Visible‐Light‐Induced Selective Photocatalytic Aerobic Oxidation of Amines into Imines on TiO2

Imines are important intermediates for the synthesis of fine chemicals, pharmaceuticals, and agricultural chemicals. Selective oxidation of amines into their corresponding imines with dioxygen is one of the most‐fundamental chemical transformations. Herein, we report the oxidation of a series of benzylic amines into their corresponding imines with atmospheric dioxygen as the oxidant on a surface of anatase TiO₂ under visible‐light irradiation (λ>420 nm). The visible‐light response of this system was caused by the formation of a surface complex through the adsorption of a benzylic amine onto the surface of TiO₂. From the analysis of products of specially designed benzylic amines, we demonstrated that a highly selective oxygenation reaction proceeds via an oxygen‐transfer mechanism to afford the corresponding carbonyl compound, whose further condensation with an amine would generate the final imine product. We found that when primary benzylic amines (13 examples), were chosen as the substrates, moderate to excellent selectivities for the imine products were achieved (ca. 38–94 %) in moderate to excellent conversion rates (ca. 44–95 %). When secondary benzylic amines (15 examples) were chosen as the substrates, both the corresponding imines and aldehydes were detected as the main products with moderate to high conversion rates (ca. 18–100 %) and lower selectivities for the imine products (ca. 14–69 %). When tribenzylamine was chosen as the substrate, imine (27 %), dibenzylamine (24 %), and benzaldehyde products (39 %) were obtained in a conversion of 50 %. This report can be viewed as a prototypical system for the activation of C? H bonds adjacent to heteroatoms such as N, O, and S atoms, and oxofuctionalization with air or dioxygen as the terminal oxidant under visible‐light irradiation using TiO₂ as the photocatalyst.     

Simple Copper Catalysts for the Aerobic Oxidation of Amines: Selectivity Control by the Counterion

We describe the use of simple copper‐salt catalysts in the selective aerobic oxidation of amines to nitriles or imines. These catalysts are marked by their exceptional efficiency, operate at ambient temperature and pressure, and allow the oxidation of amines without expensive ligands or additives. This study highlights the significant role counterions can play in controlling selectivity in catalytic aerobic oxidations.     

二氧化锰化学氧化法合成导电聚苯胺

研究了以二氧化锰为氧化剂，苯胺（ANI）化学氧化聚合的新型反应，探讨了氧化剂的用量、反应体系酸度、苯胺用量，反应温度，酸的种类等条件对聚苯胺（PANI）的产率和电导率的影响，在2．7mol/L的盐酸介质中二氧化锰与苯胺摩尔比为0．7的条件下室温氧化聚合4h，可得到电导率为12．5S/cm的聚苯胺，产率为73％，对产物聚苯胺的结构用红外光谱和紫外－可见光谱进行了表征。     

Selective Acceptorless Dehydrogenation of Primary Amines to Imines by Core–Shell Cobalt Nanoparticles

Core–shell nanocatalysts are attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic poly‐ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core–shell structure that displays excellent activity and selectivity in the self‐dehydrogenation and hetero‐dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives.     

The Determination of Cerium on Manganese Dioxide

Abstract

This paper recommends a simple and convenient procedure for the determination of cerium(III) on MnO₂ without separation of Mn. Several reducing agents and optimum conditions of determination were studied.     

Pulsed‐EPR Evidence of a Manganese(II) Hydroxycarbonyl Intermediate in the Electrocatalytic Reduction of Carbon Dioxide by a Manganese Bipyridyl Derivative

A key intermediate in the electroconversion of carbon dioxide to carbon monoxide, catalyzed by a manganese tris(carbonyl) complex, is characterized. Different catalytic pathways and their potential reaction mechanisms are investigated using a large range of experimental and computational techniques. Sophisticated spectroscopic methods including UV/Vis absorption and pulsed‐EPR techniques (2P‐ESEEM and HYSCORE) were combined together with DFT calculations to successfully identify a key intermediate in the catalytic cycle of CO₂ reduction. The results directly show the formation of a metal–carboxylic acid–CO₂ adduct after oxidative addition of CO₂ and H⁺ to a Mn⁰ carbonyl dimer, an unexpected intermediate.     

