Factorial design evaluation of the Suzuki cross-coupling reaction using a magnetically recoverable palladium catalyst

A magnetically recoverable catalyst [Fe₃O₄@SiO₂-AEAPTMS-Pd(II)] was prepared, fully characterized and had its catalytic activity evaluated on the Suzuki cross-coupling reaction under microwave irradiation. The reaction conditions for the synthesis of biaryl compounds was optimized in two stages - an initial fractional design 2⁴, in which the parameters reaction time, temperature, solvent and catalyst loading were evaluated, followed by a Doehlert design. The factorial design proved to be a viable approach for obtaining the optimal reaction conditions based on a relatively small number of experiments. Additionally, the biaryl derivatives synthesized by this method were obtained with good to excellent yields (71–96%) and the recovery and reuse of the palladium catalyst was also evaluated.     

Fluorescence and morphology modulation in a photochromic diarylethene self-assembly system

Switchable supramolecular self-assemblies on the basis of interaction between melamine group containing photochromic diarylethene unit (DTE) and naphthalimide derivate (1) were designed and fabricated. 1 can gelate several aprotic solvents with different morphologies. The gel turned into partial gel in ethyl acetate with the addition of DTE as a guest molecule. Both the absorption and fluorescence spectra of the assembly can be reversibly switched by alternating UV/visible light irradiation. Meanwhile, the morphology of the coassembly of 1(2)·DTE changed to film from original pieces of gel 1 in ethyl acetate. When 1(2)·DTE was irradiated by UV light, the film morphology was converted into aggregated flakes. Moreover, the surface wettability of the complex can also be switched by light irradiation. The photochromic diarylethene unit is able to modulate the fluorescence and morphology of the assembled system only by virtue of light irradiation. Therefore, these results provide further insights into fluorescence and morphology controlling, especially application in upscale smart responsive materials.     

Microwave-assisted Suzuki coupling reactions with an encapsulated palladium catalyst for batch and continuous-flow transformations

This article describes the design, optimisation and development of a Suzuki cross-coupling protocol mediated by an efficient palladium-encapsulated catalyst (Pd EnCat) under microwave irradiation. The methodology has been used in both batch mode for classical library preparation and in continuous-flow applications furnishing multigram quantities of material. Described is a method that uses direct focused microwave heating whilst applying an external cooling source. This enables a lower than normal bulk temperature to be maintained throughout the reaction period leading to significant improvements in the overall yield and purity of the reaction products. Additional aspects of this novel heating protocol are discussed in relation to the prolonged lifetime and enhanced reactivity of the immobilised catalyst system.     

Flexible Zirconium Metal‐Organic Frameworks as Bioinspired Switchable Catalysts

Flexible metal–organic frameworks (MOFs) are highly desirable in host–guest chemistry owing to their almost unlimited structural/functional diversities and stimuli‐responsive pore architectures. Herein, we designed a flexible Zr‐MOF system, namely PCN‐700 series, for the realization of switchable catalysis in cycloaddition reactions of CO₂ with epoxides. Their breathing behaviors were studied by successive single‐crystal X‐ray diffraction analyses. The breathing amplitudes of the PCN‐700 series were modulated through pre‐functionalization of organic linkers and post‐synthetic linker installation. Experiments and molecular simulations confirm that the catalytic activities of the PCN‐700 series can be switched on and off upon reversible structural transformation, which is reminiscent of sophisticated biological systems such as allosteric enzymes.     

Synergetic activation of carbon dioxide molecule using phenylazomethine dendrimers as a catalyst

