Aerobic oxidative dehydrogenation of benzylamines catalyzed by a cyclometalated ruthenium complex

The ruthenium(III) complex bearing phenylpyridine as a cyclometalated ligand serves as an efficient catalyst for the aerobic oxidative dehydrogenation of benzylamines to the corresponding benzonitriles under mild conditions.     

The catalytic activity of a cyclometalated ruthenium(III) complex for aerobic oxidative dehydrogenation of benzylamines

The ruthenium(III) complex bearing benzo[h]quinoline as a cyclometalated ligand was synthesized and characterized by ESI-MS, elemental analysis, cyclic voltammetry and crystallography. The complex serves as an efficient catalyst for the aerobic oxidative dehydrogenation of benzylamines to the corresponding benzonitriles under mild conditions.     

Air-stable iron catalyst for the Oppenauer-type oxidation of alcohols

An alcohol oxidation process using an air-stable iron tricarbonyl compound structurally similar to Shvo’s diruthenium bridging hydride was developed. Secondary benzylic and allylic alcohols are oxidized in high yields, and evidence for an Oppenauer-type mechanism is presented.     

Heterogeneous Shvo-type ruthenium catalyst: dehydrogenation of alcohols without hydrogen acceptors

A Shvo-type diruthenium complex is heterogenized by a sol-gel process, which catalyzes the conversion of alcohols to carbonyl compounds and molecular hydrogen without any additive. The heterogeneous catalyst is recoverable by simple filtration, stable in the air, and reusable.     

Aerobic oxidative dehydrogenation of coordinated imidazoline units of pincer ruthenium complex

A new pincer ruthenium complex (1; [RuL¹(tpy)](PF₆); L¹ = 1,3-di(2-imidazoline-2-yl)benzene, tpy = 2,2′:6′,2″-terpyridine) having a κ³NCN pincer ligand with two imidazoline units and related ruthenium complexes were synthesized and characterized. The imidazoline units of 1 were oxidized in air to give an imidazole-ligated pincer complex (2; [RuL²(tpy)](PF₆); L² = 1,3-di(2-imidazolyl)benzene). Results of the ¹H NMR spectroscopic and cyclic voltammetric studies of the complexes indicate that the σ-donor character of the pincer ligand of 1 induces the Ru-promoted oxidative dehydrogenation of coordinated imidazoline moieties to imidazole units with oxygen in air.     

Aerobic oxidation of benzyl alcohols by MoVI compounds

Selective and controlled aerobic oxidation of activated benzyl alcohols to the corresponding aldehydes is achieved in refluxing CH₃CN using catalytic amounts of MoO₂Cl₂(L)₂ where L is DMSO, DMF or THF. The catalysis reactions are possible under open air in the absence of any other external co‐oxidants. However, bubbling of oxygen to the reaction mixture is useful in making the catalysis reaction sustained. Both activated and deactivated varieties of α‐substituted benzyl alcohols (secondary alcohols) give ketones in the same reaction conditions. The inexpensive catalyst is selective towards activated primary benzyl alcohols and also, being mild, stops the oxidation at the aldehyde stage, making it synthetically useful. Copyright © 2006 John Wiley & Sons, Ltd.     

Ruthenium-catalysed oxidation of alcohols to amides using a hydrogen acceptor

A wider investigation into the synthesis of secondary amides from primary alcohols using a hydrogen acceptor using commercially available [Ru(p-cymene)Cl₂]₂ with bis(diphenylphosphino)butane (dppb) as the catalyst. The report looks at over 50 examples with varying functionality and steric bulk, whilst also covering the first reported results using microwave heating to effect the transformation.     

