Catalytic Aerobic Oxidation Research Articles

Transformation of ethers into aldehydes or ketones: a catalytic aerobic deprotection/oxidation pathway

A facile and efficient protocol for direct transformation of p-methoxybenzyl (PMB) ethers to aldehydes or ketones via a catalytic aerobic oxidation process has been developed. The reaction was performed with the combination of catalytic amounts of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,2,6,6-tetramethylpiperidine N-oxy (TEMPO), and tert-butyl nitrite (TBN), with molecular oxygen as terminal oxidant. A variety of PMB ether substrates derived from benzylic alcohols, heteroaromatic alcohols, and aliphatic alcohols, were converted to their corresponding carbonyl compounds in good conversions and selectivities.

Light-driven, proton-controlled, catalytic aerobic C-H oxidation mediated by a Mn(III) porphyrinoid complex.

The visible light-driven, catalytic aerobic oxidation of benzylic C-H bonds was mediated by a Mn(III) corrolazine complex. To achieve catalytic turnovers, a strict selective requirement for the addition of protons was established. The resting state of the catalyst was unambiguously characterized by X-ray diffraction as [Mn(III)(H2O)(TBP8Cz(H))](+), in which a single, remote site on the ligand is protonated. If two remote sites are protonated, however, reactivity with O2 is shut down. Spectroscopic methods revealed that the related Mn(V)(O) complex is also protonated at the same remote site at -60 °C, but undergoes valence tautomerization upon warming.

Catalytic Aerobic Oxidation of Alcohols using Recoverable IAPNO α‐Hydrogen Nitroxyl Radicals

Abstractα‐Hydrogen‐substituted nitroxyl radicals are of considerable interest as catalysts for oxidation and polymerization, but are usually inherently unstable. We report herein the catalytic activity of a new family of stable iso‐azaphenalene (IAPNO) α‐hydrogen nitroxyl radicals in the copper/bipyridine/N‐methylimidazole co‐catalyzed aerobic oxidation of alcohols. The nitroxyl radical Mes/TIPSO‐IAPNO (TIPSO=triisopropyloxy, IAPNO=isoazaphenalene N‐oxyl) displays higher activity than TEMPO in the oxidation of benzylic and allylic alcohols. Alkyl, benzyl, allyl, and propargyl alcohols are oxidized with yields up to 96 %. The readily prepared nitroxyl catalysts are recovered in 75–90 % yield after purification of the reaction mixture and are recycled.

Asymmetric Synthesis of Tertiary α-Hydroxy Phosphonic Acid Derivatives under Aerobic Oxidation Conditions

The copper-catalyzed asymmetric α-hydroxylation of β-ketophosphonates, using in situ generated nitrosocarbonyl compounds as electrophilic source of oxygen, is reported. The reaction merges aerobic oxidation and Lewis acid catalysis. α-Aminoxy-β-ketophosphonates were synthesized in high yields (up to 97% yield) and high enantioselectivities (up to >99% ee).

Catalytic aerobic oxidation and tandem enantioselective cycloaddition in cascade multicomponent synthesis.

An efficient multicomponent cascade transformation for the highly diastereo- and enantioselective synthesis of complex natural product inspired polycyclic products from simple starting materials is described. The cascade is initiated by copper-catalyzed aerobic CH oxidation of cyclopentadiene to cyclopentadienone followed by double catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides. The cascade synthesis efficiently yields structurally complex 5,5,5-tricyclic products with eight stereocenters with good yields and excellent diastereo- and enantiocontrol using one catalyst.

Assembling mono-, di- and tri-nuclear coordination complexes with a ditopic analogue of 2,2′:6′,2′′-terpyridine: syntheses, structures and catalytic studies

Diverse metal assemblies based on a ditopic analogue of 2,2′:6′,2′′-terpyridine are structurally characterized and applied for catalytic aerobic alcohol oxidation.

Catalytic aerobic oxidation of phenols to ortho-quinones with air-stable copper precatalysts.

A range of air-stable copper species was examined for catalytic activity in the catalytic aerobic transformation of phenols into ortho-quinones. Efficient catalysis was obtained with commercially available copper(II) acetate. The stability of all constituents before mixing makes for a practical process that advances previously reported copper(I)-based oxygenations.

