Immobilized dimeric chiral Mn(III) salen complex on short channel ordered mesoporous silica as an effective catalyst for the epoxidation of non-functionalized alkenes

Chiral dimeric Mn(III) salen complex with 1R, 2R-(?)-diaminocyclohexane collar was immobilized on short channel large pore sized silica through a long linker of {(CH₂)₃–NH–melamine–piperazine} to investigate its performance in enantioselective epoxidation of chromenes, indene, styrene and cis β-methyl styrene in the presence of pyridine N-oxide (PyNO) as an axial base using aqueous NaOCl as an oxidant at 0 °C. The immobilized catalyst system showed high turnover frequency (TOF) and enantioselectivity for the smaller and bulkier alkenes like styrene, indene, 2,2-dimethylchromene and 6-cyano-2,2-dimethylchromene (ee up to 98%). These results are the best reported for heterogeneous catalyst under biphasic reaction conditions and were comparable to the dimeric Mn(III) salen system under homogeneous condition. The performance of the immobilized catalyst was retained for six reuse experiments. This protocol was extended to the synthesis of an antihypertensive drug (S)-Levchromakalim (ee 98%) at 1 g level.     

固载Ru基催化剂上二氧化碳加氢合成甲酸Ⅱ反应条件对催化剂性能的影响

The synthesis of formic acid from carbon dioxide and hydrogen using a silica immobilized ruthenium catalyst as precursor has been studied in different reaction conditions. The results revealed that the TOF （turn over frequency） of HCOOH achieved 1481.5 h^-1 on immobilized ruthenium catalyst near the critical pressure point of CO2 with H2 pressure of 4.0 MPa, reaction temperature of 80℃ and PPh3/Ru molar ratio of 6：1. The reaction activity of immobilized catalyst was higher than that of homogeneous catalyst, and the immobilized catalyst also offered the practical advantages such as easy separation and reuse.     

PEG-400-H2O as a green and recyclable medium for asymmetric hydrogenations of aromatic ketones catalyzed by RuCl2(TPPTS)2-(S,S)-DPENDS

PEG-400-H₂O was found to be a green and recyclable reaction medium for asymmetric hydrogenations of aromatic ketones catalyzed by a ruthenium achiral monophosphine complex RuCl₂(TPPTS)₂ [TPPTS: P(m-C₆H₄SO₃Na)₃] modified by (S,S)-DPENDS [disodium salt of sulfonated (S,S)-1,2-diphenyl-1,2-ethylene-diamine]. The acetophenone product was obtained with 86.3% ee under the optimized conditions. The resulting products can be easily separated from the catalyst by extraction with n-hexane. The catalyst immobilized in PEG-400-H₂O not only exhibits excellent activity and enantioselectivity, but also can be recycled and reused several times without a loss of activity or enantioselectivity.     

Electrostatic immobilisation of copper(I) and copper(II) bis(oxazolinyl)pyridine catalysts on silica: application to the synthesis of propargylamines via direct addition of terminal alkynes to imines

Copper(I) and copper(II) complexes of two bis(oxazolinyl)pyridines were immobilized on silica via electrostatic interactions. The catalytic activity of the immobilized catalysts in the direct addition of terminal alkynes to imines leading to propargylamines was investigated under a variety of reaction conditions. The performance of the immobilized catalysts compares very well with their homogeneous equivalents. When used in toluene, the catalysts could be recycled a number of times and maintained activity. This study is the first such report of the immobilization on silica in this manner of any bis(oxazolinyl)pyridine (pybox) complex.     

Cobalt(II) schiff base functionalized mesoporous silica as an efficient and recyclable chemoselective acetalization catalyst

Cobalt(II) Schiff base functionalized mesoporous silica was synthesized from covalent attachment via the introduction of Co(OAc)₂ to salicylaldimine functionalized mesoporous silica. The catalyst proved to be chemoselective one for the acetalization of aldehydes to the corresponding acetals in alcohol. The immobilized catalyst can be easily recovered and reused for at least ten reaction cycles without significant loss of its catalytic activity.     

Catalysis of hydrosilylation,part XXII: Polymer-protected immobilized platinum complex catalysts for gas-phase hydrosilylation of acetylene

A platinum catalyst (hexachloroplatinic acid dissolved in ethanol) was immobilized by anchoring via amine and mercapto groups to silica followed by formation of a polymer layer which protected the catalyst against leaching. These catalysts (A and B) as well as precatalysts (S_A-Pt, S_B-Pt) which were not protected by polymer were tested in the gas-phase hydrosilylation reaction of acetylene with trichlorosilane. The catalytic parameters (yield 80%, selectivity 100%) obtained under optimal conditions prove the advantage of catalyst A over 300 h reaction time by the flow method.     

