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This study describes a time-dependent self-assembly generation of new copper(II) coordination compounds from an aqueous-medium reaction mixture composed of copper(II) nitrate, H3bes biobuffer (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), ammonium hydroxide, and benzenecarboxylic acid, namely, 4-methoxybenzoic (Hfmba) or 4-chlorobenzoic (Hfcba) acid. Two products were isolated from each reaction, namely, 1D coordination polymers [Cu3(μ3-OH)2(μ-fmba)2(fmba)2(H2O)2]n (1) or [Cu2(μ-OH)2(μ-fcba)2]n (2) and discrete tetracopper(II) rings [Cu4(μ-Hbes)3(μ-H2bes)(μ-fmba)]·2H2O (3) or [Cu4(μ-Hbes)3(μ-H2bes)(μ-fcba)]·4H2O (4), respectively. These four compounds were obtained as microcrystalline air-stable solids and characterized by standard methods, including the single-crystal X-ray diffraction. The structures of 1 and 2 feature distinct types of metal-organic chains driven by the μ3- or μ-OH- ligands along with the μ-benzenecarboxylate linkers. The structures of 3 and 4 disclose the chairlike Cu4 rings assembled from four μ-bridging and chelating aminoalcoholate ligands along with μ-benzenecarboxylate moieties playing a core-stabilizing role. Catalytic activity of 1-4 was investigated in two model reactions, namely, (a) the mild oxidation of saturated hydrocarbons with hydrogen peroxide to form alcohols and ketones and (b) the mild carboxylation of alkanes with carbon monoxide, water, and peroxodisulfate to generate carboxylic acids. Cyclohexane and propane were used as model cyclic and gaseous alkanes, while the substrate scope also included cyclopentane, cycloheptane, and cyclooctane. Different reaction parameters were investigated, including an effect of the acid cocatalyst and various selectivity parameters. The obtained total product yields (up to 34% based on C3H8 or up to 47% based on C6H12) in the carboxylation of propane and cyclohexane are remarkable taking into account an inertness of these saturated hydrocarbons and low reaction temperatures (50-60 °C). Apart from notable catalytic activity, this study showcases a novel time-dependent synthetic strategy for the self-assembly of two different Cu(II) compounds from the same reaction mixture.

Iron hexamesityl-5,15-diazaporphyrin was synthesized through the cross-coupling reaction of tetrabromodiazaporphyrin. The use of chloroiron(III) hexamesityl-5,15-diazaporphyrin as a catalyst for oxidation of cyclooctane showed high performance with a total TON up to 731. The introduction of bulky mesityl groups at β-positions prevented the catalyst deactivation via formation of a μ-oxo dimer.

The commercial dichloro(2-pyridinecarboxylato)gold(III) complex (1), anchored on different carbon materials, is reported for the first time as a catalyst in the cyclohexane hydrocarboxylation to cyclohexanecarboxylic acid. The reaction was carried out in the presence of CO and water, peroxodisulfate, at ca. 50 °C, with 1 in solution and anchored on carbon nanotubes, carbon xerogel or activated carbon, with three different surface chemistries: original forms (CNT, CX or AC, respectively), oxidized with HNO3 (-ox) or oxidized with HNO3 and subsequently treated with NaOH (-ox-Na). 1@CNT-ox-Na was the best catalyst, yielding up to 78% of cyclohexanecarboxylic with a selectivity of 99%. Recycling studies showed that the catalyst was stable up to 4 cycles, the first decrease (11%) on the hydrocarboxylation yield being observed on the 5th cycle. No leaching of gold was found into the solution. The hydrocarboxylation of other cycloalkanes (cyclopentane, cycloheptane and cyclooctane) was also tested in the best conditions found for cyclohexane, but the respective carboxylic acids were obtained in considerably lower yields, which can be explained by different stabilities of cycloalkyl radicals.

In this study, we prepared three polymer-anchored Schiff base ligands and their Cu(II), Co(II) and Ni(II) transition metal complexes. For this purpose, we synthesized three Schiff base ligands from the reaction of 2,4-dihydroxybenzaldehyde with diamines in the ethanol solution and characterized by the analytical and spectroscopic methods. We investigated the electrochemical and photophysical properties of the free Schiff base ligands in different solvents and concentrations. In the electrochemical studies, we found that the ligands show the reversible and irreversible redox processes. In order to obtain the polymer-anchored ligands, we used Merrifield’s peptide resin (PS) as solid support. The surface morphologies of the polymer anchored Schiff base ligands were done with the scanning electron microscopy (SEM). We did alkene epoxidation and alkane oxidation reactions of the metal complexes and used the cyclohexene, styrene, cyclohexane and cyclooctane as the substrate and they show the low catalytic activity. The metal complexes have no selectivity in the oxidation reactions. The polymer anchored Schiff base ligands and their metal complexes have high thermal stability at the higher temperatures. Keywords: Schiff base, Solid state, Oxidation, Epoxidation, Thermal

A pincer-iridium complex bearing a Lewis-base-free X-type alumanyl ligand has been synthesized. X-ray diffraction, NMR and IR spectroscopy, as well as XANES analysis confirmed its tetrahydrido-IrV structure and Lewis acidity at the Al center as supported by DFT calculations. The resulting complex was applied as a catalyst for the transfer dehydrogenation of cyclooctane.

Catalysts for the oxidation of NH3 are critical for the utilization of NH3 as a large-scale energy carrier. Molecular catalysts capable of oxidizing NH3 to N2 are rare. This report describes the use of [Cp*Ru(PtBu2 NPh2 )(15 NH3 )][BArF4 ], (PtBu2 NPh2 =1,5-di(phenylaza)-3,7-di(tert-butylphospha)cyclooctane; ArF =3,5-(CF3 )2 C6 H3 ), to catalytically oxidize NH3 to dinitrogen under ambient conditions. The cleavage of six N-H bonds and the formation of an N≡N bond was achieved by coupling H+ and e- transfers as net hydrogen atom abstraction (HAA) steps using the 2,4,6-tri-tert-butylphenoxyl radical (t Bu3 ArO. ) as the H atom acceptor. Employing an excess of t Bu3 ArO. under 1 atm of NH3 gas at 23 °C resulted in up to ten turnovers. Nitrogen isotopic (15 N) labeling studies provide initial mechanistic information suggesting a monometallic pathway during the N⋅⋅⋅N bond-forming step in the catalytic cycle.

