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Active Catalyst (active + catalyst)
Kinds of Active Catalyst Selected AbstractsChemInform Abstract: A Highly Active Catalyst for Huisgen 1,3-Dipolar Cycloadditions Based on the Tris(triazolyl)methanol,Cu(I) Structure.CHEMINFORM, Issue 11 2010Salih Oezcubukcu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Ytterbium Triflate: A Highly Active Catalyst for Addition of Amines to Carbodiimides to N,N,,N,,-Trisubstituted Guanidines.CHEMINFORM, Issue 52 2009Xuehua Zhu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Synthesis and Applications of a New Palladacycle as a High Active Catalyst in the Suzuki Couplings.CHEMINFORM, Issue 7 2009Mohammad Joshaghani Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Identification of a Highly Efficient Alkylated Pincer Thioimido,Palladium(II) Complex as the Active Catalyst in Negishi CouplingCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2009Jing Liu Dr. Abstract PdIIate complex: A novel alkylated pincer thioimido,Pd complex generated from a catalyst precursor and basic organometallic reagents (RM) was observed by in situ IR, 1H,NMR, and 13C,NMR spectroscopies for the first time and proved to be the active catalyst in stoichiometric and catalytic reactions of aryl iodides with RM (see scheme). The catalyst, as an electron-rich PdII species, promoted the Negishi coupling of aryl iodides and alkylzinc reagents with high efficiency, even at low temperatures (0 or ,20,°C). The induction period of Negishi coupling catalyzed by pincer thioamide,palladium complex 1 was investigated. A heterogeneous mechanism was excluded by kinetic studies and comparison with Negishi coupling reactions promoted by Pd(OAc)2/Bu4NBr (a palladium,nanoparticle system). Tetramer 2 was isolated from the reaction of 1 and organozinc reagents. Dissociation of complex 2 by PPh3 was achieved, and the structure of resultant complex 8 was confirmed by X-ray diffraction analysis. A novel alkylated pincer thioimido,PdII complex, 7, generated from catalyst precursor 1 and basic organometallic reagents (RM), was observed by in situ IR, 1H,NMR, and 13C,NMR spectroscopy for the first time. The reaction of 7 with methyl 2-iodobenzoate afforded 74,% of the cross-coupled product, methyl 2-methylbenzoate, together with 60,% of PdII complex 2. Furthermore, the catalyst, as an electron-rich PdII species, efficiently promoted the Negishi coupling of aryl iodides and alkylzinc reagents without an induction period, even at low temperatures (0,°C or ,20,°C). To evaluate the influence of the catalyst structure upon the induction period, complex 9 was prepared, in which the nBu groups of 1 were displaced by more bulky 1,3,5-trimethylphenyl groups. Trimer 10 was isolated from the reaction of complex 9 and basic organometallic reagents such as CyZnCl or CyMgCl (Cy: cyclohexyl); this is consistent with the result obtained with complex 1. The rate in the induction period of the model reaction catalyzed by 9 was faster than that with 1. Plausible catalytic cycles for the reaction, based upon the experimental results, are discussed. [source] Why Platinum Catalysts Involving Ligands with Large Bite Angle Are so Efficient in the Allylation of Amines: Design of a Highly Active Catalyst and Comprehensive Experimental and DFT StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2008Guilhem Mora Abstract The platinum-catalyzed allylation of amines with allyl alcohols was studied experimentally and theoretically. The complexes [Pt(,3 -allyl)(dppe)]OTf (2) and [Pt(,3 -allyl)(DPP-Xantphos)]PF6 (5) were synthesized and structurally characterized, and their reactivity toward amines was explored. The bicyclic aminopropyl complex [Pt(CH2CH2CH2NHBn- , - C,N)(dppe)]OTf (3) was obtained from the reaction of complex 2 with an excess of benzylamine, and this complex was shown to be a deactivated form of catalyst 2. On the other hand, reaction of complex 5 with benzylamine and allyl alcohol led to formation of the 16-VE platinum(0) complex [Pt(,2 -C3H5OH)(DPP-Xantphos)] (7), which was structurally characterized and appears to be a catalytic intermediate. A DFT study showed that the mechanism of the platinum-catalyzed allylation of amines with allyl alcohols differs from the palladium-catalyzed process, since it involves an associative ligand-exchange step involving formation