Heterogenization of a chiral bis(oxazoline) catalyst by grafting onto silica

[reaction: see text] We report here the first heterogenization of a bis(oxazoline) ligand on an inorganic (silica) surface. The activity and enantioselectivity of this new material as a catalyst for the Diels-Alder reaction were checked, and it was shown that under certain conditions enantioselectivities similar to those of the homogeneous catalyst are reached. It was also shown that under these conditions the catalyst can be recycled without loss of activity or selectivity.     

Synthesis of trans-4,5-diaminocyclopent-2-enones from furfural catalyzed by Er(III) immobilized on silica

An efficient and simple method is described for the synthesis of trans-4,5-diaminocyclopent-2-enones via reaction of furfural and secondary amines, using ErCl₃·6H₂O immobilized on silica allowing an efficient catalyst reuse using n-butanol/n-hexane as the reaction media.     

Synthesis,Characterization and Catalytic Behaviour of Silica Supported Zinc Salicylaldimine Complex

Zinc salicylaldimine complex immobilized on silica gel was used as a promising catalyst for the transesterification reaction of dimethyl terephthalate (DMT) and ethylene glycol (EG).The catalyst was characterized by Fourier transform infra‐red spectroscopy (FT‐IR), thermogravimetric analysis (TGA) and atomic absorption spectroscopy (AAS). The product bis‐(2‐hydroxyethyl)terephthalate (BHET)was confirmed by mass and ¹H‐NMR studies. In comparison to zinc acetate i.e., homogeneous catalyst, a polymer supported catalyst showed better stability, catalytic activity and ease of separation from the reaction product. The catalyst can be reutilized during successive catalytic cycles.     

Heterogeneous asymmetric Diels–Alder reactions using a copper–chiral bis(oxazoline) complex immobilized on mesoporous silica

A chiral bis(oxazoline)–copper complex was immobilized onto mesoporous silica and the resulting heterogeneous catalyst was employed in asymmetric Diels–Alder reactions. Reactions using the catalyst exhibited good enantioselectivity of 78% enantiomeric excess and endo/exo-selectivity (17:1) better than the corresponding homogeneous reaction. The catalyst could be easily recovered and reused several times without significant loss of the remarkable reactivity, diastereoselectivity and enantioselectivity.     

Asymmetric hydrogenation of α,β-unsaturated ketones catalyzed by Ru–TPPTS–(S,S)-DPENDS complex in ionic liquids

The asymmetric hydrogenation of α,β-unsaturated ketones catalyzed by the achiral ruthenium monophosphine complex RuCl₂(TPPTS)₂ [TPPTS: P(m-C₆H₄SO₃Na)₃] modified by (S,S)-DPENDS [disodium salt of sulfonated (S,S)-1,2-diphenyl-1,2-ethylene-diamine] was investigated in ionic liquid [RMIM]Ts (1-alkyl-3-methylimidazolium p-methylphenylsulfonates, R = ethyl, butyl, octyl, dodecyl). Chemoselectivity of 100% and 75.9% ee were obtained for benzalacetone under the optimized conditions. The resulting products can be easily separated from the catalyst immobilized in ionic liquid [EMIM]Ts by extraction with n-hexane, while the catalyst can be reused seven times without the loss of catalytic activity and enantioselectivity. Especially, the addition of water can improve the performance of the catalyst.     

Optimized Immobilization Strategy for Dirhodium(II) Carboxylate Catalysts for C−H Functionalization and Their Implementation in a Packed Bed Flow Reactor

Herein we demonstrate a packed bed flow reactor capable of achieving highly regio- and stereoselective C−H functionalization reactions using a newly developed Rh₂(S-2-Cl-5-CF₃TPCP)₄ catalyst. To optimize the immobilized dirhodium catalyst employed in the flow reactor, we systematically study both (i) the effects of ligand immobilization position, demonstrating the critical factor that the catalyst-support attachment location can have on the catalyst performance, and (ii) silica support mesopore length, demonstrating that decreasing diffusional limitations leads to increased accessibility of the active site and higher catalyst turnover frequency. We employ the immobilized dirhodium catalyst in a simple packed bed flow reactor achieving comparable yields and levels of enantioselectivity to the homogeneous catalyst employed in batch and maintain this performance over ten catalyst recycles.     

