3234-26-2

The epoxidation of olefin substrates, in both apolar organic media and under solventless conditions, with aqueous hydrogen peroxide and catalysed by molybdenum complexes has been investigated. The catalysts compounds employed were the oxodiperoxomolybdenum complexes of several pyridine, 2,2′-bipyridine and pyrazole ligands with apolar functions (alkyl chains, alkyl-trimethylsilyl groups and polydimethylsiloxanyl polymer), which showed enhanced solubility in relatively apolar organic media. Both the isolated complexes and in situ preparations were catalytically active. The solubility of the new catalyst complexes appears to facilitate the catalytic activity in these systems, since activity was not observed for the analogous, insoluble complexes of unfunctionalised ligands. In these systems, the oxidant, aqueous hydrogen peroxide, forms a separate phase and the catalyst resides in the organic phase. From a green chemistry and economic perspective the elimination of organic solvents and co-catalysts from a reaction system would present advantages and, consequently, the epoxidation reaction was also investigated under solventless conditions. The 3-hexyl-5-methylpyrazole and 3-hexyl-5-heptylpyrazole complexes were found to show heightened activities, the latter being particularly efficient in these conditions, whilst bipyridines apparently inhibit the epoxidation. In addition, the mechanism of the epoxidation reaction was studied through DFT calculations for the model olefin substrate ethylene with the oxodiperoxomolybdenum complex of 3-hexyl-5-heptylpyrazole. The oxo-transfer reaction occurred by interaction of the ethylene with the peroxo ligand via the spirocyclic transition state proposed by Sharpless.

In the present work, highly efficient epoxidation of alkenes catalyzed by Mo(CO)6 supported on multi-wall carbon nanotubes modified by 2-aminopyrazine, APyz-MWCNTs, is reported. The prepared catalyst was characterized by elemental analysis, scanning electron microscopy, FT IR and diffuses reflectance UV-vis spectroscopic methods. This new heterogenized catalysts, [Mo(CO)6@APyz-MWCNT], was used asa highly efficient catalyst for epoxidation of alkenes with tert-BuOOH. This robust catalyst was reused several times without loss of its catalytic activity. Copyright

A new magnetically separable nanocatalyst was successfully synthesized by immobilizing of vanadyl acetylacetonate complex, [VO(acac)2], onto silica coated magnetite nanoparticles previously functionalized with 3-aminopropyltriethoxysilane (3-APTES) and reacted by 5-bromosalicylaldehyde to form Schiff base moiety. The obtained nanocatalyst was characterized by elemental analysis (CHN), FT-IR spectroscopy, Powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), inductively coupled plasma optical emission spectrometry (ICP-OES) and thermogravimetric analysis (TGA). Eventually, the resulting nanoparticles were used as catalyst for epoxidation of alkenes and oxidation of sulfides using tert-butyl hydroperoxide (TBHP) as an oxidant.

The first X-ray crystal structure of an oxochromium(V) complex capable of effecting oxygen atom transfer to alkenes in stoicheiometric and catalytic systems is reported.

We present a single-component catalyst system for the epoxidation of hydrophobic olefins in aqueous solution. The aggregation of surface-active 1-alkyl-3-methylimidazolium ionic liquids (IL) containing the catalytically active tungstate dianion leads to micelles, which solubilise apolar olefins in aqueous media. The micellisation of tungstate allows for the epoxidation of cyclooctene and other olefins in water, using environmentally benign hydrogen peroxide as oxidant. The structural characterisation of the micelles under catalysis conditions as well as the substrate uptake have been studied by cryo-TEM. 183W-NMR studies revealed that the catalytically active species is a tetraperoxotungstate complex. The addition of organophosphonic acids results in a significant boost of the catalytic activity by formation of a tungstate-phosphonate adduct, investigated using electrospray ionisation mass spectrometry (ESI-MS). The versatile functionalisability of the imidazolium cation enables a covalent linkage of a phosphonate group, which is further increasing the catalytic activity.

A S-shaped organotriphosphonate polyoxotungstate, K4H6[H4{(AsW9O33)Zn(H2O)W5O11(N(CH2PO3)3)}2(μ2-O)2]·27H2O (1), has been synthesized and characterized. Compound 1 contains a different geometry of [{Zn(H2O)W5O19(N(CH2PO3)3)}]12- clusters, which forms a chiral conformation. The catalysis of 1 for alkene epoxidation was investigated with a hydrogen peroxide (H2O2) oxidant.

This work demonstrated that the specific ionic liquids (ILs) have been designed via the supramolecular complexation between 18-crown-6 (CE) and ammonium peroxoniobate (NH4-Nb). The resultant ILs have been characterized by elemental analysis, FT-IR, Raman, NMR, DSC, conductivity measurement and MALDI-TOF, etc. The IL (CE-1) consisting of CE and ammonium peroxoniobate can be further coordinated with GLY to generate a new IL (CE-2), which showed both high catalytic activity in epoxidation with H2O2 and good recyclability. The characterization of 93Nb NMR spectra revealed that the peroxoniobate anions has demonstrated a structural evolution in the presence of hydrogen peroxide, in which Nb[dbnd]O species can be easily oxidized into the catalytically active niobium?peroxo species. Especially, the supramolecular complexation can provide suitable hydrophobicity, which ensured that the hydrophobic olefins and allylic alcohols were easily accessible to the catalytically active anions, and thus facilitated the epoxidation reaction. Notably, the supramolecular IL catalysts in this work exhibited a huge advantage of the easy availability, as compared with the previously reported peroxoniobate-based ILs. As far as we know, this is the first example of the highly selective epoxidation of olefins and allylic alcohols by using supramolecular ILs as catalysts.

We present the activation of hydrogen peroxide by micellar imidazolium nitratesviaH-bond formation in water, as shown by vibrational spectroscopy and supported by DFT calculations. Mechanistic insight into the interactions of the surfactant cation, the nitrate anion and H2O2is given. The micelles solubilise and epoxidise cyclooctene in the aqueous phase.