Iridium complexes bearing PCP-type pincer ligands are the most effective catalysts reported to date for the low-temperature (≤ca. 200 °C) dehydrogenation of alkanes. To investigate the activity of formally isoelectronic ruthenium complexes, we have synthesized the neutral 2,7-di-tert-butyl-4,5-bis(diisopropylphosphino)-9,9-dimethylthioxanthene (iPrxanPSP) pincer ligand and several Ru complexes thereof. The (iPrxanPSP)Ru complexes catalyze alkane transfer dehydrogenation of the benchmark cyclooctane/t-butylethylene (COA/TBE) couple with turnover frequencies up to ca. 1 s–1 at 150 °C and 0.2 s–1 at 120 °C, the highest rates for alkane dehydrogenation ever reported at such temperatures. Dehydrogenation of n-octane, however, is much less effective. A combination of experiment and DFT calculations allow us to explain why (iPrxanPSP)Ru is more effective than (iPrPCP)Ir for dehydrogenation of COA, while the reverse is true for dehydrogenation of n-alkanes. Considering only in-cycle species and simple olefin comp...

Aerobic oxidation of hydrocarbons is one of the research fronts in organic chemistry as well as in chemical engineering. In this aspect, many efforts are devoted to develop heterogeneous catalysts that can convert hydrocarbon to its corresponding alcohol/ketone (ol/one) with selectivity more than 90%. However, achieving this target becomes difficult due to possible secondary reactions of initially formed ol/one mixture. Hence, this study aims to report the catalytic activity of Fe(BTC) (BTC: 1,3,5-benzenetricarboxylate) and tetrabutylammonium bromide (TBAB) in aerobic oxidation of cyclooctane at 73% conversion to its respective ol/one with 84% selectivity after 24 h at 120 °C in the absence of any radical initiators. Interestingly, the selectivity of ol/one is higher than 90% at cyclooctane conversion around 20% under present reaction conditions. Reusability and leaching experiments demonstrate the stability of Fe(BTC) during the oxidation reaction. Furthermore, the present catalytic system can also be extended to oxidize other linear hydrocarbons to their respective ol/one products with the selectivity ranging between 88–97 %.

A new Co(II) complex with formula [Co(tptz)Cl2]·2H2O (tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine) has been synthesized and characterized by X-ray crystallography, elemental analyses and spectroscopic methods. It was then supported on modified Fe3O4 nanoparticles using tetraethylorthosilicate (TEOS) and (3-aminopropyl)trimethoxysilane (APTMS) and designated as a Fe3O4@SiO2@APTMS@complex nanocatalyst. The prepared nanocatalyst was characterized by means of FT-IR, Raman, XPS, EDX, XRD, VSM, SEM and TEM studies. The catalytic activity of the [Co(tptz)Cl2]·2H2O complex and Fe3O4@SiO2@APTMS@complex designated as catalysts A and B was used for oxidation of activated secondary alkanes such as fluorene, diphenyl methane, ethylbenzene, cyclooctane and adamantane. Observation of 39–99% conversions and 27–100% selectivities toward the corresponding ketones as well as the heterogeneity and reusability of the catalyst B seem promising.

Mixed-metal metal organic frameworks have received considerable attention in recent years and it has been shown that the activity of the parent metal organic framework (MOF) is often enhanced upon doping with external metal ions within the framework. In this context, Cu2+ ions with different loadings were incorporated within the ZIF-8 framework to obtain a series of Cu-doped ZIF-8 materials and their activity was examined in the aerobic oxidation of hydrocarbons. The as-synthesized Cu-doped solids were characterized by powder X-ray diffraction (XRD), ultraviolet diffuse reflectance spectroscopy (UV-DRS), scanning electron microscopy (SEM), Fourier Transform infrared (FT-IR), electron paramagnetic resonance (EPR) and inductively coupled plasma (ICP) analysis. The experimental results revealed that the activity of Cu-doped ZIF-8 is much higher than that of the parent ZIF-8 in all the tested substrates at 120 °C. Furthermore, the activity of the Cu-doped ZIF-8 with the highest Cu loading was eight fold higher than that of the parent ZIF-8 in the aerobic oxidation of cyclooctane (1) at 120 °C with more than 80% selectivity to the corresponding cyclooctanol/cyclooctanone (ol/one) mixture. Cu-doped ZIF-8 was reused two times with no significant drop in its activity under identical conditions. Furthermore, comparison of the two times reused solid with that of the fresh solid by powder XRD and SEM analysis revealed identical structural integrity and morphology, respectively during the oxidation reactions.

The efficient synthesis of two new stereoisomeric 3-aminocyclooctanetriols and new halocyclitol derivatives of them starting from cis,cis-1,3-cyclooctadiene are reported. Reduction of cyclooctene endoperoxide, obtained by photooxygenation of cis,cis-1,3-cyclooctadiene, with zinc yielded a cyclooctene diol followed by acetylation of the hydroxyl group, which gave dioldiacetate by OsO4/NMO oxidation. The cyclooctane dioldiacetate prepared was converted to the corresponding cyclic sulphate via the formation of a cyclic sulphite in the presence of catalytic RuO4. Reaction of this cyclic sulphate with a nucleophilic azide followed by the reduction of the azide group provided the target, 3-aminocyclooctanetriol. The second key compound, bromotriol, was prepared by epoxidation of the cyclooctene diol with m-chloroperbenzoic acid followed by hydrolysis with HBr(g) in methanol. Treatment of bromotriol with NaN3 and the reduction of the azide group yielded the other 3-aminocyclooctanetriol desired. Hydrolysis of the epoxides with HCl(g) in methanol gave stereospecifically new chlorocyclooctanetriols.