Ruthenium(II)-salen complexes-catalyzed olefination of aldehydes with ethyl diazoacetate

Several salen-ruthenium(II) complexes, which are derived from commercial ligands or simply ethylenediamine, can be successfully applied as catalysts for the olefination of a broad variety of aldehydes. Depending on the electron richness of the applied aldehydes, good to very good olefin yields and high E:Z selectivities are reached at 60 or 80 °C reaction temperature with ethyl diazo acetate being the reaction partner. The reaction rate depends on the electron donor capabilities of the aldehydes. Electron poor aldehydes undergo faster reactions than electron rich aldehydes, but both electron rich and bulky aldehydes can be transformed to corresponding olefins in very good yields and high E-selectivity.     

Facile oxidative conversion of alcohols to esters using molecular iodine

A simple, efficient, and high-yield procedure for the oxidative conversion of alcohols to various types of esters and ketones, with molecular iodine and potassium carbonate was successfully carried out.     

Aerobic oxidative transformation of primary azides to nitriles by ruthenium hydroxide catalyst

In the presence of an easily prepared supported ruthenium hydroxide catalyst, Ru(OH)(x)/Al(2)O(3), various kinds of structurally diverse primary azides including benzylic, allylic, and aliphatic ones could be converted into the corresponding nitriles in moderate to high yields (13 examples, 65-94% yields). The gram-scale (1 g) transformation of benzyl azide efficiently proceeded to give benzonitrile (0.7 g, 90% yield) without any decrease in the performance in comparison with the small-scale (0.5 mmol) transformation. The catalysis was truly heterogeneous, and the retrieved catalyst could be reused for the transformation of benzyl azide without an appreciable loss of its high performance. The present transformation of primary azides to nitriles likely proceeds via sequential reactions of imide formation, followed by dehydrogenation (β-elimination) to produce the corresponding nitriles. The Ru(OH)(x)/Al(2)O(3) catalyst could be further employed for synthesis of amides in water through the transformation of primary azides (benzylic and aliphatic ones) to nitriles, followed by sequent hydration of the nitriles formed. Additionally, direct one-pot synthesis from alkyl halides and TBAN(3) (TBA = tetra-n-butylammonium) could be realized with Ru(OH)(x)/Al(2)O(3), giving the corresponding nitriles in moderate to high yields (10 examples, 64-84% yields).     

Ruthenium-catalyzed addition of carboxylic acids or cyclic 1,3-dicarbonyl compounds to propargyl alcohols

Monomeric ruthenium(0) complexes containing redox-coupled dienone ligands were found to catalyze the regio-selective addition of carboxylic acids or cyclic 1,3-dicarbonyl compounds to propargyl alcohols.     

Direct oxidative conversion of aldehydes and alcohols to 2-imidazolines and 2-oxazolines using molecular iodine

Aldehydes were converted to the corresponding 2-imidazolines and 2-oxazolines in good yields by the reaction with ethylenediamine and aminoethanol, respectively, using molecular iodine and potassium carbonate. Moreover, primary alcohols were directly converted to the corresponding 2-imidazolines and 2-oxazolines via aldehydes in one-pot manner with ethylenediamine and aminoethanol, respectively, using molecular iodine and potassium carbonate.     

Catalytic oxidation of alcohols with polymer-supported ruthenium complex under mild conditions

Polymer-supported ruthenium-containing complex PS–Phen–Ru was synthesized (where PS = chloromethyl polystyrene resin, Phen = 1,10-phenanthroline) and was characterized by FT-IR, ICP, and XPS. The supported complex was used to catalyze the oxidation of primary aliphatic alcohols as well as aromatic alcohols in the presence of iodosylbenzene. The oxidations were carried out in acetonitrile solution, affording the corresponding aldehydes or ketones in high substrate conversion and high selectivities under mild reaction conditions. The catalyst can be easily prepared and can be recycled.     

Synthesis of seven and higher-membered heterocycles using ruthenium catalysts

A wide variety of biological activities are possessed by nitrogen, oxygen, and sulfur containing heterocycles and many methods are explored for the preparation of these heterocyclic compounds. Metal catalysts are used in organic reactions with high activity. The synthesis of heterocycles with the help of metal catalysts became very important in organic synthesis. New protocols have been investigated for the synthesis of heterocycles in the last decades. In present review article I have concentrated on the synthesis of seven and higher-membered heterocylces in the presence of ruthenium catalyst.     

