Cobalt complexes in [EMIM]Cl – A catalyst for oxidation of alcohols to carbonyls

A coordination complex system consisting of Cobalt (II)-Schiff bases with triphenylphosphine were synthesized and characterized. These catalysts were effective in the oxidation of primary and secondary alcohols. The oxidation reactions were carried out in ethyl-methyl-imidazolium ionic liquid in presence of NaOCl. Higher catalytic activity was observed for CoL1.     

Synthesis,characterization and catalytic activities of ruthenium complexes containing triphenylphosphine/triphenylarsine and tetradentate Schiff bases

Ruthenium(II) complexes of the type [Ru(CO)(B)(L)] (B=AsPh₃, pyridine, piperidine or morpholine; L=dianion of tetradentate Schiff bases) have been synthesized and characterized by physico-chemical methods. These complexes are found to be effective catalysts in the oxidation of primary and secondary alcohols using N-methylmorpholine-N-oxide as oxidant. The catalytic activity of these triphenylarsine complexes have been compared with that of triphenylphosphine complexes and with similar ruthenium(III) complexes. The formation of high valent Ruⁿ⁺²O species as catalytic intermediate is proposed for the catalytic processes.     

Acceptorless and Base‐Free Dehydrogenation of Alcohols and Amines using Ruthenium‐Hydride Complexes

An efficient, operatively simple, acceptorless, and base‐free dehydrogenation of secondary alcohols and nitrogen‐containing heterocyclic compounds was achieved by using readily available ruthenium hydride complexes as precatalysts. The complex RuH₂(CO)(PPh₃)₃ ( 1 ) and Shvo’s complex ( 2 ) showed excellent activities for the dehydrogenation of secondary alcohols and nitrogen containing heterocycles. In addition to complexes 1 and 2 , the complex RuH₂(PPh₃)₄ ( 3 ) also showed moderate to excellent activity for the acceptorless dehydrogenation of nitrogen‐containing heterocyclic compounds. Kinetic studies on the oxidation reaction of 1‐phenylethanol using complex 1 were carried out in the presence and the absence of external triphenylphosphine (PPh₃). External addition of PPh₃ had a negative influence on the rate of the reaction, which suggested that dissociation of PPh₃ occurred during the course of the reaction. Hydrogen was evolved from the oxidation reaction of 1‐phenylethanol by using 1 mol% of 1 (88%) and 2 (92%), which demonstrated the possible usage of the catalytic systems in hydrogen generation.     

Metalloporphyrins in Oxidative Catalysis. Oxygen Transfer Reactions of Oxochromium Porphyrins

The oxidation of chloro-5-10,15,20-tetramesitylporphyrinotoiron(III) with peroxyacids affords a reactive oxoiron(IV)-porphyrin cation radical species 2. The characterization of 2 and its oxochromium analogs 3, 4 and 5 are reviewed. The nature of reactive oxochromium species derived from chromyl reagents is also reviewed. The oxidation of triphenylphosphine by CrOTPP (11), CrOTTP (13) and CrOTMP (14) is described. Variations in the rate constants indicate that steric factors affect the rate of oxygen atom transfer. Activation parameters for the oxidation of triphenylphosphine by 14 are ΔH^≠ = 6.96 kcal/mol and ΔS^≠ = −39 eu. The oxidation of t-butylphenylcarbinol (18) by CrOTPP gave predominantly benzaldehyde via carbon—carbon bond cleavage while the chromium(III) porphyrin-catalyzed oxidation of 18 by iodosylbenzene afforded t-butylphenylketone.     

Involvement of an Oxidation‐Reduction Equilibrium in Chromium‐Mediated Enantioselective Nozaki–Hiyama Reactions

Ligand induced enantioselective versions of the chromium(II)‐mediated Nozaki–Hiyama reaction to homoallyl alcohols proved to be very difficult to achieve, especially if any other nucleophile than the parent allylchromium(III) species was applied. Also, the reaction is frequently accompanied by the formation of oxidation side products, predominantly allyl ketones. This can be explained by an Oppenauer–(Meerwein–Ponndorf Verley) type mechanism (OMPV reaction). The addition of an enantiopure ligand to racemic chromium homoallyl alcoholate intermediates produced enantiomerically enriched homoallyl alcohols with an enantiomeric excess of up to 32%. This observation not only supports that the proposed OMPV oxidation‐reduction equilibrium plays a crucial role in Nozaki–Hiyama reactions, but also proves its involvement in enantioselective versions.     