Abstract Crystalline hybrid catalysts based on molybdenum or tungsten oxide and aliphatic diamines were synthesized via simple, eco-friendly reproducible methodologies, starting from commercially available and relatively inexpensive organic and inorganic precursors, and using water as solvent under mild conditions. The crystal structures of the obtained fine powdered solids were solved ab initio from powder X-ray diffraction data. The type of organic component (1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopropane) may play a structure-directing role. On the other hand, different metals (M = Mo, W) may lead to isostructural one-dimensional hybrids of the type MO3(L) with the same bidentate diamine ligand L. The prepared catalysts were investigated for the liquid phase oxidation of saturated and unsaturated hydrocarbons (cis-cyclooctene, cyclooctane), using different types of oxidants (O2, H2O2, tert-butyl hydroperoxide). Differences in catalytic performances associated with distinct structural features were investigated. Graphic Abstract

A synthetic method to prepare bicyclo[6.3.0]undeca-2,4,9,trienyl esters efficiently from gold(I)-catalyzed Rautenstrauch rearrangement/1,5-hydride shift/8-endo-dig cyclization of 1-ene-4,10-diynyl esters is described. The suggested double cycloisomerization mechanism delineates the first example of an unactivated all-carbon tethered 1,7-enyne, either preformed or formed in situ, which undergoes an 8-endo-dig cyclization pathway to give a cyclooctane motif. It also offers an extremely rare synthetic method in organic chemistry that can sequentially assemble both ring components of the bicyclic motif from an acyclic precursor in one step.

Autoxidation of cycloalkanes (C5–C8) with molecular oxygen under catalyst-free and solvent-free conditions was conducted systematically for the first time, focusing on the autoxidation temperature and product distribution. The autoxidation of cyclopentane, cyclohexane, cycloheptane and cyclooctane occurs at 120 °C, 130 °C, 120 °C, and 105 °C respectively, with obvious oxidized products formation. At 140 °C, 145 °C, 130 °C and 125 °C, acceptable yields of the oxidized products could be obtained for them, and the oxidized product distributions were investigated in detail. The autoxidation of cycloalkanes follows the pseudo-first-order kinetic model and the apparent activation energies (Ea) for the autoxidation of cyclopentane and cyclohexane are 159.76 kJ·mol− 1 and 86.75 kJ·mol− 1 respectively. This study can act as an important reference in screen of suitable reaction temperature and comparison of the performance of various catalysts in the catalytic oxidation of cycloalkanes in the attempt to enhance the oxidized product selectivity.

A series of tBu- and iPr-substituted PNP–pincer Ir and Rh complexes with pyrrole-based core were synthesized and characterized. The structures of the obtained complexes were varied depending on the size of alkyl substituents and ligands other than PNP ligand. All of them exhibit low activity toward transfer dehydrogenation of cyclooctane., ファイル公開：2019-04-23

Syntheses of new asymmetric pincer precursors 1,3-C6H4{CH2P(tBu,X)}2 (tBu,XPCPH; X = Cl, SiMe3, OPh) and a new class of hybrid donor/acceptor pincer ligands 1,3-C6H4{CH2P(tBu,Rf)}2 (tBu,RfPCPH; Rf = CF3, C2F5) are reported. All tBu,XPCPH compounds are obtained as mixtures of meso and rac diastereomers in varying ratios (meso : rac ∼ 4 : 1 to 3 : 2) which were used without separation. Treatment of Ru(cot)(cod) with tBu,CF3PCPH under 1 atm H2 in acetone at 20 °C produced the hydride solvate (tBu,CF3PCP)Ru(acetone)xH which was not isolated, but could be trapped as stable diene complexes (tBu,CF3PCP)Ru(L)2H (L2 = cod (), nbd ()). Catalytic cyclooctane dehydrogenation studies demonstrate that has ∼50% the activity of (CF3PCP)Ru(cod)(H), but significantly higher catalyst stability and is able to operate at higher catalyst loading concentrations without deactivation via bimolecular decomposition.

The mechanism of cyclooctane metathesis using confinement effect strategies in mesoporous silica nanoparticles (MSNs) is discussed by catalytic experiments and density functional theory (DFT) calculations. WMe6 was immobilized inside the pores of a series of MSNs having the same structure but different pore diameters (60, 30 and 25 A). Experiments in cyclooctane metathesis suggest that confinement effects observed in smaller pores (30 and 25 A) improve selectivity towards the dimeric cyclohexadecane. In contrast, in larger pores (60 A) a broad product distribution dominated by ring contracted cycloalkanes was found. The catalytic cycle and potential side reactions occurring at [(≡SiO-)WMe5] were examined with DFT calculations. Analysis of the geometries for the key reaction intermediates allowed to rationalize the impact of a confined environment on the enhanced selectivity towards the dimeric product in smaller pores, while in large pores the ring contracted products are favored.

A new hybrid Fe3O4@mSiO(2)@Cu-4 material was constructed by loading a bio-inspired tetracopper(II) coordination compound [Cu-4(mu(4)-O){N(CH2CH2O)(3)}(4)(BOH)(4)][BF4](2) (Cu-4) onto the Fe3O4@mSiO(2) core-shell nanoparticles (NPs) composed of a magnetite (Fe3O4) core and mesoporous silica (mSiO(2)) shell with perpendicularly aligned channels. The obtained Fe3O4@mSiO(2)@Cu-4 magnetic nanoparticles were characterized by transmission electron microscopy (TEM), FT-IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and field-dependent magnetization. This hybrid material acts as a magnetically recoverable C-H functionalization nanocatalyst, namely for the mild oxidation, by t-butyl hydroperoxide at 50-70 degrees C in acetonitrile medium, of cycloalkanes (cyclopentane, cyclohexane, cycloheptane, and cyclooctane) to the corresponding alcohols and ketones (with up to similar to 15% yields based on cycloalkane; TON 335). A related oxidation process using cyclohexanol as a more reactive substrate leads to the formation of cyclohexanone in up to similar to 25% yield (TON 570). The Fe3O4@mSiO(2)@Cu-4 nanocatalyst can be recycled five times without an appreciable loss of activity. The bond-, regio-, and stereoselectivity parameters were investigated in the oxidation of different alkane substrates (n-hexane, n-heptane, n-octane, methylcyclohexane, adamantane, cis- and trans-1,2-demethylcyclohexane), and the obtained results were compared with the homogeneous systems based on the Cu-4 catalyst. In particular, the high bond selectivity parameters detected in the oxidation of methylcyclohexane (1 degrees:2 degrees:3 degrees of 1:8:142) and adamantane (2 degrees:3 degrees of 1:21) catalyzed by Fe3O4@mSiO(2)@Cu-4 suggest that the reactions possibly occur in hydrophobic pockets of the nanocatalyst. (C) 2016 Elsevier B.V. All rights reserved.

