Pd@tetrahedral hollow magnetic nanoparticles coated with N‐doped porous carbon as an efficient catalyst for hydrogenation of nitroarenes

Hollow magnetic nanoparticles (MNPs) with tetrahedral morphology were synthesized and then covered by a shell prepared by coating with melamine–formaldehyde followed by the introduction of glucose‐derived carbon. Subsequently, Pd nanoparticles were immobilized and the core–shell nanocomposite was carbonized. The obtained magnetic catalyst was successfully applied for the hydrogenation of nitroarenes in aqueous media. To investigate the effects of the morphology of MNPs, the nature of carbon shell, and the order of incorporation of Pd nanoparticles, several control catalysts, including the MNPs with different morphologies (disc‐like and cylinder); MNPs coated with different shells (sole glucose‐derived carbon or melamine–formaldehyde carbon shell); and a nanocomposite, in which Pd was immobilized after carbonization, were prepared and examined as catalyst for the model reaction. To justify the observed different catalytic activities of the catalysts, their Pd loadings, leaching, and specific surface areas were compared. The results confirmed that tetrahedral MNPs coated with porous N‐rich carbon shell exhibited the best catalytic activity. The high catalytic activity of this catalyst was attributed to its high surface area and the interaction of N‐rich shell with Pd nanoparticles that led to the higher Pd loading and suppressed Pd leaching.     

Nickel(II) chloride as an efficient and useful catalyst for chemoselective thioacetalization of aldehydes

A wide variety of acyclic and cyclic dithioacetals can be prepared chemoselectively from the corresponding aldehydes by employing a catalytic amount of nickel(II) chloride in dry CH₂Cl₂-MeOH (5:1) at room temperature in good yields. Some of the major advantages of this procedure are high chemoselectivity, ease of operation, high yields and also compatibility with other protecting groups.     

Magnetic graphene nanocomposite as an efficient catalyst for hydrogenation of nitroarenes

Graphene-Fe₃O₄ nanocomposite（G-Fe₃O₄） was synthesized by a chemical co-precipitation method which was used as an efficient catalyst for the reduction of nitroarenes with hydrazine hydrate.The method has been applied to a broad range of compounds with different properties and the yields were in the range of 75%-92%.The G-Fe₃O₄ catalyst can be readily recovered and reused 5 times without significant loss of the catalytic activity.     

A highly efficient and reusable mesoporous supported Co(II) catalyst for chemoselective deprotection of aryl acetates

Chemoselective deprotection of aryl acetates is successfully carried out in excellent yield using a mesoporous silica-supported (Salen) Co(II) catalyst. The catalyst shows high thermal stability and also can be recovered and reused at least 10 times without any significant loss of its catalytic activity. The present process is environmentally benign and economical.     

Cobalt(II) schiff base functionalized mesoporous silica as an efficient and recyclable chemoselective acetalization catalyst

Cobalt(II) Schiff base functionalized mesoporous silica was synthesized from covalent attachment via the introduction of Co(OAc)₂ to salicylaldimine functionalized mesoporous silica. The catalyst proved to be chemoselective one for the acetalization of aldehydes to the corresponding acetals in alcohol. The immobilized catalyst can be easily recovered and reused for at least ten reaction cycles without significant loss of its catalytic activity.     

Yttrium triflate as an efficient and useful catalyst for chemoselective protection of carbonyl compounds

Carbonyl compounds have been successfully converted into their corresponding oxathiolane, dithiolane, and dithiane derivatives with 2-mercaptoethanol, 1,2-ethanedithiol, and 1,3-propanedithiol using catalytic amount of yttrium triflate. In addition, by using this catalyst, high chemoselective protection of carbonyl compounds has been achieved.     

Synergism of Pt nanoparticles and iron oxide support for chemoselective hydrogenation of nitroarenes under mild conditions

An efficient and low-cost supported Pt catalyst for hydrogenation of niroarenes was prepared with colloid Pt precursors and α-Fe₂O₃ as a support. The catalyst with Pt content as low as 0.2 wt% exhibits high activities, chemoselectivities and stability in the hydrogenation of nitrobenzene and a variety of niroarenes. The conversion of nitrobenzene can reach 3170 mol_conv h^?1 mol_Pt^?1 under mild conditions (30 °C, 5 bar), which is much higher than that of commercial Pt/C catalyst and many reported catalysts under similar reaction conditions. The spatial separation of the active sites for H₂ dissociation and hydrogenation should be responsible for the high chemoselectivity, which decreases the contact possibility between the reducible groups of nitroarenes and Pt nanoparticles. The unique surface properties of α-Fe₂O₃ play an important role in the reaction process. It provides active sites for hydrogen spillover and reactant adsorption, and ultimately completes the hydrogenation of the nitro group on the catalyst surface.     

