Catalytic Epoxidation Of Olefins Research Articles

Polymeric metal complex catalyzed enantioselective epoxidation of olefins

Spectacular achievements in catalytic asymmetric epoxidation of olefins using chiral Mn(III)-salen complexes have stimulated a great deal of interest in designing polymeric analogs of these complexes and their use as recyclable chiral catalysts. Several strategies have been devised to anchor these chiral catalytic moieties to polymer supports. Techniques of copolymerization of appropriate functional monomers and chemical modification of preformed functional polymers have been utilized to prepare these polymers. Both organic and inorganic polymers have been used as the carriers to immobilize these metal complexes. Results of these investigations are reviewed in this article.

ChemInform Abstract: A Synthetically Useful, Self‐Assembling MMO Mimic System for Catalytic Alkene Epoxidation with Aqueous H2O2.

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.

Alkene epoxidation catalysed by binuclear manganese complexes

Binuclear manganese(II) complexes with macrocyclic ligands have been synthesized by template Schiff base condensation of diethylenetriamine and pentane-2,4-dione or 1,3-diphenyl-propane-1,3-dione. Catalytic epoxidation of simple olefins with hydrogen peroxide and t-BHP were studied using the above manganese complexes in the presence of a base. The influence of reaction temperature, the additive methanol and the cocatalyst had been investigated. The major products of the oxidations were the epoxides. The new manganese complexes showed significant catalytic activities for the epoxidation of alkenes using hydrogen peroxide as oxidant and ammonium acetate as cocatalyst.

The Three-Dimensional Structure of the Titanium-Centered Active Site during Steady-State Catalytic Epoxidation of Alkenes

Combined in situ X-ray absorption fine structure (XAFS) measurements and density functional theory (DFT) computations yield a quantitative three-dimensional picture of the six-coordinated TiIV-centered active site (in Ti/SiO2 catalysts) during production of epoxides from alkenes in the presence of hydroperoxide as oxidants.

Asymmetric epoxidation of olefins catalyzed by chiral iminium salts generated in situ from amines and aldehydes.

[reaction: see text] A new approach for catalytic asymmetric epoxidation of olefins was developed that utilized chiral iminium salts, generated in situ from chiral amines and aldehydes, as catalysts. Epoxidation reactions can be conducted with 20 mol % of amines and aldehydes. The enantioselectivity of epoxides can be up to 65%. This modular approach obviates the difficulties inherent in the preparation and isolation of unstable exocyclic iminium salts.

A DFT Study on Peroxo-Complex in Titanosilicate Catalyst: Hydrogen Peroxide Activation on Titanosilicalite-1 Catalyst and Reaction Mechanisms for Catalytic Olefin Epoxidation and for Hydroxylamine Formation from Ammonia

Density functional theory calculations were performed on an activation of hydrogen peroxide over a cluster model of a titanosilicate catalyst. The calculation results showed possibility to form the hydrated peroxo-titanosilicalite complex, containing a (Ti)-O-O-(Si) peroxo-moiety, as an oxidizing agent. Using this hydrated peroxo-titanosilicalite complex as an oxidizing agent, oxidation mechanisms were postulated for ethene epoxidation and for ammonia oxidation to form hydroxylamine. The ethene molecule was oxidized with the peroxo-oxygen coordinated to the central Ti atom of the hydrated peroxo-titanosilicalite complex, to form ethylene epoxide. For the ammonia oxidation process, ammonia replaced the adsorbed water molecule of the hydrated peroxo-titanosilicalite complex. The oxidation of the adsorbed ammonia in the (ammonia)-peroxo-titanosilicalite complex led to the formation of an ammonia-N-oxide complex of the titanosilicalite catalyst model. The (ammonia-N-oxide)-titanosilicalite complex was transformed into the (hydroxylamine)-titanosilicalite complex, with a hydrogen transfer from the nitrogen to the oxygen of the ammonia-N-oxide moiety. The transition states were explored for these reaction processes. Using the peroxo-titanosilicalite complex containing a Ti−O-O-Si peroxo-moiety as an active oxidizing agent, the catalytic reaction mechanisms are proposed for ethene epoxidation and for ammonia oxidation to form hydroxylamine.