Three mononuclear imine-based non-heme manganese(III) complexes with tetradentate ligands which have two deprotonated phenolate moieties, ([(X2saloph)Mn(OAc)(H2O)], 1a for X = Cl, 1b for X = H, and 1c for X = CH3, saloph = N,N-o-phenylenebis(salicylidenaminato)), were synthesized and characterized by 1H NMR, 13C NMR, ESI-Mass and elemental analysis. MnIII complexes catalysed efficiently various olefin epoxidation reactions with meta-chloroperbenzoic acid (MCPBA) under the mild condition. MnIII complexes 1a and 1c with the electron-withdrawing group -Cl and electron-donating group –CH3 showed little substituent effect on the epoxidation reactions. Product analysis, Hammett study and competition experiments with cis- and trans-2-octene suggested that MnIV = O, MnV = O, and MnIII-OOC(O)R species might be key oxidants in the epoxidation reaction under this catalytic system. In addition, the use of PPAA as a mechanistic probe demonstrated that Mn-acylperoxo intermediate (MnIII-OOC(O)R) 2 generated from the reaction of peracid with manganese complexes underwent both the heterolysis and the homolysis to produce MnV = O (3) or MnIV = O species (4). Moreover, the MnIII-OOC(O)R 2 species could react directly with the easy-to-oxidize substrate to give epoxide, whereas the species 2 might not be competent to the difficult-to-oxidize substrate for the epoxidation reaction.

Unprecedented enantioselective resolution copolymerization of racemic cis-internal epoxides and anhydrides was mediated by dinuclear aluminum complexes with multiple chirality, affording optically active polyesters with two contiguous stereogenic centers, and the unreacted substrates in good enantioselectivity. Unexpected stereoconvergence is observed in this resolution copolymerization, where the selectivity factor for the enantioselective formation of copolymer significantly exceeds the kinetic resolution coefficient based on the unreacted epoxide at various conversions. Catalytic activity and copolymer enantioselectivity are strongly influenced by the phenolate ortho-substituents of the ligand set, as well as the axial linker and its chirality. An enantiopure binaphthol-linked bimetallic AlIII complex allows stereoconvergent access to the stereoregular semi-crystalline polyesters and a concomitant kinetic resolution of the epoxide substrates.

A targeted new dioxo molybdenum(VI) ONO Schiff base complex was prepared for catalyzing epoxidation of olefins in water. This complex was characterized by FT-IR, NMR, UV–Vis, and X-ray crystallography techniques. DFT calculations are additionally performed to find ground and transition states for finding electronic structure and UV–Vis assignment. Afterward, a new protocol was defined for sustainable catalytic epoxidation of olefin in water using this complex as a green catalyst, and also remarkable results are obtained, such as turn over number up to 1400.

The new Co(II) - carboxamide complex (1) and Co3O4 nanoparticles (2), by way of thermal decomposition of (1) have been efficiently synthesised in the environment-friendly. X-ray diffraction reveals a slightly distorted octahedral coordination of cobalt (four nitrogens and two oxygens) in (1) and regular octahedral or tetrahedral ones (oxygens only) in (2). The investigation of (1) and (2) in the Mizoroki-Heck and epoxidation of alkens reactions showed them both to be powerful, green and inexpensive catalysts.

Five salicylamides [R1R2SaAmH; R1, R2 = N-substituents: nBu, H (1a); tBu, H (1b); nOc, H (1c); Bn, H (1d); and nBu, nBu (1e)] were successfully coordinated to the dioxomolybdic fragment, resulting in MoO2(R1R2SaAm)2 complexes 2a-e, which were characterized through elemental analysis, IR, 1H- and 13C NMR, ESI-HRMS, and XRD (for 2a,b,e). All complexes are active catalysts in the solvent-free epoxidation of cis-cyclooctene with tert-butyl hydroperoxide in decane (TBHPdec), showing high turnover frequencies (TOF 1890 h–1 for 2b) at 1 % loading. Using aqueous TBHP (TBHPaq) or H2O2, selectivity to cyclooctene oxide is always 100 %, although reactions are more sluggish. The 2c/TBHPaq system, which displays the best TOF (1070 h–1) at 0.25 % loading and 75 °C, allowed for the quantitative conversion of trans-2-octene into its epoxide, while low epoxide selectivity was observed in the case of 1-octene, styrene, and methyl oleate. In the latter case, 90 % epoxide selectivity at 92 % conversion was achieved with the 2b/TBHPdec system at 55 °C, under solvent-free conditions. Compared to related MoO2X2(O-amide)-type complexes, 2a-e exhibit increased catalytic performance under the greener conditions involving the use of aqueous oxidants.

Condensation of pyrrole with various aldehydes in the presence of BF3?etherate as an acid catalyst in water provides good yield of some dipyrromethanes. Prolongation of the reaction time with aldehydes substituted by electron-donating (mesityl) or electron-withdrawing (2,6-dichlorophenyl) groups on the ortho positions of the phenyl did not lead to decomposition or scrambling. Manganese trans disubstituted porphyrin complexes which derive from various dipyrromethanes and manganese tetraaryl porphyrin complexes including various substituents with different steric and electronic properties show good catalytic activity in epoxidation of alkenes by NaIO4 in the presence of imidazole (ImH). The study of steric and electronic effects of the catalysts on the epoxidation of olefins shows that Mn-porphyrin complexes with more bulky and electron-releasing groups on meso phenyls could increase the epoxidation yield of most alkenes.

