Reduction Of Functional Groups Research Articles

Synthesis of Single Atom Based Heterogeneous Platinum Catalysts: High Selectivity and Activity for Hydrosilylation Reactions.

Catalytic hydrosilylation represents a straightforward and atom-efficient methodology for the creation of C–Si bonds. In general, the application of homogeneous platinum complexes prevails in industry and academia. Herein, we describe the first heterogeneous single atom catalysts (SACs), which are conveniently prepared by decorating alumina nanorods with platinum atoms. The resulting stable material efficiently catalyzes hydrosilylation of industrially relevant olefins with high TON (≈105). A variety of substrates is selectively hydrosilylated including compounds with sensitive reducible and other functional groups (N, B, F, Cl). The single atom based catalyst shows significantly higher activity compared to related Pt nanoparticles.

Water as a hydrogen source in palladium-catalyzed reduction and reductive amination of nitroarenes mediated by diboronic acid

An unprecedented palladium-catalyzed chemoselective reduction and reductive amination of nitroarenes with water as a hydrogen source mediated by diboronic acid have been discovered. A series of aryl amines containing various reducible functional groups were obtained in good to excellent yields.

Enhancing photoluminescence of graphene quantum dots by thermal annealing of the graphite precursor

Different approaches for enhancement of the graphene quantum dots (GQDs) photoluminescence have been developed lately. We report modified electrochemical procedure for GQDs synthesis. Graphitic rods were thermal annealing at 1700°C in vacuum and used for electrochemical quantum dots synthesis. We found that the modified GQDs (GQDs-1700) consist of two while in the structure of pristine (p-GQDs) three graphene layers are measured. The main structural difference between GQDs is the increased structural disorder, caused by a higher amount of the oxygen containing functional groups in the structure of GQDs-1700. The photoluminescence of GQDs-1700 is 4 times more intense, red shifted and with doubled Quantum Yield compared to p-GQDs. In addition, the changes in electrochemical behavior of GQDs are observed: the higher capacitance was noticed if GQDs posses more reducible functional groups, such as peroxyl, aldehyde and epoxy groups while increase in keto functional groups leads to the lower capacitance.

Platinum nanoparticles onto pegylated poly(lactic acid) stereocomplex for highly selective hydrogenation of aromatic nitrocompounds to anilines

A stereocomplexed poly(lactic acid)-polyethyleneglycol copolymer was synthesized and successfully used as recyclable support for Pt nanoparticles, generated by the metal vapor synthesis technique. The confinement of the Pt nanoparticles were determined by thermal analysis. Hydrogenation reactions of chlorinated aromatic nitro compounds, containing other reducible functional groups, to the corresponding anilines occurred with the latter supported Pt nanoparticles in MeOH under very mild reaction conditions (i.e. 30°C, p(H2)=5.0bar). The covalently attached polyethyleneglycol polymer significantly increased the catalytic activity of the supported Pt nanoparticles compared to an analogous catalytic system which did not contain polyethyleneglycol but the same sized Pt nanoparticles.

Heterogeneous Meerwein‐Ponndorf‐Verley–type Reduction of Aromatic Aldehydes Having Other Reducible Functional Groups over a TiO2 Photocatalyst

AbstractChemoselective reduction of benzaldehydes having other reducible functional groups without the use of a reducing agent such as metal hydrides is important because metal hydrides simultaneously produce a large amount of undesirable waste containing metal compounds. Here we report that a titanium(IV) oxide (TiO2) photocatalyst is effective for heterogeneous Meerwein‐Ponndorf‐Verley (MPV)‐type reduction of various benzaldehydes having reducible functional groups to corresponding benzyl alcohols at room temperature under a metal‐free condition. We also investigated the effects of physical properties of TiO2 samples on chemoselective reduction of p‐chlorobenzaldehyde (CBAD) to p‐chlorobenzyl alcohol (CBAO) and we observed a linear correlation between the amount of CBAD adsorbed and the rate of CBAO formation, suggesting that ability of TiO2 for CBAD adsorption is one of the key factors for effective MPV‐type reduction of CBAD to CBAO.

Visible light-induced heterogeneous Meerwein-Ponndorf-Verley-type reduction of an aldehyde group over an organically modified titanium dioxide photocatalyst.

An organically modified titanium dioxide photocatalyst prepared by a simple impregnation method chemoselectively and almost quantitatively converted benzaldehydes having other reducible functional groups to the corresponding benzyl alcohols under visible light irradiation.

A photocatalytic green system for chemoselective reduction of nitroarenes

A highly efficient photocatalytic reduction of nitroarenes using TiO2/polyethylene glycol 400-water (TiO2/PEG–H2O) is reported. This system at deoxygenated and illuminated (sunlight or violet LED) conditions efficiently reduced nitroarenes using oxalic acid or ammonium formate as a sacrificial electron donor. Reducible functional groups such as chloro, hydroxy, flouro, bromo and carbonyl were intact under the optimized reaction conditions. The 0.1 and 0.5–1 mmol amount of nitroarenes was used under sunlight and violet LED (400 nm) irradiation, respectively. Reusability of the nanotitania was successfully carried out four times. The analyses of the recovered catalyst after five runs including TEM, XRD, TGA and CHN were done and results showed that PEG is located on TiO2; no change in morphology, crystallinity and particle sizes was observed.

