Alkoxide Catalyst Research Articles

Quantitative Analysis of the Chiral Amplification in the Amino Alcohol-Promoted Asymmetric Alkylation of Aldehydes with Dialkylzincs

Asymmetric reaction of dimethylzinc and benzaldehyde in the presence of (2S)-3-exo-(dimethylamino)isoborneol [(2S)-DAIB] exhibits unusual nonlinear phenomena. The enantiomeric purity of the product is much higher than that of the chiral source, DAIB, while the rate of the enantioselective catalysis decreases considerably as the enantiomeric excess (ee) of DAIB is lowered. Such effects originate from the reversible homochiral and heterochiral interaction of the coexistent enantiomeric zinc amino alkoxide catalysts which are formed from dimethylzinc and (2S)- and (2R)-DAIB. The thermodynamics of the five-component equilibration between the two monomers and three dimers, when coupled with the kinetics of the alkylation, strongly affects the extent of enantioselectivity and the reaction rate of the alkylation reaction. The overall profile of the nonlinear effects has been clarified mathematically using experimentally available parameters, viz., the equilibrium constants of the dimer/monomer conversion and the...

Asymmetric Kharasch Reaction: Catalytic Enantioselective Allylic Oxidation of Olefins Using Chiral Pyridine Bis(diphenyloxazoline)−Copper Complexes and tert-Butyl Perbenzoate,

Copper complexes of chiral pyridine bis(diphenyloxazoline)-type ligands have been studied as catalysts for the enantioselective allylic oxidation of olefins. Using 2.5−5 mol % of these chiral catalysts and tert-butyl perbenzoate as oxidant, optically active allylic benzoates were obtained in up to 86% ee. A variety of copper salts was studied under different conditions and in different solvents. Acetone was found to be a superior solvent for the reaction. Use of phenylhydrazine in conjunction with the chiral copper complex played a crucial role in increasing the rate of the reaction. Use of 4 A molecular sieves increased the optical yield of product in almost every case.

Ruthenium colloids: A new catalyst for alkane oxidation by tBHP in a biphasic water-organic phase system

Efficient and highly selective conversion of cyclooctane into cyclooctanone is obtained under pure biphasic conditions through t-butylhydroperoxide activation by the in situ formation of colloidal ruthenium species arising from RuCl 3, 3H 2O. Model extension experiments to other cycloalkanes are also discussed.

98/01745 Process and high-permeability catalyst for the partial oxidation of alkanes: Goetsch, D. A. and Schmidt, L. D. U.S. US 5,654,491 (Cl. 568-469.9; C07C27/10), 5 Aug 1997, Appl. 598,920, 9 Feb 1996, 13 pp

98/01745 Process and high-permeability catalyst for the partial oxidation of alkanes: Goetsch, D. A. and Schmidt, L. D. U.S. US 5,654,491 (Cl. 568-469.9; C07C27/10), 5 Aug 1997, Appl. 598,920, 9 Feb 1996, 13 pp

On the nature of selective olefin oxidation catalysts derived from molybdate- and tungstate-intercalated layered double hydroxides

Catalysts derived from Mg 2Al layered double hydroxides (LDHs) intercalated by polyoxometalates (POMs) of molybdenum and tungsten have been previously reported to exhibit substrate shape selectivity in condensed phase olefin oxidations. On the basis of X-ray powder diffraction, Raman spectroscopy, and nitrogen adsorption studies of these and related Zn 2Al-LDH-POM systems, the present work elucidates the catalyst precursors in terms of mixtures of salt-like and interlayered LDH phases containing Mo 7O 24 6− and W 7O 24 6−. Under the conditions used to dry the precursors prior to catalysis (120°C), the LDH components are transformed into layered decomposition products that act as the active catalysts. Substrate selectivity based on the preferred access to the intragallery sites of pillared LDH phases is precluded under catalytic conditions. Even a structurally stable Zn 2Al H 2W 12O 40 6−-LDH catalyst lacks the intragallery microporosity needed for shape selective substrate access to intragallery active sites under condensed phase reaction conditions. Other factors, perhaps selective adsorption based on substrate polarity, are responsible for the observed selectivity.

ChemInform Abstract: Vanadium‐Substituted MCM‐41 Zeolites as Catalysts for Oxidation of Alkanes with Peroxides.

AbstractChemInform 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.

ChemInform Abstract: Cu(OTf)2 ‐ DBN/DBU Complex as an Efficient Catalyst for Allylic Oxidation of Olefins with tert‐Butyl Perbenzoate.

