Catalytic Aerobic Oxidation Research Articles

Substrate Promiscuity of ortho-Naphthoquinone Catalyst: Catalytic Aerobic Amine Oxidation Protocols to Deaminative Cross-Coupling and N-Nitrosation

ortho-Naphthoquinone-based organocatalysts have been identified as versatile aerobic oxidation catalysts. Primary amines were readily cross-coupled with primary nitroalkanes via deaminative pathway to give nitroalkene derivatives in good to excellent yields. Secondary and tertiary amines were inert to ortho-naphthoquinone catalysts; however, secondary nitroalkanes were readily converted by ortho-naphthoquinone catalysts to the corresponding nitrite species that in situ oxidized the amines to the corresponding N-nitroso compounds. Without using harsh oxidants in a stoichiometric amount, the present catalytic aerobic oxidation protocol utilizes the substrate promiscuity feature to provide a facile access to amine oxidation products under mild reaction conditions.

Catalytic Aerobic Oxidation of Alkenes by Ag@Metal Organic Framework with High Catalytic Activity and Selectivity

By coupling of Fe2O3@SiO2 particles with metal organic Framework (MOF) the magnetic MOF structure was fabricated. Precipitation and hydrothermal methods were applied for synthesis of core and MOF. Silver nanoparticles were deposited on nickel based metal organic framework surface and magnetic Fe2O3@SiO2@MOF@Ag was obtained. Because of strong coupling between silver nanoparticles and metal organic framework, the catalyst demonstrated high catalytic activity and selectivity in aerobic oxidation of alkenes under mild conditions. The nanostructure, exhibited high catalytic activity. Alkenes oxides (epoxy alkanes) were the main products with more than 89.9 % selectivity. Composite system of silver nanoparticles supported on Fe2O3@SiO2@Metal Organic Framework has potential to be an active catalysts for aerobic oxidation of alkenes under mild conditions.

The Role of Iodanyl Radicals as Critical Chain Carriers in Aerobic Hypervalent Iodine Chemistry

Summary Selective O 2 utilization remains a substantial challenge in synthetic chemistry. Biological small-molecule oxidation reactions often utilize aerobically generated high-valent catalyst intermediates to effect substrate oxidation. Available synthetic methods for aerobic oxidation catalysis are largely limited to substrate functionalization chemistry by low-valent catalyst intermediates (i.e., aerobically generated Pd(II) intermediates). Motivated by the need for new chemical platforms for aerobic oxidation catalysis, we recently developed aerobic hypervalent iodine chemistry. Here, we report that in contrast to the canonical two-electron oxidation mechanisms for the oxidation of organoiodides, the developed aerobic hypervalent iodine chemistry proceeds via a radical chain mechanism initiated by the addition of aerobically generated acetoxy radicals to aryl iodides. Despite the radical chain mechanism, aerobic hypervalent iodine chemistry displays substrate tolerance similar to that observed with traditional terminal oxidants, such as peracids. We anticipate that these insights will enable new sustainable oxidation chemistry via hypervalent iodine intermediates.

Aerobic Oxidation of 5-Hydroxymethylfurfural to High-Yield 5-Hydroxymethyl-2-furancarboxylic Acid by Poly(vinylpyrrolidone)-Capped Ag Nanoparticle Catalysts

An efficient method for the catalytic aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) was developed using size-controlled Ag nanoparticles (NPs) in an aqueous solution. A series of AgNPs catalysts stabilized by poly(vinylpyrrolidone) (PVP) supported on ZrO2with different Ag loadings were prepared. XRD, TEM, XPS, and FT-IR techniques were used to characterize the nature of these catalysts. The impact of the Ag loading, the molar ratio of PVP to Ag, the reaction temperature and time, and the base type on the conversion of HMF and yield of HMFCA was investigated. The reaction results show that Ag–PVP/ZrO2 catalysts with a bigger particle size (>10 nm) exhibited superior catalytic activity and HMFCA selectivity compared to Ag/ZrO2 with a smaller particle size (ca. 8.5 nm), indicating that the addition of PVP has a promoting effect on the aerobic oxidation of HMF into HMFCA. The 2.5%Ag–PVP/ZrO2(1:1) catalyst presents an excellent activity with 100% conversio...