of a tetracoordinate 18-VE complex. This DFT study also revealed that ligands with large bite angles disfavor the formation of platinum hydride complexes and therefore the formation of a bicyclic aminopropyl complex, which is a thermodynamic sink. Finally, a combination of 5 and a proton source was shown to efficiently catalyze the allylation of a broad variety of amines with allyl alcohols under mild conditions. [source] Pyridine Carboxylate Complexes of MoII as Active Catalysts in Homogeneous and Heterogeneous PolymerizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2007Maria Vasconcellos-Dias Abstract New lamellar materials intercalated with molybdenum(II) complexes with potential catalytic properties were prepared by a stepwise procedure. The lamellar material was first calcined at 823 K for four hours to eliminate all the carbonate ions; the layered structure was reconstructed after treatment with a solution of either pycH (pyridine-2-carboxylic acid) or pydcH2 (pyridine-2,6-dicarboxylic acid) in a KOH solution of dmf at 343 K. Impregnation with a solution of the organometallic precursor [Mo(CO)3I2(NCCH3)2] led to substitution of the nitrile groups by two pyridine ligands. All the materials were characterized by powder X-ray diffraction, FTIR, and 13C CP MAS and 27Al MAS solid-state NMR spectroscopy. Similar MoII complexes were also prepared by using pycH or pydcH2 and characterized by elemental analysis as well as FTIR and 1H and 13C solution NMR spectroscopy. These new materials and the complexes of pyc or pydc ligands containing 4.54 wt.-% and 6.33 wt.-% of Mo respectively, catalyze the ring-opening-metathesis polymerization of norbornene and the polymerization of styrene at 333 K, their performance increasing upon the addition of methylalumoxane (MAO) as cocatalyst.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Metal Triflates as Highly Stable and Active Catalysts for the "Immortal" Ring-Opening Polymerization of Trimethylene CarbonateCHEMCATCHEM, Issue 3 2010Marion Helou Abstract The controlled "immortal" ring-opening polymerization of trimethylene carbonate (TMC) using a two-component catalyst system based on a metal Lewis acid, such as a metal triflate M(OTf)n(M=Ca, Sc, Zn, Al, Bi; OTf=CF3SO3,) or the metallic salt Fe(acac)3, (acac=acetylacetonate) and an alcohol (ROH) as co-initiator and chain-transfer agent, is carried out in bulk at 110,150,°C. As a result of the water-tolerance of these systems, experimental operating conditions do not require any special care. The approach, valorized both with various ROH transfer agents and with either purified or unpurified monomer sources, is highly versatile. Functional telechelic polycarbonates HPTMCOR, devoid of decarboxylation sequences, are obtained [PTMC=poly(trimethylene carbonate)]. The molar mass of the PTMCs can be readily predicted by a simple model, taking into account the [TMC]0/[ROH]0 ratio and the amount of transferring impurities present in the raw/unpurified reagents. Such simple, air- and moisture-robust catalytic systems, which display quite high activities (TOF up to 28,200,h,1) and productivities (TON up to 45,000) are thus extremely valuable, especially industrially. The performances of these systems are described in comparison to the previously established valuable inorganic and organometallic catalytic systems, namely metal amido complexes ([M{N(SiMe3)2}3]) and [(BDI)Zn{N(SiMe3)2}] (BDI=,-diiminate ligand) derivatives. [source] ChemInform Abstract: Urea Derivatives Are Highly Active Catalysts for the Base-Mediated Generation of Terminal Epoxides from Aldehydes and Trimethylsulfonium Iodide.CHEMINFORM, Issue 33 2008Sarah A. Kavanagh Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Rhenium(VII) Oxo Complexes as Extremely Active Catalysts in the Dehydration of Primary Amides and Aldoximes to Nitriles.CHEMINFORM, Issue 51 2002Kazuaki Ishihara No abstract is available for this article. [source] Highly Active Catalysts for the Telomerization of Crude Glycerol with 1,3-ButadieneCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 3 2008Regina Palkovits Dr. The chain gang: Crude glycerol, a by-product in the production of biodiesel, can be telomerized with 1,3-butadiene to form C8 -chain ethers. The development of suitable catalyst systems for the direct telomerization of crude glycerol at the biodiesel plant