Alkene Epoxidations Catalyzed by Mo(VI) Supported on Imidazole-Containing Polymers

Miller, Matthew M.; Sherrington, David C.

doi:10.1006/jcat.1995.1092

Cited by 68 publications

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“…4 It also finds applications in catalysis for the epoxidation of alkenes 5 in a variety of forms, for example in solution and in presence of oxygen donors like tert-butyl hydro peroxide (TBHP), it is effective for the epoxidation of 1-octene, 6 squalene, 7 and cyclohexene. 8 It can also be used as immobilized species, either polymer bound 9 or over mesoporous silicates like MCM-41, 10 for the epoxidation of cyclohexene and cyclooctane. MoO2(acac)2 is also a precursor for heterogeneous Mo catalysts supported on Al2O3 and SiO2 for metathesis reactions.…”

Section: Introductionmentioning

confidence: 99%

Dynamic NMR and Quantum-Chemical Study of the Stereochemistry and Stability of the Chiral MoO₂(acac)₂ Complex in Solution

Conte

Hippler

2016

J. Phys. Chem. A

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The stereochemistry and dynamics of MoO2(acac)2 in benzene, chloroform and toluene was investigated by variable temperature 1 H NMR, density functional theory (SOGGA11-X, B3LYP) and ab initio (MP2) methods. In solution, an equilibrium between two chiral enantiomers with C2 symmetry was identified, Λ-cis-MoO2(acac)2 and ∆-cis-MoO2(acac)2. The two enantiomers are connected via achiral cis transition states that switch the enantiomeric conformations via a RayDutt, Bailar and a newly described racemization twisting mechanism. All three mechanisms have similar calculated activation energies. Activation parameters Ea, ∆H ‡ , and ∆S ‡ were experimentally determined for the exchange process, with a small, negative ∆S ‡ , and a positive ∆H ‡ of 68.1 kJ mol -1 in benzene, 54.9 kJ mol -1 in chloroform, and 60.6 kJ mol -1 in toluene, in reasonable general agreement with the calculations. trans configurations of MoO2(acac)2 are very much higher in energy than cis and are not relevant in the temperature range experimentally studied, 243-340 K. The enantiomers interconvert within seconds near room temperature, and much faster at elevated temperatures. Racemization will thus prevent the use of enantiomerically pure MoO2(acac)2 for chiral catalysis under practical conditions.

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Section: Introductionmentioning

confidence: 99%

Dynamic NMR and Quantum-Chemical Study of the Stereochemistry and Stability of the Chiral MoO₂(acac)₂ Complex in Solution

Conte

Hippler

2016

J. Phys. Chem. A

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“…Inspired by the excellent binding between Mo and organic compounds, many heterogenization attempts have focused on the immobilization of functional organic groups to which Mo can bind. In contrast to the previous examples, polybenzimidazole (PBI) resins couple an outstanding thermo-oxidative stability to a pronounced affinity for the active Mo complexes (Scheme 6) [90][91][92][93]. The majority of early investigations used commercially available polystyrenetype polymers with various functional groups or specially tailored chelating ion-exchange functions.…”

