Mild homogeneous oxidation of alkanes and alcohols including glycerol with tert-butyl hydroperoxide catalyzed by a tetracopper(II) complex

The effects of metals and ligands on the oxidation of n-octane using iridium and rhodium “PNP” aminodiphosphine complexes

Ir and Rh “PNP” complexes with different ligands are utilized for the oxidation of n-octane. Based on the obtained conversion, selectivity, and the characterized recovered catalysts, it is found that the combination of Ir and the studied ligands does not promote the redox mechanism that is known to result in selective formation of oxo and peroxo compounds [desired species for C(1) activation]. Instead, they support a deeper oxidation mechanism, and thus higher selectivity for ketones and acids is obtained. In contrast, these ligands seem to tune the electron density around the Rh (in the Rh-PNP complexes), and thus result in a higher n-octane conversion and improved selectivity for the C(1) activated products, with minimized deeper oxidation, in comparison to Ir-PNP catalysts.

A Comparative Study of the Catalytic Behaviour of Alkoxy-1,3,5-Triazapentadiene Copper(II) Complexes in Cyclohexane Oxidation

The mononuclear copper complexes [Cu{NH=C(OR)NC(OR)=NH}2] with alkoxy-1,3,5-triazapentadiene ligands that have different substituents (R = Me (1), Et (2), nPr (3), iPr (4), CH2CH2OCH3 (5)) were prepared, characterized (including the single crystal X-ray analysis of 3) and studied as catalysts in the mild oxidation of alkanes with H2O2 as an oxidant, pyridine as a promoting agent and cyclohexane as a main model substrate. The complex 4 showed the highest activity with a yield of products up to 18.5% and turnover frequency (TOF) up to 41 h−1. Cyclohexyl hydroperoxide was the main reaction product in all cases. Selectivity parameters in the oxidation of substituted cyclohexanes and adamantane disclosed a dominant free radical reaction mechanism with hydroxyl radicals as C–H-attacking species. The main overoxidation product was 6-hydroxyhexanoic acid, suggesting the presence of a secondary reaction mechanism of a different type. All complexes undergo gradual alteration of their structures in acetonitrile solutions to produce catalytically-active intermediates, as evidenced by UV/Vis spectroscopy and kinetic studies. Complex 4, having tertiary C–H bonds in its iPr substituents, showed the fastest alteration rate, which can be significantly suppressed by using the CD3CN solvent instead of CH3CN one. The observed process was associated to an autocatalytic oxidation of the alkoxy-1,3,5-triazapentadiene ligand. The deuterated complex 4-d32 was prepared and showed higher stability under the same conditions. The complexes 1 and 4 showed different reactivity in the formation of H218O from 18O2 in acetonitrile solutions.

Copper(ii) complexes with 2,2′:6′,2′′-terpyridine, 2,6-di(thiazol-2-yl)pyridine and 2,6-di(pyrazin-2-yl)pyridine substituted with quinolines. Synthesis, structure, antiproliferative activity, and catalytic activity in the oxidation of alkanes and alcohols with peroxides

The toxicity of six new Cu(ii) complexes was evaluated in cancer derived cell lines. A model of competitive interaction of hydroxyl radicals with CH₃CN and RH in the catalyst cavity has been proposed.

Promoting effect of solvent on Cu/CoO catalyst for selective glycerol oxidation under alkaline conditions

Cu/CoO catalysts were employed for the selective oxidation of glycerol in the aqueous phase under basic conditions.

Novel Cage-Like Hexanuclear Nickel(II) Silsesquioxane. Synthesis, Structure, and Catalytic Activity in Oxidations with Peroxides

New hexanuclear nickel(II) silsesquioxane [(PhSiO_1.5)₁₂(NiO)₆(NaCl)] (1) was synthesized as its dioxane-benzonitrile-water complex (PhSiO_1,5)₁₂(NiO)₆(NaCl)(C₄H₈O₂)₁₃(PhCN)₂(H₂O)₂ and studied by X-ray and topological analysis. The compound exhibits cylinder-like type of molecular architecture and represents very rare case of polyhedral complexation of metallasilsesquioxane with benzonitrile. Complex 1 exhibited catalytic activity in activation of such small molecules as light alkanes and alcohols. Namely, oxidation of alcohols with tert-butylhydroperoxide and alkanes with meta-chloroperoxybenzoic acid. The oxidation of methylcyclohexane gave rise to the isomeric ketones and unusual distribution of alcohol isomers.

