A manganese complex with a porphyrin-like ligand that catalyzes the highly chemoselective and enantioselective oxidation of heteroaromatic sulfides, including imidazole, benzimidazole, indole, pyridine, pyrimidine, pyrazine, sym-triazine, thiophene, thiazole, benzothiazole, and benzoxazole, with hydrogen peroxide is described, furnishing the corresponding sulfoxides in good to excellent yields and enantioselectivities (up to 90% yield and up to >99% ee) within a short reaction time (0.5 h). The practical utility of the method has been demonstrated in the gram-scale synthesis of chiral sulfoxide. Mechanistic studies, performed with 18O-labeled water (H218O), hydrogen peroxide (H218O2), and cumyl hydroperoxide, reveal that a high-valent manganese–oxo species is generated as the oxygen atom delivering agent via carboxylic acid assisted heterolysis of O–O bonds. Density functional theory (DFT) calculations were also carried out to give further insight into the mechanism of manganese-catalyzed sulfoxidation. On the basis of the theoretical study, the coupled high-valent manganese(IV)–oxo cation radical species, which bears obvious similarities with that of reactive intermediates in the catalytic oxygenation reactions based on the cytochrome P450 and metalloporphyrin models, has been proposed as the reactive oxidant in the non-heme manganese catalyst system.Keywords: asymmetric sulfoxidation; cation radical; heteroaromatic sulfides; manganese; porphyrin-like;

Here meso-N/C-900 derived from polypyridyl ligand DAA has been developed as a metal-free catalyst, for the first time, exhibiting good performance in catalytic ammoxidation of alcohols to nitriles. Systematic characterization suggests that the accessible mesopores and the effective pyridinic/pyrrolic-N are responsible for the unprecedented performance.

Mesoporous carbon derived from natural vitamin B12 is applied for the first time in organic synthesis and exhibits exceptionally high dual activity for imine formation via the cross-coupling of alcohols with amines and the self-coupling of primary amines using molecular oxygen or air as the terminal oxidant.

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.

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.

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.

Imines as valuable intermediates are widely applied in pharmaceutical syntheses and organic transformation. However, the traditional imine synthesis involves unstable aldehydes, dehydrating agents, and Lewis acid catalysts. The topic of this review is focused on three new approaches, namely, the cross-coupling of alcohols with amines, the self-coupling of primary amines, and the oxidative dehydrogenation of secondary amines, utilizing much more readily available starting materials and green oxidant (O2/air) to furnish the imine products. The related catalysts are classified into metal, metal-free, photo-, and bioinspired catalysts. Particular emphasis is placed on the high-activity, low-cost, and versatile catalysts; key factors that affect the catalytic activity and reaction mechanisms are also highlighted.Keywords: aerobic oxidation; alcohols; amines; catalysis; imines

A new series of carbon-based heterogeneous catalysts aiming at the oxidative coupling of amines to imines is disclosed here, which are easily synthesized by pyrolysis of macrocyclic compounds, including phthalocyanine and porphyrin under different temperatures. Silica colloid or ordered mesoporous silica SBA-15 is employed as the hard template to fulfill the mesoporous structures. The most active catalyst fabricated from phthalocyanine and silica colloid shows remarkable catalytic activity, excellent selectivity, and robust stability toward the imine formation in the presence of molecular oxygen under neat conditions. Kinetic analysis demonstrates that the apparent activation for benzylamine oxidation is 47.6 kJ mol–1 and that cationic species are involved in the reaction. The unprecedented performance of mesoporous carbon catalysts can be attributed to their high surface area, profitable pore volume, as well as homogeneous distribution of defect sites.Keywords: aerobic oxidation; heterogeneous catalysis; imines; mesoporous carbon; metal-free

An effective method for the construction of esters from acyl chloride and halohydrocarbon using Cs2CO3 as an oxygen source was achieved for the first time. The methodology has a wide scope of substrates and can be scaled up. The study of a preliminary reaction mechanism demonstrated that the O in the products comes from Cs2CO3 and this esterification proceeds through a free radical reaction. It was also found that CO2 can also be used in this esterification reaction as an oxygen source.

The oxidation of benzylpyridines forming benzoylpyridines was achieved based on a synergistic H4NI–AcOH catalyst and molecular oxygen in high yield under solvent-free conditions. This is the first nonmetallic catalytic system for this oxidation transformation using molecular oxygen as the oxidant. The catalytic system has a wide scope of substrates and excellent chemoselectivity, and this procedure can also be scaled up. The study of a preliminary reaction mechanism demonstrated that the oxidation of the Csp3–H bonds of benzylpyridines was promoted by the pyridinium salts formed by AcOH and benzylpyridines. The synergistic effect of H4NI–AcOH was also demonstrated by control experiments.

