Dehydrogenation Of Secondary Alcohols Research Articles

Highly efficient dehydrogenation of secondary alcohols catalyzed by iridium-CNP complexes

A new highly practical method is presented for dehydrogenation of secondary alcohols to the corresponding ketones catalyzed by the iridium-CNP complexes. The reactions are compatible with substrates bearing diverse functional groups and proceed efficiently under mild conditions.

Acceptor-free dehydrogenation of secondary alcohols by heterogeneous cooperative catalysis between Ni nanoparticles and acid–base sites of alumina supports

Nickel-nanoparticle-loaded θ-Al2O3 (Ni/θ-Al2O3), prepared by H2-reduction of NiO/θ-Al2O3, acts as an effective and reusable heterogeneous catalyst for acceptor-free dehydrogenation of alcohols in a liquid phase. Among various supports, amphoteric supports (such as θ-Al2O3), having both acidic and basic sites, gave higher activity than acidic or basic supports. Among Ni/θ-Al2O3 catalysts with different Ni particle sizes, turnover frequency (TOF) per surface Ni increases with decreasing Ni particle size. These results suggest that low-coordinated Ni0 sites and metal/support interfaces play important roles in the catalytic cycle. The reaction mechanism is investigated by in situ IR study combined with kinetic analysis (kinetic isotope effect), and the following mechanism is proposed: (1) reaction of an alcohol with Lewis acid (Alδ+)–base (AlOδ−) pair site of alumina yields an alkoxide on the Alδ+ site and a proton on the AlOδ− site, (2) CH dissociation of the alkoxide by Ni0 site to form NiH and a ketone, and (3) protolysis of NiH by a neighboring proton to release H2 gas. The proposed mechanism provides fundamental reasons for the higher activity of Ni on the acid–base bifunctional support (Al2O3) than on basic and acidic ones.

Dehydrogenation of Alcohols by Bis(phosphinite) Benzene Based and Bis(phosphine) Ruthenocene Based Iridium Pincer Complexes

Dehydrogenation of alcohols by three iridium pincer complexes, IrH(Cl)[2,6-(tBu2PO)2C6H3] (1), {IrH(acetone)[2,6-(tBu2PO)2C6H3]}{BF4} (2), and IrH(Cl)[{2,5-(tBu2PCH2)2C5H2}Ru(C5H5)] (3), is reported, in both the presence and the absence of a sacrificial hydrogen acceptor. Dehydrogenation of secondary alcohols proceeds in a catalytic mode with turnover numbers up to 3420 (85% conversion) for acceptorless dehydrogenation of 1-phenylethanol. Primary alcohols are readily decarbonylated even at room temperature to give catalytically inactive 16e Ir–CO adducts. The mechanism of this transformation was studied in detail, especially for EtOH; new intermediates were isolated and characterized.

Oxygen‐Assisted Hydroxymatairesinol Dehydrogenation: A Selective Secondary‐Alcohol Oxidation over a Gold Catalyst

Selective dehydrogenation of the biomass-derived lignan hydroxymatairesinol (HMR) to oxomatairesinol (oxoMAT) was studied over an Au/Al(2)O(3) catalyst. The reaction was carried out in a semi-batch glass reactor at 343 K under two different gas atmospheres, namely produced through synthetic air or nitrogen. The studied reaction is, in fact, an example of secondary-alcohol oxidation over an Au catalyst. Thus, the investigated reaction mechanism of HMR oxidative dehydrogenation is useful for the fundamental understanding of other secondary-alcohol dehydrogenation over Au surfaces. To investigate the elementary catalytic steps ruling both oxygen-free- and oxygen-assisted dehydrogenation of HMR to oxoMAT, the reactions were mimicked in a vacuum over an Au(28) cluster. Adsorption of the involved molecular species--O(2), three different HMR diastereomers (namely, one SRR and two RRR forms), and the oxoMAT derivative--were also studied at the DFT level. In particular, the energetic and structural differences between SRR-HMR and RRR-HMR diastereomers on the Au(28) cluster were analyzed, following different reaction pathways for the HMR dehydrogenation that occur in presence or absence of oxygen. The corresponding mechanisms explain the higher rates of the experimentally observed oxygen-assisted reaction, mostly depending on the involved HMR diastereomer surface conformations. The role of the support was also elucidated, considering a very simple Au(28) charged model that explains the experimentally observed high reactivity of the Au/Al(2)O(3) catalyst.

