Insoluble Catalyst Research Articles

Soluble and Supported Molecular CoIII Catalysts for the Regioselective Ring‐Opening of 1,2‐Epoxyhexane with Methanol

AbstractThe regioselective ring‐opening of 1,2‐epoxyhexane with methanol as a nucleophile is studied using an array of different molecular CoIII catalysts, specifically trans‐CoIII‐salen‐X (1‐X; X=Cl−, OTs−, BF4−, SbF6−, PF6−), cis/trans‐CoIII‐salen‐SbF6, CoIII‐salphen‐SbF6, and CoIII‐porphyrin‐SbF6. Catalytic studies show the nature of the ligand and counterion both play a significant role in influencing reaction rates, and to a lesser extent, the regioselectivity of the ring‐opening reaction, with CoIII‐porphyrin‐SbF6 as the most active and CoIII‐salphen‐SbF6 the least active soluble molecular catalysts. Unlike in the classical epoxide hydrolytic kinetic resolution reaction, non‐coordinating, non‐nucleophilic counterions proved most effective, and trans‐CoIII‐salen‐Cl, which gives very high initial rates in hydrolytic kinetic resolution, shows very low activity in epoxide ring‐opening with methanol. Supported soluble and insoluble unsymmetrical trans‐CoIII‐salen‐X catalysts are, thus, synthesized to evaluate cooperativity and stability of the CoIII‐salen species towards epoxide ring‐opening with methanol. Soluble supported trans‐CoIII‐salen‐X (X=SbF6 and OTs) shows better activity and selectivity in the title reaction than monomeric trans‐CoIII‐salen‐SbF6 catalyst because of the cooperativity introduced through the catalyst design. The stability of insoluble catalysts is evaluated by catalytic recycling experiments. The supported insoluble catalysts successfully are recovered and reused up to 5 times, showing reduced activity but unchanged selectivity after each cycle. Deactivation is attributed to several different causes based on elemental analysis and UV/Vis spectroscopic analysis of the used catalysts, with counterion and cobalt loss playing major roles.

ChemInform Abstract: An Effective and Catalytic Oxidation Using Recyclable Fluorous IBX.

AbstractThe insoluble catalyst can easily be recovered by filtration and reused for at least five times without significant loss of activity.

Asymmetric cyanosilylation of ketones catalyzed by recyclable polymer-supported copper(II) salen complexes

Various ketones have undergone asymmetric trimethylsilylcyanation at room temperature with (CH 3) 3SiCN (TMSCN) in the presence of a chiral-supported Cu(salen) complex and Ph 3PO as the catalyst. Aromatic, aliphatic, and heterocyclic ketones have been converted into the corresponding cyanohydrin trimethylsilyl ethers in 83−96% yields with 52−84% ee. Several factors concerning the reactivity and enantioselectivity have been discussed. A double activation where Cu(salen) plays the role of Lewis acid and Ph 3PO acts as a Lewis base is reported. Poly(ethylene glycol) monomethyl ether (MeO-PEG) has been used as a soluble support while Janda Jel (JJ) and Merrifield (MF) resins served as insoluble supports. Each polymer is linked to the salen catalyst through a glutarate spacer. The soluble catalysts were recovered by precipitation with a suitable solvent while the insoluble catalysts were simply filtered from the reaction mixture. The Janda Jel-attached Cu(salen) catalyst could be used for five cycles with the retention of efficiency and the Merrifield-bound Cu(salen) catalyst was found to loose activity with each use.

Continuous‐Flow CH Borylation of Arene Derivatives

AbstractA new continuous‐flow system for CH borylation has been developed. An insoluble catalyst prepared from chloro(1,5‐cyclooctadien)iridium(I) dimer and 2,2′‐bipyridine‐4,4′‐dicarboxylic acid in the presence of bis(pinacolato)diboron exhibited high reactivity under continuous‐flow processing without the loss of expensive iridium metal.

