Iron(II)-Catalyzed Biomimetic Aerobic Oxidation of Alcohols

We report the first Fe^II-catalyzed biomimetic aerobic oxidation of alcohols. The principle of this oxidation, which involves several electron-transfer steps, is reminiscent of biological oxidation in the respiratory chain. The electron transfer from the alcohol to molecular oxygen occurs with the aid of three coupled catalytic redox systems, leading to a low-energy pathway. An iron transfer-hydrogenation complex was utilized as a substrate-selective dehydrogenation catalyst, along with an electron-rich quinone and an oxygen-activating Co(salen)-type complex as electron-transfer mediators. Various primary and secondary alcohols were oxidized in air to the corresponding aldehydes or ketones with this method in good to excellent yields.     

A novel magnetically separable laccase-mediator catalyst system for the aerobic oxidation of alcohols and 2-substituted-2,3-dihydroquinazolin-4(1H)-ones under mild conditions

In this study, a magnetically reusable artificial metalloenzyme has been constructed by co-immobilization of palladium nanoparticles as a strong oxidizing catalyst and laccase as an oxygen-activating enzyme into the cavities of magnetic mesocellular foams silica (Pd-Laccase@MMCF). The combination of Pd-Laccase@MMCF and hydroquinone (HQ) act as electron-transfer mediator system and make stepwise electron transfer from substrate to molecular oxygen. This catalyst system was used for the aerobic (i) oxidation of alcohols to the corresponding carbonyl compounds and (ii) dehydrogenation of 2-substituted-2,3-dihydroquinazolin-4(1H)-ones in phosphate buffer (0.1 M, pH 4.5, 4 mL)/THF (4%, 1 mL) as solvent under mild conditions. The co-immobilization of both laccase and Pd onto high surface area mesoporous support, high catalytic activity and magnetically separable and reusable make the present catalyst system superior to other currently available electron-transfer mediator systems.     

双功能催化剂Ru2P在N-杂环加氢和无受体脱氢反应中的几何效应和电子效应

饱和及不饱和N-杂环化合物是非常重要的药物中间体.由于它们在催化剂表面的吸附/脱附能力不同,设计具有合适电子结构和几何结构的催化剂用于饱和与不饱和N-杂环化合物的可逆转化具有很大挑战性.目前,负载型纳米金属催化剂通常被用于饱和N-杂环化合物的加氢反应或者不饱和杂环化合物的脱氢反应.然而反应过程中N-杂环化合物与纳米金属的强配位作用,不仅影响其他反应底物与活性位点的接触,而且导致催化剂的循环稳定性较差.在之前的研究中,钌(Ru)催化剂被用于喹啉化合物的选择加氢反应,但反应条件苛刻,循环稳定性差,不能实现杂环化合物的可逆转化.本文在Ru纳米颗粒的晶格中引入杂原子,诱导催化剂表现出不同的几何结构和电子性质,从而调节反应势垒和底物在催化剂表面的脱附能力以优化反应性能.本文以活性炭(AC)为载体,制备了Ru₂P,RuO₂,RuS₂和Ru四种负载型催化剂,以喹啉和四氢喹啉为模型反应物,考察其催化性能.研究发现,Ru₂P/AC可在温和条件下同时实现喹啉的加氢反应和四氢喹啉的无受体脱氢反应,且催化剂经过8次循环使用后,其转化率仍高达95%,选择性达到99%,远优于Ru/AC.密度泛函理论计算结果表明,Ru₂P中的P原子使得两个相邻的Ru-Ru原子的间距从2.61?增加到2.9?.同时P对催化剂几何结构的变化使反应底物在催化剂表面的吸附行为发生改变,即喹啉和四氢喹啉分子都更容易在Ru₂P的表面发生脱附,从而有利于反应进行.通过差分电荷分析,P原子掺杂会将Ru从零价状态调整为缺电子状态.随着P原子掺杂到Ru金属中,反应物表面的电荷大幅度下降,提高了加氢反应和脱氢反应中产物的扩散能力.进一步计算反应路径结果表明,Ru₂P实现了N-杂环化合物可逆加氢/脱氢过程中反应与扩散之间的平衡,从而在加氢和脱氢反应中均表现出优异的催化性能.通过浸渍、热解制备的Ru₂P/AC对一系列N-杂环化合物的加氢和脱氢反应均表现出优异的催化性能.这主要归因于P原子的掺入稀释了Ru-Ru团簇,引起的几何效应和电子效应的协同作用实现了N-杂环化合物加氢/脱氢过程反应与扩散的平衡,从而提高了可逆反应的催化性能.本文通过原子掺杂调控催化活性的本征结构,从而优化出具有平衡反应和产物扩散的优异催化剂.该合成策略具有直接通用的特点,易于拓展到其它复杂的反应体系当中.     

