Sensen Shang

Iron/ABNO-Catalyzed Aerobic Oxidation of Alcohols to Aldehydes and Ketones under Ambient Atmosphere

We report a new Fe(NO3)3·9H2O/9-azabicyclo[3.3.1]nonan-N-oxyl catalyst system that enables efficient aerobic oxidation of a broad range of primary and secondary alcohols to the corresponding aldehydes and ketones at room temperature with ambient air as the oxidant. The catalyst system exhibits excellent activity and selectivity for primary aliphatic alcohol oxidation. This procedure can also be scaled up. Kinetic analysis demonstrates that C-H bond cleavage is the rate-determining step and that cationic species are involved in the reaction.

Asymmetric Epoxidation of Olefins with Hydrogen Peroxide by an in Situ-Formed Manganese Complex

Asymmetric epoxidation of a variety of cis, trans, terminal, and trisubstituted olefins in excellent yields (up to 94%) and enantioselectivities (>99% ee) by an in situ-formed manganese complex using H2O2 has been developed. A relationship between the hydrophobicity of the catalyst imposed by ligand and the catalytic activity has been observed. The influence of the amount and identity of the acid additive was examined, and improved enantioselectivities were achieved through the use of a catalytic amount of a carboxylic acid additive.

Enantioselective oxidation of sulfides with H2O2 catalyzed by a pre-formed manganese complex

A facile and environmentally friendly method is presented for the asymmetric oxidation of sulfides with H2O2, utilizing a pre-formed manganese complex. Just in the presence of a low catalytic amount of carboxylic acid (CA), a variety of sulfide substrates, including aryl alkyl, aryl benzyl and cyclic sulfides, reacted to form chiral sulfoxides in high yields (up to 95%) and excellent enantioselectivities (>99% ee) under mild conditions. Moreover, the practical utility of the method has been demonstrated by the synthesis of esomeprazole and albendazole sulfoxide (ABZO).

High catalytic activity of mesoporous Co–N/C catalysts for aerobic oxidative synthesis of nitriles

A high-efficiency and atom-economic synthetic strategy for nitriles by aerobic ammoxidation of alcohols is developed using a novel mesoporous cobalt-coordinated nitrogen-doped carbon catalyst (meso-Co–N/C) fabricated from a cobalt-coordinating polymer, which manifests superior activity towards the target reaction. The catalytic system features a broad substrate scope for various benzylic, allylic as well as heterocyclic alcohols, providing good to excellent yields of the target products with high selectivities, albeit with 0.5 mol% Co catalyst loading. 11,11′-Bis(dipyrido[3,2-a:2′,3′-c]phenazinyl) (bidppz) with extreme thermostability is selected as a robust ligand bridge between cobalt ions, resulting in the homogeneous distribution of active sites at the atomic or subnanoscale level and high catalyst yield. Silica colloid or ordered mesoporous silica SBA-15 is employed to realize the mesoporous structure. The unprecedented performance of the meso-Co–N/C catalyst is attributed to its high Brunauer–Emmett–Teller (BET) surface area (up to 680 m2 g−1) with a well-controlled mesoporous structure and homogeneous distribution of active sites. Kinetic analysis demonstrates that the catalytic oxidation of benzyl alcohol to benzaldehyde is the turnover-limiting step and that the apparent activation energy for benzonitrile synthesis is 61.5 kJ mol−1 and cationic species are involved in the reaction.

High-performance recyclable V–N–C catalysts for the direct hydroxylation of benzene to phenol using molecular oxygen

In this report, high-performance recyclable V–N–C catalysts for the direct hydroxylation of benzene to phenol using molecular oxygen were designed and prepared. Up to 12.6% yield of phenol with selectivity as high as 97.8% was achieved employing V–N–C-600 catalyst in acetonitrile. The catalytic recycling tests demonstrated that the V–N–C-600 catalyst exhibited high potential for reusability. The catalysts were characterized systematically by thermogravimetric analysis, Fourier transform infrared spectroscopy, N2 adsorption–desorption, powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy techniques and scanning electron microscopy. It was determined that the interaction between surface nitrogen of the supports and reactive vanadium species played an important role in the excellent stability in recycling of the heterogeneous V–N–C catalysts.