Biodiesel production using heteropoly acid-derived solid acid catalyst H 4PNbW 11O 40/WO 3–Nb 2O 5

A heteropoly acid-derived solid acid catalyst, H 4PNbW 11O 40/WO 3–Nb 2O 5 calcined at 773 K (HPNbW/W-Nb), showed a higher catalytic activity for transesterification between triolein and ethanol into ethyloleate compared to the activities of conventional solid acid catalysts. The HPNbW/W-Nb was insoluble to the reaction mixture, while such heteropoly acids as H 4PNbW 11O 40 and H 3PW 12O 40 showed high activities but were dissolved into the reaction mixture. The activity was sensitive to calcination temperature, and calcination around 773 K provided a highly active catalyst. The reaction rate showed the maximum at 10–30 of the ethanol/triolein molar ratio. The activity was observed in the co-presence of water and oleic acid. The reaction rate was high when methanol was used in place of ethanol. In a fixed-bed continuous-flow reaction, its potential as an insoluble catalyst is suggested by its stable activity during at least 4 days of the reaction.

Polymer and Silica Supported Tridentate Schiff Base Vanadium Catalysts for the Asymmetric Oxidation of Ethyl Mandelate – Activity, Stability and Recyclability

AbstractHomogeneous tridentate Schiff base vanadium catalysts derived from salicylaldehydes and tert‐leucinol or tert‐leucine are known to be excellent catalysts for the asymmetric oxidation of α‐hydroxy esters including ethyl mandelate. Herein, new analogous supported, semi‐soluble and insoluble catalysts are synthesized and their activities relative to the homogeneous catalyst are reported. The new catalysts are characterized by 1H and 13C NMR spectroscopy, mass spectrometry (EI, ESI, FAB), X‐ray crystallography, elemental analysis, gel permeation chromatography (GPC), Fourier transform infrared (FT‐IR) spectroscopy, and nitrogen physisorption. The effects of support material, synthesis procedure, and reaction solvent are examined to probe the utility of these catalysts. Linear poly(styrene) supported catalysts are partially soluble under the reaction conditions, and it is shown that the soluble species contribute significantly to the catalytic reactivity. Insoluble catalysts based on the same vanadyl complexes supported on cross‐linked poly(styrene) resin or mesoporous silica allow for catalyst recovery and recycle, showing equivalent selectivities over multiple reaction cycles. The mesoporous silica supported catalyst exhibits greater selectivity than the analogous homogeneous and polymer supported catalysts. Rigorous recycle studies show a loss of activity in each recycle, which is attributed to the decomposition of some portion of the vanadyl complexes in each cycle.

Selective Oxidation of Benzyl Alcohol by Heteropolytungstate as Reaction-Controlled Phase-Transfer Catalyst with Hydrogen Peroxide

Abstract The catalytic oxidation of benzyl alcohol to benzaldehyde was studied using heteropolytungstates as reaction-controlled phase-transfer catalysts with 35% aqueous H2O2 as oxidant. Under optimal conditions, 95.0% conversion of benzyl alcohol based on H2O2 and over 99% selectivity of benzaldehyde was obtained with [C7H7N(CH3)3]9PW9O34 as catalyst. In this system, once the H2O2 was consumed, the catalyst could be recovered from the system easily as a solid deposit. The catalysts were characterized by FT-IR, 31P NMR, XRD, and TGA, and the results indicated that the insoluble catalyst [C7H7N(CH3)3]9PW9O34 formed a soluble active species [C7H7N(CH3)3]3[(PO4){WO(O2)2}4] under the action of H2O2; the structure of the fresh catalyst was maintained well after the reaction. The results of catalyst recycling showed that this catalyst exhibits good stability. The effects of various reaction factors, such as solvent and the amount of H2O2 used, were studied.

Heterogeneous degradation of chitosan with H 2O 2 catalysed by phosphotungstate

Phosphotungstate (PTA), an insoluble catalyst synthesized with phosphotungstic acid (PWA) and chitosan in acidic reaction system by electrostatic attraction. The catalyst was characterized by DRS and FTIR spectra. Under the catalysis of PTA, the heterogeneous degradation of chitosan with H 2O 2 was achieved. The effect of volume of H 2O 2, dosage of catalyst, reaction temperature and time on the degradation was discussed by orthogonal tests. The experimental results show that chitosan can be effectively degradated with H 2O 2 under the catalysis of PTA. The catalyst, PTA, may have a promising application in oxidative degradation of polymer.