Selective C–O Bond Cleavage of Lignin Systems and Polymers Enabled by Sequential Palladium-Catalyzed Aerobic Oxidation and Visible-Light Photoredox Catalysis

Lignin, which is a highly cross-linked and irregular biopolymer, is nature’s most abundant source of aromatic compounds and constitutes an attractive renewable resource for the production of aromatic commodity chemicals. Herein, we demonstrate a practical and operationally simple two-step degradation approach involving Pd-catalyzed aerobic oxidation and visible-light photoredox-catalyzed reductive fragmentation for the chemoselective cleavage of the β-O-4 linkage—the predominant linkage in lignin—for the generation of lower-molecular-weight aromatic building blocks. The developed strategy affords the β-O-4 bond cleaved products with high chemoselectivity and in high yields, is amenable to continuous flow processing, operates at ambient temperature and pressure, and is moisture- and oxygen-tolerant.

Lithium promoted mesoporous manganese oxide catalyzed oxidation of allyl ethers

Herein we report the first example of the catalytic aerobic partial oxidation of allyl ether to its acrylate ester derivative. Many partial oxidations often need an expensive oxidant such as peroxides or other species to drive such reactions. In addition, selective generation of esters using porous catalysts has been elusive. This reaction is catalyzed by a Li ion promoted mesoporous manganese oxide (meso-Mn2O3) under mild conditions with no precious metals, a reusable heterogeneous catalyst, and easy isolation. This process is very attractive for the oxidation of allyl ethers. We report on the catalytic activity, selectivity, and scope of the reaction. In the best cases presented, almost complete conversion of allyl ether with near complete chemo-selectivity towards acrylate ester derivatives is observed. Based on results from controlled experiments, we propose a possible reaction mechanism for the case in which N-hydroxyphthalimide (NHPI) is used in combination with trichloroacetonitrile (CCl3CN).

Influence of the channel size of isostructural 3d–4f MOFs on the catalytic aerobic oxidation of cycloalkenes

The present work reports a new group of heterogeneous catalysts with a 3D structure, CuLnIDA, {[Cu3Ln2(IDA)6]·8H2O} (Ln: LaIII, GdIII or YbIII), with an organic linker (H2IDA: iminodiacetic acid).

Hypervalent Iodine Chemistry as a Platform for Aerobic Oxidation Catalysis

Here, we highlight the recent development of aerobic oxidation catalysis via hypervalent I(III) and I(V) intermediates. The described chemistry intercepts reactive intermediates generated during aldehyde autoxidation to accomplish the oxidation of aryl iodides. The aerobically generated hypervalent iodine intermediates are utilized to couple an array of substrate functionalization chemistry to the reduction of O2.1 Introduction2 Chemistry of Aerobically Generated I(III) Intermediates3 Chemistry of Aerobically Generated I(V) Intermediates4 Conclusions

Catalytic Aerobic Oxidation of Alcohols by Copper Complexes Bearing Redox-Active Ligands with Tunable H-Bonding Groups.

In this research article, we describe the structure, spectroscopy, and reactivity of a family of copper complexes bearing bidentate redox-active ligands that contain H-bonding donor groups. Single-crystal X-ray crystallography shows that these tetracoordinate complexes are stabilized by intramolecular H-bonding interactions between the two ligand scaffolds. Interestingly, the Cu complexes undergo multiple reversible oxidation-reduction processes associated with the metal ion (CuI, CuII, CuIII) and/or the o-phenyldiamido ligand (L2-, L•-, L). Moreover, some of the CuII complexes catalyze the aerobic oxidation of alcohols to aldehydes (or ketones) at room temperature. Our extensive mechanistic analysis suggests that the dehydrogenation of alcohols occurs via an unusual reaction pathway for galactose oxidase model systems, in which O2 reduction occurs concurrently with substrate oxidation.

Recent advances in controllable alkoxylation chemistry of Anderson-type polyoxometalates from synthetic strategies perspective