Phenylazomethine dendrimers bearing a cobalt porphyrin core act as catalysts for CO₂ reduction in the presence of a strong Lewis acid such as lanthanide trifluoromethanesulfonate (Ln(OTf)₃). We investigated the catalytic activity using electrochemical measurements (cyclic voltammetry) on a glassy carbon electrode in a DMF solution. Dissolving CO₂ gas into the solution, the cyclic voltammograms displayed an irreversible increase of the cathodic current. This result suggests the catalytic reduction of CO₂. The redox potential (–1.3 V versus Fc/Fc⁺) at which the catalytic behavior was observed is 1.1 V higher than that catalyzed by cobalt tetraphenylporphyrin (CoTPP). The generation number (n) dependence of the dendrimer catalysts showed the maximum activity at n = 3. A significant decrease of the activity for the largest dendrimer (n = 4) indicates a steric effect, which prevents transmission of the substrate (CO₂ molecule) and electrons to the catalytic center (cobalt porphyrin core). For more efficient catalysis, a novel open-shell dendrimer having a pocket on one side of the molecule was designed and synthesized. Because the accessibility to the core in the opened shell improved, this dendrimer exhibited the highest catalytic activity. These results suggest that tuning of the local domain around the cobalt porphyrin center would lead to a decisive solution for further activation of the CO₂ molecule. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5229–5236, 2006     

A new catalyst system for silyl ether synthesis

Phenyl substituted silanes are converted to silyl ethers by catalytic amounts of tetrachlorocopper(II) complexes at ambient temperature in high yields.     

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.     

Tandem mass spectrometry of silver-adducted ferrocenyl catalyst complexes

Ferrocene is a popular template in material science due to its exceptional characteristics that offer the ability to optimize the selectivity and activity of catalysts by the addition of carefully selected substituents. In combinatorial catalyst development, the high susceptibility to electrophilic substitution reactions offers the opportunity for the rapid introduction of molecular diversity. Mass spectrometry (MS)-based continuous-flow systems can be applied to rapidly evaluate catalyst performance as well as to (provisionally) identify the introduced catalyst complexes. Herein, we describe the fragmentation characteristics of the [ferrocenyl bidentate + Ag](+) catalyst complexes in dedicated (high-resolution) MS(n) experiments. The investigation of the fragmentation patterns of a selected number of catalyst classes is accompanied with a density functional theory investigation of fragmentation intermediates in order to assess the viability of a selected fragmentation mechanism.     

The first porous MOF with photoswitchable linker molecules

We synthesized a porous twofold interpenetrated MOF [Zn(2)(NDC)(2)(1)] (coined CAU-5) using 3-azo-phenyl-4,4'-bipyridine (1), 2,6-naphthalenedicarboxylic acid, and Zn(NO(3))(2)·6H(2)O. The azo-functionality protrudes into the pores, and can be switched, by irradiation with UV light (365 nm), from the thermodynamically stable trans-isomer to the cis-isomer. Back-switching was achieved thermally and with an irradiation wavelength of λ(max) = 440 nm.     

Aminimide derived from benzoylformic acid ester as photolatent base/radical initiator

An aminimide possessing a benzoyl substituent, 1,1‐dimethyl‐1‐(2‐hydroxypropyl)amine benzoylformimide (BFI), proved to serve as an excellent photobase catalyst. BFI decomposes smoothly by the UV irradiation to give products containing tertiary amines. The effective nature of BFI as a photo/thermal dual‐base catalyst was convinced by the thermal and photoinduced polymerization of epoxide/thiol system. Based on the facts that the mixture of BFI and epoxide/thiol exhibit a long pot life in dark and that it undergoes smooth polymerization by UV irradiation and heating, it was supported that BFI serves as an efficient photo/thermal latent dual‐base catalysts. It was also found that BFI initiates the free radical polymerization of vinyl monomers such as 2‐hydroxylethyl methacrylate (HEMA) under the UV irradiation while the mixture of BFI and HEMA also exhibit a long pot life in dark, indicating the excellent ability of BFI as a photoradical initiator. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Hydrocarbon production rates in Fischer-Tropsch synthesis over a Fe/Cu/La/Si catalyst

The detailed kinetics of Fischer-Tropsch synthesis over an industrial Fe/Cu/La/Si catalyst was studied in a continuous spinning basket reactor under the conditions relevant to industrial operations. Reaction rate equations were derived on the basis of Langmuir-Hinshelwood-Hougen-Watson type models for Fischer-Tropsch synthesis based on possible reactions sets originated from the carbide, enolic and combined enol/carbide mechanisms. Kinetic model candidates were evaluated by the global optimization of kinetic parameters, which were realized by first minimization of multi-response objective functions with conventional Levenberg-Marquardt method. It was found that an enolic mechanism based model could produce a good fit of the experimental data. The activation energy for paraffin formation is 95 kJ·mol^?1 which is smaller than that for olefin formation (121 kJ·mol^?1).     