Catalyst Solubility and Experimental Determination of Equilibrium Constants for Heterogeneous Atom Transfer Radical Polymerization

The solubilities of heterogeneous atom transfer radical polymerization (ATRP) catalysts are determined for the first time and used to calculate previously unquantified ATRP equilibrium constants (KATRP). These new data are essential for understanding, modeling, and designing ATRP processes with low catalyst concentrations. KATRP values for CuIBr/1,1,4,7,10,10-hexamethyltriethylenetetramine (CuIBr/HMTETA) and CuIBr/N,N,N‘,N‘,N‘ ‘-pentamethyldiethylenetriamine (CuIBr/PMDETA) are 8.66 × 10-6 and 1.44 × 10-6, respectively. The limited solubility of the CuIBr/HMTETA catalyst explains why large reductions in metal salt concentration can be made without affecting polymerization rates. Catalyst solubility and polymerization rate increase with ligand concentration. In contrast, increasing the metal salt concentration in excess of the ligand's causes a drop in catalyst solubility. This unexpected observation is attributed to the formation of insoluble catalyst networks (gels). The solubility data point to differences in the ionic character of the catalyst complexes formed. The following solubility trend is observed at ATRP conditions (toluene, 90 °C): CuIBr/PMDETA ≫ CuIIBr2/PMDETA > CuIIBr2/HMTETA > CuIBr/HMTETA.

Electropolymerized Cr–salen complexes for the heterogeneous asymmetric hetero Diels-Alder reaction

New electropolymerized chiral salen–chromium complexes have been successfully used as heterogeneous catalysts for the asymmetric hetero Diels-Alder reaction. These insoluble catalysts were reused up to six times affording the expected products with unchanged enantioselectivity along the recycling procedure. Promising attempts to use these catalysts in a multi-substrate procedure are described.

Synthesis and characterization of novel bead-shaped insoluble polymer-supported tri-site phase transfer catalyst and its efficiency in N-alkylation of pyrrole

Abstract A new bead-shaped insoluble polymer-supported multi-site (tri-site) phase transfer catalyst (PS-MPTC) viz., polymer-supported 4-(2,2,2-tris[triethylammoniummethylene chloride]-1-hydroxy ethyl) phenylether (PSTTEACHPE) has been synthesized by following a simplified procedure. Initially, polystyrene-based cross-linked beads was prepared by allowing the reaction using 2% divinylbenzene (as a cross linking monomer), 25% vinylbenzyl chloride (as a functional monomer) and styrene (as supporting monomer) to proceed through a suspension copolymerization method. The obtained terpolymer beads containing pendant benzyl chloride groups were condensed with 4-(2,2,2-tris[triethylammonium methylene chloride]-1-hydroxy ethyl) phenol, followed by quaternization using triethylamine, resulting in the formation of polymer-supported 4-(2,2,2-tris[triethylammoniummethylene chloride]-1-hydroxy ethyl) phenyl ether (PSTTEACHPE). Then the presence of tri-active site in PSTTEACHPE was examined by FT-IR, 1 H NMR, 13 C NMR, [chloride ion] and SEM analyses. The comparative results of [chloride ion] and the peak intensity of C–N stretching (quaternary onium group) in FT-IR were found to increased three fold in PSTTEACHPE on comparing with their similar types of polymer-supported bead-shaped single-site PTC (PS-BSPTC); thus we confirmed the presence of three active sites. The surface morphology study through SEM shows that the PSTTEACHPE is heterogeneous in nature with tiny nodules; whereas the single-site PS-BSPTC shows smooth homogeneous nature; this is an another piece of evidence for the availability of more numbers of active sites in PSTTEACHPE. Further, the catalytic efficiency of this new PSTTEACHPE was ascertained by N -alkylation of pyrrole with benzylchloride using 30% (w/v) aqueous sodium hydroxide at 60 °C. The pseudo-first order rate constants were calculated by following the disappearance of pyrrole through gas chromatography. The observed rate constants were found to be three-fold higher for PSTTEACHPE than with PS-BSPTC, which again confirmed the presence of three active-sites. Investigations were also made on kinetic variables such as stirring speed, [substrate], [catalyst], [NaOH] and temperature; it is observed that each variable is influenced the rate of reaction. From the Arrhenius plot, the activation energy and thermodynamic parameters were evaluated as 12.44, −7.99, 10.99 and 13.25 kcal mol −1 for E a , Δ S # , Δ H # and Δ G # respectively. Based on the observed kinetic and thermodynamic results, an interfacial mechanism was proposed for the N -alkylation of pyrrole.