BiMo基复合氧化物催化剂丙烷直接氧化至丙烯醛研究

The effects of the available zoon above the catalyst bed on the performance of the catalyst were investigated. It has been suggested that propylene is an intermediate species in the reaction of propane to acrolein， and a two-step reaction scheme is proposed， the first step is oxidative dehydrogenation of propane to propylene in the gas phase then followed by the second step， the selective oxidation of propylene to acrolein on the surface of the catalyst. The performance of the catalyst depends on both the oxidative dehydrogenation of propane to propylene in the gas phase and the selective oxidation of propylene to acrolein on the catalyst surface. The thermal cracking， homogeneous oxidative dehydrogenation and heterogeneous catalytic dehydrogenation of propane as well as the selective catalytic oxidation of propane to acrolein over BiMoO based mixed oxides catalysts were studied. Under the optimum reaction conditions of propane dehydrogenation and selective oxidation of propylene， the selectivity and the yield of acrolein approached to 45mol% and 14mol%， respectively under about 30mol% propane conversion.     

Boosting Molecular Complexity with O2: Iron-Catalysed Oxygenation of 1-Arylisochromans through Dehydrogenation,Csp3−O Bond Cleavage and Hydrogenolysis

Oxidative cleavage of the Csp³−O bond in 1-arylisochromans with stoichiometric oxidants, such as CrO₃/H₂SO₄, has been practiced for decades in synthetic chemistry. Herein, we report that a structurally well-defined Fe^II–pyridyl(bis-imidazolidine) catalyst promotes the aerobic oxygenation of 1-arylisochromans, affording highly selectively 2-(hydroxyethyl)benzophenones, compounds of potential for neuroprotective agents. Key intermediates have been isolated, indicating that the reaction proceeds through dehydrogenative oxygenation of the isochromans at the 1-position, Csp³−O bond cleavage at the iron centre and hydrogenolysis of the resulting Fe−O bond with the H₂ generated from the dehydrogenation step. In the absence of H₂ but under iron catalysis, the peroxide intermediate is converted into an unexpected ketal compound, which transfers into a 2-(hydroxyethyl)benzophenone when both O₂ and H₂ are admitted. The unique ability of the iron catalyst for oxygenation and hydrogenation in the same catalytic process under mild conditions allows for the stepwise preparation of a variety of isolable oxygenated products on a preparative scale, circumventing the need for using wasteful and/or toxic oxidants.     

Iron(II)‐Catalyzed Biomimetic Aerobic Oxidation of Alcohols

We report the first Fe^II‐catalyzed biomimetic aerobic oxidation of alcohols. The principle of this oxidation, which involves several electron‐transfer steps, is reminiscent of biological oxidation in the respiratory chain. The electron transfer from the alcohol to molecular oxygen occurs with the aid of three coupled catalytic redox systems, leading to a low‐energy pathway. An iron transfer‐hydrogenation complex was utilized as a substrate‐selective dehydrogenation catalyst, along with an electron‐rich quinone and an oxygen‐activating Co(salen)‐type complex as electron‐transfer mediators. Various primary and secondary alcohols were oxidized in air to the corresponding aldehydes or ketones with this method in good to excellent yields.     

Aerobic Dehydrogenation of N-Heterocycles with Grubbs Catalyst: Its Application to Assisted-Tandem Catalysis to Construct N-Containing Fused Heteroarenes

An aerobic dehydrogenation of nitrogen-containing heterocycles catalyzed by Grubbs catalyst is developed. The reaction is applicable to various nitrogen-containing heterocycles. The exceptionally high functional group compatibility of this method was confirmed by the oxidation of an unprotected dihydroindolactam V to indolactam V. Furthermore, by taking advantage of the oxygen-mediated structural change of the Grubbs catalyst, we integrated ring-closing metathesis and subsequent aerobic dehydrogenation to develop the novel assisted-tandem catalysis using molecular oxygen as a chemical trigger. The utility of the assisted-tandem catalysis was demonstrated by the concise synthesis of N-containing fused heteroarenes including a natural antibiotic, pyocyanine.     