AbstractChemInform 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.

Polyferroorganosiloxanes as catalysts of oxidation processes

Polyferroorganosiloxanes were studied as catalysts for homogeneous oxidation of alkanes by hydrogen peroxide tinder mild conditions. In the oxidation of cyclohexane the catalysts are characterized by high efficiency (conversion of hydrogen peroxide is 25%) and stability Kip to 80 cycles per gat NJ The min product of the oxidation W do presence a 2,4,6-tri-tert-btitylphenol is cyclohexanol (tip to 35% per H2O2).

Iron–Phthalocyanine Immobilized on Activated Carbon Black: A Selective Catalyst for Alkane Oxidation

Carbon black is tested as a support for iron–phthalocyanine within the frame of the oxidation of hydrocarbons witht-butylhydroperoxide as oxygen donor. The increased hydrophobicity of the carrier surface, with respect to zeolite Y, changes the adsorption behavior of the components in the reaction mixture towards the alkane. A major improvement in the oxidation conversion and efficiency of cyclohexane has been established. Furthermore, the kinetic isotope effect and the reactivity order of secondary and tertiary carbon atoms measured with adamantane provide evidence for an “oxygen rebound” reaction mechanism, a non-free-radical oxidation pathway where the metallo-complex is responsible for the hydrogen abstraction.

Cu(OTf) 2 - DBN/DBU complex as an efficient catalyst for allylic oxidation of olefins with tert-butyl perbenzoate

Olefins, on treatment with tert-butyl perbenzoate in the presence of a catalytic amount of a complex of Cu(OTf) 2 and chelating ligands such as DBN and DBU gave allylic benzoates under milder conditions. A variety of olefins were tested in the reaction.

Mixed ligand complexes of chromium(III) and iron(III): synthesis and evaluation as catalysts for oxidation of olefins

The mixed ligand complexes Cr III(dpa)(L)Cl and Fe III(dpa)(L)(H 2O) n Cl (where dpa = dipicolinic acid, l = ethylenediamine, 2,2-bipyridine or 1,10-phenanthroline, n = 1 or 2) were synthesized and characterized by elemental analysis and spectral, magnetic, conductance and electrochemical studies. The complexes were evaluated for their activity as catalysts for the epoxidation of olefins. The chromium complexes catalyzed epoxidation of olefins, viz., norbornene, cis-cyclooctene, styrene and cyclohexene with iodosylbenzene, to give corresponding epoxides. Oxidation of cyclohexene gave allylic oxidation products besides the epoxide. The iron complexes were nearly inactive as epoxidation catalysts under these conditions. Spectrophotometric and electrochemical measurements were used to deduce the cause of low catalytic activity.

Oxidations catalyzed by zeolite ship-in-a-bottle complexes

A brief review of oxidation reactions catalyzed by zeolite ship-in-a-bottle complexes is presented. The encapsulation of V(O)SALEN (SALEN= bis(salicylaldehyde)ethylenediimine) in zeolite NaY via the flexible ligand method is described. V(O)SALEN-NaY was found to be an effective catalyst for the room temperature epoxidation of cyclohexene using t-butylhydroperoxide ( t-BOOH) as the oxidant. The preparation of zeolite NaX in the presence of RuF 16Pc (F 16Pc= perfluorophthalocyanine) also results in occluded metal complex. RuF 16Pc-NaX has been shown to be an active catalyst for the room temperature oxidation of alkanes using t-BOOH as the oxidant.

Allylic oxidation of olefins to the corresponding α,β-unsaturated ketones catalyzed by chromium aluminophosphate-5

Chromium substituted Aluminophosphate-5 (CrAPO-5) is a heterogeneous catalyst for the liquid phase oxidation of olefins with tert-butyl hydroperoxide (TBHP) to the corresponding α,β-unsaturated ketones at 80°C. The olefins used were: menthene, limonene, α- and β-pinene, terpinolene and 3-carene. Conversions of these terpene substrates were in a range of 85–96% with in some cases high selectivities to a single product. High selectivities towards TBHP were obtained in an experiment where the substrate was used as solvent, i.e. in a large excess with respect to the oxidant. Allylic oxidation with the more bulky pinane hydroperoxide was slower than with TBHP as a result of the increased steric constraints imposed on this hydroperoxide in the channels of the aluminophosphate lattice.