provides a route to useful building blocks from cheap starting materials for commercially valuable products such as detergents and surfactants. [source] Chelate [2-(Iminoethyl)pyridine N -oxide]metal Complexes , Synthesis and Structural Comparison with Their Chemically Related 2-(Iminoethyl)pyridine-Derived SystemsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2006Katrin Nienkemper Abstract The N,O-chelate ligands 2-(iminoethyl)pyridine N -oxide (2a) and 2-(iminoethyl)-6-isopropylpyridine N -oxide (2b) were prepared by conventional synthetic routes, the latter involving a variant of the Reissert,Henze reaction. Treatment of 2a with FeCl2 resulted in a deoxygenation reaction of the ligand and formation of the salt [bis{2-(iminoethyl)pyridine}FeCl]+[FeCl4], (18a). In contrast, the reaction of 2a with PdCl2 or CoCl2 cleanly furnished the six-membered chelate [,N,O -2(iminoethyl)pyridine N -oxide]MCl2 complexes (19a, M = Pd) or (20a, M = Co), respectively, which were both characterised by X-ray diffraction. Treatment of 2b with [NiBr2(dme)], followed by crystallisation from THF, gave the complex [(,N,O - 2b)NiBr2(THF)] (21b), which features a distorted trigonal-bipyramidal coordination geometry of the central metal atom. The reaction of 2a with [NiBr2(dme)] gave the structurally related complex [(,N,O - 2a)NiBr2(,O - 2a)] (21a). The N,O-chelate Pd complex 19a was shown to be an active catalyst for the Suzuki coupling reaction. The ligand systems 2a,b and their related 2-(iminoethyl)pyridines 3a,b and a variety of metal complexes of ligands 3 were also prepared and characterised for comparison by X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Monophosphanylcalix[6]arene Ligands: Synthesis Characterization, Complexation, and Their Use in CatalysisEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2006Yasushi Obora Abstract Novel phosphanylcalix[6]arenes having mono- O -diphenylphosphanylmethyl (3) and mono- O -(4-diphenylphosphanylphenyl)methyl substituents (5) have been synthesized. The structures of these monophosphanylcalix[6]arenes were determined by NMR spectroscopy, mass spectrometry, and X-ray crystal structure analysis. The X-ray structure reveals that 3 adopts a flattened 1,2,3-alternate conformation in the crystalline state, while the NMR spectra show that 3 and 5 have a cone conformation in solution. Structure optimization and energy calculations for 3 and 5 at the B3LYP/LANL2DZ-CONFLEX5/MMFF94s level of theory show that the cone conformation is slightly more stable than the 1,2,3-alternate conformation by 0.36 kcal,mol,1 for 3 and 0.96 kcal,mol,1 for 5. Complexation of 3 with [PtCl2(COD)] and [Rh(COD)2]BF4 gives cis -coordinated [PtCl2(3)2] and [Rh(COD)(3)2]BF4, respectively. The X-ray analysis of [PtCl2(3)2] shows that 3 adopts a cone conformation upon complexation. Combination of 3 and 5 with [Rh(COD)2]BF4 provides an active catalyst for the hydroformylation of a variety of terminal alkenes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Incorporation of a (Cyclopentadienyl)molybdenum Oxo Complex in MCM-41 and Its Use as a Catalyst for Olefin EpoxidationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2004Marta Abrantes Abstract The tricarbonyl complex [(,5 -C5H4 -COOMe)Mo(CO)3Cl] was prepared from the reaction of sodium (methoxycarbonyl)cyclopentadienide, (C5H4 -CO2Me)Na, with (Bu4N)[Mo(CO)5I]. Heating the ester with 3-(triethoxysilyl)propylamine gave the amide derivative {[,5 -C5H4 -CONH-C3H6Si(OEt)3]Mo(CO)3Cl}. The functionalised tricarbonyl complex was immobilised in the ordered mesoporous silica MCM-41 with a loading of 13 wt.-% Mo (1.4 mmol·g,1) by carrying out a grafting reaction in dichloromethane. Powder X-ray diffraction and nitrogen adsorption,desorption analysis indicated that the structural integrity of the support was preserved during the grafting and that the channels remained accessible, despite significant reductions in surface area, pore volume and pore size. The success of the coupling reaction was confirmed by 29Si and 13C (CP) MAS NMR spectroscopy. A supported dioxo complex of the type [(,5 -C5H4R)MoO2Cl] was subsequently prepared by oxidative decarbonylation of the tethered tricarbonyl complex using tert -butyl hydroperoxide (TBHP). The oxidised material is an active catalyst for the liquid phase epoxidation of cyclooctene with TBHP as the oxygen source. Similar catalytic results were obtained using the tethered tricarbonyl complex directly as a pre-catalyst since fast oxidative decarbonylation occurs under the reaction conditions used. For both systems, the desired epoxide was the only product and the initial activities were about 13 mol·molMo,1·h,1. The solid catalysts were recycled several times. Some activity was lost between the first and second runs but thereafter tended to stabilise. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Stable Platinum(0) Catalysts for Catalytic Hydrosilylation of Styrene and Synthesis of [Pt(Ar-bian)(,2 -alkene)] ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2003Jeroen W. Sprengers Abstract The use of alkenes and bidentate N-ligands in the platinum(0)-catalyzed hydrosilylation of styrene with triethylsilane has been evaluated. A number of bidentate N-ligands, phen, bpy, dafo, and phenyl-bian, were tested at various reaction temperatures using in situ formed catalysts with [Pt(nbe)3] as a precursor. The main conclusions are: (i) ligands, such as phen, which form stable platinum(0) complexes, give lower catalytic activities compared to the ligands which form less stable complexes; (ii) a small ligand effect is observed with dafo and phenyl-bian compared to [Pt(nbe)3], the precursor complex, displaying the lability of these ligands. The complex [Pt(nbe)3], that only has labile alkene ligands, is an active catalyst at low temperatures. At higher temperatures, the catalyst is no longer stable and a decrease in yield is observed. Several novel complexes have been synthesized: [Pt(m,m -(CF3)2 -C6H3 -bian)(tcne)], [Pt(m,m -(CF3)2 -C6H3 -bian)(ma)], [Pt(p -MeO-C6H4 -bian)(ma)], [Pt(p -MeO-C6H4 -bian)(dmfu)] and [Pt(phenyl-bian)(dmfu)]. Whereas the two [Pt(Ar-bian)(ma)] complexes are intrinsically more active than the two [Pt(Ar-bian)(dmfu)] complexes, the latter are much more stable, i.e. the nature of the alkene in these complexes is an important factor in determining their catalytic behavior. Compared to [Pt(Me-nq)(nbe)2], the two [Pt(Ar-bian)(dmfu)] complexes are much more stable resulting in significantly higher overall yields. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Lanthanide Formamidinates as Improved Catalysts for the Tishchenko ReactionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2008Agustino Zuyls Abstract The tris(formamidinato)lanthanum(III) complexes [La(o -TolForm)3(thf)2] [1; o -TolForm = N,N, -bis(o -tolyl)formamidinate], [La(XylForm)3(thf)] [2; XylForm = N,N, -bis(2,6-dimethylphenyl)formamidinate], and [La(EtForm)3] [3, EtForm = N,N, -bis(2,6-diethylphenyl)formamidinate] are a new class of precatalysts for the Tishchenko reaction. Their catalytic activity is a result of their high Lewis acidity and the ease with which the ligand spheres can be interchanged. For the dimerization of benzaldehyde to give benzyl benzoate, which is a benchmark reaction, compound 1 is, to the best of our knowledge, the most active catalyst ever reported. On a preparative scale, the reaction can be performed in the absence of solvent. A range of aromatic, heteroaromatic, and aliphatic aldehydes was rapidly converted into the corresponding esters by using catalysts 1,3.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] A Facile Strategy for Preparing Self-Healing Polymer Composites by Incorporation of Cationic Catalyst-Loaded Vegetable FibersADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Ding Shu Xiao Abstract A two-component healing agent, consisting of epoxy-loaded microcapsules and an extremely active catalyst (boron trifluoride diethyl etherate, (C2H5)2O,·,BF3)), is incorporated into epoxy composites to provide the latter with rapid self-healing capability. To avoid deactivation of the catalyst during composite manufacturing, (C2H5)2O,·,BF3 is firstly absorbed by fibrous carriers (i.e., short sisal fibers), and then the fibers are coated with polystyrene and embedded in the epoxy matrix together with the encapsulated epoxy monomer. Because of gradual diffusion of the absorbed (C2H5)2O,·,BF3 from the sisal into the surrounding matrix, the catalyst is eventually distributed throughout the composites and acts as a latent hardener. Upon cracking of the composites, the epoxy monomer is released from the broken capsules, spreading over the cracked planes. As a