Ni-nanoparticles: an efficient green catalyst for chemoselective reduction of aldehydes

A novel method for reduction of aromatic and heteroaromatic aldehydes with ammonium formate using Ni-nanoparticles is described. The Ni-nanoparticles act as a green catalyst for selective reduction of the aldehydic group in the presence of other functional groups, viz.: -NO₂, -CN and alkenes to give the corresponding alcohols in excellent yields.     

PEG-SO3H as an efficient and reusable catalyst for chemoselective synthesis of 1,1-diacetates

An efficient and convenient procedure of the synthesis of 1,1-diacetates from aromatic aldehydes and acetic anhydride under mild and solvent-free conditions at room temperature,in the presence of PEG-SO₃H is reported.PEG-SO₃H acts as a catalyst and can be recovered and reused eight times without apparent loss of its catalytic activity.     

Solid supported Pd(0): an efficient recyclable heterogeneous catalyst for chemoselective reduction of nitroarenes

Solid supported palladium(0) (SS-Pd) catalyzed highly chemoselective reduction of nitroarenes to the corresponding anilines was accomplished under a milder reaction condition. This catalyst showed high compatibility with various reducing agents (NaBH₄, Et₃SiH, and NH₂NH₂·H₂O) and a large number of reducible functional groups such as sulfonamide, amides, carboxylic acid, ester, alcohol, halide, hetero cycle, nitrile, alkene, carbonyl, O-benzyl, and N-benzyl were tolerated. Most of the reactions were clean and high yielding. The SS-Pd catalyst could be recycled up to seven runs without significant loss of activity.     

Microenvironment engineering of supported metal nanoparticles for chemoselective hydrogenation

Selective hydrogenation with supported metal catalysts widely used in the production of fine chemicals and pharmaceuticals often faces a trade-off between activity and selectivity, mainly due to the inability to adjust one factor of the active sites without affecting other factors. In order to solve this bottleneck problem, the modulation of the microenvironment of active sites has attracted more and more attention, inspired by the collaborative catalytic mode of enzymes. In this perspective, we aim to summarize recent advances in the regulation of the microenvironment surrounding supported metal nanoparticles (NPs) using porous materials enriched with organic functional groups. Insights on how the microenvironment induces the enrichment, oriented adsorption and activation of substrates through non-covalent interaction and thus determines the hydrogenation activity and selectivity will be particularly discussed. Finally, a brief summary will be provided, and challenges together with a perspective in microenvironment engineering will be proposed.

Insights on microenvironment engineering for metal nanoparticles using porous materials enriched with organic groups and how it determines the hydrogenation performance through non-covalent interaction are highlighted.     

有序介孔碳材料负载铂纳米粒子：用于硝基苯及其衍生物液相催化氢化的高效催化剂

介孔碳材料由于具有规整的孔道结构、表面疏水性、化学惰性、大的比表面积和大的孔体积等特点,在催化领域的应用备受关注,不仅可以直接用作催化剂,还可以作为催化剂载体负载金属活性中心并用于催化反应.介孔碳材料作为载体用于加氢反应已有报道,并且其催化活性明显优于活性炭材料.有序介孔碳材料的代表之一CMK-3可以经过SBA-15翻模合成.采用浸渍法将氯铂酸负载到CMK-3载体上,经过甲酸钠还原制得质量分数为5%的Pt/CMK-3催化剂.小角XRD谱表明CMK-3保留了p6mm对称性,介孔结构完好;从广角XRD谱可以看出,金属铂粒子的衍射峰比较宽,说明铂纳米粒子分散比较均匀. CO化学吸附和透射电镜(TEM)的表征结果进一步证明铂纳米粒子分散得比较均匀,平均粒子大小约为2.5 nm (CO化学吸附), EDX结果表明铂的实际担载量为4.7%.将Pt/CMK-3催化剂用于硝基苯及其衍生物的液相加氢反应中,发现溶剂对反应结果具有很大的影响.首先参考以前的工作,选用水和乙醇体积比9：1的混合溶液为溶剂.在298 K和4 MPa氢气条件下,50 mg催化剂可以将21 mmol硝基苯在10 min内转化98.4%,产物苯胺的选择性高于99%;活性明显高于商品化Pt/C催化剂(相同条件下转化率为88.7%).在此基础上,把Pt/CMK-3催化剂用于含有不同取代基的硝基苯衍生物的液相催化加氢反应,含有吸电子基团如氯取代的硝基苯衍生物转化率为(21.4%–77.7%);苯环上含有给电子基团如甲基时,硝基甲苯加氢反应的转化率为(83.3%–98.0%);而给电子能力更大的基团如甲氧基取代的硝基苯衍生物的转化率却并不高.一方面是由于电子效应导致氯取代的硝基苯衍生物活性偏低,另一方面是由于空间位阻导致邻位取代的硝基苯衍生物活性相对其它位置取代的衍生物转化率偏低.考虑到部分反应物在混合溶剂中溶解度较低,可能导致加氢反应过程受到影响,从而影响反应结果,所以又选用无水乙醇溶剂进行了比较.首先仍用50 mg催化剂于硝基苯催化加氢反应,发现在乙醇溶剂中,21 mmol硝基苯在5 min内可以完全转化;当把硝基苯的量增加到5倍时,转化率为22.2%,苯胺选择性高于99%.因此,在乙醇溶剂中将催化剂用量减半,结果在5 min内21 mmol硝基苯衍生物均完全转化为对应的芳香胺化合物;除了硝基氯苯发生脱氯副反应外,其它衍生物选择性都很高.为了更好地区分不同取代基硝基苯衍生物的加氢活性,将2-氯硝基苯和2-甲基硝基苯的用量增大至105 mmol,反应过程中保持氢气压力恒为4 MPa,并使反应在5 min后中止,此时测得2-氯硝基苯催化加氢的TOF值为28.3 s–1,而2-甲基硝基苯的TOF值高达43.8 s–1. X射线光电子能谱(XPS)显示Pt/CMK-3表面含有带一定正电的铂物种,推测此物种有助于吸附硝基的氧原子,从而活化底物,促进加氢反应的顺利进行.最后还考察了Pt/CMK-3催化剂在硝基苯加氢中的循环使用性能,发现催化剂可以循环使用至少14次,活性没有任何下降.对反应滤液进行ICP分析,发现滤液中并没有铂离子流失;对使用过的催化剂进行透射电镜表征也没有观察到铂粒子聚集现象,说明催化剂的稳定性良好.     