ChemInform Abstract: Controlling the Catalytic Aerobic Oxidation of Phenols.

The oxidation of phenols is the subject of extensive investigation, but there are few catalytic aerobic examples that are chemo- and regioselective. Here we describe conditions for the ortho-oxygenation or oxidative coupling of phenols under copper (Cu)-catalyzed aerobic conditions that give rise to ortho-quinones, biphenols or benzoxepines. We demonstrate that each product class can be accessed selectively by the appropriate choice of Cu(I) salt, amine ligand, desiccant and reaction temperature. In addition, we evaluate the effects of substituents on the phenol and demonstrate their influence on selectivity between ortho-oxygenation and oxidative coupling pathways. These results create an important precedent of catalyst control in the catalytic aerobic oxidation of phenols and set the stage for future development of catalytic systems and mechanistic investigations.

Mechanism of Palladium/Amine Cocatalyzed Carbocyclization of Aldehydes with Alkynes and Its Merging with “Pd Oxidase Catalysis”

The reaction mechanism for the palladium and amine cocatalyzed carbocyclization of aldehydes with alkynes has been investigated by means of density functional theory calculations and experiments. The Pd/amine cocatalyzed transformation is a carbocyclization of in situ generated enaminynes where the C–C bond-forming step is most likely promoted by a Pd(II) species. Notably, the latent Pd(0)/Pd(II) catalytic redox cycle of this metal/organo cooperative catalytic reaction can be merged with catalytic direct aerobic alcohol oxidation (Pd oxidase catalysis).

Copper(II) complexes derived from bidentate N,O-ligands for catalytic aerobic oxidation

Two CuII complexes based on bidentate N,O-ligands have been synthesized and structurally characterized. X-ray structural analysis revealed that in complex 1 the CuII center adopts an unusual near tetrahedral coordination geometry, while the CuII core in 2 is traditionally square planar, albeit both of them have a N2O2 coordination environment and two compounds are mononuclear bis-ligand neutral complexes. A two-dimensional sheet-like network was observed in 2, resulting from the weak Cu…O contacts between the nitrato groups and axial CuII sites. Both complexes were tested for catalytic aerobic oxidation of benzylic alcohol and the results indicated that 2 was a better catalyst than 1. High yield of benzaldehyde was observed when using 2 as a catalyst in combination with TEMPO in an aqueous potassium carbonate solution at 60°C.

ChemInform Abstract: Merging Aerobic Oxidation and Enamine Catalysis in the Asymmetric α‐Amination of β‐Ketocarbonyls Using N‐Hydroxycarbamates as Nitrogen Sources.

AbstractThe title process includes the aerobic oxidation of N‐hydroxycarbamates to give nitrosocarbonyl intermediates which react with β‐keto compounds in the presence of an optically active amine catalyst.

ChemInform Abstract: Chemoselective Aerobic Oxidation Catalyzed by a Metal/Stable Organoradical Redox Conjugate

AbstractReview: [42 refs.

Development of ultrafine multichannel microfluidic mixer for synthesis of bimetallic nanoclusters: catalytic application of highly monodisperse AuPd nanoclusters stabilized by poly(N-vinylpyrrolidone).

On account of their novel properties, bimetallic nanoparticles and nanoclusters (NCs) are strong potential candidates for optical, magnetic, and catalytic functional materials. These properties depend on the chemical composition and size (number of constituent atoms) of the NCs. Control of size, structure, and composition is particularly important for fabricating highly functional materials based on bimetallic NCs. Size- and structure-controlled synthesis of two-element alloys can reveal their intrinsic electronic synergistic effects. However, because synergistic enhancement of activity is strongly affected by composition as well as by size and structure, controlled synthesis is a challenging task, particularly in catalytic applications. To investigate catalytic synergistic effects, we have synthesized highly monodisperse, sub-2 nm, solid-solution AuPd NCs stabilized with poly(N-vinylpyrrolidone) (AuPd:PVP) using a newly developed ultrafine microfluidic mixing device with 15 μm wide multiple lamination channels. The synergistic enhancement for catalytic aerobic oxidation of benzyl alcohol exhibited a volcano-shaped trend, with a maximum at 20-65 at. % Pd. From X-ray photoelectron spectroscopic measurements, we confirmed that the enhanced activity originates from the enhanced electron density at the Au sites, donated by Pd sites.

