Redox‐Controlled Olefin (Co)Polymerization Catalyzed by Ferrocene‐Bridged Phosphine‐Sulfonate Palladium Complexes

The facile and reversible interconversion between neutral and oxidized forms of palladium complexes containing ferrocene‐bridged phosphine sulfonate ligands was demonstrated. The activity of these palladium complexes could be controlled using redox reagents during ethylene homopolymerization, ethylene/methyl acrylate copolymerization, and norbornene oligomerization. Specifically in norbornene oligomerization, the neutral complexes were not active at all whereas the oxidized counterparts showed appreciable activity. In situ switching between the neutral and oxidized forms resulted in an interesting “off” and “on” behavior in norbornene oligomerization. This work provides a new strategy to control the olefin polymerization process.     

Hetaryl- and heteroarylvinyl-substituted nitrofurans identified as non-cytotoxic selective antitubercular agents

New (E)-5-[2-(5-nitrofuran-2-yl)vinyl]-1,2,4-oxadiazoles and 5-(5-nitrofuran-2-yl)-1,2,4-oxadiazoles were synthesized via the base-promoted condensation of nitrofuran-containing acyl chlorides with amidoximes. Testing these compounds against Gram-negative E. coli, Gram-positive B. subtilis and S. aureus as well as M. tuberculosis HRv37 strain revealed three compounds being selectively antimycobacterial. None of these compounds displayed any cytotoxicity towards human pancreatic epithelioid carcinoma cell line, PANC-1.     

Large-Scale Synthesis of a Niche Olefin Metathesis Catalyst Bearing an Unsymmetrical N-Heterocyclic Carbene (NHC) Ligand and its Application in a Green Pharmaceutical Context

A large-scale synthesis of known Ru olefin metathesis catalyst VII featuring an unsymmetrical N-heterocyclic carbene (NHC) ligand with one 2,5-diisopropylphenyl (DIPP) and one thiophenylmethylene N-substituent is reported. The optimised procedure does not require column chromatography in any step and allows for preparation of up to 0.5 kg batches of the catalyst from simple precursors. The application profile of the obtained catalyst was studied in environmentally friendly dimethyl carbonate (DMC). Although VII exhibited low efficiency in cross-metathesis (CM) with electron-deficient partners, good to excellent results were noted for substrates featuring easy to isomerise C−C double bonds. This includes polyfunctional substrates of medicinal chemistry interest, such as analogues of psychoactive 5F-PB-22 and NM-2201 and two PDE5 inhibitors—Sildenafil and Vardenafil. Finally, a larger scale ring-closing metathesis (RCM) of a Vardenafil derivative was conducted in DMC, allowing for straightforward isolation of the expected product (23 g) in high yield and with low Ru contamination level (7.7 ppm).     

通过SAPO-34分子筛笼中引入金属物种提升甲醇制烯烃反应中乙烯选择性

低碳烯烃(乙烯、丙烯)是化学工业极其重要的基本原料.甲醇制烯烃(MTO)反应是重要的烯烃生产石油替代路线.其中,磷酸硅铝类SAPO-34分子筛在MTO反应中表现出优异的低碳烯烃选择性.与丙烯相比,乙烯具有更高的经济附加值,因此提升MTO反应中乙烯的选择性有着重要的意义.本文采用传统离子交换法(CIE)、模板辅助离子引入法(TII)和醇相离子交换法(AIE)对SAPO-34分子筛进行金属Zn、Cu改性,利用多种表征手段对金属Zn、Cu改性SAPO-34分子筛的物理结构、化学组成、金属物种状态与分布、酸性及扩散性质等进行表征.首先,对金属Zn、Cu改性SAPO-34分子筛的物理结构和化学组成进行分析.X射线衍射表明,相比AIE法,CIE法和TII法改性基本保持SAPO-34分子筛的结晶度.X射线荧光分析表明,相比Co、Ni,金属Zn、Cu更易引入SAPO-34分子筛.N2物理吸附-脱附表明,CIE法改性能够保持SAPO-34分子筛的BET比表面积和微孔孔容.其次,考察了金属Zn、Cu改性SAPO-34分子筛中金属物种的状态.氢气-程序升温还原(H2-TPR)和X射线光电子能谱(XPS)结果表明,Zn物种主要以孤立态的Zn2+阳离子形式存在.H2-TPR、XPS、紫外-可见光谱和电子顺磁共振谱结果表明,Cu物种主要以孤立态的Cu2+阳离子以及部分CuO形式存在.继而对金属Zn、Cu改性SAPO-34分子筛中金属物种的分布进行表征.XPS表明,Zn阳离子改性的SAPO-34表层富硅、富Zn,呈类核壳结构;XPS和扫描式电镜-能量色散X射线光谱结果表明,Cu物种在Cu改性SAPO-34分子筛中均匀分布.进一步研究了金属Zn、Cu改性SAPO-34分子筛中酸性的变化.氨气-程序升温脱附和核磁共振氢谱结果表明,Zn、Cu改性SAPO-34酸性位点的酸量降低.最后,对金属Zn、Cu改性SAPO-34分子筛的扩散性质进行分析.智能重量分析表明,Zn、Cu阳离子的引入降低探针分子(乙烷、丙烷)的扩散系数,推断Zn、Cu阳离子的引入增加对MTO反应产物的扩散限制.热重表明,Zn阳离子改性SAPO-34分子筛反应初期积炭量略微增加.综上所述,Zn阳离子改性SAPO-34催化剂表层富硅、富Zn,呈现类核壳结构.Zn阳离子的引入增加对MTO反应产物的扩散限制,而且Zn阳离子的引入促进MTO反应初始阶段的碳沉积.因此,Zn阳离子改性SAPO-34分子筛显著增加MTO反应产物的扩散限制,对分子尺寸较大的反应产物的扩散限制更为明显,从而提高MTO反应初始阶段的乙烯选择性,增大乙烯/丙烯比.     

