Rhodium-Catalyzed Regio- and Diastereoselective [3+2] Cycloaddition of gem-Difluorinated Cyclopropanes with Internal Olefins

Direct synthesis of gem-difluorinated carbocyclic molecules represents a longstanding challenge in organic chemistry. Herein, a Rh-catalyzed [3+2] cycloaddition reaction between readily available gem-difluorinated cyclopropanes (gem-DFCPs) and internal olefins has been developed, enabling the efficient synthesis of gem-difluorinated cyclopentanes with good functional group compatibility, excellent regioselectivity and good diastereoselectivity. The resulting gem-difluorinated products can undergo downstream transformations to access various mono-fluorinated cyclopentenes and cyclopentanes. This reaction demonstrates the use of gem-DFCPs as a type of “CF₂” C3 synthon for cycloaddition under transition metal catalysis, which provides potential strategy for synthesizing other gem-difluorinated carbocyclic molecules.     

Metal Catalyzed Polymerization: From Stereoregular Poly(α-olefins) to Tailor-Made Biodegradable/Biorenewable Polymers and Copolymers

Metal catalyzed polymerizations are among the most important chemical reactions, accounting for the production of about 400 million tons per year of polymeric materials, 50 % of which are polyolefins. The CIRCC research units at the University of Salerno, founded by the late Professor Adolfo Zambelli, a coworker of Giulio Natta and a pioneer in the studies of stereospecific polymerization catalysts, has a consolidated expertise in this field. Although often considered a “mature” area of research, olefin polymerization catalysis continues to drive great interest of both industrial and academic scientists. On the other hand, strong political and economic pressure toward the development of “green” and possibly biodegradable alternatives to olefin-based polymers stimulated our group to direct increasing research efforts in the area of sustainable polymers. In this perspective, we focus on the most recent work from the CIRCC research units involved in homogeneous catalysis for polymerization of a variety of monomers, with the aim to address how the concepts and the expertise developed for olefin polymerization can be applied to the development of different metal-catalyzed polymerizations and copolymerizations. Of course, although the results are discussed in the frame of the most important literature contributions, a comprehensive review of such a wide and diversified topic is out of the scope of the paper. References to reviews covering the different types of metal catalyzed polymerizations are provided in each chapter.     

Preparation of selenofunctionalized heterocycles via iodosobenzene-mediated intramolecular selenocyclizations of olefins with diselenides

An intramolecular selenocyclizations of olefins mediated by a commercially available hypervalent iodine(III) reagent, PhIO, was developed. This method provided access to a wide range of selenenylated heterocycles under ambient conditions. The striking advantages of this protocol over all previous methods include mild reaction conditions, easy operation, good yields, high levels of functional group compatibility, large–scale application and suitability for the late-stage functionalization of complex molecules of biological importance.     

Recent Advances in Facile Liquid Phase Epoxidation of Light Olefins over Heterogeneous Molybdenum Catalysts

Molybdenum complexes are versatile and efficient for liquid phase olefin epoxidation reactions. Rational design of catalysts is critical to achieve high atom efficiency during epoxidation processes. Although liquid phase epoxidation has been a popular topic for decades, three key issues, (a) rational control of morphology of molybdenum nanoparticles, (b) manipulating metal‐support interaction and (c) altering electronic configuration at molybdenum center remains unsolved in this area. Therefore, in this paper, we have critically revised recent research progress on heterogeneous molybdenum catalysts for facile liquid phase olefin epoxidation in terms of catalyst synthesis, surface characterization, catalytic performance and structure‐function relationship. Furthermore, plausible reaction mechanisms will be systematically discussed with the aim to provide insights into fundamental understanding on novel epoxidation chemistry.     

Ru/CeO2催化剂催化苯乙烯氢甲氧基羰基化反应高选择性制备直链酯类化合物

酯类化合物在工业上具有广泛应用,例如可用于合成香水、调味剂(味精)、洗涤剂和表面活性剂等.其中,烯烃的氢烷氧基羰基化反应是一种合成酯类化合物的重要方法,其低消耗、100%的原子经济性和原料的易获得等优势使其在制备酯类化合物中成为一个有效且实际可行的方法.对于该反应,文献多采用Pd或Rh的络合均相催化剂,其中控制反应过程中直链酯类化合物(L)和支链酯类化合物(B)的选择性是一项颇具挑战性的课题.虽然目前可通过配体的设计和修饰来调节,但多集中在均相催化体系,因此在选择性调变方面的研究仍很欠缺.相对于均相催化,多相催化由于产物易分离和提纯、催化剂可循环使用等优势而逐渐引起了研究者的广泛关注.在多相催化体系中, Pd负载在强酸性树脂作为催化剂已被应用于苯乙烯氢甲氧基羰基化反应,但在该反应中支链酯类化合物为主要产物.因此,寻找一个可有效改善多相反应体系中选择性问题的方法是非常有意义的.在本研究工作中,我们分别以CeO2纳米颗粒(NP)、CeO2纳米棒(Rod)和CeO2纳米立方体为载体,利用浸渍法制备了Ru/CeO2、Ru/CeO2-rod和Ru/CeO2-cube三种催化剂,并进一步用于苯乙烯氢甲氧基羰基化反应.探究了CO压力、反应温度和反应时间对三种催化剂催化苯乙烯氢甲氧基羰基化反应的影响.结果表明, Ru/CeO2作为多相催化剂催化苯乙烯氢甲氧基羰基化反应时,苯乙烯选择性高于99%,直链酯选择性为83%,支链酯选择性为12%.机理研究表明,该反应为自由基机理.动力学分析表明,该反应的反应活化能为48.50 k Jmol^–1.结合三种催化剂的反应活性以及HRTEM结构表征结果可知,该反应中L/B比值与Ru的尺寸有较大关系.进一步的拉曼表征和NH3-TPD表征结果证明, Ru的尺寸与金属-载体之间的相互作用以及催化剂表面的氧空位浓度有直接关系.     