Tethering of nickel(II) Schiff-base complex onto mesoporous silica: An efficient heterogeneous catalyst for epoxidation of olefins

A new hybrid catalyst has been prepared by tethering a nickel(II) Schiff-base complex via post-synthesis modification of mesoporous silica, MCM-41. The Schiff-base has been derived from salicylaldehyde and 3-aminopropyltriethoxysilane (3-APTES) which is chemically anchored on MCM-41 via silicon alkoxide route. The anchored Schiff-bases imposed a stable planar coordination geometry around the central nickel ions. The catalyst has been characterized by elemental analysis, FT-IR, UV-Vis, small angle X-ray diffraction (SAX) and transmission electron microscopy (TEM) studies. The SAX and TEM measurement showed the mesoporosity of the catalyst. The activity of the catalyst has been assessed in the epoxidation of olefins using tert-butyl-hydroperoxide (tert-BuOOH) as oxidant in heterogeneous condition. Immobilized nickel catalyst was found to be catalytically more active and selective compared to the similar type of nickel(II) complex as well as Ni(NO₃)₂·6H₂O in homogeneous media. The catalyst can be recycled and reused several times without significant loss of activity.     

Homogeneous and heterogeneous olefin epoxidation catalyzed by a binuclear Mn(II)Mn(III) complex

The synthesis and characterization of a binuclear carboxylated bridged manganese complex containing the heptadentate ligand N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)-2-ol-1,3-propanediamine (H₃bbppnol) is reported. This complex was characterized by elemental analysis; infrared, electronic (UV–vis) and EPR spectroscopy; and conductivity measurements. The complex was immobilized on silica by either adsorption or entrapment via a sol–gel route. The obtained solids were characterized by thermogravimetric analyses (TG and DSC), UV–vis and infrared spectroscopy, and X-ray diffraction. The catalytic performance of the binuclear manganese complex in epoxidation reactions was evaluated for both homogeneous and heterogeneous systems. The catalytic investigation revealed that the complex performs well as an epoxidation catalyst for the substrates cyclohexene (26–39%) and cyclooctene (29–74%). The solids containing the immobilized complex can be recovered from the reaction medium and reused, maintaining good catalytic activity.     

Copper(II) Schiff Base Complex Immobilized on Superparamagnetic Fe3O4@SiO2 as a Magnetically Separable Nanocatalyst for Oxidation of Alkenes and Alcohols

A new heterogeneous catalyst containing a copper(II) Schiff base complex covalently immobilized on the surface of silica‐coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂‐Schiff base‐Cu(II)) was synthesized. Characterization of this catalyst was performed using various techniques. The catalytic potential of the catalyst was investigated for the oxidation of various alkenes (styrene, α‐methylstyrene, cyclooctene, cyclohexene and norbornene) and alcohols (benzyl alcohol, 3‐methoxybenzyl alcohol, 3‐chlorobenzyl alcohol, benzhydrol and n ‐butanol) using tert ‐butyl hydroperoxide as oxidant. The catalytic investigations revealed that Fe₃O₄@SiO₂‐Schiff base‐Cu(II) was especially efficient for the oxidation of norbornene and benzyl alcohol. The results showed that norbornene epoxide and benzoic acid were obtained with 100 and 87% selectivity, respectively. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in catalytic activity were other advantages of this catalyst     

Chlorotitanium (IV) tetradentate Schiff‐base complex immobilized on inorganic supports: Support type and other factors having effect on ethylene polymerization activity

A titanium complex with [O,N,N,O]‐type tetradentate Schiff base (LTiCl₂), never used before in polymerization of olefins, was immobilized on silica‐ and magnesium‐type carriers, and it was used in ethylene polymerization. The conducted research revealed that the catalytic properties of the complex LTiCl₂ supported on those carriers were different for both the catalytic systems studied, and simultaneously they turned out different from those of the unsupported system. The supported catalysts require the use of Me₃Al, Et₃Al, or MAO as the activator to be able to offer high catalytic activities, whereas Et₂AlCl is needed for the nonsupported catalyst. This finding, together with considerable changes in polymerization yields and in properties of polymers versus composition of the catalytic system, suggest that there are different types of active sites in the studied catalysts. The catalyst anchored on the carrier produced in the reaction of MgCl₂·3.4EtOH with Et₂AlCl is definitely the most active one within the support systems tested. Its activity remarkably increases with the increasing reaction temperature. Moreover, that catalyst does not undergo deactivation over the studied period of time, irrespective of the type of the activator used and of the process temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4811–4821, 2009     