Oxidation of para- and meta- Cresols by C- Meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-Nickel (III), to the Corresponding Aldehydes in Aqueous Media

The tervalent nickel complex with C-meso- 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, Ni-(III)L, as its disulphate form, Ni(III)L(SO₄)₂, oxidizes cresols in aqueous solutions. The major products after two electron equivalents are consumed are the corresponding hydroxybenzyl alcohols. The products after four electron equivalents are consumed are the corresponding hydroxybenzaldehydes. Excess tervalent nickel does not lead to the formation of the corresponding hydroxybenzoic acids. The results indicate that the oxidation reactions observed occur via the outer sphere mechanism. The use of NiL²⁺ as a catalyst for the oxidation of cresols is discussed.     

Polystyrene supported pyrazolinium Cr(VI) reagents: preparation and use in synthetic organic chemistry

Divinylbenzene (DVB) and ethyleneglycol dimethacrylate (EGDMA) crosslinked polystyrenes (2%) were functionalized to generate pyrazolinium chromate, chlorochromate and pyrazole–CrO₃ complex functionalities. These were found to oxidize primary and secondary alcohols to the corresponding carbonyl compounds in high yields. The influence of solvent, temperature, catalyst and molar excess of the reagent in these oxidation reactions was investigated to find out the optimum conditions for effective oxidation reactions. EGDMA crosslinked polystyrene supported reagents showed higher reactivity in terms of functional group capacity and percentage yield. Also, chlorochromate reagent was found to be very efficient in oxidizing alcohols to carbonyl compounds. The spent polymeric reagent after the oxidation step can be easily removed by filtration and can be regenerated many times. © 1998 SCI.     

Electrooxidation of methanol and ethylene glycol on gold and on gold modified with an electrodeposited polyNiTSPc film

The electrooxidation of methanol and ethylene glycol on Au and on polynickeltetrasulphophthalocyanine-modified gold (polyNiTSPc/Au/Q) electrodes in a pH 11 carbonate/hydrogen carbonate buffer electrolyte was studied by cyclic voltammetry (CV) and with an electrochemical quartz crystal microbalance (EQCM). Au shows negligible activity for methanol oxidation, in agreement with the fact that methanol does not adsorb on Au, since it does not affect the potential at which the mass increase due to Au oxidation starts. On the contrary, ethylene glycol (EG) is electrooxidized on Au at a significant rate, probably because it adsorbs rather strongly on Au, as evidenced by the positive shift by 0.35 V of the mass increase attending Au monolayer oxidation. The polyNiTSPc-modified Au electrodes are hydrophobic, as inferred from the disappearance of the large mass decrease in the double-layer region typical of the bare Au electrode, a decrease which is due to the desorption of the water molecules adsorbed at the negative potential limit. On the polyNiTSPc/Au/Q electrodes the current at the positive potential limit (at which only Ni(III) exists) of methanol oxidation, and the peak current of EG oxidation (at a potential at which only Ni(II) exists), show a Langmuir dependence on the concentration, which indicates that in both cases the reactive species are adsorbed, and that their oxidation rate is much lower than the adsorption rate. As is well known, the oxidation of Ni(II) to Ni(III) in the polyNiTSPc film is accompanied by a large mass decrease, due mostly to the expulsion of water from the film by the hydrophobic Ni(III). This mass decrease is independent of the scan rate, but in the presence of methanol or ethylene glycol it increases with increasing scan rate, which indicates that the oxidation of the alcohols involves a chemical reaction of the alcohols with Ni(III) ions, the extent of which decreases with increasing rate. Consequently, the amount of the hydrophobic Ni(III) will increase, and so will the mass loss. The mass decrease of Ni(II) oxidation decreases with increasing concentration of methanol or ethylene glycol, which again shows that there is a chemical reaction between the alcohols and Ni(III) ions, since the concentration of the latter would decrease with increasing alcohol concentration.     

A Simple and Highly Selective Biomimetic Oxidation of Alcohols with Hypervalent Iodine(III) Reagent Catalyzed by β-Cyclodextrin in Water

Abstract  

A simple, mild and highly efficient biomimetic oxidation of alcohols to the corresponding aldehydes or ketones with hypervalent iodine(III) reagent catalyzed by β-cyclodextrin was reported. β-cyclodextrin serves as a biological catalyst to enhance the reaction remarkably. The oxidation proceeded in water to afford aldehydes or ketones in excellent yields and high selectivity without remarkable over-oxidation to carboxylic acids. Selective oxidation of primary alcohols in the presence of secondary alcohols was also achieved. A possible mechanism for the oxidation was proposed.     