Self-assembly reactions of copper(II) nitrate with aminoalcohols {bis(2-hydroxyethyl)amino-tris(hydroxymethyl)methane (H5bis-tris) or 1,3-bis(tris(hydroxymethyl)methylamino)propane (H6bis-tris-propane)} as main N,O-building blocks, and isonicotinic acid (Hinic) or sodium azide (NaN3) as ancillary ligand sources resulted in two new copper(II) compounds [{Cu(H4.5bis-tris)(inic)}2](NO3)·2H2O (1) and [Cu(H5bis-tris-propane)(N3)]·2H2O (2). The obtained products were isolated as stable microcrystalline solids and fully characterized including by single-crystal X-ray diffraction, which disclosed the six-coordinate copper(II) centers with distorted octahedral {CuN2O4} or {CuN3O3} environments. The structures of 1 and 2 feature the formation of complex 3D H-bonded networks that were topologically classified as cbs-3,4-Cmmm-2 and sxd underlying nets, respectively. Both compounds 1 and 2 are soluble in water (S25 °C ≈ 6–12 mg mL−1) and act as efficient homogeneous catalysts for the mild and acid-promoter-free oxidation, by aqueous hydrogen peroxide, of C5–C8 cycloalkanes (cyclopentane, cyclohexane, cycloheptane, and cyclooctane) to give the corresponding cyclic alcohols and ketones. The influence of various reaction parameters (time, solvent composition, loading of substrate, oxidant, and catalyst, presence of a radical trap), bond- and regioselectivity features, and substrate scope were investigated and discussed in detail. A notable feature of the present catalysts concerns their high activity without the requirement for any promoter or co-catalyst, resulting in up to 46% total product yields based on cycloalkane.

The reactions of some acceptors (∙CH3, ∙OOH, ∙CCl3, O3, and Br∙) with saturated cyclic hydrocarbons, viz., cyclohexane, cycloheptane, and cyclooctane were studied by the DFT methods based on B3LYP and PBE0 functionals, the method based on the double hybrid functional B2PLYP, a combined ONIOM approach (CCSD:B3LYP)) and the coupled-cluster method (CCSD) using the 6-31+G**, aug-cc-pVDZ, Midi-X, and SVP basis sets. A specific feature of these reactions is that their rates depend on the excess ring energy, although no ring opening occurs in all cases.

The chapter provides an overview of synthetic approaches and applications in sorption and catalysis of mesoporous surface-functionalized silicas. We have synthesized a series of the mono- and bifunctional SBA-15 samples with thiol, phosphonic and amino groups in their surface layer. All of them were obtained by direct template method using P123. To determine the concentration of chemically available functional groups on the surface of silica samples the method of potentiometric titration was used. The samples with phosphonic and thiol groups for lead (II) sorption were used and cumulative effect of them was described. The value of the distribution coefficient and the exchange constant for lead (II) ions for bifunctional samples were higher than for monofunctional analogues. This indicates that the bifunctional samples are more versatile sorbents. The maximum value of the static sorption capacity to Hg (II) ions was 390 mg/g, to Pb(II) ions ‒ 150 mg/g, to uranyl-ions – 201 mg/g, and to Nd(III) ions ‒ 78 mg/g. Catalytic tests of ethanol conversion have shown that the anchoring of phosphomolybdic acid on SBA-15 functionalized with aminopropyl groups enhances oxidizing properties of heteropolycatalysts. Accordingly, the supported catalysts are characterized by higher turnover frequency values in aerobic oxidation of cyclooctane to cyclooctanone and cyclooctanol.

The search for new transition metal based catalytic systems that are active in the oxidative functionalization of such inert substrates as saturated hydrocarbons continues to be an important research direction in molecular catalysis. In the present study, two new copper(II) coordination compounds, namely a discrete dimer [Cu2(μ-H2tea)2(nfa)2]·2H2O (1) and a 1D coordination polymer [Cu2(μ-H2tea)2(μ-Htma)]n·4nH2O (2) were synthesized and applied as homogeneous catalysts for the mild oxidative functionalization of cycloalkanes (cyclopentane, cyclohexane, cycloheptane, and cyclooctane). Both products 1 and 2 were self-assembled in aqueous medium from copper(II) nitrate, triethanolamine (H3tea), sodium hydroxide, and 2-naphthoic (Hnfa) or trimesic (H3tma) acids, isolated as stable crystalline solids, and fully characterized by standard methods including single-crystal X-ray diffraction. Their structures feature a similar type of dicopper(II) triethanolaminate cores that are decorated by terminal or bridging aromatic carboxylate ligands. Two model catalytic reactions were investigated, namely the oxidation of cycloalkanes by H2O2 to produce cycloalkyl hydroperoxides as intermediate products and then a mixture of cyclic alcohols and ketones as final products, and the carboxylation of cycloalkanes with CO/S2O82−/H2O to form cycloalkanecarboxylic acids as main products. These model reactions undergo under very mild conditions (50−60 °C) and show good efficiency. Substrate scope, selectivity features, and the effects of reaction parameters were investigated and discussed in detail. This study widens the family of multicopper(II) cores capable of catalyzing the oxidative functionalization of saturated hydrocarbons under mild conditions.