Perfluoroalkylporphyrin complexes as active catalysts for the reaction of isobutane with oxygen and the decomposition of tert-butyl hydroperoxide

A new family of metalloporphyrin complexes having perfluoroalkyl groups in the meso-positions of the ring are active catalysts for the oxidation of isobutane to tert-butyl alcohol, TBA, and for the decomposition of tert-butyl hydroperoxide to TBA. This discovery extends the limited number of meso-substituents that can be used to enhance catalytic activity and fits the postulate that groups that withdraw electrons from the porphyrin periphery give rise to active catalysts for alkane oxidation. The perfluoroalkyl groups also confer oxidative stability, hydrophobicity and lower cost to the catalyst.

Vanadium-substituted MCM-41 zeolites as catalysts for oxidation of alkanes with peroxides

Alkanes are oxidized selectively to ketones using V-MCM-41 with isobutyraldehyde/dioxygen as the preferred oxidant in terms of product selectivity and catalyst stability and recycle.

Alkane Oxidation with Molecular Oxygen Using a New Efficient Catalytic System: N-Hydroxyphthalimide (NHPI) Combined with Co(acac)(n)() (n = 2 or 3).

A novel class of catalysts for alkane oxidation with molecular oxygen was examined. N-Hydroxyphthalimide (NHPI) combined with Co(acac)(n)() (n = 2 or 3) was found to be an efficient catalytic system for the aerobic oxidation of cycloalkanes and alkylbenzenes under mild conditions. Cycloalkanes were successfully oxidized with molecular oxygen in the presence of a catalytic amount of NHPI and Co(acac)(2) in acetic acid at 100 degrees C to give the corresponding cycloalkanones and dicarboxylic acids. Alkylbenzenes were also oxidized with dioxygen using this catalytic system. For example, toluene was converted into benzoic acid in excellent yield under these conditions. Ethyl- and butylbenzenes were selectively oxidized at their alpha-positions to form the corresponding ketones, acetophenone, and 1-phenyl-1-butanone, respectively, in good yields. A key intermediate in this oxidation is believed to be the phthalimide N-oxyl radical generated from NHPI and molecular oxygen using a Co(II) species. The isotope effect (k(H)/k(D)) in the oxidation of ethylbenzene and ethylbenzene-d(10) with dioxygen using NHPI/Co(acac)(2) was 3.8.

Single-site metal alkoxide catalysts for ring-opening polymerizations. Poly(dilactide) synthesis employing {HB(3-Butpz)3}Mg(OEt)

{HB(Butpz)3}Mg(OEt) in CH2Cl2 at 22 °C acts as a catalyst precursor for the fast, stereoselective, ring-opening polymerization of L,L-dilactide by the acyl cleavage mechanism yielding isotactic poly(L,L-dilactide) with PDI ≈ 1.2.

Magnesia Synthesis via Sol−Gel: Structure and Reactivity

2-Propanol decomposition at 200 °C on magnesium oxide prepared by the hydrolysis of magnesium ethoxide (sol−gel method) is reported. With hydrochloride acid, acetic acid, or ammonia as hydrolysis alkoxide catalysts, the acidity and the selectivity to propene of the catalysts follow the sequence, MgO (HCl) > MgO (acetic acid) > MgO (ammonia). In contrast, the basicity of the samples, defined as the ratio dehydrogenation rate/dehydration rate, is found to be depending on the particle size of the catalysts. The basicity trend found is MgO (acetic acid) > MgO (ammonia) > MgO (HCl) and it correlates well with the particle size determined by the Rietveld refinement.

Catalytic and physico-chemical properties of new schiff base complexes in zeolites

Abstract Adsorption of tetradentate Schiff base ligands on MnIINaY zeolites yields catalysts for selective oxidation of hydrocarbons with PhIO or tert-butylhydroperoxide (tBHP). The interaction between Mn and the ligands is proved by IR, diffuse reflectance and EPR spectroscopy. Olefin epoxidation with these catalysts suffers from formation of undesirable products when tBHP is used, but reasonable epoxide selectivities are obtained with PhIO. Very active catalysts for alkane oxidation with tBHP are produced by adsorption of the pyridine derived pyren and pyrpn ligands on MnIINaY (pyren = bis(2-pyridinecarboxaldehyde)ethylenediimine; pyrpn = bis(2-pyridinecarboxaldehyde)propylenediimine). With these catalysts, very high selectivities are obtained for formation of monoketones from alkanes. A relation is proposed between the appearance of low-field features in the Mn(II) EPR spectra and a high activity in hydrocarbon oxidation.

Simple dinuclear iron complexes as catalysts for alkane oxidation

Simple dinuclear iron complexes as catalysts for alkane oxidation