超临界(压缩)二氧化碳介质中的选择氧化

由于超临界二氧化碳（SCCO₂）具有稳定、安全、不燃、清洁无毒、粘度小、扩散快、可压缩的特殊性质,所以使得超临界二氧化碳非常适合作为催化反应的绿色溶剂.除此之外,多种气体在超临界二氧化碳中的溶解度很高,这对于那些受传质阻碍和易引起安全隐患的气相反应来讲,使用SCCO₂作为替代的反应溶剂具有重要的价值。值得指出的是：如果选择超临界二氧化碳作为氧化反应的溶剂,其自身不会发生反应而产生副产物,从而容易得到清洁的产物。本文主要讨论了超临界二氧化碳作为反应介质对醇、烯烃和烷烃等选择氧化反应的影响,通过与传统溶剂比较可以看出超临界二氧化碳作为氧化反应溶剂的优势,对近几年来以分子氧为氧化剂,以超临界二氧化碳为介质的催化选择氧化的反应体系作了综述,并对未来的发展提出了展望。     

电解二氧化锰的改性研究

应用液相表面处理法在电解二氧化锰表面包覆一层化学二氧化锰与铋的氧化物,形成EMD/CMD-Bi复合物.X射线衍射分析和扫描电镜显示,改性后的二氧化锰仍然保持EMD的γ-MnO2晶型,表面明显包覆了一层絮状物质,表面孔状结构增多.电化学测试表明,以改性后的二氧化锰作电极,其CV扫描第2电子还原峰电流约增大了1.5倍,电极放电容量和倍率性能显著提高,在截止电压为-0.8V(vs.HgO/Hg电极)和电流密度分别为30.8mA/g和102.7mA/g条件下,放电容量较改性前的各提高了40.8%和78.3%.     

改性电解二氧化锰研究

用电解法制备一种掺杂铋的改性二氧化锰材料（Ｂｉ－ＥＭＤ），通过Ｘ射线衍及光电子能谱分析，Ｂｉ－ＥＭＤ属于γ－ＭｎＯ２，Ｂｉ以Ｂｉ２Ｏ３形式存在于改性中，且材料中Ｂｉ含量随电解时Ｂｉ＾３＋浓度增加而增加，当电解液中Ｂｉ＾３＋浓度为０．００８ｍｏｌ．Ｌ＾－１时，材料中Ｂｉ含量１４．３％（重量百分比），用Ｂｉ－ＥＭＤ装配民ＡＡ型Ｚｎ／ＭｎＯ２试验电池，通过循环寿命实验，Ｂｉ－ＥＭＤ表现出良好的可逆性。     

Water Oxidation Catalysis by Synthetic Manganese Oxides with Different Structural Motifs: A Comparative Study

Manganese oxides are considered to be very promising materials for water oxidation catalysis (WOC), but the structural parameters influencing their catalytic activity have so far not been clearly identified. For this study, a dozen manganese oxides (MnO_x) with various solid‐state structures were synthesised and carefully characterised by various physical and chemical methods. WOC by the different MnO_x was then investigated with Ce⁴⁺ as chemical oxidant. Oxides with layered structures (birnessites) and those containing large tunnels (todorokites) clearly gave the best results with reaction rates exceeding 1250 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h^?1 or about 50 μmol_O2 m^?2 h^?1. In comparison, catalytic rates per mole of Mn of oxides characterised by well‐defined 3D networks were rather low (e.g., ca. 90 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h^?1 for bixbyite, Mn₂O₃), but impressive if normalised per unit surface area (>100 ${{\rm{{\rm \mu} mol}}_{{\rm{O}}_{\rm{2}} } }$ m^?2 h^?1 for marokite, CaMn₂O₄). Thus, two groups of MnO_x emerge from this screening as hot candidates for manganese‐based WOC materials: 1) amorphous oxides with tunnelled structures and the well‐established layered oxides; 2) crystalline Mn^III oxides. However, synthetic methods to increase surface areas must be developed for the latter to obtain good catalysis rates per mole of Mn or per unit catalyst mass.     