Studies on the structural change of a reaction-controlled phase-transfer [π-C 5H 5NC 16H 33] 3{PO 4[WO 3] 4} catalyst during the selective oxidation of cyclopentene to glutaric acid with aqueous H 2O 2

The selective oxidation of cyclopentene to glutaric acid (GAC) with aqueous hydrogen peroxide was carried out over a reaction-controlled phase-transfer catalyst—[π-C 5H 5NC 16H 33] 3{PO 4[WO 3] 4}. The high GAC yield of 83.1% was obtained on the fresh catalyst, while a much higher GAC yield of 98.8% was obtained over the recovered catalyst. The fresh catalyst, the one under reaction conditions and the recovered ones were all characterized by TG, FT-IR, Raman and 31P NMR spectroscopy. It is interesting to find that the atomic content of tungsten and phosphorous as well as the molecular structure of the fresh catalyst all change after the reaction. 31P NMR results reveal that under the treatment with high concentration hydrogen peroxide the insoluble catalyst can degrade into smaller and active species, which is soluble in the reaction mixture and can transfer oxygen to the C C bond, resulting in the selective cleavage of cyclopentene to glutaric acid. After the complete consumption of hydrogen peroxide, the smaller and active tungsten species will polymerize into (PW 11O 39) 7− and (PW 12O 40) 3− with stable Keggin structure by forming W O c W (edge-sharing) bond. These compounds are insoluble and will precipitate from the reaction mixture after the reaction when hydrogen peroxide is used up, making it much convenient for recovering and reusing.

Atom transfer radical polymerization of methyl methacrylate at ambient temperature using soluble Cu(I) complex catalysts formed with mixed ligands of multidentate amines and halide ions

AbstractAn Erratum has been published for this article in J Polym Sci Part A: Polym Chem (2004) 42(19) 5030.The addition of soluble quaternaryammonium halides (QX) in catalytic amounts takes into solution CuX/pentamethyldiethylenetriamine (PMDETA) complex (X = Cl, Br) in methyl methacrylate (MMA). The soluble catalyst complex provided much better control of the polymerization of MMA at ambient temperature than did the insoluble catalyst formed in the absence of QX, with CuCl/PMDETA/Aliquat® 336 (AQCl) proving to be superior to the CuBr/PMDETA/Bu4NBr catalyst system. The effect was independent of the size of the quaternaryammonium ion. Also, the presence of Cl in the catalyst–QX combination either as CuCl or as QCl was enough to give much better control than that provided by a wholly Br‐based system. Among the various initiators used, that is, ethyl 2‐bromoisobutyrate (EBiB), methyl 2‐bromopropionate (MBP), 1‐phenylethyl bromide (PEBr), and p‐toluenesulfonyl chloride (pTsCl), only EBiB gave a satisfactory result. With MBP and PEBr the initiation was slower than the propagation, whereas with pTsCl the initiation was very fast, so that instantaneous termination occurred. The living nature of the polymers was shown by block copolymer preparation. It has been suggested that some of the added halide ions entered into the coordination spheres of Cu(I) and Cu(II), leading to their improved solubility and stronger deactivation by the Cu(II) complex. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4132–4142, 2004

Highly Active Catalyst for the Heterogeneous Suzuki—Miyaura Reaction: Assembled Complex of Palladium and Non‐Cross‐Linked Amphiphilic Polymer.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A spectroscopic study on the reaction-controlled phase transfer catalyst in the epoxidation of cyclohexene