Preparation of recoverable Ru catalysts for liquid-phase oxidation and hydrogenation reactions

We here report the synthesis, characterization and catalytic performance of new supported Ru(III) and Ru(0) catalysts. In contrast to most supported catalysts, these new developed catalysts for oxidation and hydrogenation reactions were prepared using nearly the same synthetic strategy, and are easily recovered by magnetic separation from liquid phase reactions. The catalysts were found to be active in both forms, Ru(III) and Ru(0), for selective oxidation of alcohols and hydrogenation of olefins, respectively. The catalysts operate under mild conditions to activate molecular oxygen or molecular hydrogen to perform clean conversion of selected substrates. Aryl and alkyl alcohols were converted to aldehydes under mild conditions, with negligible metal leaching. If the metal is properly reduced, Ru(0) nanoparticles immobilized on the magnetic support surface are obtained, and the catalyst becomes active for hydrogenation reactions.     

Lewis Acid‐Catalyzed Oxidative Allylation: A New Approach for the Synthesis of Homoallylic Alcohols and Amines Directly from Alcohols

A new approach for the synthesis of homoallylic alcohols and amines directly from alcohols via one‐pot sequential oxidation–Barbier reaction and oxidation–condensation–Barbier reactions, respectively, is reported. The protocol involves the one‐pot ferric chloride‐catalyzed oxidation of alcohols to the corresponding aldehydes with chloramine‐T followed by indium‐mediated Barbier allylation with allyl bromide to afford homoallylic alcohols in 70–90% overall yields. The ferric chloride‐catalyzed condensation of aldehydes and oxidation by‐product p‐toluenesulfonamide followed by indium‐mediated Barbier‐type allylation of the resulting aldimines with allyl bromide affords homoallylic amines in 60–80% overall yields in the same reaction vessel. The present work demonstrates a new one‐pot approach toward homoallylic alcohol and amine synthesis directly from alcohols.     

Crystal structure and catalytic studies of heterodinuclear complex [CuZn(μ-OAc)(μ-OH)(μ-OH2)(bpy)2](ClO4)2

The heterodinuclear copper–zinc complex [CuZn(μ-OAc)(μ-OH)(μ-OH₂)(bpy)₂](ClO₄)₂ has been synthesized from solid state reaction and its crystal structure was established. The heterobimetallic complex is quite efficient catalyst for hydrogen peroxide mediated oxidation of alcohols into corresponding carbonyl compounds.     

Anchoring of Copper(II) Schiff Base Complex into Aminopropyl-Functionalised MCM-41: A Novel,Efficient and Reusable Catalyst for Selective Oxidation of Alcohols

A copper(II) complex containing tetradentate N₂O₂ Schiff base ligand immobilized into aminopropyl-functionalised MCM-41 (mobile crystalline material number 41), was prepared and characterized by Fourier-transform infrared, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, N₂ adsorption–desorption and inductively coupled plasma analysis techniques. The novel heterogeneous catalyst, MCM-41-pr-NH₂-CuL, can be successfully applied for efficient and selective oxidation of different primary and secondary alcohols to the corresponding carbonyl compounds using hydrogen peroxide as an oxidant in acetonitrile at 60 °C. The effect of reaction parameters such as solvent, amount of catalyst, temperature and kind of oxidant on the oxidation of benzyl alcohol was also studied. The prepared catalyst could be recovered and reused four times without important loss of its catalytic performance. The heterogeneous MCM-41-pr-NH₂-CuL catalyst was found to be catalytically more active in the oxidation of alcohols compared to the similar type of copper(II) Schiff base complex in homogeneous media under the same reaction conditions.     

The synthesis,spectroscopic investigation,crystal and molecular structure of [ReCl3(MeCN)(dppe)] complex

The [ReOCl₃(dppe)] complex reacts with acetonitrile in the presence of excess of triphenylphosphine to give a new monomeric nitrile rhenium(III) complex – [ReCl₃(MeCN)(dppe)] (1). This paper presents spectroscopic characterization, magnetochemical measurements, crystal and molecular structure for 1.     

Redox‐Switchable Phase Tags – Facile Mitsunobu Reactions using Ferrocenyl‐Tagged Triphenylphosphine

The use of redox‐switched phase tags in ferrocenyl‐substituted triphenylphosphine combined with DBAD (di‐tert‐butyl azodicarboxylate) allows high yield (>90 %) Mitsunobu transformations without the need for the chromatographic purification of the products. The redox‐switchable phosphine can be easily synthesized in two steps from 4‐bromoaniline, ferrocene and chlorodiphenylphosphine. It is separated from the reaction mixture by oxidation with iron(III) chloride and can be recycled efficiently by reductive treatment.     