过渡金属催化的醇类脱氧脱水反应

开发和利用环境保护型的可再生新能源是缓和与解决能源环境问题的重要举措.生物质可作为燃料和可再生平台化学品的来源.高含氧量与过度官能化的生物质原料不能直接使用,因此降低生物质原料的含氧量并将其转化为燃料与增值化学品的方法是实现生物质能广泛应用的关键.还原脱氧的方法主要有热解、水解、氢解、脱羧/脱羰反应、加氢脱氧与脱氧脱水反应等.本综述详细介绍了铼、钼、钒、钌等四种过渡金属催化的由二元醇及多元醇制备相应烯烃的脱氧脱水反应,主要从均相催化、还原剂使用、机理研究和非均相催化等方面做了多角度的总结.铼催化的脱氧脱水反应具有选择性好和烯烃产率高等优点,钼、钒、钌等金属是可能替代昂贵的铼金属的催化剂.     

The Effect of Residence Time Distribution on the Slurry‐Phase Catalytic Ethylene Polymerization: An Experimental and Computational Study

This work is focused on the development and validation of a model accounting for the impact of the reactor residence time distribution in well‐stirred slurry‐phase catalytic polymerization of ethylene. Particle growth and morphology are described through the Multigrain model, adopting a two‐site model for the catalyst and a conventional kinetic scheme. Particle size distribution and polymer properties (average molecular weights and polydispersity) are computed as a function of particle size through a segregated model, assuming that neither breakage nor aggregation occur. Reactors are modeled by means of fundamental mass conservation equations. The model is applied to a system constituted by a series of two ideal continuous stirred tank reactors, where the synthesis of polyethylene with bimodal molecular weight distribution is performed, employing the initial catalyst size distribution as the only adjustable parameter. The model provides insights at the single particle scale for each specific size, thus highlighting the inhomogeneity which arises from the synergic effects of chemical kinetics and residence time distributions in both reactors. The satisfactory agreement between model results and experimental data, in terms of particle size distribution and average molecular weights, confirmed the suitability of the model and underlying assumptions.     

One‐Step Synthesis of Hybrid Core–Shell Metal–Organic Frameworks

Epitaxial growth of MOF‐on‐MOF composite is an evolving research topic in the quest for multifunctional materials. In previously reported methods, the core–shell MOFs were synthesized via a stepwise strategy that involved growing the shell‐MOFs on top of the preformed core‐MOFs with matched lattice parameters. However, the inconvenient stepwise synthesis and the strict lattice‐matching requirement have limited the preparation of core–shell MOFs. Herein, we demonstrate that hybrid core–shell MOFs with mismatching lattices can be synthesized under the guidance of nucleation kinetic analysis. A series of MOF composites with mesoporous core and microporous shell were constructed and characterized by optical microscopy, powder X‐ray diffraction, gas sorption measurement, and scanning electron microscopy. Isoreticular expansion of microporous shells and orthogonal modification of the core was realized to produce multifunctional MOF composites, which acted as size selective catalysts for olefin epoxidation with high activity and selectivity.     

Gas‐Phase Olefin Polymerization in the Presence of Supported and Self‐Supported Ziegler‐Natta Catalysts

The RPPFM is employed to describe the gas‐phase catalytic polymerization of ethylene in the presence of supported or self‐supported Z‐N catalysts. Numerical simulations are carried out to analyze the effect of the catalyst type on the polymerization rate, particle overheating and the average molecular polymer properties of the polyolefin. It is shown that non‐porous, self‐supported Ziegler‐Natta catalysts exhibit higher particle growth rates and lower particle overheating. The average molecular weight of polyethylene produced by both catalysts is almost identical. Depending on particle size and polymer crystallinity, the average monomer solubility and the effective monomer diffusivity can significantly vary.