Aroylhydrazone Cu(II) Complexes in keto Form: Structural Characterization and Catalytic Activity towards Cyclohexane Oxidation

The reaction of the Schiff base (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) with a copper(II) salt of a base of a strong acid, i.e., nitrate, chloride or sulphate, yielded the mononuclear complexes [Cu(H2L)(NO3)(H2O)] (1), [Cu(H2L)Cl]·2MeOH (2) and the binuclear complex [{Cu(H2L)}2(µ-SO4)]·2MeOH (3), respectively, with H2L(-) in the keto form. Compounds 1-3 were characterized by elemental analysis, Infrared (IR) spectroscopy, Electrospray Ionisation Mass Spectrometry (ESI-MS) and single crystal X-ray crystallography. All compounds act as efficient catalysts towards the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, under mild conditions. In the presence of an acid promoter, overall yields (based on the alkane) up to 25% and a turnover number (TON) of 250 (TOF of 42 h(-1)) after 6 h, were achieved.

New aqua-soluble dicopper(ii) aminoalcoholate cores for mild and water-assisted catalytic oxidation of alkanes

Two new dicopper(ii) pre-catalysts were synthesized, fully characterized, and applied for the mild homogeneous oxidation of alkanes.

POSS-derived solid acid catalysts with excellent hydrophobicity for highly efficient transformations of glycerol

New POSS-derived acid catalysts were synthesized, which proved to be highly efficient, and steadily reused for glycerol transformations.

Syntheses and crystal structures of benzene-sulfonate and -carboxylate copper polymers and their application in the oxidation of cyclohexane in ionic liquid under mild conditions

Enhanced catalytic activities of copper polymers for the peroxidative oxidation of cyclohexane are observed in an ionic liquid medium.

p-Tolylimido rhenium(v) complexes with phenolate-based ligands: synthesis, X-ray studies and catalytic activity in oxidation with tert-butylhydroperoxide

The reactions of mer-[Re(p-NTol)X₃(PPh₃)₂] with phenolate-based ligands gave 16 new rhenium(v) complexes. Only a few of them exhibited high catalytic activity.

Cage-like copper(II) silsesquioxanes: transmetalation reactions and structural, quantum chemical, and catalytic studies

The transmetalation of bimetallic copper-sodium silsesquioxane cages, namely, [(PhSiO1.5 )10 (CuO)2 (NaO0.5 )2 ] ("Cooling Tower"; 1), [(PhSiO1.5 )12 (CuO)4 (NaO0.5 )4 ] ("Globule"; 2), and [(PhSiO1.5 )6 (CuO)4 (NaO0.5 )4 (PhSiO1.5 )6 ] ("Sandwich"; 3), resulted in the generation of three types of hexanuclear cylinder-like copper silsesqui- oxanes, [(PhSiO1.5 )12 (CuO)6 (C4 H9 OH)2 (C2 H5 OH)6 ] (4), [(PhSiO1.5 )12 (CuO)6 (C4 H8 O2 )4 (PhCN)2 (MeOH)4 ] (5), and [(PhSiO1.5 )12 (CuO)6 (NaCl)(C4 H8 O2 )12 (H2 O)2 ] (6). The products show a prominent "solvating system-structure" dependency, as determined by X-ray diffraction. Topological analysis of cages 1-6 was also performed. In addition, DFT theory was used to examine the structures of the Cooling Tower and Cylinder compounds, as well as the spin density distributions. Compounds 1, 2, and 5 were applied as catalysts for the direct oxidation of alcohols and amines into the corresponding amides. Compound 6 is an excellent catalyst in the oxidation reactions of benzene and alcohols.

Alkane C-H functionalization and oxidation with molecular oxygen

The application of environmentally benign, cheap, and economically viable oxidation procedures is a key challenge of homogeneous, oxidative alkane functionalization. The typically harsh reaction conditions and the propensity of dioxygen for radical reactivity call for extraordinary robust catalysts. Mainly three strategies have been applied. These are (1) the combination of a catalyst responsible for C-H activation with a cocatalyst responsible for dioxygen activation, (2) transition-metal catalysts, which react with both hydrocarbons and molecular oxygen, and (3) the introduction of very robust main-group element catalysts for C-H functionalization chemistry. Herein, these three approaches will be assessed and exemplified by the reactivity of chelated palladium (N-heterocyclic carbene) catalysts in combination with a vanadium cocatalyst, the methane functionalization by cobalt catalysts, and the reaction of group XVII compounds with alkanes.

New tricopper(ii) cores self-assembled from aminoalcohol biobuffers and homophthalic acid: synthesis, structural and topological features, magnetic properties and mild catalytic oxidation of cyclic and linear C5–C8 alkanes

Two new compounds with distinct tricopper(ii) cores were synthesised and applied as bio-inspired pre-catalysts for mild oxidation of alkanes.

Re-evaluating selectivity as a determining factor in peroxidative methane oxidation by multimetallic copper complexes

A series of multimetallic copper(ii) complexes have been re-investigated for methane oxidation with H₂O₂.