result, polymerization, triggered by the dispersed (C2H5)2O,·,BF3, takes place and the damaged sites are rebonded. Since the epoxy,BF3 cure belongs to a cationic chain polymerization, the exact stoichiometric ratio of the reaction components required by other healing chemistries is no longer necessary. Only a small amount of (C2H5)2O,·,BF3 is sufficient to initiate very fast healing (e.g., a 76% recovery of impact strength is observed within 30,min at 20,°C). [source] Fluorous-Silica-Supported Perfluoro-Tagged Palladium Complexes Catalyze Suzuki Couplings in WaterHELVETICA CHIMICA ACTA, Issue 11 2004Christoph Tzschucke Different Pd-complexes (see 2a,d and 3) with and without perfluoroalkyl tags were deposited on fluorous reversed-phase silica 1 and unmodified silica gel. These supported complexes were successfully used as precatalysts for the Suzuki reaction in H2O. H2O-Soluble aryl bromides were easily converted to the corresponding biphenyls. Although none of the complexes is H2O-soluble, the active catalyst is most likely homogeneously dissolved. Nevertheless, the Pd-leaching into the product was low. [source] Pentafluorophenylammonium Trifluoromethanesulfonimide: Mild, Powerful, and Robust Catalyst for Mukaiyama Aldol and Mannich Reactions between Ketene Silyl Acetals and Ketones or Oxime EthersADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2010Ryohei Nagase Abstract Pentafluorophenylammonium trifluoromethanesulfonimide (C6F5N+H3,NTf2,) promotes Mukaiyama aldol and Mannich reactions using ketene silyl acetals with ketones and oxime ethers, respectively. The present robust method is mild, but powerful enough to utilize less accessible electrophiles such as enolizable ketones and oxime ethers to produce a variety of ,-hydroxy esters and ,-alkoxyamino esters, respectively. Mechanistic investigation revealed in situ generation of trimethylsilyl bistriflimide [Tf2N(TMS)], the truly active catalyst, which was supported by rational 1H,NMR measurements. [source] Aerobic Oxidation of Primary Aliphatic Alcohols to Aldehydes Catalyzed by a Palladium(II) Polyoxometalate CatalystADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Delina Barats Abstract A hexadecyltrimethylammonium salt of a "sandwich" type polyoxometalate has been used as a ligand to attach a palladium(II) center. This Pd-POM compound was an active catalyst for the fast aerobic oxidation of alcohols. The unique property of this catalyst is its significant preference for the oxidation of primary versus secondary aliphatic alcohols. Since no kinetic isotope effect was observed for the dehydrogenation step, this may be the result of the intrinsically higher probability for oxidation of primary alcohols attenuated by steric factors as borne out by the higher reactivity of 1-octanol versus 2-ethyl-1-hexanol. The reaction is highly selective to aldehyde with little formation of carboxylic acid; autooxidation is inhibited. No base is required to activate the alcohol. The fast reactions appear to be related to the electron-acceptor nature of the polyoxometalate ligand that may also facilitate alcohol dehydrogenation in the absence of base. [source] A Novel Proline-Valinol Thioamide Small Organic Molecule for a Highly Enantioselective Direct Aldol ReactionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Bing Wang Abstract A new prolinethioamide compound 4, prepared from readily available natural amino acid L -proline and amino alcohol L -valinol, has been found to be an active catalyst for the direct aldol reaction of various aldehydes with acetone, cyclohexanone or cyclopentanone at 0,°C. Using only 2,mol% loading of this organocatalyst, the reaction could give high enantioselectivity with up to 96% enantiomeric excess for the reaction of 2-nitrobenzaldehyde with acetone. And as for the cyclohexanone, the excellent diastereoselectivity (anti/syn: 99/1) and enantioselectivity (99% ee) could be achieved when reacted with 3-nitrobenzaldehyde in water in the presence of this thioamide 4. This structurally simple catalyst is a highly efficient prolinethioamide derivative, and the terminal hydroxy group in this catalyst is a primary alcohol which is different from the previously reported prerequisite secondary or tertiary alcohol of prolinamides. Our results suggest a new strategy in the design of diversiform organic catalysts for direct asymmetric aldol reactions and related transformations. [source] Copper(II) Triflate as a Source of Triflic Acid: Effective, Green Catalysis of Hydroalkoxylation ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Mathieu J.