Transition metal [M = Co(II), Cu(II)] complexes of H 2 L 1 and H 2 L 2 ligands have been prepared as neat and nanohybrid zeolite-Y immobilized complexes. The various analytical tools such as FTIR, ICP-AES, elemental analysis, UV–vis, Brunauer, Emmett and Teller (BET) surface area analysis, Thermal analysis, scanning electron micrographs, Powder XRD, conductivity, magnetic moment, and AAS were employed for the characterization of the prepared catalysts. Among all catalysts, the [Cu(L 1 )]-Y (heterogeneous) and [Cu(L 1 )] (homogeneous) have offered high activity and selectivity over oxidation of cyclohexene. Moreover, the [Cu(L 1 )] and [Cu(L 1 )]-Y were employed as catalyst over various organic substrates at identical reaction condition. The immobilized catalyst [Cu(L 1 )]-Y is found to be moderate active over oxidation of cyclohexane (75.2%,), benzene (8.21%), phenol (14.5%), styrene (87.5), benzyl alcohol (21.5%), limonene (11.2%), α-pinene (9.15%), and cyclooctane (76.8%) with high TON values (21942-2054). The mechanistic study using UV–vis and FTIR suggests the participation of active metalperoxo species, which is reinforced by its high catalytic activity over limonene (16.3%) in the absence oxidant.

A series of new (tBu2PSCOPR2)IrHCl iridium complexes with ‘hybrid’ phosphinothious-phosphinite PSCOP ligands ([tBu2PSCOPR2 = 1-(SPtBu2)-3-(OPR2)-C6H4], R = tBu, 4a, R = Cy, 4b, R = iPr, 4c, and R = Et, 4d) have been synthesized and characterized. Treatment of complexes 4a–d with sodium tert-butoxide generates the active species for catalytic transfer-dehydrogenation of cyclooctane (COA) or n-octane using tert-butylethylene (TBE) as hydrogen acceptor to form cyclooctene (COE) or octenes, respectively. The catalytic activity of these complexes and the product selectivity in alkane dehydrogenation is greatly influenced by the steric properties of the pincer ligand. In general, the less sterically bulky complex exhibits higher catalytic activity than the more hindered complex. Among the new (PSCOP)Ir-type complexes, the least crowded complex (tBu2PSCOPEt2)IrHCl 4d is most active for n-octane/TBE transfer-dehydrogenation. The relatively crowded, less active, complexes (tBu2PSCOPtBu2)IrHCl (4a) and (tBu2PSCOPCy2)IrHCl (4b) exhibit high regioselectivity for α-olefin formation at the early stages of the reaction.

An efficient and potentially scalable method is described for the synthesis of the silica-supported complexes [(≡Si–O−)WMe5] and [(≡Si–O−)WMe2(≡CH)] obtained by in situ alkylation of the surface-grafted tungsten chloride [(≡Si–O−)WCl5] (1). [(≡Si–O−)WCl5] can be readily prepared by the reaction of commercially available and stable tungsten hexachloride WCl6 with partially dehydroxylated silica at 700 °C (SiO2-700). Further reaction with ZnMe2 at room temperature rapidly forms a mixture of surface-alkylated tungsten complexes. They were fully characterized by microanalysis, FTIR, mass balance, and solid-state NMR (1H, 13C, 1H–13C HETCOR, 1H–1H double quantum and triple quantum) and identified as [(≡Si–O−)WMe5] and another product, [(≡Si–O−)WMe2(≡CH)]. The latter might have been generated by partial decomposition of the tungsten methyl chloride compound, which is formed during the stepwise alkylation of [(≡Si–O−)WCl5]. DFT calculations were carried out to check the relative stability of the tungsten methyl ...

Cu(II), Co(II), Mn(II) and Ni(II) complexes of silica-supported N4O4 type bis(diazoimine) ligands were synthesized and characterized by using FT-MIR/FAR, TG/DTA, elemental analysis, ICP-OES, SEM and EDX techniques. Catalytic activities of the complexes were investigated on the selective oxidation of cyclohexane, cyclohexene, cyclooctane and styrene under microwave power. In cyclohexane oxidation, L1-Cu(II) catalyst showed the best catalytic activity with the conversion of 73.31% and 46.05% cyclohexanol and 34.87% cyclohexanone selectivity. L1-Cu(II) and L2-Cu(II) catalyst were selective for 2-cyclohexen-1-ol (40.54% and 65.01%) in the cyclohexene oxidation with high conversions (66.77% and 54.59%). Cycloctanone selective L1-Cu(II), L2-Cu(II), L2-Cu(II) and L1-Ni(II) (75–80%) complexes showed very selective catalytic properties in the catalytic oxidation of cyclooctane. L1-Ni(II), L2-Ni(II) and L3-Ni(II) catalysts have had 81.28%, 73.70% and 81.39% selectivities respectively in styrene oxidation. Generally, it can be said that Cu(II) complexes are highly active and selective catalysts on the oxidation of cyclohexane, cyclohexene and cyclooctane. Nevertheless, Ni(II) complexes of L1 and L2 showed important selective catalytic performances towards the epoxidation of styrene.

The selective oxidation of hydrocarbons is a main academic and industrial research challenge. A lot of researches have been done about this issue, but till now relatively little attention has been paid to graphene-complex oxide nanocomposites. Herein, we report our studies on a new catalyst. Silver ferrite–graphene (AgFeO 2 –G) as a separable nanocomposite from the reaction solution, was used as an effective oxidizing agent for the oxidation of various hydrocarbons (1- decene, cyclohexene, cis-cycloctene, cyclohexane, cyclooctane etc.) under mild conditions (55 ০ C, 8 h) with high conversion and selectivity using air, that is proper for ‘green’ chemistry. Metal or metal oxide nanoparticles assembled on graphene sheets revealed high electrocatalytic activity. Indeed, AgFeO 2 with graphene due to low band gap and graphene oxide with large amounts of oxygen-containing groups, provide facility catalytic activity of catalyst-supported system. We also found that, with this catalyst, selective oxidation could be achieved without the need for the addition of solvent, which is appropriate in particular for ‘green’ chemistry. The catalysts showed little deactivation and maintained their conversion and selectivity levels duration of the measurements.

Tetraspiro[2.1.2(5).1.2(9).1.2(13).1(3)]hexadecane-1,3,5,7-tetraone 4, a unique tetraketone containing a cyclooctane core and four spiroannelated cyclopropane moieties, represents the previously unknown cyclotetramer of carbonylcyclopropane. For this purpose oxidation of the parent polyspirocyclic hydrocarbon was examined under various oxidative conditions, and the reactivity of oxidants towards methylene groups of the eight-membered cycle, activated by adjacent spirocyclopropane rings, was evaluated and contrasted. Whereas the treatment of tetraspirohexadecane with ozone resulted in monooxidation, its reaction with methyl(trifluoromethyl)dioxirane afforded the product of four-fold oxidation, triketoalcohol 10. Subsequent oxidation of the latter with Dess-Martin periodinane gave the target tetraketone 4.

