A robust NNP-type ruthenium (II) complex for alcohols dehydrogenation to esters and pyrroles

A Ru (II) complex bearing pyridyl-based benzimidazole-phosphine tridentate NNP ligand was synthesized and structurally characterized by NMR, IR. The complex can efficiently and selectively catalyze the acceptorless dehydrogenation of primary alcohols to esters under relatively mild conditions and the synthesis of pyrroles by means of the reactions of secondary alcohols and β-amino alcohols through acceptorless deoxygenation condensation.     

Acceptorless photocatalytic dehydrogenation for alcohol decarbonylation and imine synthesis

It has come to light: Renewed interest in conversions of highly oxygenated materials has motivated studies of the organometallic-catalyzed photocatalytic dehydrogenative decarbonylation of primary alcohols into alkanes, CO, and H(2) . Methanol, ethanol, benzyl alcohol, and cyclohexanemethanol are readily decarbonylated. The photocatalysts are also active for amine dehydrogenation to give N-alkyl aldimines and H(2) .     

The Mn(acac)3—RCN—CCl4 system as a new efficient reagent for the oxidation of secondary alcohols into ketones

The Mn(acac)₃—RCN—CCl₄ system was found to be efficient for the oxidation of secondary alcohols into the corresponding ketones in 80—93% yields. The oxidation proceeds through the formation of alkyl hypochlorites, which are generated from CCl₄ and the alcohols in the presence of the Mn(acac)₃—RCN catalytic system (R = Me, Et, and Ph).     

Regioselective annulation of propargyl alcohols with ambident-enols: A Ca(II)-catalyzed trisubstituted benzochromene synthesis

Highly regioselective, 6-endo cyclization between propargyl alcohols and ambident enols such as naphthols, 4-hydroxy coumarin, cyclohexane-1,3-dione, 5,5-dimethylcyclohexane-1,3-dione is described using Ca(OTf)₂ under solvent free conditions. The reaction proceeds through a cascade annulation which involves an etherification, Claisen type rearrangement, allene formation and endocyclization. Further, we extended this method to the synthesis of iodo-derivative and demonstrated the reactivity in cross-coupling reactions.     

Synthesis and transformations of metallacycles. 30. Aluminacyclopentanes in the synthesis of secondary and tertiary alcohols

A method for the synthesis of secondary and tertiary alcohols was developed. The method is based on cycloalumination of olefins with trialkylalanes in the presence of Zr-containing catalysts followed by the CuCl-catalyzed in situ reaction of the corresponding aluminacyclopentanes with aldehydes or ketones.     

Cobalt phthalocyanine catalyzed aerobic oxidation of secondary alcohols: an efficient and simple synthesis of ketones

A variety of activated and non-activated secondary alcohols have been efficiently oxidized to their corresponding ketones in excellent yields with molecular oxygen using cobalt phthalocyanine as catalyst in the presence of powdered potassium hydroxide.     

Hydrotalcite-supported gold catalyst for the oxidant-free dehydrogenation of benzyl alcohol: studies on support and gold size effects

Gold nanoparticles with uniform mean sizes (≈3 nm) loaded onto various supports have been prepared and studied for the oxidant-free dehydrogenation of benzyl alcohol to benzaldehyde and hydrogen. The use of hydrotalcite (HT), which possesses both strong acidity and strong basicity, provides the best catalytic performance. Au/HT catalysts with various mean Au particle sizes (2.1-21 nm) have been successfully prepared by a deposition-precipitation method under controlled conditions. Detailed catalytic reaction studies with these catalysts demonstrate that the Au-catalyzed dehydrogenation of benzyl alcohol is a structure-sensitive reaction. The turnover frequency (TOF) increases with decreasing Au mean particle size (from 12 to 2.1 nm). A steep rise in TOF occurs when the mean Au particle size becomes smaller than 4 nm. Our present work suggests that the acid-base properties of the support and the size of Au nanoparticles are two key factors controlling the alcohol dehydrogenation catalysis. A reaction mechanism is proposed to rationalize these results. It is assumed that the activation of the β-C-H bond of alcohol, which requires the coordinatively unsaturated Au atoms, is the rate-determining step.     

Copper(II)-catalyzed allylation of propargylic and allylic alcohols by allylsilanes: a facile synthesis of 1,5-enynes

Propargylic alcohols undergo smooth deoxygenative allylation with allylsilanes in the presence of a solution of 10 mol % of copper(II) tetrafluoroborate in acetonitrile to afford the corresponding 1,5-enynes in good to high yields under mild and neutral conditions. Scandium triflate is also found to catalyze efficiently the nucleophilic substitution of propargylic alcohols with allylsilanes.     