中温商业SCR催化剂碱和碱土中毒特性研究

在实验室条件下对选择性催化还原(SCR)商业催化剂的碱(K)和碱土(Ca)中毒进行了模拟,并采用液氮吸附、扫描电镜、能谱分析、NH_3-程序升温脱附、H_2-程序升温还原等方法对催化剂中毒前后的物理化学性质变化进行了表征。结果表明,K和Ca的中毒没有破坏商业中温SCR催化剂孔的基本结构,但K和Ca的中毒使催化剂的比表面积和孔容减小。K和Ca的中毒在一定程度上改变了催化剂表面钒的价态,导致了钒的还原能力减弱,同时降低催化剂表面化学吸附氧。钾中毒和钙中毒使催化剂的表面酸量降低。钾和钙中毒造成中温SCR催化剂的脱硝活性降低,并且Ca中毒造成的催化剂活性降低要明显高于K中毒。     

Branched polyethylene prepared by in situ copolymerization of ethylene with monotitanocene and modified methylaluminoxane catalyst

Branched polyethylene was synthesized in heptane used as a polymerization medium with monotitanocene catalyst composed of η⁵‐pentamethylcyclopentadienyl tribenzyloxy titanium and modified methylaluminoxane (mMAO) that contained different amounts of residual trimethylaluminum (TMA). The residual TMA more strongly reduced Ti(IV) complexes to Ti(III) and Ti(II) ones, and Ti(IV) active species were suggested to be more effective for ethylene polymerization. Influences of the polymerization temperature and Al/Ti molar ratio on the catalytic activity and the degree of branching, branch length, and molecular weight of polyethylene were investigated. The obtained polymers were confirmed by ¹³C NMR to be higher molecular weight polyethylene containing significant amounts of isolated ethyl branches, butyl branches, or both. Branched polyethylene was prepared by the in situ copolymerization of ethylene with 1‐butene and 1‐hexene, which were formed through a proposed mechanism including metallcycloheptane and metallcyclopentane intermediates of Ti(II) species that were produced by the reaction of Ti(IV) complexes with TMA coexisting in mMAO. There was a remarkable increase in the chance of 1‐butene being produced from metallcyclopentane of Ti(II) intermediates with an increase in the polymerization temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4258–4263, 2000     

Reversible switching on superhydrophobic TiO2 nano-strawberry films fabricated at low temperature

Superhydrophobic TiO2 nano-strawberry rutile films, on which superhydrophobicity and superhydrophilicity can be reversibly switched by alternation of ultraviolet (UV) irradiation and dark storage, were fabricated on a large scale from aqueous solution via a seeded growth method at low temperature without any pressure equipment.     

Copolymerization of butadiene and styrene with neodymium naphthenate based catalyst

Copolymerization of butadiene (Bd) and styrene (St) was carried out in toluene at 50 °C by a conventional rare earth catalytic system, Nd(naph)₃-Al(i-Bu)₃-Al(i-Bu)₂Cl. It exhibited a high catalytic activity and high stereospecificity in the copolymerization. The influences of the conditions in polymerization on the yield, composition, microstructure and molecular weight of copolymer were thoroughly studied. According to the 13C-NMR spectrum, the resultant copolymer containing 18% St units, and the diad fraction of St-trans Bd or St-vinyl Bd can hardly be found in its 13C-NMR. The cis-1,4 content of Bd unit of the copolymer decreased little with the increase of St content. The GPC curves indicate the presence of two kinds of active sites in the polymerization.     

