Olefin Epoxidation by H2O2/MeCN Catalysed by Cyclopentadienyloxidotungsten(VI) and Molybdenum(VI) Complexes: Experiments and Computations

Heterogeneous catalysis with an organic–inorganic hybrid based on MoO3 chains decorated with 2,2′-biimidazole ligands

Polymeric [MoO₃(2,2′-biimidazole)]·H₂O outperforms other one-dimensional MoO₃-ligand hybrid materials as a heterogeneous and recyclable catalyst for (bio)olefin epoxidation and sulfoxidation.

Ionic Liquids Based on Oxidoperoxido-Molybdenum(VI) Complexes with a Chelating Picolinate Ligand for Catalytic Epoxidation

Ionic oxidoperoxido-molybdenum(VI) complexes of the type [Cat][MoO(O2)2(pic)], with pic = N,O-chelated picolinate ligand and Cat = monocation, were prepared in high yields (82–95%) from the precursor complex [H3O][MoO(O2)2(pic)] via [H]+ cation exchange for 1-ethyl-3-methylimidazolium [EMIM]+, 1-butyl-3-methylimidazolium [BMIM]+, 1-octyl-3-methylimidazolium [OMIM]+, N-cetylpyridinium [C16Py]+, and N-methyl-N,N,N-trioctylammonium [Aliquat]+. The structure and purity of the ionic compounds were assessed by 1H and 13C NMR, FT-IR, and elemental analysis (C, H, N), and the electrochemical properties were studied by differential pulse voltammetry (DPV) and cyclic voltammetry (CV). The [Cat][MoO(O2)2(pic)] compounds showed promising catalytic epoxidation activity based on the model reaction of cis-cyclooctene with tert-butyl hydroperoxide as oxidant. The type of cation influenced the physical state of the compound and the catalytic performance.

Recent Advances in Facile Liquid Phase Epoxidation of Light Olefins over Heterogeneous Molybdenum Catalysts

Molybdenum complexes are versatile and efficient for liquid phase olefin epoxidation reactions. Rational design of catalysts is critical to achieve high atom efficiency during epoxidation processes. Although liquid phase epoxidation has been a popular topic for decades, three key issues, (a) rational control of morphology of molybdenum nanoparticles, (b) manipulating metal-support interaction and (c) altering electronic configuration at molybdenum center remains unsolved in this area. Therefore, in this paper, we have critically revised recent research progress on heterogeneous molybdenum catalysts for facile liquid phase olefin epoxidation in terms of catalyst synthesis, surface characterization, catalytic performance and structure-function relationship. Furthermore, plausible reaction mechanisms will be systematically discussed with the aim to provide insights into fundamental understanding on novel epoxidation chemistry.

An effective strategy for creating asymmetric MOFs for chirality induction: a chiral Zr-based MOF for enantioselective epoxidation

A simple and rapid procedure was used to prepare chiral NU-1000 as a robust Zr-based MOF without complexity. The functionalization of NU-1000 was performed by utilizing chirall-(+)-tartaric acidviasolvent-assisted linker incorporation, resulting in [C-NU-1000]. A Mo-complex was immobilized onto chiral NU-1000 for enantioselective epoxidation.

Dioxotungsten(vi) complexes with isoniazid-related hydrazones as (pre)catalysts for olefin epoxidation: solvent and ligand substituent effects

The catalytic performances (activity and selectivity) of the mononuclear dioxotungsten(vi) complexes [WO₂(L^R)(D)] towards alkene epoxidation by tert-butyl hydroperoxide (TBHP) were investigated under different conditions.

Crystal Structure and Catalytic Behavior in Olefin Epoxidation of a One-Dimensional Tungsten Oxide/Bipyridine Hybrid

The tungsten oxide/2,2'-bipyridine hybrid material [WO3(2,2'-bpy)]·nH2O (n = 1-2) (1) has been prepared in near quantitative yield by the reaction of H2WO4, 2,2'-bpy, and H2O in the mole ratio of ca. 1:2:700 at 160 °C for 98 h in a rotating Teflon-lined digestion bomb. The solid-state structure of 1 was solved and refined through Rietveld analysis of high-resolution synchrotron X-ray diffraction data collected for the microcrystalline powder. The material, crystallizing in the orthorhombic space group Iba2, is composed of a one-dimensional organic-inorganic hybrid polymer, ∞(1)[WO3(2,2'-bpy)], topologically identical to that found in the previously reported anhydrous phases [MO3(2,2'-bpy)] (M = Mo, W). While in the latter the N,N'-chelated 2,2'-bpy ligands of adjacent corner-shared {MO4N2} octahedra are positioned on the same side of the 1D chain, in 1 the 2,2'-bpy ligands alternate above and below the chain. The catalytic behavior of compound 1 for the epoxidation of cis-cyclooctene was compared with that for several other tungsten- or molybdenum-based (pre)catalysts, including the hybrid polymer [MoO3(2,2'-bpy)]. While the latter exhibits superior performance when tert-butyl hydroperoxide (TBHP) is used as the oxidant, compound 1 is superior when aqueous hydrogen peroxide is used, allowing near-quantitative conversion of the olefin to the epoxide. With H2O2, compounds 1 and [MoO3(2,2'-bpy)] act as sources of soluble active species, namely, the oxodiperoxo complex [MO(O2)2(2,2'-bpy)], which is formed in situ. Compounds 1 and [WO(O2)2(2,2'-bpy)] (2) were further tested in the epoxidation of cyclododecene, trans-2-octene, 1-octene, (R)-limonene, and styrene. The structure of 2 was determined by single-crystal X-ray diffraction and found to be isotypical with the molybdenum analogue.