Polyoxometalates (POMs) are an exceptional family of inorganic oxide anions consisting of Mo, W, V, etc. early transition metal ions at their highest oxidization states with structural versatility. The Anderson-type hetreopolyanions are one of the most important subclass since their most flexibility benefited from the central heteroatom. Among the frontier of current POMs investigations, organic modification and functionalization of POMs stands for one of most hot topics. The organic modification of POMs can incorporate POMs with advanced functional organic moieties on their surfaces to make the structure versatility more accessible and the design of advanced functional materials more rational. In this review, recent advances in controllable alkoxylation chemistry of Anderson-type polyoxometalates are briefly summarized into 9 parts as following: (1) the synthesis strategy development of direct modification protocol for the synthesis of single-side triol-functionalized Anderson δ isomer organic hybrids. (2) Based on direct modification protocol, the synthesis strategy development of μ 2-O atom pronation and activation chemistry in Anderson cluster to afford single-side triol-functionalized Anderson χ and ψ isomer organic hybrids. The proton-controlled isomer transformation between the δ , χ and ψ isomer was discovered. This will open up a new era for developing chemical reactivity of μ 2-O atoms in the Anderson cluster. (3) By precise proton control, the synthesis strategy development to obtain diol functionalized Anderson organic hybrids. Such diol functionalization mode not only works for some specific triol ligands but also can readily be extended to the diol ligands, which will greatly enrich the species of alkoxo-derivatized Anderson POM clusters. (4) Based on direct modification protocol, extending special tripodal ligands with carboxyl group to symmetrically functionalized the Anderson cluster. Such Anderson organic hybrids cannot be obtained for the traditional reconstruction protocol. This has extended the versatility of tripodal ligands applied for Anderson-type POMs modification. (5) Through stepwise synthesis strategy, single-side δ isomer was utilized as a precursor to efficiently synthesized asymmetrically triol-functionalized Anderson organic hybrids. (6) The synthesis strategy development of direct parent Anderson alkoxylation protocol for triol-functionalized butterfly-shaped β isomers of Anderson POMs hybrids. (7) The synthesis strategy development to extend the triol-functionalized Anderson from polymolybdates(Mo6O24) to polyoxotungstates(W6O24). (8) The newly development and revised synthesis strategy of Mo8 reconstruction protocol. (9) The original concept proposed by our group, organic ligand protected and inorganic-ligand supported atomically precise Anderson nanocluster based molecular armor hybrid material design as effective catalysts for green aerobic oxidation catalysis applications. In summary, the synthetic strategies and structures of novel alkoxyl-functionalized Anderson cluster have been discussed in this review. These newly developed synthesis strategies have greatly enriched the category of organoalkoxylation derivatives of Anderson cluster, providing a reliable and convenient synthetic methodology for the controllable design of triol-functionalized Anderson organic hybrids with specific and desirable functionalization modes. The extension of triol ligands with functional groups to other POMs units are still need to be developed. One of the important application fields for POMs is catalysis, however, the exploration of catalysis of alkoxyl-functionalized Anderson nanoclusters is quite limited to the recent cases we mentioned in this review. It is worth exploring to develop more alkoxyl-functionalized Anderson nanoclusters as catalysts for useful reactions, because alkoxyl-functionalized Anderson nanoclusters have multiple active sites and special properties derived from functional groups of alkoxyl ligands as well as cooperativities. The charge transfer properties between POMs and organic moieties in alkoxyl-functionalized Anderson nanoclusters have also attracted widely attentions. Using alkoxyl ligands with conjugated groups to functionalize Anderson nanoclusters may enhance the ability of electron transfer to improve the intrinsic redox properties of Anderson nanoclusters. It can be concluded with confidence that the persistent and dedicated efforts of chemists have revealed a vast advance in alkoxylation of Anderson nanoclusters, which may in fact just be the reason why the alkoxylation chemistry of Anderson nanoclusters research field has flourished in recent years. Of course, more Anderson nanoclusters-based materials with novel structures, interesting and functional properties remain to be explored and the alkoxylation chemistry of Anderson nanoclusters still has great growing opportunities in the future.

Advances in Catalytic Aerobic Oxidations by Activation of Dioxygen-Monooxygenase Enzymes and Biomimetics

Monooxygenases are not only some of the most versatile machineries in our lives, but also some of the most explored enzymes in modern organic synthesis. They provide knowledge and inspiration on how the most abandoned oxidant, dioxygen, can be activated and utilized to deliver selective oxidations. This review presents an outline in the mechanisms that Nature uses to succeed in these processes and recent indicative examples on how chemists use this knowledge to develop selective oxidation protocols based on dioxygen as the terminal oxidant.1 Introduction2 Monooxygenases2.1 Metal-Based Monooxygenases2.1.1 Cytochromes2.1.2 Copper-Dependent Monooxygenases2.1.3 Heme-Independent Iron Monooxygenases2.1.4 Pterin-Dependent Monooxygenases2.2 Metal-Free Monooxygenases2.2.1 Flavin-Dependent Monooxygenases2.2.2 Systems without Cofactors3 Biomimetic Aerobic Oxidations3.1 Aerobic Oxidations Based on Metal Catalysts3.1.1 Epoxidations and Allylic Oxidations3.1.2 Oxidations of Unactivated Carbon Atoms and Benzylic Oxidations3.1.3 Oxidations of Aryl Groups3.1.4 Heteroatom Oxidations3.2 Aerobic Oxidations Based on Organocatalysts3.2.1 Baeyer–Villiger Oxidations3.2.2 Oxidations of Aryl Groups3.2.3 Heteroatom Oxidations4 Conclusion

Aerobic Catalytic Features in Photoredox- and Copper-Catalyzed Iodolactonization Reactions.