ChemInform Abstract: A Mild and Highly Efficient Laccase‐Mediator System for Aerobic Oxidation of Alcohols

Abstract25 examples

Drastic Enhancement of Catalytic Activity via Post‐oxidation of a Porous MnII Triazolate Framework

Mn(III) is a powerful active site for catalytic oxidation of alkyl aromatics, but it can be only stabilized by macrocyclic chelating ligands such porphyrinates. Herein, by using benzobistriazolate as a rigid bridging ligand, a porous Mn(II) azolate framework with a nitrogen-rich coordinated environment similar to that of metalloporphyrins was synthesized, in which the Mn(II) ions can be post-oxidized to Mn(III) to achieve drastic increase of catalytic (aerobic) oxidation performance.

Chiral tetranuclear and dinuclear copper(ii) complexes for TEMPO-mediated aerobic oxidation of alcohols: are four metal centres better than two?

The one-pot reaction of 3,5-di-tert-butyl-2-hydroxybenzaldehyde, (R)-2-aminoglycinol and Cu(OAc)2·2H2O in a 1 : 1 : 1 ratio in the presence of triethylamine led to the isolation of X-ray quality crystals of the chiral complex (R)- in high yield. The single crystal structure of (R)- reveals a tetranuclear copper(ii) complex that contains a {Cu4(μ-O)2(μ3-O)2N4O4} core. A reaction using (1S,2R)-2-amino-1,2-diphenylethanol as precursor under the same conditions generated the chiral complex (S,R)-; its structure was determined by single crystal X-ray crystallography and was found to contain a {Cu2(μ-O)2N2O2} core. Both (R)- and (S,R)- have been used for catalytic aerobic oxidation of benzylic alcohols in combination with the TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) radical. (R)- selectively catalyses the conversion of various aromatic primary alcohols to the corresponding aldehydes with high yields (99%) and TONs (770) in the air, while (S,R)- exhibits less promising catalytic performance under the same reaction conditions. The role of the cluster structures in (R)- and (S,R)- in controlling the reactivity towards aerobic oxidation reactions is discussed.

ChemInform Abstract: Aerobic Oxidation Catalysis with Stable Radicals

AbstractReview: 141 refs.

Efficient aerobic oxidation of alcohols using magnetically recoverable catalysts

A simple, highly efficient and mild catalytic aerobic oxidation of alcohol, in particularly benzoin was studied using iron oxide nanoparticles as a reusable catalyst. Moreover, benzyl was synthesized in large scale using inexpensive, readily available and environmentally friendly protocol in the presence of air. This novel and green methodology will allow further development not only in the geochemistry, but also in the oxidation of alcohols to replace expensive metals and corrosive reagents.

Controlling the catalytic aerobic oxidation of phenols.

The oxidation of phenols is the subject of extensive investigation, but there are few catalytic aerobic examples that are chemo- and regioselective. Here we describe conditions for the ortho-oxygenation or oxidative coupling of phenols under copper (Cu)-catalyzed aerobic conditions that give rise to ortho-quinones, biphenols or benzoxepines. We demonstrate that each product class can be accessed selectively by the appropriate choice of Cu(I) salt, amine ligand, desiccant and reaction temperature. In addition, we evaluate the effects of substituents on the phenol and demonstrate their influence on selectivity between ortho-oxygenation and oxidative coupling pathways. These results create an important precedent of catalyst control in the catalytic aerobic oxidation of phenols and set the stage for future development of catalytic systems and mechanistic investigations.

Trinuclear Pd3O2 Intermediate in Aerobic Oxidation Catalysis

The activation of O2 is a key step in selective catalytic aerobic oxidation reactions mediated by transition metals. The bridging trinuclear palladium species, [(LPd(II))3(μ(3)-O)2](2+) (L=2,9-dimethylphenanthroline), was identified during the [LPd(OAc)]2(OTf)2-catalyzed aerobic oxidation of 1,2-propanediol. Independent synthesis, structural characterization, and catalytic studies of the trinuclear compound show that it is a product of oxygen activation by reduced palladium species and is a competent intermediate in the catalytic aerobic oxidation of alcohols. The formation and catalytic activity of the trinuclear Pd3O2 species illuminates a multinuclear pathway for aerobic oxidation reactions catalyzed by Pd complexes.