Water-soluble compounds [VOCl2{CH3SO2OCH2C(pz)3}] (pz = pyrazol-1-yl) 1, [FeCl2{CH3SO2OCH2C(pz)3}] 2, [NiCl2{CH3SO2OCH2C(pz)3}] 3 and [Cu{CH3SO2OCH2C(pz)3}2](OTf)24 were obtained by reactions between the corresponding metal salts and 2,2,2-tris(pyrazol-1-yl)ethyl methanesulfonate, CH3SO2OCH2C(pz)3. They were isolated as air-stable solids and fully characterized by IR, FTIR, NMR (for 2), EPR (for 1), ESI-MS(+/−), elemental analysis and (for 4) single-crystal X-ray diffraction. In all, half- (1–3) or full-sandwich (4), compounds the C-scorpionate ligand shows the N,N,N-coordination mode. 3 and 4 appear to provide the first examples of a Ni(II) and a full-sandwich Cu(II) compound respectively, bearing that scorpionate ligand. Compound 3 is the first Ni(II) tris(pyrazol-1-yl)methane type complex to be applied as catalyst for the oxidation of alkanes. Compounds 1–4 exhibit catalytic activity for the peroxidative (with aq. H2O2) oxidation, in water/acetonitrile medium and under mild homogeneous conditions, of cyclooctane to the corresponding alcohol and ketone (yields up to ca. 27%). The effect of the presence of additives, such as nitric acid or pyridine, was studied.

Combustion kinetics of the cyclooctane and o -xylene, alone and in their binary mixture, have been experimentally investigated over a commercial Pt/γ - alumina catalyst. The studies were carried out in a laboratory set-up, with diluted hydrocarbon-air mixtures, typical for depollution applications. The experiments were conducted at atmospheric pressure and temperatures between 140 and 400 °C, hydrocarbons concentration 200–1000 ppmv and WHSW (mass flow rate to catalyst weight ratios) in the range 280–590 h −1 . The results evidenced an important inhibition of cyclooctane combustion by the presence of o -xylene, throughout the working domain. Based on the experimental measurements and postulating surface mechanisms, rate expressions were developed for the combustion of the two hydrocarbons, in pure state and as binary mixtures. The cyclooctane was found to react by an Eley–Rideal type mechanism, whereas the o -xylene combustion was explained by a Langmuir-Hinshelwood scheme.

An iPr-substituted PBP-pincer ligand was synthesized and introduced to iridium metal to give iPr-(PBP)Ir(H)Cl and iPr-(PBP)Ir(C2H4) complexes. Both of these complexes were found to be moderately active for the catalytic transfer dehydrogenation of cyclooctane.

The intramolecular aldol condensation of 4-substituted heptane-2,6-diones leads to chiral cyclohexenones. The origins of the enantioselectivities of this reaction, disclosed by List et al. using a cinchona alkaloid-derived primary amine (cinchona amine) organocatalyst, have been determined with dispersion-corrected density functional theory (DFT). The stereocontrol hinges on the chair preference of the substrate-enamine intermediate and the conformational preferences of a hydrogen-bonded nine-membered aldol transition state containing eight heavy atoms. The conformations of the hydrogen-bonded ring in the various stereoisomeric transition structures have been analyzed in detail and shown to closely resemble the conformers of cyclooctane. A model of stereoselectivity is proposed for the cinchona amine catalysis of this reaction. The inclusion of Grimme's dispersion corrections in the DFT calculations (B3LYP-D3(BJ)) substantially improves the agreement of the computed energetics and experiment, attesting to the importance of dispersion effects in stereoselectivity.

A multifunctional organic–inorganic hybrid based on a Cu coordination polymer capped polyoxometalate (H3PMo12O40) designated as compound 1 with [CuI(4,4′-bipy)]3[PMo 10 VI Mo 2 V O40{CuII(2,2′-bipy)}] formula was prepared using CuCl2·2H2O, 4,4′-bipy, 2,2′-bipy and H3PMo12O4 in water under hydrothemal conditions. The prepared compound 1 was characterized by FTIR, XRD and chemical analysis techniques. It was found that the compound successfully catalyzes the epoxidation of various alkenes such as diphenyl ethylene, trans-stilbene, cyclohexene, norbornene, styrene and cyclooctene and oxidation of alkanes such as fluorene, adamantane, diphenylmethane, cyclohexane and cyclooctane, in acetonitrile with 20–99 % conversion and 53–100 % selectivity with tert-butyl hydroperoxide as oxidant under optimized condition. This heterogeneous catalyst could be easily recovered and reused after reaction without loss of activity.

Cp*-Ir(III) complexes with additional chelating ligands are known active pre- catalysts for the oxygenation of C–H bonds. We present here eight examples of such complexes where the denticity of the chelating ligands has been varied from the well-known 2,2′-bpy through pyridyl-triazole, bi-triazole to ligands containing pyridyl-triazolylidene, triazolyl-triazolylidene and bi- triazolylidenes. Additionally, we also compare the catalytic results to complexes containing chelating cyclometallated ligands with additional triazole or triazolylidene donors. Single crystal X-ray structural data are presented for all the new complexes that contain one or more triazolylidene donors of the mesoionic carbene type. We present the first example of a metal complex containing a chelating triazole-triazolylidene ligand. The results of the catalytic screening show that complexes containing unsymmetrical donors of the pyridyl-triazole or pyridyl-triazolylidene types are the most potent pre- catalysts for the C–H oxygenation of cyclooctane in the presence of either m-CPBA or NaIO4 as a sacrificial oxidant. These pre-catalysts can also be used to oxygenate C–H bonds in other substrates such as fluorene and ethyl benzene. The most potent pre-catalysts presented here work with a lower catalyst loading and under milder conditions while delivering better product yields in comparison with related literature known Ir(III) pre-catalysts. These results thus point to the potential of ligands with unsymmetrical donors obtained through the click reaction in oxidation catalysis.