Bioinspired aerobic oxidation of alcohols with a bifunctional ligand based on bipyridine and TEMPO

A novel bioinspired bifunctional ligand incorporating metal-binding site and stable free radical has been synthesized. The catalytic system obtained from the bifunctional ligand with copper(I) iodide in the presence of N-methylimidazole is highly efficient for the oxidation of a broad range of primary benzylic, allylic, alkynyl, aliphatic alcohols and secondary benzylic alcohols to the corresponding aldehydes and ketones in good to excellent yields. The catalyst system exhibits broad functional-group compatibility. The reaction is carried out in acetonitrile as solvent under air balloon at room temperature. The catalyst system features excellent activity for primary aliphatic alcohol oxidation and a high chemoselective oxidation of primary alcohols over the secondary alcohols. This oxidation process is readily amenable to larger-scale application. The interaction of the different components in the reaction mixtures was studied by UV-visible spectroscopy. The data indicated that Cu(I) existed throughout the reaction. A plausible mechanism of the catalytic cycle is proposed.

Synthesis of 6,7-dihydro-5H-cyclopenta[b]pyridin-5-one analogues through manganese-catalyzed oxidation of the CH2 adjacent to pyridine moiety in water

Direct oxidation of 2,3-cyclopentenopyridine analogues to 6,7-dihydro-5H-cyclopenta[b]pyridin-5-one analogues was achieved using Mn(OTf)2 as a catalyst and t-BuOOH (65% in H2O) as an oxidant at 25 °C in H2O with high yield and excellent chemoselectivity for the first time. The catalytic system was also used efficiently for the direct oxidation of substituted benzylpyridines and 2-ethylpyridine in t-BuOH.

Zirconium triflate grafted on SBA-15 as a highly efficient solid acid catalyst for ring opening of epoxides by amines and alcohols

Abstract Metal (Al, Ti, Zr) triflate grafted mesoporous SBA-15 (AlTf/S, TiTf/S, ZrTf/S) samples were synthesized as inexpensive solid acid materials by a simple one-pot-two-step synthesis methodology. These materials were characterized by X-ray diffraction, N2-sorption, thermogravimetric analysis, Fourier transform infrared spectroscopy (FT-IR), in-situ pyridine FT-IR spectroscopy, and elemental analysis. ZrTf/S was found to be a highly efficient and reusable solid acid catalyst for ring opening of epoxides with amines and alcohols and produced β-amino alcohols and β-alkoxy alcohols respectively under ambient reaction conditions. The ZrTf/S catalyst showed the highest activity, which was attributed to its high acidity compared with that of the Ti and Al containing samples.

Superior performance of Co-N/m-C for direct oxidation of alcohols to esters under air

Abstract A convenient, expeditious, and high-efficiency protocol for the transformation of alcohols into esters using a Co-modified N-doped mesoporous carbon material (Co-N/m-C) as the catalyst is proposed. The catalyst was prepared through direct pyrolysis of a macromolecular precursor. The catalyst prepared using a pyrolysis temperature of 900 °C (labeled Co-N/m-C-900) exhibited the best performance. The strong coordination between the ultra-dispersed cobalt species and the pyridine nitrogen as well as the large area of the mesoporous surface resulted in a high turnover frequency value (107.6 mol methyl benzoate mol−1 Co h−1) for the direct aerobic oxidation of benzyl alcohol to methyl benzoate. This value is much higher than those of state-of-the-art transition-metal-based nanocatalysts reported in the literature. Moreover, the catalyst exhibited general applicability to various structurally diverse alcohols, including benzylic, allylic, and heterocyclic alcohols, achieving the target esters in high yields. In addition, a preliminary evaluation revealed that Co-N/m-C-900 can be used six times without significant activity loss. In general, the process was rapid, simple, and cost-effective.