Cycloaddition reactions of benzyne with olefins

Some novel cycloaddition reactions based on benzyne and olefins have been developed.These reactions were performed in the absence of a transition metal catalyst,and they displayed good yields.These cycloaddition reactions of benzyne with olefins provide effective routes for synthesizing benzocyclobutenes,biaryl compounds and 9,10-dihydrophenanthrene derivatives.     

Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst for 1-hexene aromatization

The promotional effect of Fe-Mo species introduced into HZSM-5 (Zeolyst Int., SiO₂/Al₂O₃ ≈ 30) zeolite catalyst by the wetness impregnation method for the 1-hexene aromatization was investigated. The structure and catalytic performance for the aromatization of 1-hexene over xFeyMo-ZSM-5 catalysts in comparison with unmodified HZSM-5 catalysts were studied. The xFeyMo-ZSM-5 catalysts contain fixed loading (5 wt%) and variable Fe/Mo ratio. The catalysts were characterized by BET, ICP-AES, HRSEM-EDS, HRTEM, XRD, FTIR, H₂-TPR, NH₃-TPD, and pyridine DRIFT spectroscopy. The characterization data confirmed the existence of Fe and Mo species in the zeolite matrix. With Fe and Mo species implementation to HZSM-5 zeolite, the amount of the acid sites decreased, but the selectivities to C₉₊ aromatics increased. The catalyst evaluation was performed at 350 °C for 6 h on-stream at atmospheric pressure using a fixed-bed quartz tube reactor. The selectivity to products of different carbon number was affected by the Fe/Mo ratio within the zeolite. It was found the product distribution of grouped fractions of C₁–C₁₇₊ from the liquid product. The results indicate that the optimum ratio of Fe/Mo is 1–1.5. The highest selectivity for gasoline and distillate ranges was obtained for the 2.5wt%Fe2.5wt%Mo- and 3wt%Fe2wt%Mo-ZSM-5 samples, which was higher than that for parent HZSM-5 catalyst.     

Remarkable enhancement of aerobic epoxidation reactivity for olefins catalyzed by μ-oxo-bisiron(III) porphyrins under ambient conditions

With μ-oxo dimeric iron(III) porphyrins [(Fe^IIITPP)₂O] as catalyst, isobutylaldehyde as co-reductant, and dioxygen as oxidant, an efficient model system for epoxidation of olefins has been developed. Compared with mono-metalloporphyrins as catalyst, a remarkable enhancement of reactivity was obtained for the present olefin epoxidation system, in which the turnover number (TON) of the catalyst has doubled from about 700 million to 1400 million. Moreover, a plausible mechanism involving both binuclear and mononuclear intermediate has been proposed.     

Hypervalent iodine-mediated aminobromination of olefins in water

The PhI(OAc)₂-catalyzed aminobromination of electron-deficient olefins has been achieved in pure water with TsNH₂ and NBS as nitrogen and bromine sources, respectively. With a catalytic amount of PhI(OAc)₂, various olefins including α,β-unsaturated ketones, cinnamates, and cinnamides could be aminobrominated efficiently, giving the vicinal bromoamines in good yields and high regio- and diastereoselectivities. Utilizing water as solvent was crucial to realize this aminobromination reaction catalytically. The regioselectivity for the aminobromination of styrenes under the present aqueous conditions was also dramatically improved.     

Bipyridine‐Modulated Palladium‐Catalyzed Oxidative Heck‐Type Reactions of Arylboronic Acids with Olefins

We have demonstrated that 4,4′‐dimethyl 2,2′‐bipyridine as ligand for Pd(II) catalysts was very efficient for oxidative Heck‐type coupling reaction of arylboronic acids with olefins in DMA or CH₃CN under atm air at 80 °C. The presence of chelated bipyridine ligand isindispensable to achieve high reaction yields and to suppress the formation of biphenyl as homocoupled byproduct.