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

AbstractAn 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.

Enantioselective iridium-catalyzed vinylogous Reformatsky-aldol reaction from the alcohol oxidation level: linear regioselectivity by way of carbon-bound enolates.

Enantioselective iridium-catalyzed vinylogous Reformatsky-aldol reaction from the alcohol oxidation level: linear regioselectivity by way of carbon-bound enolates.

Discovery of Environmentally Benign Catalytic Reactions of Alcohols Catalyzed by Pyridine-Based Pincer Ru Complexes, Based on Metal–Ligand Cooperation

We have developed a new mode of metal–ligand cooperation, based on aromatization–dearomatization of pyridine-based pincer-type ligands, and have demonstrated it in the activation of H2 and C–H bonds by PNP Ir complexes. This type of metal–ligand cooperation plays a key role in the recently discovered environmentally benign reactions of alcohols, catalyzed by PNP and PNN pincer complexes of ruthenium, including (a) dehydrogenation of secondary alcohols to ketones (b) dehydrogenative coupling of primary alcohols to form esters and H2 (c) hydrogenation of esters to alcohols under mild conditions (d) unprecedented amide synthesis: catalytic coupling of amines with alcohols, with liberation of H2. Ligand modification in the latter reaction has led to unprecedented synthesis of imines with H2 liberation. These reactions are very efficient, proceed under neutral conditions and produce no waste.

An evaluation of the Noyori system “in reverse”: Thermodynamic and kinetic parameters of secondary alcohol transfer dehydrogenation catalyzed by [(η 6-1- iPr-4-Me-C 6H 4)Ru(HN-CR′R″-CR′R″NTs)], R′ = H, Me; Ph, R″ = H, Me

The 16 electron ruthenium complexes [(η 6-1-isopropyl-4-methyl-benzene)(X-N)Ru(II)], where X-N is 2-amido-1-ethoxide ( 2), 1- N- p-tosyl-1,2-diamido-ethane ( 3), 1- N- p-tosyl-1,2-diamido-benzene ( 7), 1- N-( p-tosyl)-1,2-diamido-1,1,2,2-tetramethyl-ethane ( 8) and 1- N-( p-tosyl)-1,2-diamido- meso-1,2-diphenyl-ethane ( 9) have been evaluated as catalysts for the transfer dehydrogenation of secondary alcohols to ketones in acetone and/or cyclohexanone solvent. Complexes 2 and 3 cannot be isolated and decompose under these conditions. In contrast complexes 7, 8 and 9 are supported by ligands designed to resist β-hydride elimination and can with the exclusion of oxygen be held in solution for weeks. Complex 7 is not active as a catalyst. Complexes 8 and 9 are highly air-sensitive and active as catalysts for transfer (de)hydrogenations under oxidizing and reducing conditions, respectively. There is no coordinative inhibition of the catalysts by the ketone solvent under oxidizing conditions, but both catalysts show a correlation between the reaction rates and the Δ G values of the reactions with reactions leading to α, β-unsaturated ketones proceeding faster. For all alcohol/ketone substrate pairs where the ketone is not α, β-unsaturated, the hydrogenation reactions under reducing conditions ( iso-propanol solvent) are at least one order of magnitude faster than the corresponding dehydrogenation reaction under oxidizing conditions (acetone solvent).

Electron-rich, bulky PNN-type ruthenium complexes: synthesis, characterization and catalysis of alcohol dehydrogenation

