K-Sn-Pd/SiO2催化剂上甲苯气相乙酰氧基化制乙酸苄酯

 采用分步初湿浸渍法制备了K-Sn-Pd/SiO2催化剂,研究了该催化剂对甲苯乙酰氧基化反应制乙酸苄酯的催化活性. 发现锡氧化物和乙酸钾对催化剂活性有很大的促进作用,而氯离子对催化剂活性有抑制作用,PdCl2和锡氧化物的负载顺序对催化剂的活性有显著的影响. 在先负载PdCl2再负载锡氧化物所得的K-Sn-Pd/SiO2催化剂上,当反应温度为453 K,混合原料气空速为1634 h-1时,甲苯的转化率达到8.00%,乙酸苄酯的选择性为84%.     

二维核磁共振法研究线型聚乙二醇与树枝状聚苄醚形成的三嵌段共聚物

嵌段共聚物是由几个不同的高分子链段通过化学键相连所构成的 .在合成方法上一般是通过几类不同的活性聚合 ,调控单体的加料次序或者通过不同的大分子链段末端的反应活性点偶联而成[1～ 3 ] .所形成的化学键将嵌段共聚物中不相溶的几段相连 ,于是在特定的条件下就产生了微相分离的现象 ,继而可以在 1 0～ 1 0 0nm尺度范围内形成各种各样的微区结构[4,5] .在过去的几十年里 ,研究的重点是认定嵌段共聚物的微区结构和研究微相分离的动力学 ,已发表了大量重要的结果 ,至今仍然是高分子科学中的热门课题 .非常重要的一点是 ,正是由于不同的高分…     

Controllable Assembly of Vanadium-Containing Polyoxoniobate-Based Materials and Their Electrocatalytic Activity for Selective Benzyl Alcohol Oxidation

During the controllable synthesis of two vanadium-containing Keggin-type polyoxoniobates (PONbs), [Ni(en)₂]₅[PNb₁₂O₄₀(VO)₅](OH)₅·18H₂O (1) and [Ni(en)₃]₅[PNb₁₂O₄₀(VO)₂]∙17H₂O (2, en = ethylenediamine) are realized by changing the vanadium source and hydrothermal temperature. Compounds 1 and 2 have been thoroughly characterized by single-crystal X-ray diffraction analysis, FT-IR spectra, X-ray photoelectron spectrum (XPS), powder X-ray diffraction (PXRD), etc. Compound 1 contains a penta-capped Keggin-type polyoxoniobate {PNb₁₂O₄₀(VO)₅}, which is connected by adjacent [Ni(en)₂]²⁺ units into a three-dimensional (3D) organic-inorganic framework, representing the first nickel complexes connected vanadoniobate-based 3D material. Compound 2 is a discrete di-capped Keggin-type polyoxoniobate {PNb₁₂O₄₀(VO)₂} with [Ni(en)₃]²⁺ units as counter cations. Compounds 1 and 2 have poor solubility in common solvents and can keep stable in the pH range of 4 to 14. Notably, both 1 and 2 as electrode materials are active for the selective oxidation of benzyl alcohol to benzaldehyde. Under ambient conditions without adding an alkaline additive, compound 1 as a noble metal free electrocatalyst can achieve 92% conversion of benzyl alcohol, giving a Faraday efficiency of 93%; comparatively, 2 converted 79% of the substrate with a Faraday efficiency of 84%. The control experiments indicate that both the alkaline polyoxoniobate cluster and the capped vanadium atoms play an important role during the electrocatalytic oxidation process.     

η3‐Benzyl‐Nickel‐Diimine Complex: Synthesis and Catalytic Properties in Ethylene Polymerization

The oxidative addition of benzyl chloride to Ni(cod)₂ in the presence of 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediimine followed by chloride abstraction affords [(η³‐CH₂C₆H₅)Ni(α‐diimine)][PF₆] (α‐diimine = 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediimine) in 70% yield. The complex is active in ethylene polymerization in the presence of methylaluminoxane and under mild reaction conditions. The polyethylenes obtained are highly branched, have very low densities, do not show T_m or measurable crystallinity and have molecular weights ranging from 80 × 10³ to 290 × 10³ g · mol⁻¹.

     

Cross-Electrophile Coupling between Two Different Tosylates Enabled by Nickel/Palladium Cooperative Catalysis

Cross-electrophile coupling reactions are efficient for the construction of carbon-carbon bonds under relatively mild conditions, and hence widely used for making new molecules. Among various electrophiles, the cross-electrophile coupling reaction between two different tosylates has been rarely studied. Herein, we present a cross-electrophile coupling of gem-difluoroalkenyl tosylate (C(sp²)−OTs) and α-CF₃ benzyl tosylate (C(sp³)−OTs) by nickel/palladium cooperative catalysis. Mechanistic investigation indicated that the activation of C(sp²)−OTs bond and C(sp³)−OTs bond was facilitated by nickel and palladium respectively.