Efficient and selective N-alkylation of amines with alcohols catalysed by manganese pincer complexes.

Borrowing hydrogen (or hydrogen autotransfer) reactions represent straightforward and sustainable C–N bond-forming processes. In general, precious metal-based catalysts are employed for this effective transformation. In recent years, the use of earth abundant and cheap non-noble metal catalysts for this process attracted considerable attention in the scientific community. Here we show that the selective N-alkylation of amines with alcohols can be catalysed by defined PNP manganese pincer complexes. A variety of substituted anilines are monoalkylated with different (hetero)aromatic and aliphatic alcohols even in the presence of other sensitive reducible functional groups. As a special highlight, we report the chemoselective monomethylation of primary amines using methanol under mild conditions.

Selective Deoxygenation of Pyridine N‐Oxides through Photoredox Catalysis of a Dilacunary Silicotungstate

AbstractIn this paper, we report a highly selective and widely applicable method for deoxygenation of pyridine N‐oxides using ethanol as the reducing agent through the visible‐light‐responsive photoredox catalysis of a divacant lacunary silicotungstate TBA4H4[γ‐SiW10O36] (I, TBA=tetra‐n‐butylammonium). By irradiation with visible light (λ > 385 nm), the two‐electron and two‐proton transfers from the coordinated ethanol to I efficiently took place. Then, the transiently stored electrons and protons within I could be effectively utilized for the selective deoxygenation of pyridine N‐oxides. Various kinds of structurally diverse pyridine N‐oxides could be converted into the corresponding substituted pyridines in high yields, even in the presence of other reducible functional groups, such as olefinic, chloro, cyano, carbonyl, and amide groups. In addition, I could be readily retrieved after the reaction, and the retrieved I could be reused with keeping its high catalytic performance. The lacunary site of I played an important dual role as the electron transfer site from ethanol to I and the selective electron transfer site from the reduced I to pyridine N‐oxides.

ChemInform Abstract: Metal‐Free Reduction of Aromatic Nitro Compounds to Aromatic Amines with B2pin2 in Isopropanol.

A metal-free reduction of aromatic nitro compounds to the corresponding amines has been achieved by a combination of B2pin2 and KOtBu in isopropanol. A series of nitro compounds containing various reducible functional groups were chemoselectively reduced in good to excellent yields.

Pd nanoparticles supported on Fe3O4@C: An effective heterogeneous catalyst for the transfer hydrogenation of nitro compounds into amines

Catalytic reduction of nitro compounds to the amines is of high importance in modern synthetic chemistry. In this study, an efficient method was developed for the transfer hydrogenation of nitro compounds over a magnetic Pd catalyst by the use of NaBH4 as the hydrogen donor. Full nitrobenzene conversion and high selectivity (>99%) of aniline were produced after 1 h at 60 °C in ethanol. The reductions are successfully carried out in presence of a wide variety of other reducible functional groups in the molecule, except halogen and vinyl substitute nitrobenzene. Kinetic studies indicated the active energy for the transfer hydrogenation of nitrobenzene was 20.93 KJ mol−1. The transfer hydrogenation of nitrobenzene was confirmed to proceed via azobenzene as the intermediate. More importantly, the catalyst was very stable without the loss of its catalytic activity.

Heterogenized Bimetallic Pd-Pt-Fe3O4 Nanoflakes as Extremely Robust, Magnetically Recyclable Catalysts for Chemoselective Nitroarene Reduction.

A very simple synthesis of bimetallic Pd-Pt-Fe3O4 nanoflake-shaped alloy nanoparticles (NPs) for cascade catalytic reactions such as dehydrogenation of ammonia-borane (AB) followed by the reduction of nitro compounds (R-NO2) to anilines or alkylamines (R-NH2) in methanol at ambient temperature is described. The Pd-Pt-Fe3O4 NPs were easily prepared via a solution phase hydrothermal method involving the simple one-pot coreduction of potassium tetrachloroplatinate (II) and palladium chloride (II) in polyvinylpyrrolidone with subsequent deposition on commercially available Fe3O4 NPs. The bimetallic Pd-Pt alloy NPs decorated on Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. Various nitroarene derivatives were reduced to anilines with very specific chemoselectivity in the presence of other reducible functional groups. The bimetallic Pd-Pt-Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. The nitro reduction proceeded in 5 min with nearly quantitative conversions and yields. Furthermore, the magnetically recyclable nanocatalysts were readily separated using an external magnet and reused up to 250 times without any loss of catalytic activity. A larger scale (10 mmol) reaction was also successfully performed with >99% yield. This efficient, recyclable Pd-Pt-Fe3O4 NPs system can therefore be repetitively utilized for the reduction of various nitro-containing compounds.

ChemInform Abstract: Extremely Efficient Hydroboration of Ketones and Aldehydes by Copper Carbene Catalysis.