A praseodymium(iii)-containing arsenotungstate K16H15Li7[Pr2(H2O)3(pzdc)As3W29O103]2·38H2O (1) (pzdc = pyrazine-2,3-dicarboxylic acid) was synthesized by a conventional aqueous solution method and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and single crystal X-ray diffraction. Structural analysis revealed that compound 1 was constructed by two identical subunits {Pr2(H2O)3(AsW9O33)3W2O4} bridged together by two pzdc ligands. In addition, compound 1 could act as an efficient catalyst for the epoxidation of olefins and oxidation of alcohols with hydrogen peroxide (H2O2) as the oxidant. In particular, the turnover frequency (TOF) in the oxidation of 1-phenylethanol reached up to 10170 h-1, which is higher than that of previously reported catalysts.

The reaction of N-(2-pyridylmethyl)iminodiisopropanol (H2pmidip), sodium azide, and manganese(II) salt in methanol leads to the isolation of a monomeric manganese complex of [Mn(Hpmidip)(N3)2]·CH3OH (1). The structure of 1 has been verified by single crystal X-ray diffractometry. The manganese ion in 1 is bonded with one Hpmidip? as tetradentate and two azido ligands in cis position in which the manganese ion is displayed a distorted octahedral geometry. One of two hydroxyl groups in the coordinated Hpmidip? ligand is protonated, while the other one is deprotonated. The manganese ion is assigned as 3+ oxidation state that verified by bond lengths and bond valence sum. Furthermore, the complex reveals a dimeric structure by O[sbnd]H?O hydrogen bonding interactions. 1 exhibited selective and effective catalytic properties for various olefins with moderate yields using m-CPBA (meta-chloroperoxybenzoic acid). The mechanistic studies of 1 for olefin epoxidation have been investigated by the Hammett study, the O[sbnd]O bond cleavage of PPAA (peroxyphenylacetic acid) as a mechanistic probe, and competitive experiments of cis- and trans-2-octene.

A monomeric tellurotungstate(iv)-supported rhenium carbonyl derivative: Na2H2[(CH3)4N]6[Te2W20O70{Re(CO)3}2]·20H2O (1) has been successfully isolated and structurally characterized by single crystal X-ray diffraction crystallography, IR and UV-Vis spectroscopy, thermogravimetric analysis, etc. In particular, complex 1 could act as a efficient and reusable heterogeneous catalyst for selective epoxidation of various alkenes including different cycloalkenes, styrene derivatives, internal and long-chain alkenes. For example, cis-cyclooctene undergoes up to 98.2% conversion and >99% selectivity at 75 °C in acetonitrile with 30% H2O2 as an oxidant. Additionally, the electrocatalytic property of 1 for NO2? reduction was also investigated.

A new class of tantalum-based peroxocarbonate ionic liquid ([P4,4,4,4]3[Ta(η2-O2)3(CO4)]) has been generated through the reaction of pressurized CO2 with [P4,4,4,4]3[Ta(O)3(η2-O2)] in the presence of H2O2 during the reaction process. The newly formed species has been verified by NMR, FT-IR, HRMS and density functional theory (DFT) calculations. The CO2-induced monomeric peroxocarbonate anion-based ionic liquid is more advantageous than the monomeric peroxotantalate analogue for the epoxidation of olefins under very mild conditions. Interestingly, the transformation between peroxotantalate and peroxocarbonate species is completely reversible, and CO2 can actually act as a trigger agent for epoxidation reaction. The further mechanism studies by DFT calculation reveal that peroxo η2-O2 (site a) affords higher reactivity towards the CC bond than that of peroxocarbonate-CO4 (site b). These quantitative illustrations of the relationship between structural properties and kinetic consequences enable rational design for an efficient and environmental IL catalyst for the epoxidation of olefins.

The organic carboxylic acid coordinated monomeric peroxoniobate-based ionic liquids (ILs) [TBA][NbO(OH)2(R)] (TBA = tetrabutylammonium; R = lactic acid (LA), glycolic acid (GLY), malic acid (MA)) were prepared and fully characterized by elemental analysis, NMR, IR, Raman, TGA, 93Nb NMR, and HRMS. These IL catalysts exhibited not only high catalytic activity for the epoxidation of olefins under very mild reaction conditions, as the turnover frequency of [TBA][NbO(OH)2(LA)] reached up to 110 h-1, but also satisfactory recyclability in the epoxidation by using only 1 equiv of hydrogen peroxide as an oxidant. Meanwhile, this work revealed that the ILs underwent structural transformation from [NbO(OH)2(R)]- to [Nb(O-O)2(R)]- (R = LA, GLY, MA) in the presence of H2O2 by a subsequent activity evaluation, characterization, and first-principles calculations. Moreover, the organic carboxylic acid coordinated monomeric peroxoniobate-based ILs were investigated using density functional theory (DFT) calculations, which identified that [Nb(O-O)2LA]- was more advantageous than [Nb(O-O)2(OOH)2]- for the epoxidation of olefins. Due to the coordination between the α-hydroxy acids and the monomeric peroxoniobate anions, the functionalized ILs can efficiently catalyze the epoxidation of a wide range of olefins and allylic alcohols under very mild conditions. Additionally, the effect of solvents on the reaction is illustrated. It was found that methanol can lower the epoxidation barriers by forming a hydrogen bond with a peroxo ligand attached to the niobium center.

The new coordination polymer formulated as [Et3SnVO3] (1) has been synthesized and shown by a combined single-crystal and synchrotron powder X-ray diffraction structural analysis, supported by solid-state NMR, to possess a three-dimensional network structure with the sodalite topology, formed by tetravanadate polyanions, [V4O12]4?, that are linked by Et3Sn+ spacers. The catalytic versatility of compound 1 for liquid phase organic reactions was demonstrated by applying it for the epoxidation of olefins, the oxidative dehydrogenation of alcohols, and the oxidation of benzyl alcohol to benzaldehyde and benzoic acid, using tert-butyl hydroperoxide (TBHP) as oxidant. Compound 1 acts a solid reservoir for soluble, catalytically active species, which promote high selectivities to the epoxide and carbonyl (aldehyde/ketone/acid) products. The epoxidation activity compares favorably with those reported for other organotin molybdate, tungstate and vanadate coordination polymers, and is superior to that displayed by the starting materials used for its synthesis (Et3SnBr and NH4VO3) and the metavanadate NBu4VO3.