Ruthenium-catalyzed one-pot hydroformylation of alkenes using carbon dioxide as a reactant

A new hydroformylation of alkenes using carbon dioxide as a reactant is shown to take place in the presence of ruthenium cluster complexes and halide salts. Similar or even better yields of alcohols were formed as compared to the conventional hydroformylation with CO under the same reaction conditions. The reaction proceeded in three steps: CO₂ is first converted to CO; then it is used as a reagent for hydroformylation to give aldehyde; subsequently, it is hydrogenated to alcohol. ESI-mass spectrometric analyses of the reaction solutions indicated formation of four kinds of ruthenium anionic complexes including tetra-, tri-, and mononuclear species. On the basis of experimental findings, possible roles of these complexes are discussed.     

Aerobic oxidation of alcohols to aldehydes and ketones using ruthenium(III)/Et3N catalyst

A simple, efficient method for oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones has been developed. Using RuCl₃/Et₃N as catalyst, the oxidation of benzyl alcohol with oxygen could be achieved with 332 h⁻¹ turnover frequency in the absence of solvent. The influence of versatile N‐containing additives on the catalytic efficiency has been discussed. The presence of minor water would substantially promote the catalytic efficiency, and its role in catalysis has been investigated in detail. The insensitive Hammett correlations of the substituted benzyl alcohols, the normal substrate isotope effect (k_H/k_D = 3.5 at 335 K), and the linear relationship between O₂ pressure and turnover frequency imply that the reoxidation of the Ru(III) hydride intermediate to the active species shares the rate‐determining step with the hydride transfer in the catalytic cycle. Copyright © 2011 John Wiley & Sons, Ltd.     

Efficient alkylation of ketones with primary alcohols catalyzed by ruthenium(II)/P,N ligand complexes

An efficient catalytic system containing [RuCl₂(η⁶-p-cymene)]₂ and one P,N ligand, N-diphenylphosphino-2-aminopyridine (L1) was loaded in catalyzing the alkylation of ketones with primary alcohols for a diverse array of substrates. Other five P,N ligands based on pyridin-2-amine and pyrimidin-2-amine were also examined in this reaction to explore the influence of steric hindrance and electronic effects. Monitoring by ¹H NMR and ESI-MS reveals a stable cationic L1-coordinated ruthenium hydride intermediate, identified as [Ru(η⁶-p-cymene)(κ²-L1)H]⁺. Organic intermediates consistent with a three-step dehydrogenation, alkylation and hydrogenation pathway were also observed. The final step in this reaction, the ruthenium-catalysed transfer hydrogenation reduction of α,β-unsaturated ketone with benzyl alcohol was performed separately.     

Synthetic, spectral and catalytic activity studies of ruthenium bipyridine and terpyridine complexes: Implications in the mechanism of the ruthenium(pyridine-2,6-bisoxazoline)(pyridine-2,6-dicarboxylate)-catalyzed asymmetric epoxidation of olefins utilizing H2O2

Various Ru(L₁)(L₂) (1) complexes (L₁ = 2,2′-bipyridines, 2,2′:6′,2″-terpyridines, 6-(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl-2,2′-bipyridinyl or 2,2′-bipyridinyl-6-carboxylate; L₂ = pyridine-2,6-dicarboxylate, pyridine-2-carboxylate or 2,2′-bipyridinyl-6-carboxylate) have been synthesized (or in situ generated) and tested on epoxidation of olefins utilizing 30% aqueous H₂O₂. The complexes containing pyridine-2,6-dicarboxylate show extraordinarily high catalytic activity. Based on the stereoselective performance of chiral ruthenium complexes containing non-racemic 2,2′-bipyridines including 6-[(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl]-[2,2′]bipyridinyl new insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed enantioselective epoxidation are proposed. In addition, a simplified protocol for epoxidation of olefins using urea hydrogen peroxide complex as oxidizing agent has been developed.