Iridium-Catalyzed Silylation of Five-Membered Heteroarenes: High Sterically Derived Selectivity from a Pyridyl-Imidazoline Ligand

The steric effects of substituents on five-membered rings are less pronounced than those on six-membered rings because of the difference in bond angles. Thus, the regioselectivities of reactions of five-membered heteroarenes that occur with selectivities dictated by steric effects, such as the borylation of C−H bonds, have been poor in many cases. We report that the silylation of five-membered-ring heteroarenes occurs with high sterically derived regioselectivity when catalyzed by the combination of [Ir(cod)(OMe)]₂ (cod=1,5-cyclooctadiene) and a phenanthroline ligand or a new pyridyl-imidazoline ligand that further increases the regioselectivity. The silylation reactions with these catalysts produce high yields of heteroarylsilanes from functionalization at the most sterically accessible C−H bonds of these rings under conditions that the borylation of C−H bonds with previously reported catalysts formed mixtures of products or products that are unstable. The heteroarylsilane products undergo cross-coupling reactions and substitution reactions with ipso selectivity to generate heteroarenes that bear halogen, aryl, and perfluoroalkyl substituents.     

Nanocatalysts for Suzuki cross-coupling reactions

This critical review deals with the applications of nanocatalysts in Suzuki coupling reactions, a field that has attracted immense interest in the chemical, materials and industrial communities. We intend to present a broad overview of nanocatalysts for Suzuki coupling reactions with an emphasis on their performance, stability and reusability. We begin the review with a discussion on the importance of Suzuki cross-coupling reactions, and we then discuss fundamental aspects of nanocatalysis, such as the effects of catalyst size and shape. Next, we turn to the core focus of this review: the synthesis, advantages and disadvantages of nanocatalysts for Suzuki coupling reactions. We begin with various nanocatalysts that are based on conventional supports, such as high surface silica, carbon nanotubes, polymers, metal oxides and double hydroxides. Thereafter, we reviewed nanocatalysts based on non-conventional supports, such as dendrimers, cyclodextrin and magnetic nanomaterials. Finally, we discuss nanocatalyst systems that are based on non-conventional media, i.e., fluorous media and ionic liquids, for use in Suzuki reactions. At the end of this review, we summarise the significance of nanocatalysts, their impacts on conventional catalysis and perspectives for further developments of Suzuki cross-coupling reactions (131 references).     

环钯化合物在Heck反应中的应用研究

钯催化交叉偶联反应在化学工业、合成天然产物及生物活性物质中有着广泛的应用。催化剂体系是交叉偶联反应研究的核心。环钯化合物结构简单、性能稳定,在催化交叉偶联反应中具有高活性、高选择性,引起研究者们的极大关注,不断有新的环钯化合物被合成出来,其催化性能也得到了研究。本文综述了环钯化合物的合成方法及其在Heck反应中的应用。     

环钯化合物在Heck反应中的应用研究

钯催化交叉偶联反应在化学工业、合成天然产物及生物活性物质中有着广泛的应用.催化剂体系是交叉偶联反应研究的核心.环钯化合物结构简单、性能稳定,在催化交叉偶联反应中具有高活性、高选择性,引起研究者们的极大关注,不断有新的环钯化合物被合成出来,其催化性能也得到了研究.本文综述了环钯化合物的合成方法及其在Heck反应中的应用.     

金属锌在有机合成反应中的应用

综述了近年来以金属锌作为还原剂的各种反应，以及它在有机合成中的应用。 讨论了金属锌在催化剂的作用下，还原碳碳、碳氮、碳氧重键及碳氧、碳硫、碳卤 等单键的还原和偶联。     

Monoligated palladium species as catalysts in cross-coupling reactions

Palladium-mediated cross-coupling reactions are attractive organometallic transformations for the generation of C--C, C--N, C--O, and C--S bonds. Despite being widely employed in small-scale syntheses, cross-coupling reactions have not found important industrial applications because until recently, only reactive aryl bromides and iodides could be used as substrates. These substrates are generally more expensive and less widely available than their chloride counterparts. Over the past few years, new catalytic systems with the ability to activate unreactive and sterically hindered aryl chlorides have been developed. The new catalysts are based on palladium complexes that contain electron-rich and bulky phosphine or carbene ligands. The enhanced reactivity observed with these new systems has been attributed to the formation of unsaturated and reactive [PdL] species which can readily undergo oxidative addition reactions with ArX to yield [Pd(Ar)X(L)].     

Photoactive Nickel Complexes in Cross-Coupling Catalysis

Transition metal catalyzed cross-coupling reactions are important in chemical synthesis for the formation of C−C and C-heteroatom bonds. Suitable catalysts are frequently based on palladium or nickel, and lately the cheaper and more abundant first-row transition metal element has been much in focus. The combination of nickel catalysis with photoredox chemistry has opened new synthetic possibilities, and in some cases electronically excited states of nickel complexes play a key role. This is a remarkable finding, because photo-excited metal complexes are underexplored in the context of organic bond-forming reactions, and because the photophysics and the photochemistry of first-row transition metal complexes are underdeveloped in comparison with their precious metal-based congeners. Consequently, there is much potential for innovation at the interface of synthetic-organic and physical-inorganic chemistry. This Minireview highlights recent key findings in light-driven nickel catalysis and identifies essential concepts for the exploitation of photoactive nickel complexes in organic synthesis.     