Abstract The epoxidation of cyclohexene with hydrogen peroxide in a biphase medium (H 2 O/CHCl 3 ) was carried out with the reaction-controlled phase transfer catalyst composed of quaternary ammonium heteropolyoxotungstates [π-C 5 H 5 N(CH 2 ) 15 CH 3 ] 3 [PW 4 O 16 ]. A conversion of about 90% and a selectivity of over 90% were obtained for epoxidation of cyclohexene on the catalyst. The fresh catalyst, the catalyst under reaction conditions and the used catalysts were characterized by FT-IR, Raman and 31 P NMR spectroscopy. It appears that the insoluble catalyst could degrade into smaller species, [(PO 4 ){WO(O 2 ) 2 } 4 ] 3− , [(PO 4 ){WO(O 2 ) 2 } 2 {WO(O 2 ) 2 (H 2 O)}] 3− , and [(PO 3 (OH)){WO(O 2 ) 2 } 2 ] 2− after the reaction with hydrogen peroxide and becomes soluble in the CHCl 3 solvent. The active oxygen in the [W 2 O 2 (O 2 ) 4 ] structure unit of these soluble species reacts with olefins to form the epoxides and consequently the corresponding WObW (corner-sharing) and WOcW (edge-sharing) bonds are formed. The peroxo group [W 2 O 2 (O 2 ) 4 ] can be regenerated when the WObW and WOcW bonds react with hydrogen peroxide again. These soluble species lose active oxygen and then polymerize into larger compounds with the WObW and WOcW bonds and then precipitate from the reaction solution after the hydrogen peroxide is consumed up. Part of the used catalyst seems to form more stable compounds with Keggin structure under the reaction conditions.

Highly active catalyst for the heterogeneous Suzuki-Miyaura reaction: assembled complex of palladium and non-cross-linked amphiphilic polymer.

An assembled insoluble catalyst, PdAS, prepared from palladium ((NH4)2PdCl4 (1)) and non-cross-linked amphiphilic copolymer poly(N-isopropylacrylamide-co-4-diphenylstyrylphosphine) (2) was developed. It was found that PdAS is an excellent catalyst for the Suzuki-Miyaura reaction on three points: (1) The use of 8 x 10(-7) to 5 x 10(-4) mol equiv of PdAS afforded the coupling products efficiently after easy workup, with the turnover number reaching up to 1,250,000. (2) The catalyst was reusable many times without loss of catalytic activity. (3) PdAS showed good stability in any reaction medium (i.e., water or aqueous or anhydrous organic solvents). Analytical study of PdAS indicates that the phosphines in 2 coordinate to palladium to form PdCl2(PPh2Ar)2 species.

Synthesis of Enantiopure 1,2-Diamine Attached to Cross-Linked Polystyrene and Its Application to an Insoluble Catalyst for Asymmetric Hydrogenation.

A novel enantiopure 1,2-diamine (5) having two phenolic hydroxy groups was attached into chloromethylated polystyrene through benzyl ether linkage, which was used as a chiral ligand of the catalyst in asymmetric hydrogenation of acetophenone.

Supported ruthenium nanoparticles on polyorganophosphazenes: preparation, structural and catalytic studies

Supported Ru nanoparticles on a number of polyorganophosphazenes were prepared and tested for the hydrogenation of unsaturated compounds. The complex Ru(η 6-cycloocta-1,3,5-triene)(η 4-cycloocta-1,5-diene) was found to be a suitable precursor to deposit metallic nanoparticles on polyorganophosphazenes; upon the removal of cycloolefin ligands under hydrogen atmosphere, highly dispersed metal particles on the polymeric support can be obtained. Ru on polydimethylphosphazene was found to be an active catalyst for the hydrogenation of a wide range of unsaturated substrates (olefins, carbonyl compounds and aromatic compounds) under mild conditions. Polyorganophosphazenes are interesting in their ability to act as either soluble or insoluble catalyst supports, depending upon the dispersing liquid; thus, it is possible to operate in heterogeneous phase as well as in homogeneous phase. The reaction in homogeneous phase can be performed in environmental-friendly solvents such as alcohols and water. The catalyst exhibits high stability towards agglomeration. No significant change in the ruthenium nanoparticles surface as well as catalyst activity was observed.

An Efficient Heterogeneous Heck Reaction Promoted by a New Assembled Catalyst of Palladium and Non‐Cross‐Linked Amphiphilic Polymer.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of enantiopure 1,2-diamine attached to cross-linked polystyrene and its application to an insoluble catalyst for asymmetric hydrogenation

A novel enantiopure 1,2-diamine ( 5 ) having two phenolic hydroxy groups was attached into chloromethylated polystyrene through benzyl ether linkage, which was used as a chiral ligand of the catalyst in asymmetric hydrogenation of acetophenone.