An in situ formed porphyrin-inspired iron complex that catalyzes asymmetric epoxidation of di- and trisubstituted enones is described. The reaction provides highly enantioenriched α,β-epoxyketones (up to 99% ee). The practical utility of the new catalyst system is demonstrated by the gram-scale synthesis of optically pure epoxide. Hammett analysis suggests that the transition state of the reaction is electron-demanding and the active oxidant is electrophilic.

A novel strategy for catalytic oxidation of a variety of benzylic, allylic, propargylic, and aliphatic alcohols to the corresponding aldehydes or ketones by an in situ formed porphyrin-inspired manganese complex in excellent yields (up to 99%) has been successfully developed.

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.

Manganese oxides loaded on various supports have been prepared and studied for the direct imine formation by oxidative coupling of alcohols and amines. Among the catalysts, hydroxyapatite supported manganese oxides (MnOx/HAP) show the best activity and selectivity for this reaction in the absence of an additional base using air as the environmentally benign terminal oxidant. NH3-/CO2-TPD results show that the amphoteric properties of MnOx/HAP are crucial for this reaction to obtain a satisfactory yield. Various aromatic alcohols and amines are smoothly transformed into the corresponding imines in good to excellent yields. The catalyst is reusable and gives 98% yield of the product in all 9 reuse tests. Compared with the fresh catalyst, the XRD and SEM of the reactivated MnOx/HAP after nine reactions do not show any obvious change.

A facile and efficient methodology is presented for the direct oxidative esterification of alcohols with alcohols catalyzed by NaAuCl4. Just in the presence of a low catalytic amount of base additive, the newly developed catalytic system proceeds with high selectivity and broad substrate scope under mild conditions with dioxygen or air as the environmentally benign terminal oxidant. Various alcohols including benzylic and allylic alcohols were smoothly reacted with methanol and even with long-chain aliphatic alcohols, affording the desired products in good to excellent yields (up to 95% yield). The present system showed high catalytic activity with a TOF up to 219 h−1. Kinetic studies of the reaction process provide fundamental insights into the catalytic pathway, and a possible reaction pathway was proposed based on the results of the control experiments. XPS, TEM, and UV-vis were carried out to characterize the chemical state of the Au catalyst in the present catalytic system. The results indicate that the Au nanoparticles were generated in situ and supported on K2CO3, forming a simple, recyclable and selective catalyst system for the direct oxidative esterification of alcohols.

•MOF-199 encapsulated Keggin polyoxometalate catalyst was facilely confined in mesoporous SBA-15.•This material was exploited to act as a stable heterogeneous catalyst in a liquid hydroxylation of benzene.•Cycling experiments of the catalyst were carried out and demonstrated unprecedented stability.We present here a new hybrid material (POM@MOF@SBA-15, PMS) in which metal organic framework (MOF) MOF-199 encapsulated Kegginpolyoxometalate (POM) catalyst (names as POM@MOF) was facilely confined in mesoporous SBA-15. This mesoporous SBA-15 confined MOF-199 with encapsulated Keggin POM material was exploited to act as a stable heterogeneous POMs-based catalyst in a liquid oxidative reaction medium. Cycling experiments of the PMS catalyst were carried out in the direct synthesis of phenol from benzene and demonstrated unprecedented stability of this novel type PMS catalyst.Graphical abstract

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).

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.

The first genuinely promising porphyrin-inspired manganese-catalyzed asymmetric sulfoxidation method using hydrogen peroxide has been successfully developed, allowing for rapidly oxidizing (0.5–1.0 h) a wide variety of sulfides in high yields with excellent enantioselectivities (up to >99% ee).

A novel strategy for catalytic asymmetric epoxidation of a wide variety of olefins by a porphyrin-inspired chiral manganese complex using H2O2 as a terminal oxidant in excellent yield with up to greater than 99% ee has been successfully developed.

We have developed a simple and practical process for the oxidation of alcohols to the corresponding carbonyl compounds by using a low catalytic amount of DDQ, NaNO2 as a cocatalyst, and molecular oxygen as terminal oxidant. Nitric oxide generated in situ by NaNO2 in the presence of AcOH is essential for the realization of the catalytic cycle at room temperature. The practical utility of this catalytic process has been demonstrated in the gram-scale oxidation of cinnamyl alcohol.

A new catalytic system for oxidation of alcohols with oxygen by N-hydroxyphthalimide (NHPI) combined with CuBr has been developed. The reaction results showed that this catalytic system can effectively catalyze the oxidation of alcohols to the corresponding carboxylic acids or ketones. We obtained 100% selectivity for acetophenone at 94.2% conversion of phenylethanol at 75 °C for 20 h. A mechanism of oxidation of alcohols catalyzed by NHPI/CuBr was proposed.