In search of catalytically active species in the surfactant-mediated biphasic alkene epoxidation with Mimoun-type complexes.

[figure: see text] A biphasic protocol for the catalytic olefin epoxidation with Mimoun-type complexes [MoO(O2)2(OPR3)] (1) was recently patented by BASF. Density-functional calculations have been carried out to identify potentially active species in addition to the parent complex 1. It has been found that the (mu 2,eta 1:eta 2-O2)-bridged dimer [MoO(O2)2(OPR3)]2 is significantly less reactive than the monomer. The calculations show that the parent complex is strongly activated by protons coordinating with the peroxo functionalities.

Nanostructured amorphous metals, alloys, and metal oxides as new catalysts for oxidation

Abstract The oxidation of cyclohexane with molecular oxygen in the presence of isobutyraldehyde catalyzed by nanostructured iron and cobalt oxides and iron oxide supported on titania has been studied. Nanostructured cobalt oxide on MCM-41 is found to be efficient for catalytic aerobic epoxidation of olefins.

Asymmetric Mn(III)-salen catalyzed epoxidation of unfunctionalized alkenes with in situ generated peroxycarboxylic acids

Unfunctionalized aromatic alkenes were enantioselectively epoxidized with peroxycarboxylic acids prepared in situ from urea-H 2O 2 (and other anhydrous adducts of H 2O 2) and carboxylic acid anhydrides (maleic, phthalic, and acetic anhydride) using chiral Mn(III)-salen complexes as catalysts and N-methylmorpholine N-oxide (NMO) as an additive. Experimental results were compared with those reported earlier that employed aqueous hydrogen peroxide as the primary oxidant and the method presented here was found to offer both higher enantioselectivities and shorter reaction times. This novel epoxidation system was also compared with the Jacobsen’s MCPBA/NMO system, and some differences in reactivity and selectivity were observed. These differences could possibly be explained assuming the presence of alternative mechanistic pathways during the catalytic cycle of the asymmetric epoxidation.

1H NMR and EPR spectroscopic monitoring of the reactive intermediates of (Salen)Mn III catalyzed olefin epoxidation

Using 1H NMR and EPR spectroscopy, manganese species formed in the catalytic systems 1+iodosobenzene (PhIO) and 1+meta-chloroperoxybenzoic acid ( m-CPBA), where 1 is ( R, R)-(−)- N, N′-bis(3,5-di- tert-butylsalicylidene)-1,2-cyclohexanediamino-manganese(III) chloride ([(Salen)Mn III]) were studied. Three types of manganese complexes were characterized in the catalytic system 1+PhIO ( 4– 6). Complex 4 is very unstable and reacts with styrene at −20°C to afford styrene oxide. It exhibits three signals of tBu groups at 1.68, 1.64 and 1.42 ppm. This pattern closely resembles that for a model complex [(Salen)Mn V≡N]. Based on these data, 4 was identified as d 2 low-spin oxomanganese(V) complex [(Salen)Mn V=O] +. Complexes 5 and 6 are relatively stable at −20°C and poorly reactive towards styrene at this temperature. They display 1H NMR spectra characteristic for antiferromagnetically coupled μ-oxo-dinuclear Mn IV species and are identified as dinuclear complexes [(Salen)LMn IV- O-Mn IV(Salen)L′] with L, L′=Cl − and PhIO. It was found by EPR that the acylperoxo complex (Salen)Mn III(OOCOAr) ( 7) was formed at the first stage of the interaction of 1 with m-CPBA in CH 2Cl 2. Complex 7 is unstable and converts into manganese(IV) oxo complex [(Salen)Mn IV(O)] ( 8). The evaluated first order rate constant of this conversion is 0.25±0.08 min −1 at −70°C. Complex 7 reacts with styrene with the rate constant 1.1±0.4 M −1 min −1 at −70°C to give epoxide and restore 1. Complex 8 is inert towards styrene at low temperature. The effect of donor ligand N-methylmorpholine- N-oxide (NMO) on the epoxidation of styrene by the system 1+ m-CPBA was studied. Addition of NMO (2–5 equiv.) to the solution of 1 in CH 2Cl 2 before interaction with m-CPBA was found to dramatically increase the rate of undesirable transformation of the reactive acylperoxo complex 7-NMO into relatively inert oxo complex- 8-NMO. However, in the presence of styrene, such undesirable conversion is entirely suppressed by very rapid reaction of 8-NMO with styrene to afford styrene oxide and restore 1-NMO.

