Iron(II) complexes with bio-inspired N,N,O ligands as oxidation catalysts: olefin epoxidation and cis-dihydroxylation

The Rieske dioxygenases are a group of non-heme iron enzymes, which catalyze the stereospecific cis-dihydroxylation of its substrates. Herein, we report the iron(II) coordination chemistry of the ligands 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its neutral propyl ester analogue propyl 3,3-bis(1-methylimidazol-2-yl)propionate (PrL1). The molecular structures of two iron(II) complexes with PrL1 were determined and two different coordination modes of the ligand were observed. In [Fe(II)(PrL1)(2)](BPh(4))(2) (3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [Fe(II)(PrL1)(2)(MeOH)(2)](OTf)(2) (4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cis arrangement with respect to each other. Complex 4 is a close structural mimic of the crystallographically characterized non-heme iron(II) enzyme apocarotenoid-15-15'-oxygenase (APO). The mechanistic features of APO are thought to be similar to those of the Rieske oxygenases, the original inspiration for this work. The non-heme iron complexes [Fe(II)(PrL1)(2)](OTf)(2) (2) and [Fe(II)(PrL1)(2)](BPh(4))(2) (3) were tested in olefin oxidation reactions with H(2)O(2) as the terminal oxidant. Whereas 2 was an active catalyst and both epoxide and cis-dihydroxylation products were observed, 3 showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction.     

稀土改性CuO-ZnO-ZrO_2/SAPO-34分子筛催化CO_2加氢合成低碳烯烃

采用共沉淀法分别制备了Y_2O_3,La_2O_3和Ce O_2改性的Cu O-Zn O-Zr O_2,表征结果表明,稀土改性的Cu O-Zn O-Zr O_2分散性良好,比表面积增大.将稀土改性的Cu O-Zn O-Zr O_2与SAPO-34分子筛机械混合用于催化CO_2加氢一步法合成了低碳烯烃,在反应温度400℃,压力3 MPa,空速为1800 m L·g~(-1)_(cat)·h~(-1),氢碳体积比为3∶1,Ce O_2改性Cu O-Zn O-Zr O_2与SAPO-34质量比为1∶1,催化剂用量为1.0 g时,CO_2的单程转化率为54.6%,低碳烯烃的选择性和产率分别为51.1%和27.9%.     

Regio- and stereoselective co-iodination of olefins using NH4I and Oxone

A simple, efficient, and environmentally benign protocol for the synthesis of vicinal iodohydrins and iodoesters from olefins using NH₄I and Oxone in CH₃CN/H₂O (1:1) and dimethylformamide (DMF) / dimethylacetamide (DMA), respectively, without employing a catalyst at room temperature is described. Regio- and stereoselective iodohydroxylation and iodoesterification of various olefins with anti fashion, following Markonikov’s rule, was achieved and the corresponding products were obtained in good to excellent yields. In addition, 1,2-disubstituted olefins afforded excellent diastereoselectivity.     

NHC‐CAAC Heterodimers with Three Stable Oxidation States

The synthesis of N‐heterocyclic carbene (NHC)–cyclic (alkyl)(amino) carbene (CAAC) heterodimers is presented. As the free carbenes do not react together in solution, the synthetic approach involves the addition of a free NHC to a cyclic iminium salt, which results in the formation of the protonated heterodimer. Subsequent deprotonation leads to the isolation of the corresponding mixed Wanzlick dimers. One‐ and two‐electron oxidations of these triazaolefins result in the formation of stable cationic radicals and bis(cations), respectively, which have been isolated and fully characterized. Cyclic voltammetry, UV/Vis spectroscopy, spin density, and DFT calculations suggest that these heterodimers feature complementary electronic properties to tetrathiafulvalenes (TTFs).     