Selective oxidation of alcohols with hydrogen peroxide catalyzed by hexadentate binding 8-quinolinolato manganese(III) complexes

A series of hexadentate 8-quinolinolato manganese(III) complexes were synthesized and proven to own a distorted octahedral geometry via elemental analysis, solid UV–vis spectroscopy and Hartree–Fock/3-21G+ calculation. These Mn(III) complexes were found to be more efficient than their corresponding tetradentate 8-quinolinolato manganese(II) and salen-Mn^IIIOAc for the oxidation of alcohols in acetone medium, being due to their special hexadentate binding structures that could open an axial MnO bond to form the more active pentadentate structures in the presence of aqueous hydrogen peroxide, as supported by UV–vis spectra. The halogen substituents in ligand's aryl ring could significantly enhance the catalytic activities and 5-chloro-7-iodo-8-quinolinolato manganese(III) gave the highest turnover number (TON). A reasonable mechanism for the present catalytic system was proposed.     

3,5‐Dimethylpyrazolium Fluorochromate(VI)‐Catalysed Oxidation of Organic Substrates by Hydrogen Peroxide under Solvent‐Free Conditions

3,5‐Dimethylpyrazolium fluorochromate (VI), C₅H₈N₂H[CrO₃F], DmpzHFC , serves as an efficient catalyst for oxidation of primary, secondary and allylic alcohols to the corresponding carbonyl compounds using H₂O₂ at room temperature under solvent‐free conditions. Oxidation of methyl phenyl sulfides and triphenylphosphine were also carried out successfully.     

Novel efficient catalysts based on Ru or Pd oxide for selective liquid-phase oxidation of alcohols with nitrous oxide

Ru^IV–M and Pd^II–M (MCo^III, Fe^III and Mn^III) binary oxides supported on γ-alumina are demonstrated to be novel, active catalysts for selective liquid-phase oxidation of primary and secondary alcohols to, respectively, aldehydes and ketones with nitrous oxide under 10 bar N₂O pressure and 100 °C. The Ru and Pd catalysts have comparable activities but Ru ones are more selective, the Ru–Co system (Ru/Co=1:1) showing the best performance. Activated primary alcohols (benzyl and cinnamyl alcohol) and secondary alcohols give aldehydes or ketones with 100% selectivity at 95–100% conversion. Non-activated primary alcohols (e.g. 1-dodecanol) give aldehydes with some over-oxidation to acids; the latter is completely inhibited by adding a radical scavenger. The Ru–Co catalyst can be reused without loss of selectivity, although with a gradual decrease in its activity. Compared to the Ru–Co catalysed oxidation of alcohols with O₂ studied earlier, the oxidation with N₂O has the advantage of considerably higher selectivity, albeit occurring under higher pressures.     

Metalloporphyrin/Iodine(III)‐Cocatalyzed Oxygenation of Aromatic Hydrocarbons

Hypervalent iodine species have a pronounced catalytic effect on the metalloporphyrin‐mediated oxygenations of aromatic hydrocarbons. In particular, the oxidation of anthracene to anthraquinone with Oxone readily occurs at room temperature in aqueous acetonitrile in the presence of 5–20 mol% of iodobenzene and 5 mol% of a water‐soluble iron(III)‐porphyrin complex. 2‐tert‐Butylanthracene and phenanthrene also can be oxygenated under similar conditions in the presence of 50 mol% of iodobenzene. The oxidation of styrene in the presence of 20 mol% of iodobenzene leads to a mixture of products of epoxidation and cleavage of the double bond. Partially hydrogenated aromatic hydrocarbons (e.g., 9,10‐dihydroanthracene, 1,2,3,4‐tetrahydronaphthalene, and 2,3‐dihydro‐1H‐indene) afford under these conditions products of oxidation at the benzylic position in moderate yields. The proposed mechanism for these catalytic oxidations includes two catalytic redox cycles: 1) initial oxidation of iodobenzene with Oxone producing the hydroxy(phenyl)iodonium ion and hydrated iodosylbenzene, and 2) the oxidation of iron(III)‐porphyrin to the oxoiron(IV)‐porphyrin cation‐radical complex by the intermediate iodine(III) species. The oxoiron(IV)‐porphyrin cation‐radical complex acts as the actual oxygenating agent toward aromatic hydrocarbons.     

Enantioselective oxidation of racemic secondary alcohols catalyzed by chiral Mn(III)-salen complex with sodium hypochlorite as oxidant

Chiral Mn(III)-salen complex catalyzed oxidative kinetic resolution (OKR) of secondary alcohols has been achieved with cheap and easily available sodium hypochlorite (NaClO) as oxidant. The novel protocol is very efficient for the OKR of a variety of secondary alcohols at room temperature.