A readily available copper carbene complex, (IPr)CuOtBu, catalyses the hydroboration of ketones and aldehydes even at very low catalyst loadings (0.1 mol%), in some cases with turnover frequencies exceeding 6000 h(-1). Carbonyl reduction occurs selectivitily in the presence of other reducible functional groups including alkenes, nitriles, esters, and alkyl chlorides.

Metal-Free Reduction of Aromatic Nitro Compounds to Aromatic Amines with B2pin2 in Isopropanol.

A metal-free reduction of aromatic nitro compounds to the corresponding amines has been achieved by a combination of B2pin2 and KOtBu in isopropanol. A series of nitro compounds containing various reducible functional groups were chemoselectively reduced in good to excellent yields.

ChemInform Abstract: Direct Amidation of N‐Boc‐ and N‐Cbz‐Protected Amines via Rhodium‐Catalyzed Coupling of Arylboroxines and Carbamates.

AbstractA novel and direct route for converting N‐Boc‐ and N‐Cbz‐protected amines to amides is developed that is tolerant to a variety of acid‐sensitive and reducible functional groups.

Chemoselective Reduction of Tertiary Amides under Thermal Control: Formation of either Aldehydes or Amines

AbstractThe chemoselective reduction of amides in the presence of other more reactive reducible functional groups is a highly challenging transformation, and successful examples thereof are most valuable in synthetic organic chemistry. Only a limited number of systems have demonstrated the chemoselective reduction of amides over ketones. Until now, the aldehyde functionality has not been shown to be compatible in any catalytic reduction protocol. Described herein is a [Mo(CO)6]‐catalyzed protocol with an unprecedented chemoselectivity and allows for the reduction of amides in the presence of aldehydes and imines. Furthermore, the system proved to be tunable by variation of the temperature, which enabled for either C−O or C−N bond cleavage that ultimately led to the isolation of both amines and aldehydes, respectively, in high chemical yields.

Chemoselective Reduction of Tertiary Amides under Thermal Control: Formation of either Aldehydes or Amines

The chemoselective reduction of amides in the presence of other more reactive reducible functional groups is a highly challenging transformation, and successful examples thereof are most valuable in synthetic organic chemistry. Only a limited number of systems have demonstrated the chemoselective reduction of amides over ketones. Until now, the aldehyde functionality has not been shown to be compatible in any catalytic reduction protocol. Described herein is a [Mo(CO)6 ]-catalyzed protocol with an unprecedented chemoselectivity and allows for the reduction of amides in the presence of aldehydes and imines. Furthermore, the system proved to be tunable by variation of the temperature, which enabled for either C-O or C-N bond cleavage that ultimately led to the isolation of both amines and aldehydes, respectively, in high chemical yields.

Alloying Gold with Copper Makes for a Highly Selective Visible-Light Photocatalyst for the Reduction of Nitroaromatics to Anilines

Finely control of product selectivity is an essential issue in organic chemical production. In the synthesis of functionalized anilines via reduction of the corresponding nitroarenes, the challenge is to selectively reduce only the nitro group in the presence of other reducible functional groups in nitroarene molecules at a high reaction rate. Normally, the nitroarene is reduced stepwise through a series of intermediates that remain as byproducts, increasing the aniline synthesis cost. Here we report that alloying small amounts of copper into gold nanoparticles can alter the reaction pathway of the catalytic reduction under visible-light irradiation at ambient temperature, allowing nitroaromatics to be transformed directly to anilines in a highly selective manner. The reasons for the high efficiency of the photocatalytic reduction under these comparatively benign conditions as well as the light-excited reaction mechanisms are discussed. This photocatalytic process avoids byproducts, exhibits a high reaction rate and excellent substituent tolerance, and can be used for the synthesis of many useful functionalized anilines under environmentally benign conditions. Switching of the reaction pathway simply by tailoring the bimetallic alloy NPs of the photocatalysts is effective for engineering of product chemoselectivity.

Direct Amidation of N-Boc- and N-Cbz-Protected Amines via Rhodium-Catalyzed Coupling of Arylboroxines and Carbamates.

N-Boc- and N-Cbz-protected amines are directly converted into amides by a novel rhodium-catalyzed coupling of arylboroxines and carbamates, replacing the traditional two-step deprotection-condensation sequence. Both protected anilines and aliphatic amines are efficiently transformed into a wide variety of secondary benzamides, including sterically hindered and electron-deficient amides, as well as in the presence of acid-labile and reducible functional groups.

A Rhodium Nanoparticle–Lewis Acidic Ionic Liquid Catalyst for the Chemoselective Reduction of Heteroarenes

AbstractWe describe a catalytic system composed of rhodium nanoparticles immobilized in a Lewis acidic ionic liquid. The combined system catalyzes the hydrogenation of quinolines, pyridines, benzofurans, and furan to access the corresponding heterocycles, important molecules present in fine chemicals, agrochemicals, and pharmaceuticals. The catalyst is highly selective, acting only on the heteroaromatic ring, and not interfering with other reducible functional groups.