Composites of [γ-H2PV2W10O40]3− and [α-SiW12O40]4− supported on Fe2O3 as heterogeneous catalysts for selective oxidation with aqueous hydrogen peroxide

The titled heterogeneous catalysts showed high performance for selective oxidation with H₂O₂.

Hafnium catalysts for direct alkene epoxidation using molecular oxygen as oxidant

Direct alkene epoxidation catalytic cycles were computed for hafnium-based catalysts containing bis(dinitrone) and bis(imine nitrone) ligation using molecular oxygen as oxidant without co-reductant.

Cyclopentadienyl molybdenum alkyl ester complexes as catalyst precursors for olefin epoxidation

Piano-stool organomolybdenum complexes of formula [CpMo(CO)₃(CHR²COOR¹)] are described and applied for olefin epoxidation with tert-butyl hydroperoxide as an oxidant.

Speciation of [Cp*(2)M(2)O(5)] in polar and donor solvents

The speciation of compounds [Cp*2 M2 O5 ] (M=Mo, W; Cp*=pentamethylcyclopentadienyl) in different protic and aprotic polar solvents (methanol, dimethyl sulfoxide, acetone, acetonitrile), in the presence of variable amounts of water or acid/base, has been investigated by (1) H NMR spectrometry and electrical conductivity. Specific hypotheses suggested by the experimental results have been further probed by DFT calculations. The solvent (S)-assisted ionic dissociation to generate [Cp*MO2 (S)](+) and [Cp*MO3 ](-) takes place extensively for both metals only in water/methanol mixtures. Equilibrium amounts of the neutral hydroxido species [Cp*MO2 (OH)] are generated in the presence of water, with the relative amount increasing in the order MeCN≈acetone<MeOH<DMSO. Addition of a base (Et3 N) converts [Cp*2 M2 O5 ] into [Et3 NH](+) [Cp*MO3 ](-) , for which the presence of a NH⋅⋅⋅OM interaction is revealed by (1) H NMR spectroscopy in comparison with the sodium salts, Na(+) [Cp*MO3 ](-) . These are fully dissociated in DMSO and MeOH, but display a slow equilibrium between free ions and the ion pair in MeCN and acetone. Only one resonance is observed for mixtures of [Cp*MO3 ](-) and [Cp*MO2 (OH)] because of a rapid self-exchange. In the presence of extensive ionic dissociation, only one resonance is observed for mixtures of the cationic [Cp*MO2 (S)](+) product and the residual undissociated [Cp*2 M2 O5 ] because of a rapid associative exchange via the trinuclear [Cp*3 M3 O7 ](+) intermediate. In neat methanol, complex [Cp*2 W2 O5 ] reacts to yield extensive amounts of a new species, formulated as the mononuclear methoxido complex [Cp*WO2 (OMe)] on the basis of the DFT study. An equivalent product is not observed for the Mo system. The addition of increasing amounts of water results in the rapid decrease of this product in favor of [Cp*2 W2 O5 ] and [Cp*WO2 (OH)].

Mechanistic studies on the roles of the oxidant and hydrogen bonding in determining the selectivity in alkene oxidation in the presence of molybdenum catalysts

When the molybdenum oxo(peroxo) acetylide complex [CpMo(O-O)(O)C≡CPh] is used as a catalyst for the oxidation of olefins, completely different product selectivity is obtained depending on the oxidant employed. When tert-butyl hydroperoxide (TBHP, 5.5 M) in dodecane is used as the oxidant for the oxidation of cyclohexene, cyclohexene oxide is formed with high selectivity. However, when H(2)O(2) is used as the oxidant, the corresponding cis-1,2-diol is formed as the major product. Calculations performed by using density functional theory revealed the nature of the different competing mechanisms operating during the catalysis process and also provided an insight into the influence of the oxidant and hydrogen bonding on the catalysis process. The mechanistic investigations can therefore serve as a guide in the design of molybdenum-based catalysts for the oxidation of olefins.