含骨架铁ZSM-5的合成及其负载Pt催化剂在正十二烷脱氢反应中的催化性能

采用水热合成法使铁进入分子筛MFI骨架结构,成功合成出含骨架铁的分子筛Na-[Fe]-ZSM-5,并通过离子交换法负载Pt制备脱氢催化剂Pt/Na-[Fe]-ZSM-5。通过正十二烷脱氢反应,研究了该催化剂对长链烷烃脱氢制单烯烃反应的催化性能。采用N2吸附-脱附测试、X射线衍射(XRD)、傅立叶变换红外光谱(FT-IR)、氨气程序升温脱附(NH3-TPD)、吡啶吸附的红外光谱(Py-IR)、CO化学吸附、透射电子显微镜(TEM)等不同方法对催化剂进行了表征。结果表明,通过控制骨架铁含量可调控催化剂表面酸性;含骨架铁的ZSM-5分子筛载体具有抑制负载金属晶粒长大,保持金属高分散度的作用;其负载铂催化剂Pt/Na-[Fe]ZSM-5-50具有表面弱酸中心(0.69 mmol·g^-1)和高分散Pt中心,因而具有良好的长链烷烃脱氢活性、稳定性和单烯烃选择;在转化率稳定在~20%时,TOF为4.56 s^-1,单烯烃选择性为92.7%;在实验范围内,Pt/Na-[Fe]ZSM-5催化剂表面弱酸量和脱氢反应的本征活性(TOF)均随催化剂铁含量的增加而增加。     

Effect of the paste molding pressure on the activity of iron oxide catalyst in dehydrogenation of methylbutenes

The effect of the paste molding pressure on the activity of an iron oxide catalyst in dehydrogenation of methylbutenes was studied. The study involved detailed analysis of the pore structure of the samples by mercury porosimetry and determination of the mode of the catalytic process (kinetic or diffusion control). The range of pore sizes in which dehydrogenation reactions occur was determined.     

Efficient ruthenium-catalyzed aerobic oxidation of amines by using a biomimetic coupled catalytic system

Efficient aerobic oxidation of amines was developed by the use of a biomimetic coupled catalytic system involving a ruthenium-induced dehydrogenation. The principle for this aerobic oxidation is that the electron transfer from the amine to molecular oxygen occurs stepwise via coupled redox systems and this leads to a low-energy electron transfer. A substrate-selective ruthenium catalyst dehydrogenates the amine and the hydrogen atoms abstracted are transported to an electron-rich quinone (2a). The hydroquinone thus formed is subsequently reoxidized by air with the aid of an oxygen-activating [Co(salen)]-type complex (27). The reaction can be used for the preparation of ketimines and aldimines in good to high yields from the appropriate corresponding amines. The reaction proceeds with high selectivity, and the catalytic system tolerates air without being deactivated. The rate of the dehydrogenation was studied by using quinone 2a as the terminal oxidant. A catalytic cycle in which the amine promotes the dissociation of the dimeric catalyst 1 is presented.     

助剂钾添加方式对多乙苯脱氢催化性能的影响

The catalyst for dehydrogenation of diethylbenzene(DEB) to divinylbenzene(DVB) was studied. Potassium-promoted iron oxide catalyst was mainly used for ethylbenzene dehydrogenation. If potassium alkli or salt was used directly as promoter, it was noted that the loss of potassium component from the surface of the catalysts pellet result in deactivation. When potassium promoter was added as kaliophilite(KAlSiO4). It was shown that the latter way of adding potassium promoter not only keeps the depression of carbonaceous deposits but also controls the loss of potassium component(the value of loss of potassium component has been reduced three times) , thus making the catalyst having a higher dehydrogention activity.     

Understanding the dehydrogenation mechanism over iron nanoparticles catalysts based on density functional theory

The conversion of chemical feedstock materials into high value-added products accompanied with dehydrogenation is of great value in the chemical industry.However,the catalytic dehydrogenation reaction is inhibited by a limited number of expensive noble metal catalysts and lacks understanding of dehydrogenation mechanism.Here,we report the use of heterogeneous non-noble metal iron nanoparticles(NPs) incorporated mesoporous nitrogen-doped carbon to investigate the dehydrogenation mechanism based on experiment observation and density functional theory(DFT) method.Fe NPs catalyst displays excellent performance in the dehydrogenation of 1,2,3,4-tetrahydroquinoline(THQ)with 100% selectivity and 100% conversion for 10-12 h at room temperature.The calculated adsorption energy implies that THQ prefers to adsorb on Fe NPs as compared with absence of Fe NPs.What is more,the energy barrier of transition state is relatively low,illustrating the dehydrogenation is feasible.This work provides an atomic scale mechanism guidance for the catalytic dehydrogenation reaction and points out the direction for the design of new catalysts.     