First success of catalytic epoxidation of olefins by an electron-rich iron(III) porphyrin complex and H 2O 2: imidazole effect on the activation of H 2O 2 by iron porphyrin complexes in aprotic solvent

An electron-rich iron(III) porphyrin complex ( meso-tetramesitylporphinato)iron(III) chloride [Fe(TMP)Cl], was found to catalyze the epoxidation of olefins by aqueous 30% H 2O 2 when the reaction was carried out in the presence of 5-chloro-1-methylimidazole (5-Cl-1-MeIm) in aprotic solvent. Epoxides were the predominant products with trace amounts of allylic oxidation products, indicating that Fenton-type oxidation reactions were not involved in the olefin epoxidation reactions. cis-Stilbene was stereospecifically oxidized to cis-stilbene oxide without giving isomerized trans-stilbene oxide product, demonstrating that neither hydroperoxy radical (HOO·) nor oxoiron(IV) porphyrin [(TMP)Fe IVO] was responsible for the olefin epoxidations. We also found that the reactivities of other iron(III) porphyrin complexes such as ( meso-tetrakis(2,6-dichlorophenyl)porphinato)iron(III) chloride [Fe(TDCPP)Cl], ( meso-tetrakis(2,6-difluorophenyl)porphinato)iron(III) chloride [Fe(TDFPP)Cl], and ( meso-tetrakis(pentafluorophenyl)porphinato)iron(III) chloride [Fe(TPFPP)Cl] were significantly affected by the presence of the imidazole in the epoxidation of olefins by H 2O 2. These iron porphyrin complexes did not yield cyclohexene oxide in the epoxidation of cyclohexene by H 2O 2 in the absence of 5-Cl-1-MeIm in aprotic solvent; however, addition of 5-Cl-1-MeIm to the reaction solutions gave high yields of cyclohexene oxide with the formation of trace amounts of allylic oxidation products. We proposed, on the basis of the results of mechanistic studies, that the role of the imidazole is to decelerate the O–O bond cleavage of an iron(III) hydroperoxide porphyrin (or H 2O 2–iron(III) porphyrin adduct) and that the intermediate transfers its oxygen to olefins prior to the O–O bond cleavage.

Synthesis, characterization and catalytic activity of polynuclear manganese complexes of 2,5-dihydroxyterephthalaldehyde for epoxidation of olefins with H 2O 2

Polynuclear manganese complexes of 2,5-dihydroxyterephthalaldehyde (dhterH 2) and its Schiff base polymer ligand (PdhterenH 2) [Mn II(dhter)] n , [Mn n II(Pdhteren)] and [Mn n III(Pdhteren)(OAc) n ] were synthesized. The manganese complexes were characterized by elemental analysis, thermal analysis, IR and EPR spectroscopic techniques. Catalytic epoxidation of olefins with hydrogen peroxide was studied using the above manganese complexes under heterogenized homogeneous reaction conditions in the presence of a base. The effect of imidazole and olefin concentrations on effective oxygen transfer were studied. [Mn n II(Pdhteren)] and [Mn n III(Pdhteren)(OAc) n ] are more efficient than the oxygen-bonded manganese complex [Mn II(dhter)] n for the activation of hydrogen peroxide.

Catalytic epoxidation of alkenes with hydrogen peroxide over first mesoporous titanium-containing zeolite

Novel mesoporous TS-1 catalyst is shown to be active in epoxidation of oct-1-ene and significantly more active in epoxidation of cyclohexene than conventional TS-1.