The one-dimensional organic-inorganic hybrid material [MoO3(2,2′-bipy)] (1) (2,2′-bipy = 2,2′-bipyridine) has been used as a starting material to prepare the bipy-deficient phases [Mo2O6(2,2′-bipy)] (2) and [Mo3O9(2,2′-bipy)2] (3) in excellent yields. The hybrid 2 was obtained by a solid-state thermal treatment of 1 (300 °C, 10 min) while 3 was obtained by a hydrothermal treatment of 1 (160 °C, 6 d). A study was performed to compare the catalytic properties of 1-3 in the epoxidation of cis-cyclooctene at 55 °C with tert-butylhydroperoxide (TBHP) or aqueous H2O2 as oxidant. In all cases Cy was converted to cyclooctene oxide (CyO) with 100% selectivity, and Cy conversions increased in the order 1 2O2 (cosolvent CH3CN). The catalytic reactions occurred in homogeneous phase with active species formed in situ from 1-3. All three hybrids react with aqueous H2O2 to give the catalytically active oxodiperoxo complex [MoO(O2)2(2,2′-bipy)]. The 2:1 hybrid 2 was further examined for the epoxidation of other cyclic and linear non-functionalised olefins with TBHP, namely cyclododecene, 1-octene and trans-2-octene, and the biomass-derived olefins dl-limonene, α-pinene and methyl oleate.

Mn(III)-porphyrin containing #heterogeneous catalyst based on microporous polymeric constituents as a new class of #catalyst support from Korea University and Seoul National University of Science and Technology.

The aerobic oxidative C?C bond cleavage of vicinal diols catalyzed by vanadium amino triphenolates is described. Our results show that C?C bond cleavage can be performed in different solvents, under an air or oxygen atmosphere, with a large variety of glycols (cyclic or linear, with aromatic or aliphatic substituents) affording the corresponding carbonyl derivatives with high chemoselectivity. Reactions can be performed with as little as 10 ppm of catalyst reaching TON up to 81,000 and TOFs of up to 4150 h?1. A reaction mechanism, rationalized by density functional theory calculations, is also proposed. (Figure presented.).

The present work reports a study on the isomerization reactions of several alkyl epoxides to the corresponding allylic alcohols or bicyclic alcohols under microwave irradiation. The reaction occurred in the presence of lithium diisopropylamide as a base and different experimental conditions in terms of solvent, amount of the base, times and temperatures. The traditional heating with an oil-bath and the use of alternative organometallic bases, as the Lochmann-Schlosser bases, have been furthermore compared with the microwave heating. The results obtained show that the use of microwave irradiations on promoting the isomerization of epoxides gives access to a series of synthetically useful products, among which allylic alcohols and bicyclic alcohols, depending on the starting substrate.

Three organic ligands bearing 1,2,4-triazolyl donor moieties, (S)-4-(1-phenylpropyl)-1,2,4-triazole (trethbz), 4-(1,2,4-triazol-4-yl)benzoic acid (trPhCO2H), and 3-(1H-imidazol-4-yl)-2-(1,2,4-triazol-4-yl)propionic acid (trhis), were prepared to evaluate their coordination behavior in the development of molybdenum(VI) oxide organic hybrids. Four compounds, [Mo2O6(trethbz)2]·H2O (1), [Mo4O12(trPhCO2H)2]·0.5H2O (2a), [Mo4O12(trPhCO2H)2]·H2O (2b), and [Mo8O25(trhis)2(trhisH)2]·2H2O (3), were synthesized and characterized. The monofunctional tr-ligand resulted in the formation of a zigzag chain [Mo2O6(trethbz)2] built up from cis-{MoO4N2} octahedra united through common μ2-O vertices. Employing the heterodonor ligand with tr/-CO2H functions afforded either layer or ribbon structures of corner- or edge-sharing {MoO5N} polyhedra (2a or 2b) stapled by tr-links in axial positions, whereas -CO2H groups remained uncoordinated. The presence of the im-heterocycle as an extra function in trhis facilitated formation of zwitterionic molecules with a protonated imidazolium group (imH+) and a negatively charged -CO2- group, whereas the tr-fragment was left neutral. Under the acidic hydrothermal conditions used, the organic ligand binds to molybdenum atoms either through [N-N]-tr or through both [N-N]-tr and μ2-CO2- units, which occur in protonated bidentate or zwitterionic tetradentate forms (trhisH+ and trhis, respectively). This leads to a new zigzag subtopological motif (3) of negatively charged polyoxomolybdate {Mo8O25}n2n- consisting of corner- and edge-sharing cis-{MoO4N2} and {MoO6} octahedra, while the tetradentate zwitterrionic trhis species connect these chains into a 2D net. Electronic spectra of the compounds showed optical gaps consistent with semiconducting behavior. The compounds were investigated as epoxidation catalysts via the model reactions of achiral and prochiral olefins (cis-cyclooctene and trans-β-methylstyrene) with tert-butylhydroperoxide. The best-performing catalyst (1) was explored for the epoxidation of other olefins, including biomass-derived methyl oleate, methyl linoleate, and prochiral dl-limonene.

The reaction between [MoO2(acac)2] and an ONO type Schiff-base ligand (L?=?4-bromo-2-((2-hydroxy-5-methylphenylimino)methyl)phenol) resulted a new oligomer molybdenum complex ([MoO2(L)]n). The oligomer complex was characterized by elemental analysis, FT-IR, 1H and 13C NMR spectroscopies. A suitable single crystal of the complex was grown in DMSO and characterized by X-ray single crystal diffraction as monomer stabilized by one DMSO molecule, [MoO2L(DMSO)]. The [MoO2(L)]n complex was used as a catalyst in epoxidation of olefins. Besides the high activity and selectivity, very high turnover numbers were a remarkable advantage of the catalytic system.