Reaction of the electron-rich, bulky tridentate PNN ligand (PNN=2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine) with Ru(PPh3)3Cl2 at 65 degrees C resulted in formation of the mononuclear dinitrogen complex (PNN)Ru(Cl)2N2 (minor) and the N2 bridged Ru(II) dinuclear complex [(PNN)Ru(Cl)2]2(micro-N2) (major). These complexes can be interconverted; passing argon through a solution of the mixture resulted in formation of pure . The cationic square-pyramidal [(PNN)Ru(PPh3)Cl]OTf was obtained by the reaction of complex with silver triflate followed by PPh3. Reaction of complex with CO yielded (PNN)Ru(CO)Cl2, which upon reaction with one equiv. of AgBF4 gave the cationic [(PNN)Ru(CO)Cl]BF4. The dicationic [(PNN)Ru(CO)(H2O)(acetone)](BF4)2 was obtained from with 2 equiv. of AgBF4 in acetone solution. Complexes , and were structurally characterized by X-ray crystallography. Complexes and upon addition of an equivalent of base, catalyzed the dehydrogenation of secondary alcohols to the corresponding ketones and primary alcohols to esters in good yields and high selectivity accompanied with the evolution of hydrogen gas.

Dinuclear Ruthenium Complexes Bearing Dicarboxylate and Phosphine Ligands. Acceptorless Catalytic Dehydrogenation of 1-Phenylethanol

Reaction of RuH2CO(PPh3)3 with tetrafluorosuccinic acid at 100 °C gave rise to the formation of the dinuclear bis(tetrafluorosuccinate)-bridged Ru(II) complex 2, containing two water ligands. Exchange of the PPh3 in complex 2 with various diphosphine ligands afforded a series of analogous complexes 3. Reaction of the latter with 1-phenylethanol at 130 °C or with 2-propanol/Et3N at room temperature furnished the dinuclear dihydrido-bridged Ru(II) complexes 4. Complexes 2 and 4 were characterized by X-ray diffraction analysis. Both bis(tetrafluorosuccinate)-bridged complexes 3 and dihydrido-bridged complexes 4 catalyze the acceptorless dehydrogenation of 1-phenylethanol to acetophenone and dihydrogen with good yields and excellent selectivity under relatively mild conditions in the absence of acid or base. A tentative catalytic cycle for the dehydrogenation of secondary alcohols by Ru(II) complexes of type 3 is presented.

Electron-Rich, Bulky Ruthenium PNP-Type Complexes. Acceptorless Catalytic Alcohol Dehydrogenation

Reaction of the electron-rich, bulky tridentate PNP ligand (2,6-bis-(di-tert-butylphosphinomethyl)pyridine) with Ru(PPh3)3Cl2 at 65 °C resulted in formation of a solution containing the dinitrogen monomeric Ru(II) complex 1a and the N2-bridged dinuclear Ru(II) complex 1b, which can be interconverted. Passing argon through the solution results in formation of pure 1b. The Ru(II) hydride dinitrogen complex 2 was obtained by the reaction of complex 1b with 2 equiv of NaBEt3H. Complex 1b reacted with 4 equiv of AgOCOCF3 to yield [Ru(PNP)(CF3COO)2], 3. The Ru(II) carbonyl hydride complex 4 was obtained by the reaction of PNP and Ru2(OAc)4 in methanol as a result of O−H activation and decarbonylation of methanol. Complexes 1b, 2, and 4 were structurally characterized by X-ray crystallography. Complexes 1b and 2 catalyze the dehydrogenation of secondary alcohols to the corresponding ketones with good yields and high selectivity accompanied with the evolution of dihydrogen in a homogeneous system without a need f...

Chemical model of oxidases. CuI-catalyzed oxidation of secondary alcohols by dioxygen

Oxidation of secondary alcohols (2-propanol, 2-butanol, and cyclohexanol) by dioxygen, catalyzed by CuI ando-phenanthroline complexes, in the presence of alkali, was studied. The conditions under which oxidative dehydrogenation of secondary alcohols result in fast formation of ketones as the only primary oxidation products were found. Bis-phenanthrolinates [Cu(phen)2]+ are the active forms of the catalyst. The catalytic turnover number for complexes between copper(i) ando-phenanthroline is 1 to 2 s−1 at room temperature.