Mechanistic evaluations and comparison of two important aerobic catalytic oxidation processes, aerobic copper catalysis and photoredox catalysis, are performed. Interesting and distinct catalytic behaviors were observed for a common reaction of iodolactonization of alkenoic acids. Namely, the aerobic copper catalysis requires the formation of a copper carboxylate, whereas the aerobic photoredox catalysis requires the addition of proton sources to proceed to completion. Furthermore, the iodolactone products obtained from these catalytic processes are extensively derivatized to a number of functionalized lactones, including aryl lactones generated from the nickel-catalyzed reductive coupling with aryl halides.

N‐Hydroxyphthalimide (NHPI) Promoted Aerobic Baeyer‐Villiger Oxidation in the Presence of Aldehydes

AbstractMetal‐free aerobic Baeyer‐Villiger (BV) oxidation of ketones to lactones or esters in the presence of aldehydes promoted by N‐hydroxyphthalimide (NHPI) has been developed. The reaction proceeded under mild conditions with excellent selectivity and high yields. Compared with the methods that use metal complexes as catalysts, this strategy not only showed good environmental advantages, but also increased aldehyde efficiency up to 84 %. Control experiments indicated that NHPI accelerated the oxidation of aldehydes to peroxy acids but did not improve the BV oxidation while peroxy acids were already generated. Peroxy acids generated from aldehydes in situ were the key intermediates, and the phthalimide‐N‐oxyl radical (PINO) contributed to high aldehyde efficiency by stabilizing the radical species, which are necessary for the chain propagation reactions. This study may offer some useful strategies for new transition metal‐free catalytic aerobic oxidation reactions in which aldehydes act as sacrificial agents.

Synthesis of 3-Sulfenylindoles from Indoles and Various Sulfenylation Agents through Aerobic Oxidative C–S Bond Coupling

A novel aerobic catalytic oxidation system for the sulfenylation of indoles with a variety of sulfenylation agents through oxidative C–S bond coupling has been successfully developed. The reactions were performed with potassium iodide as the catalyst, sodium nitrite as the co-catalyst, and molecular oxygen as the terminal oxidant in the presence of acetic acid. Under the optimal reaction conditions, a number of indoles could be sulfenylated with Bunte salts, thiols, or disulfides to generate 3-sulfenylindoles in good yields. This protocol provided an efficient and environmentally benign strategy for the synthesis of 3-sulfenylindoles.

DFT and experimental study of nitrosyl carboxylate palladium clusters Pd4(NO)2(RCO2)6 as catalysts for aerobic oxidation of alcohols

Possible activation pathways for palladium nitrosyl carboxylate complexes Pd4 (μ-NO)2 (μ-RCO2)6 in reaction of catalytic aerobic oxidation of alcohols are reported. The study was carried out using scalar-relativistic DFT calculations for the system palladium nitrosyl acetate (RCH3) + methanol. Exchange-correlation functional PBE was found to be the best choice in terms of accuracy and time for calculations. The main pathway includes dissociation of starting 4-nuclear molecule into binuclear species Pd2(NO) (CH3CO2)3, where nitrosyl group keeps bridging coordination mode. Experimental studies showed that palladium nitrosyl acetate (RCH3) and nitrosyl pivalate (RCMe3) are moderately active catalysts for aerobic oxidation of benzylic alcohol, (E)-2-hexen-1-ol, (−)-menthol, trans-1,3-diphenyl-2-propen-1-ol and dodecanol-1. The addition of pyridine substantially improved the catalysts performance.