A flexible one-pot strategy with pyramidal SeIV heteroatoms was employed for the assembly of the praseodymium-containing gly-decorated polyoxotungstate [{Pr3(H2O)10[Se2W22O76(gly)2]}2(Se2W7O30H2)]18? (1 a), which is constructed from one {Se2W7O30H2} unit and two identical {Pr3(H2O)10[Se2W22O76(gly)2]} units. Furthermore, the catalytic performance of Cs2Na4H12[{Pr3(H2O)10[Se2W22O76(gly)2]}2(Se2W7O30H2)]?25 H2O (1) for alkene epoxidation with hydrogen peroxide was investigated under mild reaction conditions, and the experimental results suggested that compound 1 exhibits good catalytic performance for the epoxidation of cyclooctene.

Dinuclear FeIII and NiII complexes, [(phenO)Fe(N3)]2(NO3)2 (1) and [(phenOH)Ni(N3)2]2 (2), were prepared by treating Fe(NO3)3?9 H2O and Ni(NO3)2?6 H2O in methanol, respectively, with phenOH (=N-(2-pyridylmethyl)-N′-(2-hydroxyethyl)ethylenediamine) and NaN3; both 1 and 2 were characterized by elemental analysis, IR spectroscopy, X-ray diffraction, and magnetic susceptibility measurements. Two ethoxo-bridged FeIII and two azido-bridged NiII were observed in 1 and 2, respectively; corresponding antiferromagnetic interaction via the bridged ethoxo groups and strong ferromagnetic coupling via the bridged end-on azido ligands within the dimeric unit were observed. Complex 1 did not exhibit any catalytic activity, while 2 exhibited excellent catalytic activities for the epoxidation of aliphatic, aromatic, and terminal olefins.

A new mononuclear nickel(II) complex, [NiII(dpaq)Cl] (1), containing a tetradentate monoamido ligand, dpaq (dpaq=2-[bis(pyridin-2-ylmethyl)amino]-N-(quinolin-8-yl)acetamide), has been synthesized and characterized by IR spectroscopy, elemental analysis, and UV/Vis spectroscopy. The structure of the nickel complex has been determined by X-ray crystallography. This nonheme NiII complex 1 catalyzed the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (m-CPBA) under mild conditions. Olefin epoxidation using this catalytic system has been proposed to involve a new reactive NiIV–oxo (4) species, based on the evidence from a PPAA (peroxyphenylacetic acid) probe, Hammett studies, H218O exchange experiments, and ESI mass spectroscopic analysis. Moreover, the nature of solvent significantly influenced partitioning between heterolytic and homolytic O?O bond cleavage of the Ni–acylperoxo intermediate (2). The O?O bond of 2 proceeded predominantly through heterolytic cleavage in a protic solvent, such as CH3OH. These results suggest that possibly a NiIV–oxo species is a common reactive intermediate in protic solvents. The two active oxidants, namely NiIV–oxo (3) and NiIII–oxo (4), which are responsible for stereospecific olefin epoxidation and radical-type oxidations, respectively, operate in aprotic solvents.

Product release is the rate-determining step in the arene syn-dihydroxylation reaction taking place at Rieske oxygenase enzymes and is regarded as a difficult problem to be resolved in the design of iron catalysts for olefin syn-dihydroxylation with potential utility in organic synthesis. Toward this end, in this work a novel catalyst bearing a sterically encumbered tetradentate ligand based in the tpa (tpa = tris(2-methylpyridyl)amine) scaffold, [FeII(CF3SO3)2(5-tips3tpa)], 1 has been designed. The steric demand of the ligand was envisioned as a key element to support a high catalytic activity by isolating the metal center, preventing bimolecular decomposition paths and facilitating product release. In synergistic combination with a Lewis acid that helps sequestering the product, 1 provides good to excellent yields of diol products (up to 97% isolated yield), in short reaction times under mild experimental conditions using a slight excess (1.5 equiv) of aqueous hydrogen peroxide, from the oxidation of a broad range of olefins. Predictable site selective syn-dihydroxylation of diolefins is shown. The encumbered nature of the ligand also provides a unique tool that has been used in combination with isotopic analysis to define the nature of the active species and the mechanism of activation of H2O2. Furthermore, 1 is shown to be a competent synthetic tool for preparing O-labeled diols using water as oxygen source.

Fluorophilic polyoxotungstates perform the selective epoxidations of internal and terminal double bonds by hydrogen peroxide (H2O2) activation in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), under mild temperature conditions. A hybrid synergy of supramolecular interactions, involving the inorganic cluster and the fluorinated solvent, is envisaged to boost H2O2 activation and the oxygen transfer mechanism. 1,2-Epoxides have been obtained with >99% selectivity and 98% yield at T = 40-70 °C.

We report a new and readily accessible class of titanium salalen complexes derived from cis-1,2-diaminocyclohexane (cis-DACH) and fluorinated salicylic aldehyde derivatives. With aqueous hydrogen peroxide as the oxidant, these complexes catalyze the epoxidation of terminal, nonconjugated olefins in high yields with high enantioselectivities. We furthermore discovered that the addition of certain acidic or basic co-catalysts significantly accelerated the epoxidation. For example, in the presence of 1 mol % Ti catalyst and 1 mol % pentafluorobenzoic acid, 1-octene epoxidation (95 % ee) was completed at room temperature within 8 h. The catalytic process was compatible with many functional groups (e.g., ethers, esters, halides, nitriles, and nitro groups), whereas free hydroxy groups appeared to slow down the reaction to some extent. Catalyst recycling was possible.

