Olefin Epoxidation Catalyzed by Molybdenum Peroxo Complexes: A Mechanistic Study

Thiel, Werner R.; Barz, Michael; Glas, Holger; Pleier, Anna-Katharina

doi:10.1002/3527600396.ch20

Cited by 11 publications

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“…Although the details of the mechanism may vary, non-molybdenum enzymes such as cytochrome P450 are also thought to proceed via similar reactions. Catalytic OAT reactions are also important in industrial processes such as the epoxidation of olefin. − …”

Section: Introductionmentioning

confidence: 99%

Substituent Effect on Oxygen Atom Transfer Reactivity from Oxomolybdenum Centers: Synthesis, Structure, Electrochemistry, and Mechanism

2009

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Dioxo molybdenum complexes of general formula Tp*MoO(2)(S-p-RC(6)H(4)) (1), where Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate and R = OMe, Me, SMe, NHCOMe, H, Cl, CF(3), NO(2), were reacted with trimethyl phosphine (PMe(3)) to convert into complexes of general formula Tp*MoO(S- p-RC(6)H(4))(OPMe(3)) (2) (where R = OMe, Me, SMe, H, Cl, and CF(3)). These complexes were isolated and characterized by NMR, IR, UV/vis, and single crystal X-ray crystallography. Electronic and NMR spectra, as well as redox potentials vary as a function of substituent on the thiophenolato ligand. When viewed entirety of the oxygen atom transfer (OAT) reactivity, the reaction of Tp*MoO(2)(S-p-RC(6)H(4)) with PMe(3) shows a biphasic behavior, indicating the formation of at least one intermediate. The kinetics of the both steps, that is, the formation of the phosphoryl intermediate and the formation of the solvent coordinated species have been investigated by UV-vis spectroscopy. The first step follows a second order process, first order with respect to both the complex and PMe(3), and the overall second order rate constants at 25 degrees C range from 98.2 (+/-0.01) x 10(-2) M(-1) s(-1) (for R = OMe) to 223.0 (+/-0.20) x 10(-2) M(-1) s(-1) (for R = CF(3)); activation parameters were in the ranges DeltaH(++) = 49.3(+/-4.1) kJ x mol(-1) (for R = OMe) to 34.0 (+/-7.5) kJ x mol(-1) (for R = CF(3)), DeltaS(++) = -154.0 (+/-14.2) J x mol(-1) x K(-1) (for R = OMe) to -184.3 (+/-26.1) J x mol(-1) K(-1) (for R = CF(3)), and DeltaG(++) = 95.0 kJ x mol(-1) (for R = OMe) to 88.7 kJ x mol(-1) (for R = CF(3)). Formation of the acetonitrile complex from the phosphoryl complex follows a first order process with respect to the complex. The first order rate constants at 25 degrees C range from 3.60 (+/-0.01) x 10(-4) sec(-1) (for R = OMe) to 6.32 (+/-0.11) x 10(-4) sec(-1) (for R = CF(3)), and the enthalpy of activation and entropy of activation show variation; DeltaH(++) = 62.5 (+/-2.2) to 67.8 (+/-1.0) kJ x mol(-1), DeltaS(++) = -82.5 (+/-3.3) to -101.3 (+/-7.5) J x mol(-1) x K(-1), but the free energy of activation remains constant DeltaG(++) approximately 92 (+/-1) kJ x mol(-1). Large entropies of activation associated with both steps are consistent with associative transition states. The comparable magnitude of the activation energy of the two steps underscores the difficulty in identifying the rate-limiting step in the overall OAT reaction. The first step, however, is more sensitive toward the substituent effects than the second step. Therefore, a change in the substituent can play an important role in deciding the rate-limiting step involved in a two-step OAT reaction.

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Section: Introductionmentioning

confidence: 99%

Substituent Effect on Oxygen Atom Transfer Reactivity from Oxomolybdenum Centers: Synthesis, Structure, Electrochemistry, and Mechanism

2009

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“…A more consistent mechanism supported by spectroscopic studies and kinetic data was reported by Thiel et al , The authors used a series of synthesized oxodiperoxo molybdenum complexes chelated with pyrazolylpyridine ligands as catalysts in the epoxidation of olefin with t -BuOOH or H 2 O 2 . The study concluded that the complexes do not catalyze the olefin epoxidation by transferring an oxygen atom of a peroxo ligand but by activating H 2 O 2 , which gives rise to a new reaction mechanism.…”

Section: Resultsmentioning

confidence: 99%

Formation, Reactivity, and Catalytic Behavior of a Keggin Polyoxometalate/Bipyridine Hybrid in the Epoxidation of Cyclooctene with H₂O₂

