钛氧纳米管固载Rh催化剂催化氰基烯烃氢甲酰化反应性能

为了调控含碱性基团功能烯烃的催化氢甲酰化反应,设计合成了不同表面酸性的钛氧纳米管和Zr-掺杂钛氧纳米管负载Rh催化剂（Rh/TNTs,Rh/Zr-TNTs）。用XRD、XPS、FT-IR、TEM和低温N2吸脱附等对所合成的催化剂进行了结构及组成表征。催化剂没有显现出与Rh和Zr相关的XRD衍射峰,Rh在纳米管中高度分散;Zr-掺杂钛氧纳米管的比表面积比纯钛氧纳米管的要高,催化剂的比表面积随着载Rh量的增加而减小,其中Rh0百分率也会降低,催化剂中Rh能对CO进行化学吸附。所合成的催化剂能有效地催化氰基烯烃氢甲酰化,催化活性随载Rh量而变化,最佳值为0.13 w;提高催化温度虽能增加2-甲基-3-丁烯腈的转化率,但也有利于它的异构化;Rh/Zr-TNTs表面更强的B酸性有利于催化反应生成直链产物醛,负载催化剂能表现出良好的协同作用。     

铑催化吲哚C(4)—H选择性活化构建氮杂-螺[4,5]吲哚骨架※

螺环吲哚是天然产物和药物化学中的一类重要骨架, 通过导向基团导向的C—H键活化反应已经成为构建螺环吲哚的重要方法. 目前在吲哚的吡咯片段上引入螺环结构已经比较成熟, 然而在吲哚的苯环片段上引入螺环还存在挑战. 以过渡金属铑催化, 选择性地活化吲哚C(4)—H键, 高效构建了氮杂-螺[4,5]吲哚骨架.     

碳纳米管负载铑催化剂上丙烯氢甲酰化

Effect of carbon nanotubes, as a novel support material, on the performance of Rh-catalyst supported by them was studied. Catalysts based on carbon nanotubes, SiO2, carbon molecular sieves, active carbon, and GDX-l02(a copolymer of styrene with divinylbenzene),were prepared, and their catalytic behaviors for propene hydroformylation were investigated and compared. The results showed that, over the carbon nanotubes-supported Rh-catalyst, C3H6 conversion and regioselectivity of butyric aldehyde (represented by n/i, a ratio of n-butyric aldehyde to its isomer, i-butyric aldehyde, in the products) were pronouncedly improved: the average turnover frequency(TOF) for the catalytic hydroformylation of propene was 0.079 s-1 at 393K, which was 2.1 times faster than that over the Rh catalyst based on SiO2, and the n/i ratio of the aldehyde products reached to 11.6, which was 1.9 times higher than that over the catalyst based on SiO2. The roles of six-membered C-ring at the surface of the carbon-nanotubes on the stability of the catalytically active Rh-complexes and of the tubular nano-channel on the spatiospecific seletivity of reaction intermediate state and butyric aldehyde produced were discussed.     

Synthesis of C_2 oxygenated compounds from syngas in supercritical cyclohexane

Catalytic synthesis of C2 oxygenated compounds from syngas in supercritical cyclohexane was reported in this paper. The effect of the molar ratio of media to feed on the conversion and selectivity was mainly discussed. The results showed that the selectivity of C2 oxygenated compounds in supercritical cyclohexane was greatly improved, and the by-products of acetic acid, ace tic ester and alkanes were efficiently suppressed. Although the CO conversion was slightly declined, the space-time yield of C2 oxygenated compounds basically kept the constant at high media/feed ratio.     

A comparative theoretical study on CO insertion into Rh–C bond

A DFT study on CO insertion into Rh–C(alkylethyl, ethenyl, 2-propenyl, trans-propenyl, cis-propenyl, and allyl) bonds were carried out comprehensively. All structures were optimized completely and the mechanism of the CO insertion was discussed in detail. The present results indicated that except for the CO insertion into Rh–C(allyl), other CO insertions were feasible from the thermodynamics point of view. The CO insertion into Rh–C(cis-propenyl) was the easiest process with 24.42 kJ/mol of the lowest activation free energy and the most difficult was the CO insertion into Rh–C(allyl). Also, entropy played a critical role in the CO insertion except for the CO insertion into Rh–C(ethenyl).     

C-H键活化反应的密度泛函理论模拟对简化模型的评估

采用密度泛函理论方法, 模拟了Rh(PPh₃)₃Cl催化的C-H键活化/C-C键偶联反应. 将反应机理分为C-H键活化、 迁移插入和还原消除3个过程进行讨论. 计算结果表明, 势能面的最高点为迁移插入的过渡态, 相对于初始原料的自由能为108.3 kJ/mol. 为了探索简化计算模型对模拟反应机理的影响, 使用2种模型催化剂Rh(PMe₃)₃Cl和Rh(PH₃)₃Cl表征相同的反应过程, 结果表明配体简化模型不合理, 主要是因为PPh₃配体的空间效应和熵效应非常明显.