The reaction of [Fe(CF3SO3)2(PyNMe3)] with excess peracetic acid at -40 °C leads to the accumulation of a metastable compound that exists as a pair of electromeric species, [FeIII(OOAc)(PyNMe3)]2+ and [FeV(O)(OAc)(PyNMe3)]2+, in fast equilibrium. Stopped-flow UV/Vis analysis confirmed that oxygen atom transfer (OAT) from these electromeric species to olefinic substrates is exceedingly fast, forming epoxides with stereoretention. The impact of the electronic and steric properties of the substrate on the reaction rate could be elucidated, and the relative reactivities determined for the catalytic oxidations could be reproduced by kinetic studies. The observed fast reaction rates and high selectivities demonstrate that this metastable compound is a truly competent OAT intermediate of relevance for nonheme iron catalyzed epoxidations. A metastable nonheme iron-oxygen species undergoes exceedingly fast oxygen atom transfer (OAT) to olefins, providing epoxides with stereoretention. The reaction rates determined by stopped-flow UV/Vis analysis are in good agreement with the relative reactivities of different olefins, confirming that this compound is a competent OAT intermediate of relevance to nonheme iron catalyzed epoxidations.

An in situ generated catalyst system based on Mn(CF3SO3)2, picolinic acid, and peracetic acid converts an extensive scope of olefins to their epoxides at 0 °C in 5 min, with remarkable oxidant efficiency and no evidence of radical behavior. Competition experiments indicate an electrophilic active oxidant, proposed to be a high-valent Mn = O species. Ligand exploration suggests a general ligand sphere motif contributes to effective oxidation. The method is underscored by its simplicity and use of inexpensive reagents to quickly access high value-added products.

The epoxidation of unfunctionalized terminal aliphatic alkenes over heterogeneous catalysts is still a challenging task. Due to the tuning of a peculiar catalyst/oxidant/solvent combination, it was possible to attain good alkene conversions (73%) and excellent selectivity values (>98%) in the desired terminal 1,2-epoxide. Over the titanium-silica catalyst and in the presence of tert-butylhydroperoxide, the use of α,α,α-trifluorotoluene as an uncommon non-toxic solvent was the key factor for a marked enhancement of selectivity. The titanium-silica catalyst was efficiently recycled and reused after a gentle rinsing with fresh solvent.

The hybrid metal oxide-triazole materials [MoO3(trz)0.5] (1) and [W2O6(trz)] (2) (trz?=?1,2,4-triazole) have been hydrothermally synthesized and characterized by different techniques (TGA, SEM, 1H and 13C MAS NMR, FT-IR spectroscopy, and structure determination by Rietveld analysis of high resolution synchrotron powder XRD data). Materials 1 and 2 display distinct behaviors when applied as catalysts for oxidation reactions with alcohol, aldehyde, olefin and sulfide substrates, and are more effective with hydrogen peroxide as the oxidant than with tert-butylhydroperoxide. The MoVI hybrid 1 transforms into soluble active species during cis-cyclooctene epoxidation with H2O2. When consumption of H2O2 reaches completion, spontaneous reassembly of the 2-dimensional molybdenum oxide network of 1 takes place and the hybrid precipitates as a microcrystalline solid that can be easily separated and recycled. Reaction-induced self-separation behavior occurs with 1, H2O2 and other substrates such as methyl oleate and methylphenylsulfide. The WVI hybrid 2 behaves differently, preserving its structural features throughout the heterogeneous catalytic process.

This paper describes how the polymeric structure and environment surrounding supported catalysts can be used to affect the product outcome from a reaction. As well as reporting a size/shape selectivity, we also describe a significant effect on product distribution. Specifically, how the polymeric environment can favour or disfavour particular products. As such, these results illustrate how it may be possible to target more or less of a specific compound (from a possible mix) by careful choice of the polymer architecture surrounding a catalyst.

Treatment of the solvent adduct [MoO2Cl2(THF)2] with either 2 equivalents of N,N-dimethylbenzamide (DMB) or 1 equivalent of N,N′-diethyloxamide (DEO) gave the dioxomolybdenum(vi) complexes [MoO2Cl2(DMB)2] (1) and [MoO2Cl2(DEO)] (2). The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. Both complexes present a distorted octahedral geometry and adopt the cis-oxo, trans-Cl, cis-L configuration typical of complexes of the type [MoO2X2(L)n], with either the monodentate DMB or bidentate DEO oxygen-donor ligands occupying the equatorial positions trans to the oxo groups. The complexes were applied as homogeneous catalysts for the epoxidation of olefins, namely cis-cyclooctene (Cy), 1-octene, trans-2-octene, α-pinene and (R)-(+)-limonene, using tert-butylhydroperoxide (TBHP) as oxidant. In the epoxidation of Cy at 55°C, the desired epoxide was the only product and turnover frequencies in the range of ca. 3150-3200 mol molMo-1 h-1 could be reached. The catalytic production of cyclooctene oxide was investigated in detail, varying either the reaction temperature or the cosolvent. Complexes 1 and 2 were also applied in liquid-liquid biphasic catalytic epoxidation reactions by using an ionic liquid of the type [C4mim][X] (C4mim = 1-n-butyl-3-methylimidazolium; X = NTf2, BF4 or PF6] as a solvent to immobilise the metal catalysts. Recycling for multiple catalytic runs was achieved without loss of activity.

Organometallic Fe complexes with exceptionally high activities in homogeneous epoxidation catalysis are reported. The compounds display FeII and FeIII oxidation states and bear a tetracarbene ligand. The more active catalyst exhibits activities up to 183 000 turnovers per hour at room temperature and turnover numbers of up to 4300 at -30°C. For the FeIII complex, a decreased Fenton-type reactivity is observed compared with FeII catalysts reported previously as indicated by a substantially lower H2O2 decomposition and higher (initial) turnover frequencies. The dependence of the catalyst performance on the catalyst loading, substrate, water addition, and the oxidant is investigated. Under all applied conditions, the advantageous nature of the use of the FeIII complex is evident.