The selective aliphatic carbon–carbon activation of cyclo-octane (c-octane) was achieved via the RhII(ttp)-catalyzed 1,2-addition of Rh(ttp)H to give Rh(ttp)(n-octyl) (ttp = tetratolylporphyrinato dianion) in good yield under mild reaction conditions. This mechanism is further supported by DFT calculations. The reaction worked only with the sterically accessible Rh(ttp) porphyrin complex but not with the bulky Rh(tmp) system (tmp = tetrakismesitylporphyrinato dianion), thus showing the highly steric sensitivity of carbon–carbon bond activation by transition metal complexes.

A series of imidazolinium-based CCC pro-ligands featuring N-Mes, Dipp, iPr and tBu substituents (1·2HCl) have been prepared. The corresponding free carbenes are readily generated through deprotonation by strong bases and, in addition to being characterised in situ by 1H and 13C NMR spectroscopy, were trapped through reaction with CuCl. Iridium pincer compounds of the N-Mes (5a) and N-Dipp (5b) substituted ligands, viz. [Ir(1)HCl(NCMe)], were obtained through reaction between the respective pro-ligand, [Ir(COE)2Cl]2, and Et3N in acetonitrile at ca. 80 °C. Under similar conditions the N-iPr and N-tBu analogues were not formed. The new iridium pincer complexes 5a and 5b were fully characterised in solution, by NMR spectroscopy and ESI-MS, and in the solid-state by X-ray diffraction. Under relatively forcing reaction conditions neither 5a nor 5b, in combination with KOtBu, show any significant catalytic activity for the transfer dehydrogenation of cyclooctane to cyclooctene using tert-butylethylene as the sacrificial hydrogen acceptor (ca. 2 TONs, 150 °C, 24 h).\ud \ud

The results of low-temperature investigations of the oxidations of 9,10-dihydroanthracene, cumene, ethylbenzene, [D10]ethylbenzene, cyclooctane, and cyclohexane by an iron(V)-oxo TAML complex (2; see Figure 1) are presented, including product identification and determination of the second-order rate constants k2 in the range 233-243 K and the activation parameters (ΔH(≠) and ΔS(≠)). Statistically normalized k2 values (log k2') correlate linearly with the C-H bond dissociation energies DC-H, but ΔH(≠) does not. The point for 9,10-dihydroanthracene for the ΔH(≠) vs. DC-H correlation lies markedly off a common straight line of best fit for all other hydrocarbons, suggesting it proceeds via an alternate mechanism than the rate-limiting C-H bond homolysis promoted by 2. Contribution from an electron-transfer pathway may be substantial for 9,10-dihydroanthracene. Low-temperature kinetic measurements with ethylbenzene and [D10]ethylbenzene reveal a kinetic isotope effect of 26, indicating tunneling. The tunnel effect is drastically reduced at 0 °C and above, although it is an important feature of the reactivity of TAML activators at lower temperatures. The diiron(IV) μ-oxo dimer that is often a common component of the reaction medium involving 2 also oxidizes 9,10-dihydroanthracene, although its reactivity is three orders of magnitude lower than that of 2.

A new arsenic-based pincer (AsOCOAs) dehydrogenation catalyst has been synthesized, IrHCl{2,6-C6H3-(O-AsBut2)} (3). Treatment with an equivalent of base (NaO-tert-butoxide) under an atmosphere of hydrogen gas affords the dihydride catalyst IrH2{2,6-C6H3-(O-AsBut2)} (4). The activity of 3 was explored under transfer dehydrogenation conditions with cyclooctane and tert-butyl ethylene, giving a maximum turnover number of 960 at 175 °C in 24 h. Acceptorless dehydrogenations were also explored with pyrrolidine-based molecules, ethylperhydrocarbazole (5), methylperhydroindole (6), and butylpyrrolidine (7), in which all results indicate 3 is roughly half as active as the analogous phosphine-based pincer catalyst 2. Akin to the phosphine pincer catalysts the activity was seen to steadily improve with increasing temperature, peaking at 175 °C, upon which thermal decomposition sets in.

Iridium complexes of CCC-pincer bis-N-heterocyclic carbenes, including a newly synthesized trifluoromethyl-substituted complex, were examined as catalysts for the acceptorless dehydrogenation of cyclooctane and n-undecane. Up to 103 turnovers were observed for the dehydrogenation of cyclooctane, and up to 97 turnovers were observed for the dehydrogenation of n-undecane. The catalysts showed high initial turnover frequencies, followed by a gradual loss of activity over 24 h. Experiments indicate that this loss of activity is due to catalyst decomposition rather than product inhibition. Stoichiometric reactivity was investigated for the precatalysts, focusing on the synthesis of dihydride and trihydride complexes as well as the dissociation and addition of neutral ligands.

In the presence of an iridium 3,4,7,8-tetramethyl-1,10-phenanthroline catalyst, a methyl group on the silicon atom of alkyltrimethylsilanes undergoes selective C–H borylation with bis(pinacolato)diboron in cyclooctane at 135 °C to give alkyl(borylmethyl)dimethylsilanes. The C–H borylation of tetramethylsilane takes place efficiently at 100 °C. Permethyloligosilanes can also undergo C–H borylation without cleavage of the Si–Si bonds.

Iron, chromium or tin containing mesoporous materials MSU-X were synthesized using Pluronic F127 as templating agent under the neutral pH condition by one-step method. The samples were characterized by XRD, N2 adsorption, TEM, FT-IR, UV-Vis. The surface acid nature of Sn-MSU-X was investigated by FT-IR of pyridine adsorption. The results indicate that Fe, Cr and Sn have been successfully incorprated into the framework of the MSU-X samples. And these samples have an uniform pore size distribution. Fe-MSU-X and Cr-MSU-X exhibit disordered worm-like mesostructure. However, Sn-MSU-X exhibits highly ordered hexagonal-pores mesostructure. The Fe-MSU-X and Cr-MSU-X catalysts are more active for the selective oxidation of phenol and cyclooctane, respectively.There are both Lewis and Brönsted acid sites on the surface of Sn-MSU-X.