Decavanadates anchored into micropores of graphene-like boron nitride: Efficient heterogeneous catalysts for aerobic oxidative desulfurization

Catalytic aerobic oxidation of aromatic sulfides to their corresponding sulfones could provide a novel route for producing fuels with ultra-low sulfur content, solving the increasingly severe air pollution problems. In this work, a series of heterogeneous catalysts were synthesized by anchoring decavanadate ionic liquids (ILs) into the micropores of graphene-like hexagonal boron nitride (g-BN). The as-prepared catalysts could inherit both the catalytic ability of polyoxometalate ILs (POM-ILs) and the separation efficiency of g-BN. Besides, the usage amount of POM-ILs could be reduced sharply. Under the optimized reaction conditions, sulfur removal of dibenzothiophene (DBT), as one of the most stubborn residuals in oil refining process, could rise up to 99.8% (≤1 ppm) in this proposed adsorptive and aerobic oxidative desulfurization (AAODS) process. In addition, excellent sulfur removal with oils of different sulfide concentrations, substrates and aromatics/olefins addition could also be achieved. Moreover, renewable recycling performance with 99.4% sulfur removal was observed after 6 times recycle. Finally, a possible reaction process was proposed depending on the experiment evidence from different aspects.

Oxidation Catalysis by an Aerobically Generated Dess-Martin Periodinane Analogue.

Hypervalent iodine(V) reagents, such as Dess-Martin periodinane (DMP) and 2-iodoxybenzoic acid (IBX), are broadly useful oxidants in chemical synthesis. Development of strategies to generate these reagents from dioxygen (O2 ) would immediately enable use of O2 as a terminal oxidant in a broad array of substrate oxidation reactions. Recently we disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidation. In this work, aerobic oxidation of iodobenzenes is coupled with disproportionation of the initially generated I(III) compounds to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidation chemistry analogous to that of DMP. The developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidation catalysis.

Oxidation Catalysis by an Aerobically Generated Dess–Martin Periodinane Analogue

AbstractHypervalent iodine(V) reagents, such as Dess–Martin periodinane (DMP) and 2‐iodoxybenzoic acid (IBX), are broadly useful oxidants in chemical synthesis. Development of strategies to generate these reagents from dioxygen (O2) would immediately enable use of O2 as a terminal oxidant in a broad array of substrate oxidation reactions. Recently we disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidation. In this work, aerobic oxidation of iodobenzenes is coupled with disproportionation of the initially generated I(III) compounds to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidation chemistry analogous to that of DMP. The developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidation catalysis.

Aerobic Oxidation Catalysis by a Molecular Barium Vanadium Oxide.

Aerobic catalytic oxidations are promising routes to replace environmentally harmful oxidants with O2 in organic syntheses. Here, we report a molecular barium vanadium oxide, [Ba4 (dmso)14 V14 O38 (NO3 )] (={Ba4 V14 }) as viable homogeneous catalyst for a series of oxidation reactions in N,N-dimethyl formamide solution under oxygen (8 bar). Starting from the model compound 9,10-dihydroanthracene, we report initial dehydrogenation/ aromatization leading to anthracene formation; this intermediate is subsequently oxidized by stepwise oxygen transfer, first giving the mono-oxygenated anthrone and then the di-oxygenated target product, anthraquinone. Comparative reaction analyses using the Neumann catalyst [PV2 Mo10 O40 ]5- as reference show that oxygen diffusion into the reaction mixture is the rate-limiting step, resulting in accumulation of the reduced catalyst species. This allows us to propose improved reactor designs to overcome this fundamental challenge for aerobic oxidation catalysis.

Investigation of hollow bimetal oxide nanomaterial and their catalytic activity for selective oxidation of alcohol

The aerobic oxidation procedure utilized sustainable non-noble-metal catalysts has been a long-standing objective in laboratory and industrial research. The synthesized hollow bimetal oxide nanoparticles catalysts (HNPs) as a stable and efficient catalyst, which was applied to the selective oxidation of alcohols with molecular oxygen as oxidant, is reported. The catalytic performance of Co3O4/Fe3O4@C HNPs was tested via selective aerobic oxidation catalytic reaction of cinnamyl alcohol in the liquid phase. The results prove that the Co3O4/Fe3O4@C HNPs exhibit ∼ 90% yield for alcohol oxidation, which can be conveniently separated and recycled from reaction system by an external magnetism. Forthrmore, the catalyst can be reutilized for at least 5 runs without a distinct activity reduction. A feasible reaction mechnism over the bimetal catalyst for the alcohol oxidation was proposed. The surface effect between metal oxide nanoparticle and carbon support, and relatively high and easy reducibility grant favorable catalytic activity of Co3O4/Fe3O4@C HNPs. This make the Co3O4/Fe3O4@C HNPs a very significant catalyst for aerobic catalytic oxidation reaction of alcohols in the liquid phase for industrial manufacture.