Herein, we report the formation of a highly reactive nickel-oxygen species that has been trapped following reaction of a NiII precursor bearing a macrocyclic bis(amidate) ligand with meta-chloroperbenzoic acid (HmCPBA). This compound is only detectable at temperatures below 250 K and is much more reactive toward organic substrates (i.e., CH bonds, CC bonds, and sulfides) than previously reported well-defined nickel-oxygen species. Remarkably, this species is formed by heterolytic OO bond cleavage of a Ni-HmCPBA precursor, which is concluded from experimental and computational data. On the basis of spectroscopy and DFT calculations, this reactive species is proposed to be a NiIII-oxyl compound. A highly reactive nickel-oxygen species has been spectroscopically trapped after heterolytic OO bond cleavage during the reaction of a NiII precursor with meta-chloroperbenzoic acid (HmCPBA). This species is used to carry out the oxidation of different substrates, such as olefins, sulfides, and CH bonds (see scheme).

We prepared supported phosphorus-containing tetranuclear peroxotungstate ([PO4{WO(O2)2}4]3-, denoted by PW4) catalysts by using zinc-modified SnO2 supports with different zinc contents [PW4-Zn(x)/SnO2, in which x denotes the zinc content (wt%)]. The supported catalysts, in particular PW4-Zn(0.8)/SnO2, could act as efficient and reusable heterogeneous catalysts for selective oxidation with aqueous H2O2 as the terminal oxidant. The catalytic performance of PW4-Zn(0.8)/SnO2 was much superior to those of the corresponding homogeneous analogue THA3PW4 (THA=tetra-n-hexylammonium) and the previously reported tungstate-based heterogeneous catalysts such as our W-Zn/SnO2. In the presence of PW4-Zn(0.8)/SnO2, various types of organic substrates such as alkenes, amines, silanes, and sulfides could be converted into the corresponding oxygenated products in high to excellent yields by using near-stoichiometric amounts of H2O2 with respect to the substrates (typically 1.2 equiv.). The PW4 species interacting with highly dispersed Zn2+ species on SnO2 likely plays an important role in the present oxidation.

Composites of [γ-H2PV2W10O40]3- and [α-SiW12O40]4- supported on Fe2O3 (PV2-SiW12/Fe2O3, in particular, the molar ratio of PV2/SiW12 = 1/1) could act as effective and reusable heterogeneous catalysts for selective oxidation with aqueous hydrogen peroxide. In the presence of PV2-SiW12/Fe2O3, various kinds of organic substrates such as alkenes, sulfides, arenes, and alkanes could selectively be converted into the corresponding oxygenated products in moderate to high yields. The observed catalyses for the present oxidations were intrinsically heterogeneous, and PV2-SiW12/Fe2O3 could be reused at least three times for each oxidation (epoxidation, sulfoxidation, and arene hydroxylation) without appreciable losses of the high catalytic performance.

A new bis-facial dinuclear ruthenium complex, {[RuII(bpy)]2(μ-bimp)(μ-Cl)}2+, 22+, containing a hexadentate pyrazolate-bridging ligand (Hbimp) and bpy as auxiliary ligands has been synthesized and fully characterized in solution by spectrometric, spectroscopic, and electrochemical techniques. The new compound has been tested with regard to its capacity to oxidize water and alkenes. The in situ generated bis-aqua complex, {[RuII(bpy)(H2O)]2(μ-bimp)}3+, 33+, is an excellent catalyst for the epoxidation of a wide range of alkenes. High turnover numbers (TN), up to 1900, and turnover frequencies (TOF), up to 73 min-1, are achieved using PhIO as oxidant. Moreover, 33+ presents an outstanding stereospecificity for both cis and trans olefins toward the formation of their corresponding epoxides due to specific interactions transmitted by its ligand scaffold. A mechanistic analysis of the epoxidation process has been performed based on density functional theory (DFT) calculations in order to better understand the putative cooperative effects within this dinuclear catalyst. (Figure Presented).

A simple route has been established for grafting molybdenum carbonyl onto the surface of a diaminosilane-modified SBA-15 molecular sieve. The successful grafting of the molybdenum carbonyl species onto diamine-functionalized SBA-15 was evident from FT-IR studies. The resultant molybdenum-carbonyl-complex-grafted SBA-15 (SBA-DA-Mo) materials show promising activity for the epoxidation of various olefins with good conversion (90-95%) and the formation of epoxide as the major product. The catalytic activity remains constant over several runs.

A method for the regioselective transformation of dienes to carbonyl compounds has been developed. Electron-rich olefins react selectively to yield valuable aldehydes and ketones. The method is based on the catalyst [Fe(OTf)2(mix-BPBP)] with an oxidant combination of H2O2 (1.0 equiv.) and NaIO4 (1.5 equiv.); it uses mild conditions and short reaction times, and it outperforms other olefin cleavage methodologies. The combination of an Fe-based catalyst, [Fe(OTf)2(mix-BPBP)], and the oxidants H2O2 and NaIO4 can discriminate between electronically different double bonds and oxidatively cleave the electron-rich bond in dienes to yield aldehydes and ketones in a regioselective manner. The reaction requires mild conditions (0-50 C) and short reaction times (70 min).

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.

Ru-aqua complex {[RuII(trpy)(H2O)] 2(μ-pyr-dc)}+ is a powerful epoxidation catalyst for a wide range of linear and cyclic alkenes. High turnover numbers (TNs), up to 17000, and turnover frequencies (TOF), up to 24120 h-1 (6.7 s -1), have been obtained using PhIO as oxidant. This species presents an outstanding stereospecificity for both cis and trans olefins towards the formation of their corresponding cis and trans epoxides. In addition, it shows different reactivity to cis and trans olefins due to a substrate orientation supramolecular effect transmitted by its ligand scaffold. This effect together with the impressive reaction rates are rationalized using electrochemical techniques and DFT calculations. A new Ru-aqua complex that behaves as a powerful epoxidation catalyst for a wide range of linear and cyclic alkenes is reported. High turnover numbers and frequencies are obtained by using PhIO as oxidant. The complex shows an outstanding stereospecificity for both cis and trans olefins towards the formation of their corresponding cis and trans epoxides (see figure).