Section: B Oxygenation Of Enaminesmentioning

confidence: 99%

Oxidations on Immobilized Molecular Catalysts

Wahlen

Vos

2008

Handbook of Heterogeneous Catalysis

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IntroductionThe immobilization of homogeneous catalysts has been the focal point of extensive research effort over the past few decades. Heterogenization facilitates separation of the catalyst from the reagents and products, simplifies the recovery of the often expensive or toxic catalysts, and also allows the reuse or continuous operation of the immobilized catalyst. The immobilization of a homogeneous oxidation catalyst often greatly enhances its stability, due to the suppression of bimolecular deactivation pathways. For example, soluble metal complexes tend to react with each other, leading to oxidative degradation of the organic ligands. Another non-productive side reaction is the formation of inactive μ-oxo-bridged dimers. Such self-destruction and dimerization processes are almost impossible with a properly immobilized complex. Many approaches allow the careful control of metal complex loading of the support, and often truly site-isolated metal centers are obtained. Moreover, immobilization sometimes leads to an improved activity of the catalyst. For example, the microenvironment of the catalytic center may provide the correct polarity and acidobasicity for the desired catalytic activity. * Corresponding author.In this chapter, existing immobilization techniques are reviewed with special focus on their application in liquid-phase catalytic oxidations. General aspects such as the type of metal and oxidant, the choice of support, and the issue of leaching are discussed. The discussion is limited to the immobilization of achiral oxidation catalysts; chiral catalysts and metal-free organic catalysts are not included. The focus is on reactions employing clean, inexpensive oxidants such as molecular oxygen, hydrogen peroxide, or organic peroxides. Finally, the concepts are illustrated with examples selected among early seminal work and more recent publications. Only synthetically useful oxidative transformations of organic compounds are discussed; bleaching or deep oxidation of organics and oxidation of inorganic compounds are not included. Solid catalytic materials are only discussed if there exist homogeneous analogues for these materials. The immobilization of nanoclusters (e.g., Au, Pd) is not included, however. Emphasis is placed on examples where the heterogeneous nature of the catalysis has clearly been proven, preferably by employing stringent filtration tests. Immobilization MethodsIn designing an immobilization method for homogeneous oxidation catalysts, it is preferable to first have a clear idea of all chemical states of the catalyst that must be withheld by the support. This implies knowledge of the catalytic cycle, and of all metal species in the system. Only then can a mechanism for catalyst immobilization be proposed which is effective for all chemical states of the metal involved, particularly for the most oxidized form of the redox metal. Although this is a more demanding approach, it may often be the only rewarding method [1].Several different methodologies and concepts may be followed to achie...

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“…Sherrington group has synthesized polystyrene, polymethacrylate, polybenzimidazole and polysiloxane resins for immobilization of Mo(VI) catalysts and investigated their catalytic activity in the alkene epoxidation with tert-butylhydroproxide [6][7][8][9][10][11]. Recently, we showed that molybdenum hexacarbonyl immobilized on 1,2-Dichloroethane, reflux MoOiacac)2-MCM-41, t-BuOOH ) = < ---Scheme 1.…”

Section: Introductionmentioning

confidence: 99%

MoO2(acac)2 supported on MCM-41: An efficient and reusable catalyst for alkene epoxidation with tert-BuOOH

Tangestaninejad

Mirkhani

Mohammadpoor‐Baltork

et al. 2008

JICS

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This paper is dedicated to Professor H. Firouzabadi on the occasion of his 65 th birthday and his honorable retirement A new heterogeneous catalyst prepared by immobilization of M0 2(acac)2 on Mobil Catalytic Material, MCM-4l, is reported. This catalyst, Mo0 2(acac)TMCM-4l, was successfully applied for efficient epoxidation of olefins with tert-BuOOH in 1,2-dichloroethane as solvent. The catalyst was characterized by elemental analysis, FT-IR, UV-Vis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). This catalyst can be reused several times without significant loss of its catalytic activity.

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Alkene Epoxidations Catalyzed by Mo(VI) Supported on Imidazole-Containing Polymers

Cited by 68 publications

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Dynamic NMR and Quantum-Chemical Study of the Stereochemistry and Stability of the Chiral MoO₂(acac)₂ Complex in Solution

Dynamic NMR and Quantum-Chemical Study of the Stereochemistry and Stability of the Chiral MoO₂(acac)₂ Complex in Solution

Oxidations on Immobilized Molecular Catalysts

MoO2(acac)2 supported on MCM-41: An efficient and reusable catalyst for alkene epoxidation with tert-BuOOH

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Alkene Epoxidations Catalyzed by Mo(VI) Supported on Imidazole-Containing Polymers

Cited by 68 publications

References 0 publications

Dynamic NMR and Quantum-Chemical Study of the Stereochemistry and Stability of the Chiral MoO2(acac)2 Complex in Solution

Dynamic NMR and Quantum-Chemical Study of the Stereochemistry and Stability of the Chiral MoO2(acac)2 Complex in Solution

Oxidations on Immobilized Molecular Catalysts

MoO2(acac)2 supported on MCM-41: An efficient and reusable catalyst for alkene epoxidation with tert-BuOOH

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Dynamic NMR and Quantum-Chemical Study of the Stereochemistry and Stability of the Chiral MoO₂(acac)₂ Complex in Solution

Dynamic NMR and Quantum-Chemical Study of the Stereochemistry and Stability of the Chiral MoO₂(acac)₂ Complex in Solution