et al. 2023

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The present study further explores the behavior of polyoxometalate-based hybrid compounds as catalysts for liquidphase cyclooctene epoxidation with H 2 O 2 . Precisely, it unveils the nature of the relevant active species derived from the hybrid based on Keggin polyoxometalate (POM) and bipyridines (bpy) of formula (2,2′-Hbpy) 3 [PW 12 O 40 ] (1). Whereas (i) it is generally accepted that the catalytic oxidation of organic substrates by H 2 O 2 involving Keggin HPAs proceeds via an oxygen transfer route from a peroxo intermediate and (ii) the catalytically active peroxo species is commonly postulated to be the polyperoxotungstate {PO 4 [W(O)(O 2 ) 2 ] 4 } 3− complex (PW 4 ), we show that the studied epoxidation reaction seems to be more sophisticated than commonly reported. During the catalytic epoxidation, 1 underwent a partial transformation into two oxidized species, 2 and 3. Compound 3 corresponding to 2,2′-bipyridinium oxodiperoxotungstate of formula [WO(O 2 ) 2 (2,2′-bpy)] was shown to be the main species responsible for the selective epoxidation of cyclooctene since 2 (in which the POM is associated with a protonated mono-Noxide derivative of 2,2′-bpy of formula (2,2′-HbpyO) 3 [PW 12 O 40 ]) exhibited no activity. The structures of 1, 2, and 3 were solved by single-crystal X-ray diffraction and were independently synthesized. The speciation of 1 was monitored under catalytic conditions by 1 H and 1 H DOSY NMR spectroscopies, where the formation in situ of 2 and 3 was revealed. A reaction mechanism is proposed that highlights the pivotal, yet often underestimated, role of H 2 O 2 in the reached catalytic performances. The active species responsible for the oxygen transfer to cyclooctene is a hydroperoxide intermediate species that is formed by the interaction between the anionic structure of the catalyst and H 2 O 2 . The latter operates as a "conservative agent" whose presence in the catalytic system is required to prevent the catalysts from deactivating irreversibly.

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“…This observation strongly suggests that the stability is indeed a result of the binding of the peroxido ligand to the molybdenum center. In a study conducted, [48] it was reported that binding of η 2 ‐coordinated species acts as weak π donors and effectively maintain the Lewis acidity of the metal center. Therefore, the presence of the pyrazolone ligand coordinated to Mo centre is possibly the reason why the reaction proceeds without H 2 O 2 .…”

Section: Resultsmentioning

confidence: 99%

Catalytic Potential of Pyrazolone Based Dioxidomolybdenum(VI) Complexes for Multicomponent Biginelli Reactions, Epoxidation of Olefins and Oxidative Bromination of Phenol Derivatives

Maurya,

Singh,

Bisht

et al. 2023

Eur J Inorg Chem

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Three different types of dioxidomolybdenum(VI) complexes of 4‐acetyl‐3‐methyl‐1‐phenyl‐5‐pyrazolone (Hmp, I)), 3‐methyl‐1‐phenyl‐4‐propionyl‐5‐pyrazolone (Hpp, II), 4‐butyryl‐3‐methyl‐1‐phenyl‐5‐pyrazolone (Hbutp, III), and 4‐isobutyryl‐3‐methyl‐1‐phenyl‐5‐pyrazolone (isobutp, IV) have been isolated and characterized by various spectroscopic (FT‐IR, UV/Vis, 1H and13C NMR) techniques, thermal analysis and single crystal X‐ray analysis. These complexes adopt a distorted six‐coordinated octahedral geometry where ligands act as bidentate, coordinating through the two O atoms. These complexes have been used as catalysts to explore a single pot multicomponent (benzaldehyde or its derivatives, urea/thiourea and ethyl acetoacetate/phenyl acetoacatate) Biginelli reaction producing biologically active 3,4‐dihydropyrimidin‐2‐(1H)‐one and 3,4‐dihydropyrimidin‐2‐(1H)‐thione based biomolecules under solvent‐free conditions. Presence of H2O2 improves the yield of dihydropyrimidin‐2‐(1H)‐one but it acts as poisons for the later molecule. Epoxidation of internal and terminal alkenes mainly resulted in the formation of the corresponding epoxide selectively. The catalytic oxidative bromination of thymol, a reaction facilitated by vanadium dependent haloperoxidases, resulted in the formation of three product namely 2‐bromothymol, 4‐bromothymol and 2,4‐bromothymol. Other phenol derivatives have also been brominated effectively.

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Olefin Epoxidation Catalyzed by Molybdenum Peroxo Complexes: A Mechanistic Study

Cited by 11 publications

References 0 publications

Substituent Effect on Oxygen Atom Transfer Reactivity from Oxomolybdenum Centers: Synthesis, Structure, Electrochemistry, and Mechanism

Substituent Effect on Oxygen Atom Transfer Reactivity from Oxomolybdenum Centers: Synthesis, Structure, Electrochemistry, and Mechanism

Formation, Reactivity, and Catalytic Behavior of a Keggin Polyoxometalate/Bipyridine Hybrid in the Epoxidation of Cyclooctene with H₂O₂

Catalytic Potential of Pyrazolone Based Dioxidomolybdenum(VI) Complexes for Multicomponent Biginelli Reactions, Epoxidation of Olefins and Oxidative Bromination of Phenol Derivatives

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Olefin Epoxidation Catalyzed by Molybdenum Peroxo Complexes: A Mechanistic Study

Cited by 11 publications

References 0 publications

Substituent Effect on Oxygen Atom Transfer Reactivity from Oxomolybdenum Centers: Synthesis, Structure, Electrochemistry, and Mechanism

Substituent Effect on Oxygen Atom Transfer Reactivity from Oxomolybdenum Centers: Synthesis, Structure, Electrochemistry, and Mechanism

Formation, Reactivity, and Catalytic Behavior of a Keggin Polyoxometalate/Bipyridine Hybrid in the Epoxidation of Cyclooctene with H2O2

Catalytic Potential of Pyrazolone Based Dioxidomolybdenum(VI) Complexes for Multicomponent Biginelli Reactions, Epoxidation of Olefins and Oxidative Bromination of Phenol Derivatives

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Formation, Reactivity, and Catalytic Behavior of a Keggin Polyoxometalate/Bipyridine Hybrid in the Epoxidation of Cyclooctene with H₂O₂