A novel organic-inorganic hybrid heterogeneous catalyst system was obtained from the reaction of the molybdenum(VI) complex of salicylidene 2-picoloyl hydrazone with mesoporous silica containing 3-chloropropyl groups prepared by a direct synthetic approach involving hydrolysis and co-condensation of tetraethylorthosilicate (TEOS) and 3-chloropropyltrimethoxysilane in the presence of the triblock copolymer P123 as template under acidic conditions. Characterization of the functionalized materials by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), N2 adsorption/desorption, FT-IR and UV-Vis spectroscopy, and thermogravimetric analysis (TGA) reveals that the molybdenum complex is successfully grafted into the pores of the host silica structure. Furthermore, the resulting hybrid material was found to be highly active catalyst in the liquid-phase epoxidation of olefins with t-BuOOH as the oxygen source. Leaching tests and metal analysis of reaction solutions show that the catalytic activity stemmed from the immobilized species, not from the leaching of active species into solution.

Bis(pyrazolyl)methanetetracarbonyl-molybdenum(0), cis-[Mo(CO) 4(BPM)] (1), was prepared from Mo(CO)6 and the ligand bis(pyrazolyl)methane (BPM), and examined as a catalyst precursor for the epoxidation of olefins using tert-butylhydroperoxide (TBHP) as oxidant. Catalytic activities followed the sequence 1-octene Mo-1 h-1 at 55°C and 1175 mol molMo-1 h-1 at 75°C, which compare favourably with those found for other molybdenum carbonyl complexes used as catalyst precursors for the same reaction under similar conditions. Catalytic activities were lower in the presence of organic co-solvents, decreasing in the sequence 1,2-dichloroethane > nitromethane > ethanol > hexane > acetonitrile. It is proposed that the oxodiperoxo complex [MoO(O2)2(BPM)] (2) may be the active catalyst formed in situ by oxidative decarbonylation of 1, since crystals of 2 suitable for structure determination by X-ray diffraction were obtained from the reaction solution recovered after a catalytic run at 55°C with cis-cyclooctene as substrate. In support of this hypothesis, the catalytic performance of 2 for the epoxidation of cyclooctene at 55°C is very similar to that for 1.

The molybdenum tricarbonyl complexes [Mo(CO)3(HC(3,5-Me 2pz)3)] (1) and [Mo(CO)3(HC(pz)3)] (2) (HC(3,5-Me2pz)3 = tris(3,5-dimethyl-1-pyrazolyl) methane, HC(pz)3 = tris(1-pyrazolyl)methane) were obtained in good yields by the microwave-assisted reaction of Mo(CO)6 with the respective organic ligand. Complete oxidative decarbonylation of 1 and 2 was achieved by reaction with excess tert-butylhydroperoxide (TBHP) in 1,2-dichloroethane at 55 °C. For complex 1, the (μ2-oxo) bis[dioxomolybdenum(VI)] hexamolybdate of composition [{MoO2(HC(3,5- Me2pz)3)}2(μ2-O)][Mo 6O19] (3) was obtained in good yield, and its structure was determined by single crystal X-ray diffraction. The compound (4) obtained by oxidative decarbonylation of 2 was not unambiguously identified, but may be chemically analogous to 3. Compounds 1-4 were examined for the first time as homogeneous (pre)catalysts for the epoxidation of olefins with TBHP, using different types of cosolvents at 55 °C. During the catalytic reactions 1 and 2 transform in situ into 3 and 4, respectively, and the latter two are fairly stable catalysts. Catalytic tests and characterization studies of the recovered catalysts were carried out in an attempt to understand the kinetic differences observed between the compounds prepared in situ during the catalytic reaction and those prepared prior to the catalytic reaction, from the same precursor complex.

We developed a series of micro-size hexagon-faced plate and rods from Mn(III)-porphyrin and In(III) whose lengths were modulated by water. Regardless of a wide range of length distribution, they are isostructural. In addition, the heterogeneous olefin oxidation was performed.

A novel visible light photocatalyst of iron(II) bipyridine complex encapsulated within NaY zeolite forselective oxygenation of styrene with high turnover (1800) and high benzaldehyde selectivity (86%) usinghydrogen peroxide as the oxidant under ambient conditions was explored. This photocatalyst was alsoeffective for the oxidation of other olefins, such as 4-cyanostyrene, 4-methoxystyrene, 3-methylstyrene,1,1-diphenylethylene, cis-stilbene, trans-stilbene, trans- β-methylstyrene, α-methylstyrene, triph-enylethylene, 1-octene, 2-octene, cyclohexene and cyclooctene, into the corresponding aldehydes,ketones or olefin oxides. The study shows that the photooxygenation of styrene occurs within thesupercages of zeolite Y, the products benzaldehyde and formaldehyde escape into the solution afterreaction, leading to high turnovers. Based on the experimental results, the photooxidation mechanism isalso discussed.

Didecyldimethylammonium tungstate has been designed as a balanced catalytic surfactant to form acidic three-liquid-phase microemulsion systems at room temperature in the presence of water, a non-chlorinated solvent and dimethyldioctylammonium salts (hydrogen sulfate and dihydrogen phosphate). The triphasic system is efficient for the oxidation of olefins, sulfides and thiophenes under mild conditions. Moreover, the recovery and reusability of the catalyst, the straightforward separation of products and catalysts in two distinct phases as well as the possible use of environmentally friendly solvents such as tert-butyl acetate, make this system particularly attractive for catalytic oxidation reactions involving hydrogen peroxide as the primary oxidant under acidic or neutral conditions.