing on the steric changes that accompany the E → Z photoisomerizations of azobenzene or stilbene derivatives. More recently, photochromic diarylethene moieties have been used to switch the intrinsic catalytic activities and selectivities through alteration of the steric and electronic properties displayed by a supporting ligand. In addition to detailing the aforementioned advances, this perspective summarizes other important developments in photoswitchable catalysis and offers a viewpoint on the future outlook of the field.

Recent Advances in Asymmetric Catalysis in Flow

Asymmetric catalysis in flow has been attracting much attention very recently because of the potential advantages over its batchwise counterpart, such as high-throughput screening and synthesis, easy automation with the integration of on-demand reaction analysis, little or no reaction workup, and potential long-term use of the catalysts in the case of heterogeneous catalysis. Homogeneous asymmetric catalysis performed in a microreactor has demonstrated successful examples in fast catalyst screening, integrated inline/onlineanalysis, microflow photocatalysis, multistep transformation with unstable intermediates, and potential for lower catalyst loading or homogeneous catalyst recylcing. Since heterogeneous asymmetric catalysis serves as a better way than its homogeneous analogue for catalyst separation and recycling, this Review Article summarizes recent development via different catalyst immobilization methods, such as covalent support, a self-supported method, an adsorption method, and H-bonding, electro...

A Remarkably Active Iron Catecholate Catalyst Immobilized in a Porous Organic Polymer

A single-site, iron catecholate-containing porous organic polymer was prepared and utilized as a stable and remarkably active catalyst for the hydrosilylation of ketones and aldehydes. In some instances, catalyst loadings of 0.043–2.1 mol % [Fe] were sufficient for complete hydrosilylation of aldehydes and ketones within 15 min at room temperature. The catalyst can be recycled at least three times without a drop in catalytic activity. This system is an example of an immobilized homogeneous catalyst with no homogeneous analogue.

Encapsulation of tetraazamacrocyclic complexes of cobalt(II), copper(II) and oxovanadium(IV) in zeolite-Y and their use as catalysts for the oxidation of styrene

Encapsulation of tetraazamacrocyclic complexes of Co(II), Cu(II) and V(IV) into zeolite-Y has been accomplished, and the resulting materials were used as heterogeneous catalysts for aerobic oxidation of styrene. The materials were prepared by a ship-in-a-bottle method, in which the transition metal cations were first ion-exchanged into zeolite-Y and then reacted with ethylenediamine, followed by acetylacetone. The pure tetraazamacrocyclic complexes were characterized by FTIR, solid UV–Vis and elemental analysis. The structural integrity throughout the immobilization procedure, the successful immobilization of the macrocyclic complexes, and the loadings of metal ions and macrocyclic ligands were determined by characterization techniques such as FTIR, diffuse reflection UV–Vis, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, TG/DTA and powder X-ray diffraction. Compared with their homogeneous analogues, the catalytic properties of the encapsulated macrocyclic complexes in the oxidation of styrene with air were investigated. The immobilized complexes proved to be active catalysts and could be reused without significant loss in activity.

Oxovanadium(iv) and iron(iii) salen complexes immobilized on amino-functionalized graphene oxide for the aerobic epoxidation of styrene

Oxovanadium(IV) and iron(III) salen complexes grafted onto amino-modified graphene oxide (NH2–GO) have been synthesized via a stepwise procedure and the prepared materials were used as heterogeneous catalysts in the aerobic oxidation of styrene. The structures of these materials have been thoroughly investigated using different characterization techniques such as XRD, N2 adsorption–desorption, TEM, FT-IR, diffuse reflectance UV-visible spectroscopy, ICP-AES, TEM, TG, Raman, and XPS. The results of XRD, N2 adsorption–desorption and TEM revealed that the structures of the prepared catalysts were well preserved. In addition, the results of FT-IR, diffuse reflectance UV-visible spectroscopy, ICP-AES, TG, Raman and XPS suggested that the oxovanadium(IV) and iron(III) complexes had been incorporated onto amino-modified graphene oxide (GO). It was found that the heterogeneous oxovanadium(IV) catalyst was more active than its homogeneous analogue in the epoxidation of styrene, using acetonitrile as solvent and air as the oxidant in combination with the sacrificial co-reductant isobutyraldehyde, due to site-isolation. Furthermore, the tethered vanadium catalyst was quite stable and could be recycled many times.

Stabilizing unstable species through single-site isolation: a catalytically active TaV trialkyl in a porous organic polymer

A catechol-functionalized porous organic polymer (POP) has been successfully metallated with a TaV trialkyl and remains thermally and structurally robust. The resulting POP-supported (catecholato)TaV trialkyl sites remain accessible to small molecules and can undergo reactions to yield stable, monomeric complexes that are quite different from those observed with the homogeneous analogues. Using a combination of reactivity studies, high-resolution solid-state NMR spectroscopy, and X-ray absorption spectroscopy (XAS), we are able to precisely determine the functionality and coordination environment of the active (catecholato)TaV trialkyl site and its products in reactions with Bronsted acids. Additionally, the Ta-metallated POP was found to have enhanced catalytic activity in the hydrogenation of cyclohexene and toluene relative to a homogeneous analogue.