-L. Abstract The hydroalkoxylation of dicyclopentadiene (DCPD) and norbornene (NB) with 2-hydroxyethyl methacrylate (HEMA) for the synthesis of industrially relevant monomers has been investigated with various metal-based Lewis acids and strong Brønsted acids. In the absence of other additives, copper(II) triflate is the most efficient catalyst system. Kinetics, electron spin resonance (ESR), catalyst poisoning and cross experiments indicate that triflic acid (TfOH) is the true active catalyst in these reactions. This in situ generation of TfOH occurs via reduction of Cu(OTf)2 by the olefin reagent (DCPD, NB). The copper ions present in the reaction mixture act as radical polymerization retardants, preventing polymerization of HEMA (which is observed with most other metal salts and strong Brønsted acids investigated), thus improving the selectivity and yield (up to 95%) for the desired products. These observations have led to the development of a highly effective green process, using bulk reagents (no solvent) and a cheap, metal-free catalyst system, based on TfOH and a phenolic radical inhibitor (2,5-di- tert -butylhydroxytoluene, BHT). [source] Silica-Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 2.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Activity, Recycling, Regeneration Abstract The catalytic activity of both supported and soluble molecular zirconium complexes was studied in the transesterification reaction of ethyl acrylate by butanol. Two series of catalysts were employed: three well defined silica-supported acetylacetonate and n -butoxy zirconium(IV) complexes linked to the surface by one or three siloxane bonds, (SiO)Zr(acac)3 (1) (SiO)3Zr(acac) (2) and (SiO)3Zr(O- n -Bu) (3), and their soluble polyoligosilsesquioxy analogues (c -C5H9)7Si8O12(CH3)2Zr(acac)3 (1,), (c -C5H9)7Si7O12Zr(acac) (2,), and (c -C5H9)7Si7O12Zr(O- n -Bu) (3,). The reactivity of these complexes were compared to relevant molecular catalysts [zirconium tetraacetylacetonate, Zr(acac)4 and zirconium tetra- n -butoxide, Zr(O- n- Bu)4]. Strong activity relationships between the silica-supported complexes and their polyoligosilsesquioxane analogues were established. Acetylacetonate complexes were found to be far superior to alkoxide complexes. The monopodal complexes 1 and 1, were found to be the most active in their respective series. Studies on the recycling of the heterogeneous catalysts showed significant degradation of activity for the acetylacetonate complexes (1 and 2) but not for the less active tripodal alkoxide catalyst, 3. Two factors are thought to contribute to the deactivation of catalyst: the lixivation of zirconium by cleavage of surface siloxide bonds and exchange reactions between acetylacetonate ligands and alcohols in the substrate/product solution. It was shown that the addition of acetylacetone to the low activity catalyst Zr(O- n- Bu)4 produced a system that was as active as Zr(acac)4. The applicability of ligand addition to heterogeneous systems was then studied. The addition of acetylacetone to the low activity solid catalyst 3 produced a highly active catalyst and the addition of a stoichiometric quantity of acetylacetone at each successive batch catalytic run greatly reduced catalyst deactivation for the highly active catalyst 1. [source] The First Catalytic Enantioselective Aldol-Type Reaction of Ethyl Diazoacetate to KetonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Fides Benfatti Abstract The aldol-type addition to ketones still represents a great challenge in asymmetric catalysis. Recently, the direct aldol reaction between the commercially available ethyl diazoacetate and aldehydes has attracted increasing attention. Ethyl diazoacetate is economical and allows further transformation of the aldol adduct obtained. We present a solution for the arduous, and not previously described, addition of diazoacetate to ketones. Our procedure employs commercially available norephedrine-derived ligands and dialkylzinc reagents [R2Zn: (diethylzinc, Et2Zn; dimethylzinc, Me2Zn)] as starting materials, therefore the active catalyst is prepared with a very straightforward