Ferrous methanesulfonate as an efficient and recyclable catalyst for chemoselective synthesis of 1,1-diacetate from aldehydes

Ferrous methanesulfonate catalysing the conversion of aromatic,heteroaromatic,unsaturated,and aliphatic aldehydes to 1,1- diacetates at room temperature under solvent-free condition has been developed.The catalytic activity of seventeen metal methanesulfonates was compared under the same condition,ferrous methanesufonate proved to be the best.It can be easily recovered and reused for several times without distinct deterioration in catalytic activity.During the competitive protection between a ketone and ...     

Tetrabutylammonium tribromide (TBATB) as an efficient generator of HBr for an efficient chemoselective reagent for acetalization of carbonyl compounds

Acyclic and cyclic acetals of various carbonyl compounds were obtained in excellent yields under a mild reaction condition in the presence of trialkyl orthoformate and a catalytic amount of tetrabutylammonium tribromide (TBATB) in absolute alcohol. Chemoselective acetalization of an aldehyde in the presence of ketone, unsymmetrical acetal formation, shorter reaction times, mild reaction conditions, the stability of acid-sensitive protecting groups, high efficiencies, facile isolation of the desired products, and the catalytic nature of the reagent make the present methodology a practical alternative.     

Au/FeOx-TiO2 as an efficient catalyst for the selective hydrogenation of phthalic anhydride to phthalide

<正>Au/FeO_x-TiO_2,prepared by deposition-precipitation method,is an efficient and stable catalyst for the liquid phase selective hydrogenation of phthalic anhydride to phthalide under mild reaction conditions.     

Luminescent silole nanoparticles as chemoselective sensors for Cr(VI)

Colloidal suspensions of 3-aminopropylmethyl(tetraphenyl)silole nanoparticles can be used as selective chemosensors for carcinogenic chromium(VI) analyte. Methylhydrosilole is functionalized by hydrosilation of allylamine, and the colloid is prepared by the rapid addition of water to a THF solution of the silole. The method of detection is through electron-transfer quenching of the fluorescence of the silole colloid (lambda(em) = 485 nm at 360 nm excitation) by the analytes, with hundred parts per billion detection limits. Stern-Volmer plots are linear up to 10 ppm in the case of chromium, but exhibit saturation behavior near 5-10 ppm for arsenic. Dynamic light scattering experiments and AFM measurements show the particle sizes to be around 100 nm in diameter and dependent on solvent composition, with a particle size dispersity of +/-25%. The fluorescence lifetimes of the silole in solution and colloid are approximately 31 ps and approximately 4.3 ns, respectively, while the silole has a lifetime of 6 ns in the bulk solid. A minimum volume fraction of 80% water is necessary to precipitate the colloid from THF, and the luminescence continues to rise with higher water fractions. Colloids in a pH 7 phosphate-buffered suspension show both higher sensitivity and greater selectivity (100-fold) for CrO4(2-) detection than for other oxoanion interferents, NO3-, NO2-, SO4(2-), and ClO4-.