烯烃光敏氧化反应机理——Ⅲ.丙烯与单重态氧Ene反应途径的解析

用MINDO/3法对丙烯与单重态氧Ene反应机理进行了详细研究。利用Fukui提出的IRC理论计算了整个反应途径。计算结果预期反应是分步进行的,且经由桥环过氧化物中间体。通过沿反应途径的分析,对反应过程中,反应物间的相互作用的情况,立体化学等进行了较为详细的讨论。     

负载型中孔分子筛上苯与长链烯烃烷基化反应

在合成纯硅及含铝MCM-41中孔分子筛基础上,制备负载PW12、SiW12及PMo12杂多酸的催化剂。用XRD、N2吸附和苯与1-十二烯烷基化反应对几种催化剂进行表征。结果表明,与HY、HM和Hβ分子筛相比,HAlMCM-41和HSiMCM-41中孔分子筛具有较好的线性烷基苯选择性,其苯基十二烷异构体分布优于HY而不及HM和Hβ分子筛;负载型中孔分子筛催化剂具有杂多酸分散性好、比表面积大和孔径分布集中的性质,与载体相比其催化活性明显提高;关于催化活性,负载型催化剂载体或负载杂多酸种类比较结果为HAlMCM-41>HSiMCM-41、PW12>SiW12>PMo12,其中SiW12HAlMCM-41催化剂的苯基十二烷选择性和异构体分布为最佳。     

铑催化不对称氢化官能烯烃的进展--单齿磷配体的兴起

本文比较全面而又简要地综述了铑催化不对称氢化官能烯烃的历史发展过程,对最近兴起的单齿磷配体进行重点论述,并对该领域今后发展方向作了富有建设性的展望.     

ZrO2晶相对ZnO/ZrO2+SAPO-34双功能催化剂上合成气制烯烃反应的影响

烯烃是重要的化工原料,目前主要通过石油催化裂化得到.随着石油资源的消耗以及人们对烯烃需求的日益增长,开发非石油路线制取烯烃势在必行.合成气可以从煤、天然气和生物质等获得,由合成气作为重要的C1平台分子一步制取烯烃(STO)的过程受到了广泛关注.将合成气制甲醇/二甲醚的金属催化剂与甲醇制烯烃的分子筛催化剂耦合得到的混合双...     

Exocyclic Olefinic Maleimides: Synthesis and Application for Stable and Thiol‐Selective Bioconjugation

Michael addition reactions between biological thiols and endocyclic olefinic maleimides are extensively used for site‐specific bioconjugation. The resulting thio‐succinimidyl linkages, however, lack stability because of their susceptibility to thiol exchange. Reported herein is that in contrast to their endocyclic counterparts, exocyclic olefinic maleimides form highly stable thio‐Michael adducts which resist thiol exchange at physiological conditions. A high‐yielding approach for synthesizing a variety of exocyclic olefinic maleimides, by 4‐nitrophenol‐catalyzed solvent‐free Wittig reactions, is reported. Mechanistic studies reveal that the catalyst facilitates the formation of the Wittig ylide intermediate through sequential proton donation and abstraction. Overall, this report details an improved thiol bioconjugation approach, a facile method for synthesizing exocyclic olefinic maleimides, and demonstrates that phenolic compounds can catalyze ylide formation.     

Effect of Phenyl CI Substituent Position on the Catalytic Performance for Olefin Epoxidation of Tetraphenylmetalloporphyrins

以苯乙烯、环己烯和反式二苯乙烯为烯烃底物,以双氧水、叔丁基过氧化氢和异丙苯过氧化氢为氧化剂,以苯环上对位和邻位氯取代的四苯基金属卟啉为仿生催化剂,对烯烃的催化环氧化反应进行了对比研究.讨论了不同氯取代位的四苯基金属卟啉对烯烃环氧化性能的影响.实验结果表明,在没有助催化剂存在下,邻位氯代的四（2,6-二氯苯基）铁（锰）卟啉对烯烃的环氧化具有优异的催化性能,烯烃底物的转化率和环氧选择性都比对位氯代的四苯基铁（锰）卟啉高,且反应条件温和.其中FeⅢ（TDCPP）Cl的催化性能最好,环氧化选择性最高,催化氧化苯乙烯时,环氧苯乙烷的选择性达到了90.4%.相同金属离子不同配体的金属卟啉传递氧原子的能力为TDCPP〉T（p-Cl）PP〉TPP.氧化剂的结构对环氧化物的选择性有较大影响.过氧键连有吸电子基团的异丙苯过氧化氢对环氧化物的选择性最高.根据实验结果,对金属卟啉催化环氧化机理进行了分析.