Cobalt(II)-catalyzed oxidation of alcohols into carboxylic acids and ketones with hydrogen peroxide

The oxidation of aliphatic and aromatic alcohols into the corresponding carboxylic acid analogues and ketones has been carried out using 30% H₂O₂ and cobalt(II) complex 1 in good to high yields. The reaction is safe, clean and functions in the absence of additives.     

Triruthenium dodecacarbonyl/triphenylphosphine catalyzed dehydrogenation of primary and secondary alcohols

Dehydrogenation of alcohols into aldehydes and ketones by Ru₃(CO)₁₂/PPh₃ based homogeneous catalysis has been investigated as an alternative for the classical Oppenauer oxidation. Several catalytic systems have been screened in the Oppenauer-like oxidation of alcohols. A systematic study of various combinations of Ru₃(CO)₁₂, mono- and bidentate ligands and hydride acceptors was performed to enable dehydrogenation of primary alcohols to stop at the aldehyde stage. Among many H-acceptors screened, diphenylacetylene (tolane) proved the most suitable judged from its smooth reduction. Electron rich and deficient analogues of tolane have been synthesized and, based on competition experiments between these H-acceptors, a tentative catalytic cycle for the Ru₃(CO)₁₂/PPh₃-catalyzed dehydrogenations has been proposed.     

The Synthesis of Benzimidazoles and Quinoxalines from Aromatic Diamines and Alcohols by Iridium‐Catalyzed Acceptorless Dehydrogenative Alkylation

Benzimidazoles and quinoxalines are important N‐heteroaromatics with many applications in pharmaceutical and chemical industry. Here, the synthesis of both classes of compounds starting from aromatic diamines and alcohols (benzimidazoles) or diols (quinoxalines) is reported. The reactions proceed through acceptorless dehydrogenative condensation steps. Water and two equivalents of hydrogen are liberated in the course of the reactions. An Ir complex stabilized by the tridentate P^N^P ligand N²,N⁶‐bis(di‐isopropylphosphino)pyridine‐2,6‐diamine revealed the highest catalytic activity for both reactions.     

Efficient copper(II)-catalyzed transamidation of non-activated primary carboxamides and ureas with amines

Amid(e) them all: primary carboxamides and ureas react with aromatic and aliphatic amines in the presence of a copper catalyst to give a wide range of functionalized amides.     

Copper nanoparticles on dichromium trioxide: a highly efficient catalyst from copper chromium hydrotalcite for oxidant‐free dehydrogenation of alcohols

Stable copper(0) nanoparticles supported on chromium (Cu(0)/Cr₂O₃) are prepared from the composite precursor copper chromium hydrotalcite. The resulting Cu(0)/Cr₂O₃ catalyst is first used in the selective dehydrogenation of alcohols to aldehydes. More impressively, these dehydrogenations are performed without oxidants and yields of products are high. The stability of Cu(0)/Cr₂O₃ is also assessed by studying its recoverability and reusability for up to five cycles. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,Structure, and Catalytic Activity of Cyclometalated Iridium Complexes with a Bidentate POC Ligand

Synthesis, characterization and catalytic activity of cyclometalated iridium complexes with a bidentate POC ligand is presented. Metalation of POC-H (di-tert-butyl(phenoxy)phosphane) with [Ir(COD)Cl]₂ proceeded rapidly at room temperature and afforded mixture of (POC)(POC-H)IrHCl ( 1 a ) and (POC)(COD)IrHCl ( 1 b ), from which complexes (POC)(L)IrHCl where L=PPh₃ ( 1 c ), bipyridine ( 1 d ) and [2,2′-bipyridine]-6,6′-diol ( 1 e ) were prepared through ligand exchange. The compounds were tested in acceptorless dehydrogenation of 1-phenylethanol and transfer dehydrogenation of ethanol in a context of comparison with pincer counterparts (POCOP)IrHCl and (PCN)IrHCl. An attempt to prepare a dihydride complex from 1 e led to dimeric complex [(POC)(bipy-diol−)IrH]₂ ( 3 ) that could explain the low activity of 1 e . DFT studies provided insight into POC-H vs POCOP-H metalation mechanism.     

Metal-free oxidation of secondary benzylic alcohols using aqueous TBHP

We report a simple, yet efficient metal-free oxidation of secondary benzylic alcohols in the presence of t-butyl hydroperoxide (70% TBHP) with high yields of up to 98%. This type of reaction can be carried out using a wide variety of substrates, requires no other organic solvent, and proves to be tolerant toward a variety of different functional groups.