水热处理对二氧化锰电容性能的影响

采用化学共沉淀法制备了二氧化锰。XRD测试表明，产物为α-MnO₂和γ-MnO₂无定形粉末，经水热处理后的二氧化锰晶化程度增加，为α-MnO₂和γ-MnO₂混晶相结构。电化学测试表明，二氧化锰单电极比容量达252.72 F·g^-1。经水热处理后单电极比容量达到299.15 F·g^-1，比处理前的提高18.37%。经400次循环后，水热处理后的样品比容量衰减极小。     

Non-Pincer-Type Manganese Complexes as Efficient Catalysts for the Hydrogenation of Esters

Catalytic hydrogenation of carboxylic acid esters is essential for the green production of pharmaceuticals, fragrances, and fine chemicals. Herein, we report the efficient hydrogenation of esters with manganese catalysts based on simple bidentate aminophosphine ligands. Monoligated Mn PN complexes are particularly active for the conversion of esters into the corresponding alcohols at Mn concentrations as low as 0.2 mol % in the presence of sub-stoichiometric amounts of KO^tBu base.     

掺Fe3+MnO2超级电容器电极材料的制备

化学掺杂;掺Fe3+MnO2超级电容器电极材料的制备     

沉淀方法及铈掺杂对铜锰氧化物催化剂催化氧化CO性能的影响

The influence of Ce doping and the precipitation method on structural properties and the catalytic activity of copper manganese oxides for CO oxidation at ambient temperature have been investigated. The catalysts were characterized by means of the powder X-ray diffraction and N₂ adsorption-desorption, the inductively coupled plasma atomic emission spectrometry, the temperature programmed reduction, diffuse reflectance UV-Vis spectra, and the X-ray photoelectron spectroscopy. It was found that after doping little amount of Ce in copper manganese oxide, CeO₂ phase was highly dispersed and could prevent sintering and aggregating of the catalyst, the size of the catalytic material was decreased, the reducibility was enhanced, the specific surface area was increased and the formation of the active sites for the oxidation of CO was improved significantly. Therefore, the activity of the rare earth promoted catalyst was enhanced remarkably.     

Factors Influencing the Regioselectivity of the Oxidation of Asymmetric Secondary Amines with Singlet Oxygen

Aerobic amine oxidation is an attractive and elegant process for the α functionalization of amines. However, there are still several mechanistic uncertainties, particularly the factors governing the regioselectivity of the oxidation of asymmetric secondary amines and the oxidation rates of mixed primary amines. Herein, it is reported that singlet‐oxygen‐mediated oxidation of 1° and 2° amines is sensitive to the strength of the α‐C?H bond and steric factors. Estimation of the relative bond dissociation energy by natural bond order analysis or by means of one‐bond C?H coupling constants allowed the regioselectivity of secondary amine oxidations to be explained and predicted. In addition, the findings were utilized to synthesize highly regioselective substrates and perform selective amine cross‐couplings to produce imines.     

Graphite‐Supported Gold Nanoparticles as Efficient Catalyst for Aerobic Oxidation of Benzylic Amines to Imines and N‐Substituted 1,2,3,4‐Tetrahydroisoquinolines to Amides: Synthetic Applications and Mechanistic Study

Selective oxidation of amines using oxygen as terminal oxidant is an important area in green chemistry. In this work, we describe the use of graphite‐supported gold nanoparticles (AuNPs/C) to catalyze aerobic oxidation of cyclic and acyclic benzylic amines to the corresponding imines with moderate‐to‐excellent substrate conversions (43–100 %) and product yields (66–99 %) (19 examples). Oxidation of N‐substituted 1,2,3,4‐tetrahydroisoquinolines in the presence of aqueous NaHCO₃ solution gave the corresponding amides in good yields (83–93 %) with high selectivity (up to amide/enamide=93:4) (6 examples). The same protocol can be applied to the synthesis of benzimidazoles from the reaction of o‐phenylenediamines with benzaldehydes under aerobic conditions (8 examples). By simple centrifugation, AuNPs/C can be recovered and reused for ten consecutive runs for the oxidation of dibenzylamine to N‐benzylidene(phenyl)methanamine without significant loss of catalytic activity and selectivity. This protocol “AuNPs/C+O₂” can be scaled to the gram scale, and 8.9 g (84 % isolated yield) of 3,4‐dihydroisoquinoline can be obtained from the oxidation of 10 g 1,2,3,4‐tetrahydroisoquinoline in a one‐pot reaction. Based on the results of kinetic studies, radical traps experiment, and Hammett plot, a mechanism involving the hydrogen‐transfer reaction from amine to metal and oxidation of M‐H is proposed.