氮掺杂碳纳米管包覆碳化硅作为不含金属的催化剂(英文)

A hierarchical metal-free catalyst consisting of nitrogen-doped carbon nanotubes decorated onto a silicon carbide (N-CNTs/SiC) macroscopic host structure was prepared. The influence of N-CNTs incorporation on the physical properties of the support was evaluated using different characterization techniques. The catalyst was tested as a metal-free catalyst in the selective oxidation of H2S and steam-free dehydrogenation of ethylbenzene. The N-CNTs/SiC catalyst exhibited extremely good desulfurization performance compared to a Fe2O3/SiC catalyst under less conducive reaction conditions such as low temperature, high space velocity, and a low O2-to-H2S molar ratio. For the dehy-drogenation of ethylbenzene, a higher dehydrogenation activity was obtained with the N-CNTs/SiC catalyst compared to a commercial K-Fe/Al2O3 catalyst. The N-CNTs/SiC catalyst also displayed good stability as a function of time on stream for both reactions, which was attributed to the strong anchoring of the nitrogen dopant in the carbon matrix. The extrudate shape of the SiC support allowed the direct macroscopic shaping of the catalyst for use in a conventional fixed-bed reactor without the problems of catalyst handling, transportation, and pressure drop across the catalyst bed that are encountered with nanoscopic carbon-based catalysts.     

Theoretical and Experimental Study on Reaction Coupling： Dehydrogenation of Ethylbenzene in the Presence of Carbon Dioxide

Dehydrogenation of ethylbenzene (EB) to styrene (ST) in the presence of CO2, in which EB dehydrogenation is coupled with the reverse water-gas shift (RWGS), was investigated extensively through both theoretical analysis and experimental characterization. The reaction coupling proved to be superior to the single dehydrogenation in several respects. Thermodynamic analysis suggests that equilibrium conversion of EB can be improved greatly by reaction coupling due to the simultaneous elimination of the hydrogen produced from dehydrogenation. Catalytic tests proved that iron and vanadium supported on activated carbon or Al2O3 with certain promoters are potential catalysts for this coupling process. The catalysts of iron and vanadium are different in the reaction mechanism, although ST yield is always associated with CO2 conversion over various catalysts. The two-step pathway plays an important role in the coupling process over Fe/Al2O3, while the one-step pathway dominates the reaction over V/Al2O3. Coke deposition and deep reduction of active components are the major causes of catalyst deactivation. CO2 can alleviate the catalyst deactivation effectively through preserving the active species at high valence in the coupling process, though it can not suppress the coke deposition.     

Transformation of the phase structure of an iron oxide catalyst for dehydrogenation of methyl butenes under industrial exploitation conditions

X-ray phase, differential-thermal, and elemental analyses were used to study the transformation of the phase structure of an iron oxide catalyst for dehydrogenation of methyl butenes after exploitation.     

乙苯氧化脱氢反应Fex/TiO2的催化性能研究

新型氧化钛负载铁催化剂Fex/TiO2在低温乙苯空气氧化脱氢制苯乙烯反应中具有良好的催化活性。350 ℃,使用Fe7/TiO2催化剂,当Fe的质量分数为7%时,可获得14.6%乙苯单程转化率和99.0%的苯乙烯选择性。通过X衍射、表面吸附、热分析及扫描电镜仪器分析表征,考察氧化钛负载铁催化剂在乙苯低温氧化脱氢反应中的催化作用。350 ℃乙苯可被活化,催化剂活性的高低取决于活性物种Fe(III)的分布状态和质量分数。     

Oxygen‐Assisted Hydroxymatairesinol Dehydrogenation: A Selective Secondary‐Alcohol Oxidation over a Gold Catalyst

Selective dehydrogenation of the biomass‐derived lignan hydroxymatairesinol (HMR) to oxomatairesinol (oxoMAT) was studied over an Au/Al₂O₃ catalyst. The reaction was carried out in a semi‐batch glass reactor at 343 K under two different gas atmospheres, namely produced through synthetic air or nitrogen. The studied reaction is, in fact, an example of secondary‐alcohol oxidation over an Au catalyst. Thus, the investigated reaction mechanism of HMR oxidative dehydrogenation is useful for the fundamental understanding of other secondary‐alcohol dehydrogenation over Au surfaces. To investigate the elementary catalytic steps ruling both oxygen‐free‐ and oxygen‐assisted dehydrogenation of HMR to oxoMAT, the reactions were mimicked in a vacuum over an Au₂₈ cluster. Adsorption of the involved molecular species—O₂, three different HMR diastereomers (namely, one SRR and two RRR forms), and the oxoMAT derivative—were also studied at the DFT level. In particular, the energetic and structural differences between SRR‐HMR and RRR‐HMR diastereomers on the Au₂₈ cluster were analyzed, following different reaction pathways for the HMR dehydrogenation that occur in presence or absence of oxygen. The corresponding mechanisms explain the higher rates of the experimentally observed oxygen‐assisted reaction, mostly depending on the involved HMR diastereomer surface conformations. The role of the support was also elucidated, considering a very simple Au₂₈ charged model that explains the experimentally observed high reactivity of the Au/Al₂O₃ catalyst.     