Cobalt aminodiphosphine complexes as catalysts in the oxidation of n-octane

New cobalt “PNP” aminodiphosphine complexes have been prepared and characterised. They show good catalytic activity in the oxidation of n-octane to C8 oxygenates using tert-butyl hydroperoxide as an oxidant.

Sulfonated Schiff base dinuclear and polymeric copper(ii) complexes: crystal structures, magnetic properties and catalytic application in Henry reaction

Aqueous medium syntheses and nitroaldol catalytic studies of three pseudohalide bridged copper(ii) complexes characterized by single crystal X-ray structure analysis and variable temperature magnetic studies are reported.

Alkane oxidation with peroxides catalyzed by cage-like copper(ii) silsesquioxanes

Copper(ii) silsesquioxanes [(PhSiO_1.5)₁₂(CuO)₄(NaO_0.5)₄] or [(PhSiO_1.5)₁₀(CuO)₂(NaO_0.5)₂] are catalysts for alkane oxidation with H₂O₂ort-BuOOH.

Copper-organic frameworks assembled from in situ generated 5-(4-pyridyl)tetrazole building blocks: synthesis, structural features, topological analysis and catalytic oxidation of alcohols

Two new metal-organic compounds {[Cu3(μ3-4-ptz)4(μ2-N3)2(DMF)2](DMF)2}n (1) and {[Cu(4-ptz)2(H2O)2]}n (2) {4-ptz = 5-(4-pyridyl)tetrazolate} with 3D and 2D coordination networks, respectively, have been synthesized while studying the effect of reaction conditions on the coordination modes of 4-pytz by employing the [2 + 3] cycloaddition as a tool for generating in situ the 5-substituted tetrazole ligands from 4-pyridinecarbonitrile and NaN3 in the presence of a copper(ii) salt. The obtained compounds have been structurally characterized and the topological analysis of 1 discloses a topologically unique trinodal 3,5,6-connected 3D network which, upon further simplification, results in a uninodal 8-connected underlying net with the bcu (body centred cubic) topology driven by the [Cu3(μ2-N3)2] cluster nodes and μ3-4-ptz linkers. In contrast, the 2D metal-organic network in 2 has been classified as a uninodal 4-connected underlying net with the sql [Shubnikov tetragonal plane net] topology assembled from the Cu nodes and μ2-4-ptz linkers. The catalytic investigations disclosed that 1 and 2 act as active catalyst precursors towards the microwave-assisted homogeneous oxidation of secondary alcohols (1-phenylethanol, cyclohexanol, 2-hexanol, 3-hexanol, 2-octanol and 3-octanol) with tert-butylhydroperoxide, leading to the yields of the corresponding ketones up to 86% (TOF = 430 h(-1)) and 58% (TOF = 290 h(-1)) in the oxidation of 1-phenylethanol and cyclohexanol, respectively, after 1 h under low power (10 W) microwave irradiation, and in the absence of any added solvent or additive.

Cytochrome P450 catalyzed oxidative hydroxylation of achiral organic compounds with simultaneous creation of two chirality centers in a single C-H activation step

Regio- and stereoselective oxidative hydroxylation of achiral or chiral organic compounds mediated by synthetic reagents, catalysts, or enzymes generally leads to the formation of one new chiral center that appears in the respective enantiomeric or diastereomeric alcohols. By contrast, when subjecting appropriate achiral compounds to this type of C-H activation, the simultaneous creation of two chiral centers with a defined relative and absolute configuration may result, provided that control of the regio-, diastereo-, and enantioselectivity is ensured. The present study demonstrates that such control is possible by using wild type or mutant forms of the monooxygenase cytochrome P450 BM3 as catalysts in the oxidative hydroxylation of methylcyclohexane and seven other monosubstituted cyclohexane derivatives.

New p-tolylimido rhenium(v) complexes with carboxylate-based ligands: synthesis, structures and their catalytic potential in oxidations with peroxides

Novel p-tolylimido rhenium(v) complexes were obtained and calculations at the DFT level were undertaken. The complexes exhibited high catalytic activity in oxidation of alkanes and alcohols with H₂O₂ or TBHP.

Mn(ii) acetate: an efficient and versatile oxidation catalyst for alcohols

A homogeneous catalytic system consisting of Mn(ii) acetate, tert-butylhydroperoxide, acetonitrile and trifluoroacetic acid oxidises various alcohols efficiently and selectively.

Coordination chemistry of Co complexes containing tridentate SNS ligands and their application as catalysts for the oxidation of n-octane

Fully characterized cobalt complexes of tridentate SNS ligands were selective (up to 90%) for the oxidation of n-octane to octanones.

Oxidation of hydrocarbons with H2O2/O2 catalyzed by osmium complexes containing p-cymene ligands in acetonitrile

Osmium π-complexes containing p-cymene ligands efficiently catalyze (TONs up to 200 000) the oxidation of alkanes to alkyl hydroperoxides with H₂O₂.