methodology. Remarkably, the reaction gives good enantiomeric excesses with ,-halo ketones, a class of compounds that has not been commonly used in enolate addition. [source] Polynorbornene with pentafluorophenyl imide side chain groups: Synthesis and sulfonationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2010Arlette A. Santiago Abstract The mixtures of exo-endo -monomers and isomerically pure endo -monomers of N -pentafluorophenyl-norbornene-5,6-dicarboximide (2a) and N -phenyl-norbornene-5,6-dicarboximide (2b) were synthesized and polymerized via ring opening metathesis polymerization using bis(tricyclohexylphosphine) benzylidene ruthenium (IV) dichloride (I) and tricyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene] ruthenium dichloride (II). Ring opening metathesis polymerization of mixtures of exo-endo -monomers (2a) and (2b) and pure endo - 2b gave the corresponding high molecular weights poly(N -pentafluorophenyl-norbornene-5,6-dicarboximide) (3a) and poly(N -phenyl-norbornene-5,6-dicarboximide) (3b). The isomerically pure endo - 2a did not polymerize by I in these conditions, since I is the least active catalyst and endo - 2a is the least active monomer because of the intramolecular complex formation between the Ru active center and the fluorine atom of ring-opened endo - 2a on the one hand and steric hindrances caused by the pentafluorinated ring on the other. The quantitative hydrogenation of the polymer 3a, at room temperature and 115 bar, was achieved by a Wilkinson's catalyst. The new polynorbornene bearing highly fluorinated sulfonic acid groups (5) was obtained by the reaction of the hydrogenated poly(N -pentafluorophenyl-norbornene-5,6-dicarboximide) (4) with sodium 4-hydroxybenzenesulfonate dihydrate. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2925,2933, 2010 [source] Yttrium(III) complex as a highly active catalyst for lactide polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2006Linda M. Hodgson The synthesis, characterization, and X-ray crystal structure of a well-defined yttrium(III) amide complex with the bis(thiophosphinic amide) ligand is reported. The new complex exhibits high rates and good control for lactide polymerization. The polymerization kinetics and mechanism are studied under a range of different conditions, and these show that even under mild conditions this complex exhibits polymerization rates among the fastest known. [source] Novel cyclohexyl-substituted salicylaldiminato,nickel(II) complex as a catalyst for ethylene homopolymerization and copolymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004Junquan Sun Abstract The cyclohexyl-substituted salicylaldiminato,Ni(II) complex [O(3-C6H11)(5-CH3)C6H2CHN-2,6-C6H3iPr2]Ni(PPh3)(Ph) (4) has been synthesized and characterized with 1H NMR and X-ray structure analysis. In the presence of phosphine scavengers such as bis(1,5-cyclooctadiene)nickel(0) [Ni(COD)2], triisobutylaluminum (TIBA), and triethylaluminum (TEA), 4 is an active catalyst for ethylene polymerization and copolymerization with the polar monomers tert -butyl-10-undecenoate, methyl-10-undecenoate, and 4-penten-1-ol under mild conditions. The polymerization parameters affecting the catalytic activity and viscosity-average molecular weight of polyethylene, such as the temperature, time, ethylene pressure, and catalyst concentration, are discussed. A polymerization activity of 3.62 × 105 g of PE (mol of Ni h),1 and a weight-average molecular weight of polyethylene of 5.73 × 104 g.mol,1 have been found for 10 ,mol of 4 and a Ni(COD)2/4 ratio of 3 in a 30-mL toluene solution at 45 °C and 12 × 105 Pa of ethylene for 20 min. The polydispersity index of the resulting polyethylene is about 2.04. After the addition of tetrahydrofuran and Et2O to the reaction system, 4 exhibits still high activity for ethylene polymerization. Methyl-10-undecenoate (0.65 mol %), 0.74 mol % tert -butyl-10-undecenoate, and 0.98 mol % 4-penten-1-ol have been incorporated into the polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6071,6080, 2004 [source] Polymerization of Methyl Acrylate by a 2,6-Bis(2-benzimidazyl)pyridine Zirconium Dichloride/MAO Catalyst SystemMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2006Hyun Yong Cho Abstract Summary: A novel non-metallocene Zr(IV) complex bearing a bianionic form of the ligand 2,6-bis(2-benzimidazolyl)pyridine