Production of 10-Ketostearic Acid from Oleic Acid by Flavobacterium sp. Strain DS5 (NRRL B-14859)

A microbial isolate, Flavobacterium sp. strain DS5, produces 10-ketostearic acid (10-KSA) from oleic acid in 85% yield. This is the first report on this type of reaction catalyzed by a Flavobacterium strain. The product was purified to give white, plate-like crystals melting at 79.2 degrees C. The optimum time, pH, and temperature for the production of 10-KSA are 36 h, 7.5, and 30 degrees C, respectively. A small amount of 10-hydroxystearic acid (10-HSA) (about 10% of the amount of the main product, 10-KSA) is also produced during the bioconversion. 10-KSA is not further metabolized by strain DS5 and accumulates in the medium. In contrast to growing cells, a resting-cell suspension of strain DS5 produces 10-HSA and 10-KSA in a ratio of 1:3. The crude cell extract obtained from ultrasonic disruption of the cells converts oleic acid mainly to 10-HSA (10-HSA/10-KSA ratio, 97:3). This result strongly suggested that oleic acid is converted to 10-KSA via 10-HSA. Enzymes catalyzing the hydration and secondary alcohol dehydrogenation are cell associated. Product 10-HSA from strain DS5 is 66% enantiomeric excess in the 10(R) form. The oleic acid conversion enzyme(s) reacts with unsaturated fatty acids in the order oleic acid > palmitoleic acid > linoleic acid > linolenic acid > gamma-linolenic acid > myristoleic acid.

Substituent effects on the rate of dehydrogenation of primary and secondary alcohols

The kinetics of catalytic dehydrogenation of eight secondary alcohols to ketones on a ZnOCr 2O 3 catalyst has been studied in a flow reactor at 360°C and atmospheric pressure. The experimental data were fitted to several kinetic models using a nonlinear least-squares method. The most suitable model was found to be a Langmuir-Hinshelwood-type equation, assuming single-site adsorption of alcohol and surface reaction as the rate-determining step. Reaction rate constants and adsorption coefficients of dehydrogenation of secondary alcohols were correlated by the Taft equation with structural parameters characterizing polar or steric effects of substituents in R 1CH(OH)R 2. Similar data, obtained previously, on nine primary alcohols were included in this correlation. The reaction mechanism is discussed.

Novel reactions catalyzed by iridium pentahydride complex

Abstract

Photocatalytic dehydrogenation of secondary alcohols with rhodium porphyrin complex

Photocatalytic dehydrogenation of secondary alcohols with rhodium porphyrin complex

Study of the heterogeneously catalyzed dehydrogenation of secondary alcohols using gas chromatography

Study of the heterogeneously catalyzed dehydrogenation of secondary alcohols using gas chromatography

Spectroscopic study of chromia catalysts for dehydrogenation of secondary alcohols

Infrared, EPR and reflectance spectra in the uv and visible region were measured for six different chromium(III) oxide preparations. With some samples also the changes of spectra caused by the use of the catalysts for dehydrogenation of isopropanol to acetone at 350 °C were studied. The results are interpreted in terms of the change of coordination of surface Cr 3+ atoms and interaction between them due to preparation variables, surface hydration and influence of the reactants. A linear correlation was found between the Racah parameter calculated from the reflectance spectra and sensitivity of the reaction rate of dehydrogenation of secondary alcohols R · CHOH · CH 3 to the change in the structure of the group R.

Surface and catalytic properties of chromia in dehydrogenation of secondary alcohols

The rates of dehydrogenation of a series of 2-alkanols, the selectivity of the decomposition of 3,3-dimethyl-2-butanol, adsorption heats of diethyl ether by gas chromatographic method, crystallite size, total water content and surface concentration of hydroxyl groups were measured with six samples of chromium(III) oxide differing in the method of preparation. Correlation of the results showed that the catalytic properties of chromium oxide depend mainly on its temperature of calcination which governs the surface concentration of hydroxyl groups and the state of coordination of surface Cr 3+ ions.

Mechanism of dehydrogenation of secondary alcohols on chromia

Using chromium(III) oxide as catalyst, there were measured the kinetics of dehydrogenation of 2-propanol, the kinetic isotope effects with deuterated 2-propanols, the effect of pretreatment of the catalyst in hydrogen and in oxygen on its activity and the influence of some substances added to the feed on conversion. On the basis of these experimental data, together with some results from the following paper and quantum-chemical models of adsorption and surface reaction, a mechanism of dehydrogenation of secondary alcohols on Cr 2O 3 was proposed. It consists of adsorption and surface reaction, in which the breaking of the C αH α bond is considered the rate determining step, on active centers formed by groups of surface Cr 3+ and O 2− atoms.