Five catalysts containing PW or W active species that anchored onto aminosilylated mesoporous silica SBA-15 by a post-grafting route were prepared and the resulting PW or W/APTES/SBA-15 hybrid materials were characterized by XRD, N2 adsorption/desorption, surface area analysis, TEM, FT-IR, and ICP (inductively coupled plasma atomic emission spectroscopy). The names of these catalysts have been abbreviated as SBA-15m-a, SBA-15m-b, SBA-15m-c, SBA-15m-d, and SBA-15m-e according to the different active species. The PW or W active species were highly dispersed in the channels of the modified mesoporous materials. The interaction between PW or W species and amino groups grafted on the channel surface of SBA-15 led to the immobilization of PW or W species. Their catalytic activity in the epoxidation of cyclooctene with H2O2 as oxidant was investigated. Among them, SBA-15m-a showed the best performance, with 98.9% conversion and 98.4% selectivity. The catalyst could be reused for six times with a little decrease in activity.

A series of transition metal substituted polyoxometalates with a Keggin structure were prepared and utilized for the hydroxylation of benzene to phenol. Among the compounds tested, [(CH3)4N]4PMo11VO40 exhibits the highest phenol yield (13.0%) and selectivity (90.6%) in acetic acid/acetonitrile. Vanadium peroxo is the active site of the reaction, and ammonium also plays an important role. The influence of various reaction parameters, such as solvent, reaction time, reaction temperature, and amount of hydrogen peroxide used were investigated to obtain the optimal reaction conditions.

Cyclohexene can be oxidized directly to 1, 2-cyclohexanediol with aqueous hydrogen peroxide under solvent-free condition using a heteropolyphosphatotungstate catalyst. And an isolated yield of 54% was obtained in this catalytic system.

[n-C16H33N(CH3)3]3PW12O40 (1a) catalyzed the oxidation of secondary alcohols with 27.5% aqueous hydrogen peroxide under solvent-free conditions. The isolated yields of all ketones were higher than 92%. The turnover number of the catalyst 1a was above 368, and the highest TON and TOF were up to 3840 and 320 h−1. In this catalytic system, the catalytic active species was {PO4[WO(O2)2]4}3−, which was formed from 1a in the reaction. It was discovered that {PO4[WO(O2)2]4}3− (PW4) and [PW12O40]3− (PW12) kept an equilibrium during the alcohol oxidation by simultaneous monitoring the distribution of species in organic and aqueous phases. The analysis of the W content in the aqueous phase by ICP and the detection of the species transformation in the organic phase by 31P NMR revealed that the most of the PW4 species were transformed to the PW12 species again after the reaction. PW12 and PW4 were in the transform-and-retransform process.A new transform-and-retransform process was first discovered between [PW12O40]3− and {PO4[WO(O2)2]4}3− in alcohol oxidation catalyzed by 12-phosphotungstate. The PW4 was formed from PW12 by reacting with H2O2, PW4 and PW12 kept equilibrium during reaction, and the most of PW4 could transform to PW12 again after reaction.

In this paper, we have developed a highly efficient method for the direct preparation of propylene carbonate from propylene and carbon dioxide (CO2) using quaternary ammonium heteropolyphosphatotungstate–quaternary ammonium halide catalytic system with anhydrous hydrogen peroxide as an oxidant through one-pot two-step process. The effects of the amount of tetrabutylammonium bromide (TBAB), the concentration of hydrogen peroxide and other reaction conditions were investigated. The catalyst system gave an optimum propylene oxide yield (91%) at 75 °C in oxidation step and the highest propylene carbonate yield (99%) at 140 °C and 3.0 MPa in cycloaddition step. Based on the results, a reaction mechanism has been proposed.In this study, we successfully combined the epoxidation of propylene catalyzed by reaction-controlled phase-transfer quaternary ammonium heteropolyphosphatotungstate and the cycloaddition of CO2 to propylene oxide through one-pot two-step process.Download full-size image

Here meso-N/C-900 derived from polypyridyl ligand DAA has been developed as a metal-free catalyst, for the first time, exhibiting good performance in catalytic ammoxidation of alcohols to nitriles. Systematic characterization suggests that the accessible mesopores and the effective pyridinic/pyrrolic-N are responsible for the unprecedented performance.

A novel strategy for catalytic oxidation of a variety of benzylic, allylic, propargylic, and aliphatic alcohols to the corresponding aldehydes or ketones by an in situ formed porphyrin-inspired manganese complex in excellent yields (up to 99%) has been successfully developed.

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.

Mesoporous carbon derived from natural vitamin B12 is applied for the first time in organic synthesis and exhibits exceptionally high dual activity for imine formation via the cross-coupling of alcohols with amines and the self-coupling of primary amines using molecular oxygen or air as the terminal oxidant.