is synthesized. This Zr complex is an active catalyst for the polymerization of MA via coordination polymerization in the presence of methylaluminoxane MAO. The activity and MWD are increased as the polymerization temperature increases. The maximum activity is observed at Al/Zr molar ratio of 100 and the deactivation is shown above 100, resulting from an inactive bimetallic complex between catalyst and free TMA presented in MAO. Decrease in MWD is observed with higher MAO concentration due to its role in chain transfer during the chain propagation. The reaction of the ligand and catalyst synthesis. [source] Asymmetric hydrogenation ofo -Cresol andm -Cresol catalyzed by silica-supported methylcellulose,L-alanine,Pd complexPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2001Kai Huang Abstract Silica-supported methylcellulose,L-alanine,palladium complex (SiO2 -MC,LA,Pd) has been prepared and found to be a high optically active catalyst for asymmetric hydrogenation of o -cresol and m -cresol to give (S)-2-methylcyclohexanone and (R)-3-methylcyclohexanone, respectively, at 25,°C and under an atmospheric hydrogen pressure. The optical yields of (S)-2-methylcyclohexanone and (R)-3-methylcyclohexanone amounted to 91.5 and 68.5%, respectively, when optimum Pd content in SiO2 -MC,LA,Pd complex, reaction temperature and solvent were selected. SiO2 -MC,LA,Pd catalyst also has shown high stability. The optical yields for (S)-2-methylcyclohexanone and (R)-3-methylcyclohexanone were kept over 90 and 60%, respectively, when the catalyst was reused several times. Moreover, SiO2 -MC,LA,Pd complex is an economical catalyst. The methylcellulose is an abundant natural biopolymer and the procedure for preparation of the complex is very simple. Copyright © 2001 John Wiley & Sons, Ltd. [source] Hydroformylation , amidocarbonylation of androstene and pregnene derivatives ,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 11 2002Emese Nagy Abstract Androstene and pregnene derivatives were functionalized by amides with rhodium or binary rhodium,cobalt catalysts. Whereas the Rh,PPh3 catalyzed reaction results in the unsaturated amido-methylidene derivatives, the rapid hydrogenation of these compounds takes place in the presence of a basic PR3 ligand. Using a binary rhodium,cobalt system, amidocarbonylation of the steroids occurs with high chemo- and regio-selectivity. Our experiments did not support literature reports claiming the essential role of a bimetallic cluster as the active catalyst. Copyright © 2002 John Wiley & Sons, Ltd. [source] Dichloro-Bis(aminophosphine) Complexes of Palladium: Highly Convenient, Reliable and Extremely Active Suzuki,Miyaura Catalysts with Excellent Functional Group ToleranceCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2010Jeanne Abstract Dichloro-bis(aminophosphine) complexes are stable depot forms of palladium nanoparticles and have proved to be excellent Suzuki,Miyaura catalysts. Simple modifications of the ligand (and/or the addition of water to the reaction mixture) have allowed their formation to be controlled. Dichlorobis[1-(dicyclohexylphosphanyl)piperidine]palladium (3), the most active catalyst of the investigated systems, is a highly convenient, reliable, and extremely active Suzuki catalyst with excellent functional group tolerance that enables the quantitative coupling of a wide variety of activated, nonactivated, and deactivated and/or sterically hindered functionalized and heterocyclic aryl and benzyl bromides with only a slight excess (1.1,1.2,equiv) of arylboronic acid at 80,°C in the presence of 0.2,mol,% of the catalyst in technical grade toluene in flasks open to the air. Conversions of >95,% were generally achieved within only a few minutes. The reaction protocol presented herein is universally applicable. Side-products have only rarely been detected. The catalytic activities of the aminophosphine-based systems were found to be dramatically improved compared with their phosphine analogue as a result of significantly faster palladium nanoparticle formation. The decomposition products of the catalysts are dicyclohexylphosphinate, cyclohexylphosphonate, and phosphate, which can easily be separated from the coupling products, a great advantage when compared with non-water-soluble phosphine-based systems. [source] | |||||||||||||||||||||||||