Evidence for a charge-transfer intermediate in the catalytic epoxidation of alkenes by ruthenium complexes: a comparison between electrochemical and kinetic data

The catalytic oxidation of various olefins by iodosobenzene in the presence of the diphosphino complexes of ruthenium(II) [RuCl(LL) 2]PF 6, where LL is 1,3-bis(diphenylphosphino)propane (DPP) or 1-diphenylphosphino-2-(2′-pyridyl)ethane (PPY), gives rise to epoxides, obeying the Michaelis–Menten kinetic law. The calculated kinetic parameters ( K m) follow a free energy correlation with the one-electron oxidation potentials of the olefins, measured in the reaction conditions, thus suggesting that the reaction intermediate of the epoxidation is substantially charge-transfer in character.

Ruthenium-oxo and -tosylimido porphyrin complexes for epoxidation and aziridination of alkenes

Abstract

Catalytic epoxidation of alkenes in the presence of a weakly acidic cation exchanger containing transition metal ions

Heterogeneous polymeric catalysts containing Mo, V and Ti for the epoxidation of alkenes by organic hydroperoxides were prepared by a simple modification of the weakly acidic cation exchanger Wofatit CA 20 (Germany) with aqueous solutions of the corresponding inorganic salts. The molybdenum-containing catalyst showed the highest activity for the epoxidation of cyclohexene in benzene solution of t-butylhydroperoxide (TBHP, 0.490–1.200 mol l −1) at 79°C. The catalytic activity for alkenes with different structures was evaluated and compared to other catalysts under the similar conditions of cyclohexene epoxidation. Some data concerning the catalyst stability on heating and multiple recycling were also obtained.

Asymmetric Mn(III)-salen catalyzed epoxidation of unfunctionalized alkenes with tetrabutylammonium monopersulfate

Asymmetric Mn(III)-salen catalyzed epoxidation of simple cis-disubstituted and trisubstituted alkenes in mild conditions was performed using tetrabutylammonium monopersulfate (Bu 4NHSO 5) as the oxidant together with N-methylmorpholine N-oxide as an additive. Particularly high yields of epoxides (up to 97 %) and good enantiomeric excesses (ee up to 93 %) were obtained in the epoxidation of 2,2-dialkylchromenes and trisubstituted alkenes.

A Supramolecular Cytochrome P450 Mimic

Turnover numbers comparable to those of the enzyme itself in the catalytic epoxidation of alkenes are attained by a supramolecular cytochrome P450 mimic, in which an amphiphilic rhodium complex and a manganese porphyrin are incorporated in a dihexadecyl phosphate vesicle bilayer (shown schematically above). The electrons required for activation of dioxygen are supplied by rhodium-catalyzed dehydrogenation of formate ions.

ChemInform Abstract: Catalytic Epoxidation of Alkenes with Oxone. Part 3. 6‐Oxo‐1,1,4,4‐tetramethyl‐1,4‐diazepinium Salts. A New Class of Catalysts for Efficient Epoxidation of Olefins with Oxone.

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.

Metal Ion-Planted MCM-41: 2. Catalytic Epoxidation of Stilbene and Its Derivatives withtert-Butyl Hydroperoxide on Mn-MCM-41

Manganese ion-planted MCM-41 (Mn-MCM-41) prepared by the template ion-exchange (TIE) method has been found to be active for catalytic epoxidation of aromatic olefins. The activity of Mn-MCM-41 was the greatest among those of Mn/MCM-41, Mn/SiO2, Mn/Al2O3, which were prepared by a conventional impregnation method, and Mn-ZSM-5 prepared by an ion-exchange method. The proper reaction conditions have first been determined fortrans-stilbene as the substrate. The most effective oxidant wastert-butyl hydroperoxide (TBHP) at 328–348 K among H2O2, PhIO, TBHP, and O2. The highest yield of 93% oftrans-stilbene oxide was obtained by using a mixed solvent of acetonitrile and dimethylformamide of 9:1 (v/v) at 328 K. Mn-MCM-41 could be used repeatedly for the reaction without decrease in the catalytic activity. The epoxidation oftransandcisisomers of various aromatic olefins has then been studied. The oxidation of olefins having bulky substituents such as 4-tert-butylphenyl and 2-naphthyl could proceed in the mesopores of Mn-MCM-41. The epoxidation oftransisomers was easier than that ofcisisomers. The olefins withcisconfiguration all gave the correspondingtransoxides with small amounts oftransolefins as by-products. A radical mechanism has been suggested for the oxidation on the basis of the product distributions.