Chaofeng Zhang

tert-Butyl hydroperoxide (TBHP)-mediated oxidative self-coupling of amines to imines over a α-MnO2 catalyst

We here demonstrate a simple, efficient and eco-friendly protocol for the direct synthesis of imines from amines via a facile α-MnO2 catalyzed-procedure at rt. Up to 13 benzylic, heterocyclic, and normal aliphatic imines were synthesized with 95–99% selectivity at 82–99% conversion.

Transfer hydrogenation of nitroarenes with hydrazine at near-room temperature catalysed by a MoO2 catalyst

We present an experimental and computational study of the elementary steps of hydrazine hydrogen transfer on crystalline MoO2, and demonstrate its unique bifunctional metallic-basic properties in a catalytic hydrogenation reaction. Density functional theory (DFT) calculations suggest that the stepwise hydrogen transfer via the prior cleavage of the N–H bond rather than the N–N bond, is the key step to create the dissociated hydride and proton species on the dual Mo and O sites, marking its difference with common oxides. Crystalline MoO2 shows exceptionally high chemoselectivity toward the nitro reduction over CC, CC, and CN groups at room temperature and lower, down to 0 °C, rendering it as a promising catalytic material for hydrogenation reactions.

Cleavage of the lignin β-O-4 ether bond via a dehydroxylation–hydrogenation strategy over a NiMo sulfide catalyst

The efficient cleavage of lignin β-O-4 ether bonds to produce aromatics is a challenging and attractive topic. Recently a growing number of studies have revealed that the initial oxidation of CαHOH to CαO can decrease the β-O-4 bond dissociation energy (BDE) from 274.0 kJ mol−1 to 227.8 kJ mol−1, and thus the β-O-4 bond is more readily cleaved in the subsequent transfer hydrogenation, or acidolysis. Here we show that the first reaction step, except in the above-mentioned pre-oxidation methods, can be a Cα–OH bond dehydroxylation to form a radical intermediate on the acid-redox site of a NiMo sulfide catalyst. The formation of a Cα radical greatly decreases the Cβ–OPh BDE from 274.0 kJ mol−1 to 66.9 kJ mol−1 thereby facilitating its cleavage to styrene, phenols and ethers with H2 and an alcohol solvent. This is supported by control experiments using several reaction intermediates as reactants, analysis of product generation and by radical trap with TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) as well as by density functional theory (DFT) calculations. The dehydroxylation–hydrogenation reaction is conducted under non-oxidative conditions, which are beneficial for stabilizing phenol products.

Nanocoating of magnetic cores with sulfonic acid functionalized shells for the catalytic dehydration of fructose to 5-hydroxymethylfurfural

Abstract A magnetically recyclable acid catalyst composed of an Fe3O4 core and sulfonic acid functionalized silica shell has been prepared using the reverse microemulsion method. The Fe3O4 core was coated with a phenyl modified silica shell nanolayer, and the phenyl groups were subsequently sulfonated to generate a solid sulfonic acid catalyst. The resulting acid catalyst showed higher activity than the conventional A-15 catalyst and comparable activity to several homogeneous sulfonic acid catalysts for the dehydration of fructose to 5-hydroxymethylfurfural (HMF). This process gave a fructose conversion of 99% with an HMF yield of 82% following 3 h in dimethylsulfoxide at 110 °C. Furthermore, the catalyst could be magnetically separated and recycled several times without losing its activity.

CN and NH Bond Metathesis Reactions Mediated by Carbon Dioxide

Herein, we report CO2 -mediated metathesis reactions between amines and DMF to synthesize formamides. More than 20 amines, including primary, secondary, aromatic, and heterocyclic amines, diamines, and amino acids, are converted to the corresponding formamides with good-to-excellent conversions and selectivities under mild conditions. This strategy employs CO2 as a mediator to activate the amine under metal-free conditions. The experimental data and in situ NMR and attenuated total reflectance IR spectroscopy measurements support the formation of the N-carbamic acid as an intermediate through the weak acid-base interaction between CO2 and the amine. The metathesis reaction is driven by the formation of a stable carbamate, and a reaction mechanism is proposed.