Three new oxodiperoxomolybdenum complexes with nicotinic acid have been synthesized and charac- terized with the use of single-crystal analysis, XRPD versus temperature, TG/DSC, SEM and IR spectros- copy. The investigated compounds are: 1 – (NH 4 ) 2 [MoO(O 2 ) 2 .N-nicO] 2 , 2 – (nicH) 2 [MoO(O 2 ) 2 .N- nicO] 2 2(H 2 O), 3 – MoO(O 2 ) 2 (H 2 O)nicH; (N-nicO, nicH denote nicotinic acid N-oxide and protonated nicotinic acid, respectively). Compounds 1, 2 are salts of the same acid with cyclic dinuclear anions, whereas compound 3 can be regarded as an inner salt. Compounds 1–3 are stable in ambient conditions, the respective percentages of oxygen in peroxo groups are 19.21%, 14.06% and 20.19%, respectively. Above 125 ° C peroxo compounds 1–3 decompose, forming nanometric MoO 2 and MoO 3 . TG/DSC curves reveal clear effects connected with the release of oxygen and strong exothermic effects connected with final loss of organic components. All the investigated complexes were found to be active in the oxidation of cyclooctane to cyclooctanone and cyclooctanol with molecular oxygen.

A sandwich-type polyoxometalate {(TBA)7H3[Co4(H2O)2(PW9O34)2]} was immobilized for the first time into the three-dimensional porous metal-organic framework, MIL-101. The composite material Co4(PW9)2@MIL-101 was prepared and the incorporation of the Co4(PW9)2 was confirmed using a myriad of solid state methods (FT-IR, FT-Raman, powder XRD, SEM-EDX and ICP analysis). Co4(PW9)2@MIL-101 reveals to be an active, selective and recyclable catalyst for the oxidation of different substrates: geraniol, R-(+)-limonene, styrene and cyclooctane, using H2O2 as eco-sustainable oxidant. The stability and robustness of the heterogeneous catalyst was confirmed by different techniques. The MIL-101 framework demonstrates to be a suitable and efficient support to accommodate catalytically active sandwich-type polyoxotungstates.

This work reports the catalytic activity, in homogeneous phase, of transition-metal complexes of the first-row (V(IV), Mn(III), Fe(III) Co(III) and Cu(II)) with biomimetic Schiff base ligands with N2O2 coordination sphere, as well as an N-4 (Fe(II)), in the room-temperature oxidation of cyclohexane using environmentally benign reagents: hydrogen peroxide (30 wt%) as the oxygen source and acetonitrile as the solvent. Nitric acid is also used as promoter of the oxidation reaction. The structure of the ligands is confirmed by FTIR, H-1 NMR and high-resolution ESI mass spectrometry. The corresponding transition metal complexes are characterized by elemental analysis, high resolution ESI mass spectrometry, FTIR and UV-vis. Cyclohexanone and cyclohexanol are the main products of the oxidation of cyclohexane, obtained when the following complexes are used as homogeneous catalysts in only 1 mol% based on the substrate: VO(IV), Fe(III) and Cu(II) complexes with the N2O2 Schiff base, new Fe(II) complex with the Schiff base with N-4 coordination sphere and commercial [VO(acac)(2)] with O-4 coordination sphere. The Fe(III) complex with N2O2 Schiff base ligand ([Fe(salhd)Cl]) is the homogeneous catalyst with highest activity, which could be further enhanced by the addition of methyl electron donating groups to the N2O2 Schiff base aldehyde fragment (reaching 46% oxygenate yields and 45 turnover numbers). Cyclooctane and n-hexane could also be oxidized to the corresponding ketones and alcohols with higher turnover numbers than cyclohexane by the Fe(III) complex with N2O2 Schiff base ligand. (C) 2012 Elsevier B. V. All rights reserved.

A novel whole cell cascade for double oxidation of cyclooctane to cyclooctanone was developed. The one-pot oxidation cascade requires only a minimum of reaction components: resting E. coli cells in aqueous buffered medium (=catalyst), the target substrate and oxygen as environmental friendly oxidant. Conversion of cyclooctane was catalysed with high efficiency (50% yield) and excellent selectivity (>94%) to cyclooctanone. The reported oxidation cascade represents a novel whole cell system for double oxidation of non-activated alkanes including an integrated cofactor regeneration. Notably, two alcohol dehydrogenases from Lactobacillus brevis and from Rhodococcus erythropolis with opposite cofactor selectivities and one monooxygenase P450 BM3 were produced in a coexpression system in one single host. The system represents the most efficient route with a TTN of up to 24363 being a promising process in terms of sustainability as well.

The reisolation and structural revision of brassicicene D is described, and inspired us to reassign the core skeletons of brassicicenes C-H, J and K, ranging from dicyclopenta[a,d]cyclooctane to tricyclo[9.2.1.0(3,7)]tetradecane using quantum-chemical predictions and experimental validation strategies. Three novel, highly modified fusicoccanes, brassicicenes L-N, were also isolated from the fungus Alternaria brassicicola, and their structures were unequivocally established by spectroscopic data, ECD calculations, and crystallography. The reassigned structures represent the first class of bridgehead double-bond-containing natural products with a bicyclo[6.2.1]undecane carbon skeleton. Furthermore, their stabilities were first predicted with olefin strain energy calculations. Collectively, these findings extend our view of the application of computational predictions and biosynthetic logic-based structure elucidation to address problems related to the structure and stability of natural products.

The aim of this work was to study the effect of substituents on the catalytic activity of iron μ-oxo porphyrins in oxidation of cycloalkanes. Electron-donating or electron-withdrawing substituents were introduced in meso-aryl groups of iron μ-oxo porphyrins. An important part of the work was the characterization of the catalysts, in particular their redox properties. Catalytic performance and selectivity were evaluated using cyclopentane, cyclohexane, and cyclooctane as model compounds. It was shown that not only electron-withdrawing but also electron-donating substituents improved the catalytic performance of iron μ-oxo complexes. Moreover, catalytic activity of iron μ-oxo porphyrins with electron-withdrawing substituents correlated with the half-wave potential E1/2 while the catalytic activity of iron μ-oxo porphyrins with electron-donating substituents increased with the decrease of reduction potential ERED.