Oxidative dehydrogenation of crotonaldehyde overK2HPMo12O40catalyst

Summary The oxidative dehydrogenation of crotonaldehyde to furan and maleic anhydride was carried out over K₂HPMo₁₂O₄₀catalyst. A positive effect of water vapor on furan formation is explained by ability of the catalyst to isomerize 2E- to 2Z-crotonaldehyde.</o:p>     

Copper-catalyzed aerobic oxidative dehydrogenation for conversion of 2-(alkylthio)-1,4-dihydropyrimidines to 2-(alkylthio)pyrimidines

A simple and efficient aerobic oxidative dehydrogenation reaction method for the conversion of 2-(alkylthio)-1,4-dihydropyrimidines to 2-(alkylthio)pyrimidines using copper catalyst with no additives, such as an oxidant, acid, or base, has been developed. The reaction was successful with a wide range of 2-(alkylthio)-1,4-dihydropyrimidine substrates.     

双功能MoNi4电极实现水参与的氮杂环化合物转移氢化与脱氢

氮杂环的催化氢化在有机合成、药物研发、石油化工等领域有着重要应用.尽管发展了一系列均相和非均相催化加氢体系,但由于通常使用易燃易爆的氢气或价格昂贵且毒性较高的试剂(如:水合肼和硼氢化钠)为氢源,给安全生产及生态环境带来了严重的问题.此外,由于动力学同位素效应,氘代药物具有重要应用.氮杂环结构作为生物医药的构筑单元与关键中间体,现有的策略由于没有合适的氘源难以用于氘代氮杂环化合物的合成.因此,急需开发一种基于非贵金属催化剂和安全易得氢(氘)源的氮杂环催化氢(氘)化策略.水相中的电化学氢化可利用水电解原位产生的活性氢替代传统的氢气裂解实现有机氢化产物的合成,已成为一种理想氢化策略,被广泛应用于二氧化碳还原、硝酸根还原和生物质氢解等.本课题组前期研究已经实现了以氘水为氘源的氘代分子的高效电化学合成(Angew.Chem.Int.Ed.,2020,59,18527–18531;Angew.Chem.Int.Ed.,2020,59,21170–21175;CCS Chem.,2021,3,507–515).然而,要开发一种电化学的杂环氢化方法,一方面要克服氮杂环化合物对催化剂的毒化,另一方面要在电极表面产生大量的活性氢.因此,开发具有较好的水离解性能的非贵金属电极材料是实现氮杂芳烃电化学氢化和氘代的关键.基于上述要求,MoNi4(目前用于碱性电催化水分解制氢的活性较高的非贵金属材料)成为理想的电极材料.本文以喹喔啉(1,2,3,4-四氢喹喔啉骨架作为重要的结构单元存在于许多生物活性化合物中)作为模板底物,设计并制备了三维自支撑的MoNi4多孔纳米片为双功能电极,以水和氘水为氢源和氘源,实现了喹喔啉及其他氮杂环分子的氢化与氢化,同时实现了四氢喹喔啉的电化学氧化脱氢.制备了MoNi4纳米片阵列,利用扫描电子显微镜、透射电子显微镜、X射线衍射和X光电子能谱等手段进行表征,评估了其在碱性电解液中用于喹喔啉电化学转移氢化的性能.结果表明,MoNi4电极加速了动力学缓慢的Volmer步骤,在仅50 mV的过电势下以80％的法拉第效率实现了喹喔啉的电化学氢化.电子顺磁共振等证实水电解生成了H*,并与喹喔啉自由基阴离子偶联实现喹喔啉的氢化.同时,该电化学转移氢化方法可很好地应用于一系列喹喔啉衍生物和其他氮杂芳烃化合物.克级合成体现了该电化学转移氢化方法的潜在应用性.原位拉曼实验结果表明,在MoNi4表面形成的NiOOH是实现1,2,3,4-四氢喹喔啉氧化脱氢的重要物种.此外,以D2O代替H2O,可以较好的收率和高达99％的氘化率实现氘代氮杂环的合成.与传统的氮杂环氢化方法相比,本文的电化学转移氢化策略具有绿色、温和、高效的特点,同时拓宽了电化学氢化在合成化学中的应用.