Immobilized copper catalyst for atom transfer radical addition and polymerization

A novel multidentate amine grafted on silica gel and magnetic microsphere was prepared. Its chemical structure was confirmed by C¹³ NMR, XPS and FTIR, and the nitrogen content was determined by elemental analysis. It was also used as a ligand for CuCl and successfully catalyzed the atom transfer radical addition of both carbon tetrachloride (CCl₄) to methyl methacrylate and methyl trichloroacetate to styrene, repeatedly. The conversion and purity of the product were determined through gas chromatography and ¹H NMR, respectively. The immobilized copper catalyst complex was also used in atom transfer radical polymerization of styrene initiated by 1,1,1,3‐tetrachloro‐3‐phenylpropane and methyl methacrylate initiated by methyl 2‐methyl‐2,4,4,4‐tetrachlorobutyrate, respectively. Although the polymerization took place successfully, it did not proceed in a controlled fashion. Copyright © 2010 John Wiley & Sons, Ltd.     

Microwave-assisted degradation of acid orange using a conjugated polymer,polyaniline, as catalyst

Microwave-assisted photocatalytic degradation of dyes is one of the emerging technologies for waste water remediation. Microwave effectively accelerates photocatalytic degradation, when microwave electrodeless lamp (MEL) substitutes traditional UV lamp as light source. This setup can be extremely simplified if MEL and photocatalyst can be replaced by a catalyst which can work under microwave irradiation in the absence of any light source. The present work reports for the first time degradation of acid orange 7 (AO) under microwave irradiation using polyaniline (PANI) as catalyst in the absence of any UV lamp as light source. The degradation/decolourization was carried out in neutral acidic and basic media and was monitored spectrophotometrically to evaluate the ability of microwave irradiation to degrade AO. Microwave irradiation showed excellent performance as it completely decolourizes AO dye solution in 10 min. With the advantages of low cost and rapid processing, this novel catalyst is expected to gain promising application in the treatment of various dyestuff wastewaters on a large scale.     

Crystal structures of Ziegler-Natta catalyst supports

The crystal structures of three MgCl(2)·nEtOH complexes with n=1.5, 2.8, and 3.3 have been fully determined. Such complexes are the fundamental precursors for Ziegler-Natta polymerization catalysts used to produce polyolefins on a multimillion-ton scale worldwide. The ab initio structure solution showed that the structure of MgCl(2)·nEtOH complexes with n=1.5 and 2.8 are based on ribbons of metal-centered octahedra, whereas for n=3.3 this chainlike arrangement breaks into a threadlike structure of isolated octahedra linked by hydrogen bonds. A clear correlation between catalyst performance and the crystal structure of precursors has been found, and reveals the fundamental role of the latter in determining catalyst properties. The direct knowledge of building blocks in the precursor structures will help to develop more accurate models for activated catalysts. These models will not require the arbitrary and oversimplified assumption of locating the catalyst active sites on selected cut surfaces of the α-MgCl(2) crystal lattice.     

Roads less traveled: Nitrogen reduction reaction catalyst design strategies for improved selectivity

Direct electrochemical nitrogen reduction for ammonia production is necessary to reduce the use of fossil fuels from conventional Haber–Bosch methods. Applications of nitrogen reduction electrocatalysts remain inhibited by slow reaction kinetics and low faradaic efficiencies because of competitive H₂ production pathways. Current strategies to address this challenge in selectivity have focused on catalyst design, reactor configuration, and electrolyte conditions. This brief review discusses the thermodynamic and kinetic challenges in the field as well as current underused approaches for selective catalyst development including bimetallic catalysts, transition metal nitrides, and carbon supports.     

Neodymium Ziegler-Natta catalysts: Evaluation of catalyst ageing effect on 1,3-butadiene polymerization

Catalysts constituted by neodymium versatate, diisobutylaluminium hydride and t-butyl chloride were used in this work. After their synthesis, they were aged at 40 °C for 48 h. Afterwards, they were maintained at 10 °C for more 5, 15, 40, 80, 160 and 250 days and finally the aged catalysts were evaluated in butadiene polymerization. The polybutadienes were characterized by size exclusion chromatography (SEC) to determine the molecular weight characteristics and by infrared spectroscopy (FTIR) to determine the microstructure. The aim of this work is to evaluate the effect of ageing time on 1,4 polymerization of butadiene. The results showed that the stereoselectivity of the active sites was not affected by the ageing conditions. However, the catalyst activity increased for long times of ageing.