Enhanced hydrogenation of olefins and ketones with a ruthenium complex covalently anchored on graphene oxide

Graphene oxide (GO) is a promising support for anchoring homogeneous metal complexes because of its two-dimensional structure, huge surface area and diversity for chemical functionalizations. In this study, a ruthenium supported catalyst has been synthesized by covalently bonding a ruthenium complex (RuCl2(PPh3)3) onto the GO surface through coordination interaction with aminosilane ligand spacers. The supported catalyst showed enhanced catalytic performance towards hydrogenation of olefins and ketones compared with the homogeneous analogue, and it could be readily recycled and reused several times without discernible loss of its activity.

Back Cover: Magnetic Polystyrene Nanosphere Immobilized TEMPO: A Readily Prepared, Highly Reactive and Recyclable Polymer Catalyst in the Selective Oxidation of Alcohols (ChemCatChem 1/2013)

An alco-hole in one The cover picture shows the use of 2,2,6,6-tetramethyl-piperidine-1-oxyl-modified polymer nanospheres (TEMPO/MNPs) in alcohol oxidation. In their Full Paper on p. 307 ff., J. Wang et al. describe the preparation, characterization, and catalytic studies of TEMPO/MNPs. The catalyst exhibits similar activity and versatility to the homogeneous TEMPO analogues, and its magnetic property ensures the catalyst recycling by simple magnetic decantation.

Catalytic Roles of Metal Centers in the Selective Oxidation of Cyclohexanol by Cr(salten) Complexes Immobilized on MCM-41

A series of transition metal complexes of 3-[N,N′-bis-3-(salicylidenamino)ethyltriamine] (salten) immobilized on MCM-41 were prepared for the solvent and additive-free selective oxidation of cyclohexanol with 30 % hydrogen peroxide (H2O2). The immobilized complexes were effective catalysts and exhibited much higher catalytic performance than their homogeneous analogues. Moreover, the metal centers were found to play important roles in the catalytic performance of immobilized complexes. When the immobilized chromium complex was used as catalyst, the optimal cyclohexanol conversion could reach 90.5 % with 100 % of the selectivity to cyclohexanone. In addition, the catalytic performance remained after being recycled five times. Owing to the different 3d electronic numbers of metal centers, eight kinds of immobilized Schiff base complexes exhibited significantly different catalytic performance in the selective oxidation of cyclohexanol with 30 % H2O2. The optimal cyclohexanol conversion could reach 90.5 % with 100 % of the selectivity to cyclohexanone over immobilized chromium complex.

Comparative Study of Immobilized Phthalocyanines in Oxidative Degradation

Immobilized iron phthalocyanine catalysts were prepared, via two heterogenization methods: anchoring by Augustine's method and the preparation of a ship-in-a-bottle type catalyst by intrazeolite synthesis method. The heterogenized catalysts were applied in the oxidative destruction of 4-chlorophenol, as a common pollutant of waste water. The performance of the two heterogenized and the homogeneous complexes were compared and it was found that the immobilized complexes had about the same activity as the homogeneous analog. Both heterogenized samples could be recycled in three subsequent runs and the ship-in-a-bottle type showed stable activity. Meanwhile, the anchored complex lost some activity in every subsequent run. Consequently, the first catalyst was better for practical application.

Mediated Improvement in Catalytic Performance of MCM-41 Immobilized Chromium Schiff Base Complex for Solvent-Free Oxidation of Cyclohexanol

A series of chromium (III) Schiff base complexes immobilized on MCM-41 were prepared and used for the selective oxidation of cyclohexanol with 30% hydrogen peroxide. The results revealed that the immobilized complexes were active catalysts and exhibited much higher catalytic performance than their homogeneous analogue. This could be ascribed to the dispersion effect of the support. Simultaneously, the linker flexibility and the surface property of support were also found to play important roles in the catalytic performance of immobilized complexes.

Universal graded Specht modules for cyclotomic Hecke algebras

The graded Specht module Sλ for a cyclotomic Hecke algebra comes with a distinguished generating vector zλ∈Sλ, which can be thought of as a ‘highest weight vector of weight λ’. This paper describes the defining relations for the Specht module Sλ as a graded module generated by zλ. The first three relations say precisely what it means for zλ to be a highest weight vector of weight λ. The remaining relations are homogeneous analogues of the classical Garnir relations. The homogeneous Garnir relations, which are simpler than the classical ones, are associated with a remarkable family of homogeneous operators on the Specht module which satisfy the braid relations.

Chiral Nanoporous Metal–Metallosalen Frameworks for Hydrolytic Kinetic Resolution of Epoxides

Chiral nanoporous metal-organic frameworks are constructed by using dicarboxyl-functionalized chiral Ni(salen) and Co(salen) ligands. The Co(salen)-based framework is shown to be an efficient and recyclable heterogeneous catalyst for hydrolytic kinetic resolution (HKR) of racemic epoxides with up to 99.5% ee. The MOF structure brings Co(salen) units into a highly dense arrangement and close proximity that enhances bimetallic cooperative interactions, leading to improved catalytic activity and enantioselectivity in HKR compared with its homogeneous analogues, especially at low catalyst/substrate ratios.