Palladium nanoparticles supported on poly (N-vinylpyrrolidone)-grafted silica as new recyclable catalyst for Heck cross-coupling reactions

Novel catalytic system based on palladium nanoparticles supported on poly (N-vinylpyrrolidone) (PVP) grafted silica was prepared. Aminopropylsilica was reacted with acryloyl chloride to form acrylamidopropylsilica, and onto this functionalized silica vinylpyrrolidone monomer was polymerized by free-radical polymerization. The complexation of PVP-grafted silica with PdCl₂ was carried out to obtain the heterogeneous catalytic system. X-ray diffraction (XRD) technique and transmission electron microscopy (TEM) image showed that palladium dispersed through the support in nanometer size. This catalytic system exhibited excellent activity in cross-coupling reactions of aryl iodides, bromides and also chlorides with olefinic compounds in Heck-Mizoraki reactions in short reaction time and high yields. Elemental analysis of Pd by inductively coupled plasma (ICP) technique and hot filtration test showed low leaching of the metal into solution from the supported catalyst. The catalyst can be reused several times in repeating Heck reaction cycles without considerable loss in its activity.     

Stereoselective Synthesis and Diels-Alder Reactions of (Z)- and (E)-1,2-bis(Phenylthio)-1,3-Butadiene

Bromination of 3-phenylthio-2-sulfolene (2) with N-bromosuccinimide gave 2-bromo-3-phenylthio-2-sulfolene (3) which was converted mainly to 2,3-bis(phenylthio)-2-sulfolene (4) by treatment with sodium phenylthiolate. Thermal desulfonylation of 4 at different temperatures in the presence of a base (DBU) yielded stereoselectively the (Z)- and (E)-1,2-bis(phenylthio)-1,3-butadiene (6). These two geometric isomers could be thermally interconverted. The Diels-Alder reactions of 6 were also investigated. Only the (Z)-diene 6a could undergo the Diels-Alder reaction; the (E)-diene 6b was in situ converted to the Z isomer before undergoing (he Diels-Alder reaction. The reaction of 6a with N-phenylmaleimide gave the cycloaddition product 7 with complete endo selectivity, but under daylight or during chromatography it readily underwent a thioallylic rearrangement to yield 8 with inversion of configuration. The cycloaddition of 6a with methyl acrylate proceeded regiospecifically, but generating a mixture of endo and exo isomers. The endo/exo ratio could be increased by using ZnCl₂ as the catalyst.     

Highly regio- and stereo-selective copolymerization of CO2 with racemic propylene oxide catalyzed by unsymmetrical (S,S,S)-salenCo(III) complexes

A novel unsymmetrical (S,S,S)-salen ligand bearing a derived chiral-BINOL was synthesized by the reaction of the condensation product of (1S,2S)-1,2-diaminocyclohexane mono(hydrogen chloride) with 3-adamanyl-5-tert-butyl-2-hydroxybenzaldehyde and 3-formoyl-2-hydroxy-2′-alkyloxy-1,1′-binaphthyl, which originated from (S)-1,1′-bi-2-naphthol via a four-step reaction. The cobalt complexes of this ligand, in conjunction with a nucleophilic cocatalyst, exhibited excellent activity in catalyzing asymmetric, regio- and stereo-selective copolymerization of CO₂ and racemic propylene oxide. The highest record of kinetic resolution coefficient (K _rel) was obtained with the use of binary catalyst system consisting of (S,S,S)-salenCo(III) complex 1c and bulky bis(triphenylphosphine)-iminium chloride (PPNCl). The resulting poly(propylene carbonate)s have more than 99% carbonate linkages and more than 98% head-to-tail content.     

负载型双噁唑啉催化剂上的不对称Diels-Alder反应

 分别以乙烷桥键磺酸官能化的有机-无机杂化介孔材料、十二钨磷酸铯、活化硅胶以及SBA-15为载体,通过非共价键作用制备了负载型双噁唑啉催化剂,并将该催化剂用于催化3-((E)-2-丁烯酰基)-1,3-噁唑啉-2-酮和环戊二烯的不对称Diels-Alder反应. 研究表明,催化剂的性能取决于载体本身以及载体表面阴离子的性质. 以SBA-15为载体时产物的对映体选择性较低,可归因于载体表面较低的羟基浓度.