Thermally robust silica-enclosed Au 25 nanocluster and its catalysis

Well-defined gold nanoclusters with average size less than 2 nm have emerged as a new and novel catalyst. The gold nanocluster loaded on the oxide surface usually aggregates to larger particles at high temperature (>300℃), which is caused by the removal of the surface ligands. We herein present a novel method to prepare Au 25 cluster catalyst (~1.3 nm) with high thermal stability (up to 400℃). Au 25 @SiO 2 is synthesized via a co-hydrolyzing reaction of Au 25 [SC 3 H 6 Si(OCH 3 ) 3 ] 18 and tetraethyl orthosilicate, and then it is treated at different temperature (e.g., 200, 300, 400℃) in air to remove the organic ligands. Au 25 @SiO 2 is well characterized by transmission electron microscopy, ultraviolet-visible spectroscopy and diffuse reflectance UV-vis spectroscopy. Further, the Au 25 @SiO 2 catalysts are investigated in the hydrogenation of p -nitrophenol into p -aminophenol.

The cascade synthesis of α,β-unsaturated ketones via oxidative C–C coupling of ketones and primary alcohols over a ceria catalyst

We herein report the oxidative C–C coupling of ketones and primary alcohols to produce α,β-unsaturated ketones in the absence of base additives. This cascade synthetic reaction was conducted at 150 °C in 12 h using a heterogeneous CeO2 catalyst. The conversion of acetophenone reached 74% with 89% selectivity to chalcone. A correlation between the CeO2 crystal plane and catalytic performance is established as the catalytic activities decrease in the sequence of (110) > (111) > (100). Characterization using Raman spectroscopy, CO2 temperature-programmed desorption (CO2-TPD), and in situ active site-capping tests has shown that the unusual catalysis of the CeO2 catalyst is attributed to the coexistence of basic and redox active sites. These sites synergistically catalyze the oxidation of alcohols to aldehydes and the aldol condensation to ketones. Moreover, the CeO2 catalyst can be reused several times after calcination to remove the surface-adsorbed substances.

Generation and Confinement of Long-lived N-oxyl Radical and its Photocatalysis

Generation of controllable carbon radical under the assistance of N-oxyl radical is an efficient method for the activation of C-H bonds in hydrocarbons. We herein report that irradiation of α-Fe2O3 and N-hydroxyphthalimide (NHPI) under 455 nm light generates phthalimide-N-oxyl radical (PINO*), which after being formed by oxidation with holes, is confined on α-Fe2O3 surface. The half-life time of the confined radical reaches 22 s as measured by in situ electron paramagnetic resonance (EPR) after the light being turned off. This allows the long-lived N-oxyl radical to abstract the H from C-H bond to form a carbon radical that reacts with molecular oxygen to form R3C-OO· species, decomposition of which leads to oxygenated products.

Ru/ceria-catalyzed direct formylation of amines and CO to produce formamides

We herein report a new strategy of directly converting amines and CO to formamides with 100% atom utilization efficiency. It is suitable for up to 25 amine substrates with no additives. Ru/ceria is found to be an excellent catalyst for this reaction due the efficient co-activation of CO and amine on Ru species.

Chemoselective transfer hydrogenation to nitroarenes mediated by oxygen-implanted MoS2

We present an efficient approach for the chemoselective synthesis of arylamines from nitroarenes and formate over an oxygen-implanted MoS 2 catalyst(O-MoS 2 ). O-MoS 2 was prepared by incomplete sulfiidation and reduction of an ammonium molybdate precursor. A number of Mo-O bonds were implanted in the as-synthesized ultrathin O-MoS 2 nanosheets. As a consequence of the different coordination geometries of O(MoO2) and S(MoS 2 ), and lengths of the Mo-O and Mo-S bonds, the implanted Mo-O bonds induced obvious defects and more coordinatively unsaturated(CUS) Mo sites in O-MoS 2 , as confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and extended X-ray absorption fine structure characterization of various MoS 2 -based materials. O-MoS 2 with abundant CUS Mo sites was found to efficiently catalyze the chemoselective reduction of nitroarenes to arylamines.