Palladium-catalyzed C-N bond formation via direct C-H bond functionalization. Recent developments in heterocyclic synthesis

The formation of carbon-nitrogen bonds by reaction between a nitrogen atom and an unactivated carbon-hydrogen bond is a highly atom-economical process that attracted the attention of the chemists in the last two decades. The widely useful amination and hydroamination reactions, which furnish acyclic or cyclic products, give access to various nitrogen-containing basic and fine chemicals. This review highlights recent progress in the development of palladium-catalyzed reactions that occur by direct functionalization of simple carbon-hydrogen bonds to give heterocyclic products. Pd(0)- and Pd(II)-catalyzed reactions are described separately, emphasizing the different behavior of the metal in these two oxidation states.     

氧化铟基纳米催化剂用于二氧化碳选择性加氢的研究进展

二氧化碳选择性加氢反应不仅能减少二氧化碳排放, 而且能够制备多种含碳产物, 可以作为生产高附加价值化学品与燃料的平台化合物. 然而, 由于二氧化碳的高化学惰性、 碳-碳偶联过程的高能垒和诸多的竞争反应, 开发高效的纳米催化剂以促进二氧化碳的活化并转化为多样性的产物显得至关重要. 最近, 基于氧化铟的纳米催化剂在催化二氧化碳加氢方面受到广泛关注, 主要由于其成本低廉, 且具有丰富的氧缺陷位点, 可有效吸附并活化二氧化碳和氢气. 为深入了解反应机理并设计更高性能的潜在纳米催化剂, 需对氧化铟基纳米催化剂在二氧化碳加氢方面的研究进展进行总结. 本综述首先总结了不同晶型的氧化铟及其与金属氧化物或金属纳米粒子形成的复合催化剂用于催化二氧化碳选择性加氢制备C1产物的性能. 随后, 探讨了氧化铟与不同类型的沸石的复合物用于催化二氧化碳加氢制备C₂₊产物的性能. 最后, 提出了目前氧化铟基纳米催化剂在催化二氧化碳选择性加氢方面存在的挑战和未来的发展方向. 希望本文能够为设计具有高活性、 高选择性和高稳定性催化二氧化碳加氢的新型氧化铟基纳米催化剂提供一些思路.     

铜催化碳杂偶联反应的新进展

某些过渡金属可催化亲电性不饱和碳与含活泼氢的氮、氧、硫、碳原子直接成键,这种交叉偶联反应是现代有机合成中重要的手段之一.与钯、镍等过渡金属相比,铜是一种廉价且毒性低的金属,用铜来催化这些交叉偶联反应不仅可以节省贵金属的消耗,降低成本,而且可以减少对环境的污染,促进绿色化学的发展.对铜催化碳杂键偶联反应的最新研究进展做了综述。     

Recyclable Catalysts for Alkyne Functionalization

In this review, we present an assessment of recent advances in alkyne functionalization reactions, classified according to different classes of recyclable catalysts. In this work, we have incorporated and reviewed the activity and selectivity of recyclable catalytic systems such as polysiloxane-encapsulated novel metal nanoparticle-based catalysts, silica–copper-supported nanocatalysts, graphitic carbon-supported nanocatalysts, metal organic framework (MOF) catalysts, porous organic framework (POP) catalysts, bio-material-supported catalysts, and metal/solvent free recyclable catalysts. In addition, several alkyne functionalization reactions have been elucidated to demonstrate the success and efficiency of recyclable catalysts. In addition, this review also provides the fundamental knowledge required for utilization of green catalysts, which can combine the advantageous features of both homogeneous (catalyst modulation) and heterogeneous (catalyst recycling) catalysis.     

过渡金属催化氟代烯烃参与的交叉偶联反应进展

过渡金属催化（类）卤化物和不同金属试剂的交叉偶联反应是构建不同类型碳碳键和碳杂原子键的重要方法之一。该类反应一般使用活性较高的氯、溴、碘或类卤化物作为亲电试剂,尽管C—F键的键能较强,利用过渡金属直接活化较为惰性的芳基C—F键并参与实现的交叉偶联反应已有较多报道。此外,近期的研究表明,也可以通过直接活化烯基C—F键并催化实现该类底物参与不同类型的交叉偶联反应,从而进一步拓展了交叉偶联反应的底物适用范围,并应用于具有高附加值精细化学品的选择性合成。本文围绕钯或镍催化活化单氟或者多氟烯烃等底物参与的Negishi、Suzuki-Miyaura、Kumada、Hiyama和Sonogashira等5类交叉偶联反应,通过探讨已有方法的反应机理及其适用范围,综述了该领域的研究进展并进行了展望。     

Catalysis with transition metal nanoparticles in colloidal solution: nanoparticle shape dependence and stability

While the nanocatalysis field has undergone an explosive growth during the past decade, there have been very few studies in the area of shape-dependent catalysis and the effect of the catalytic process on the shape and size of transition metal nanoparticles as well as their recycling potential. Metal nanoparticles of different shapes have different crystallographic facets and have different fraction of surface atoms on their corners and edges, which makes it interesting to study the effect of metal nanoparticle shape on the catalytic activity of various organic and inorganic reactions. Transition metal nanoparticles are attractive to use as catalysts due to their high surface-to-volume ratio compared to bulk catalytic materials, but their surface atoms could be so active that changes in the size and shape of the nanoparticles could occur during the course of their catalytic function, which could also affect their recycling potential. In this Feature Article, we review our work on the effect of the shape of the colloidal nanocatalyst on the catalytic activity as well as the effect of the catalytic process on the shape and size of the colloidal transition metal nanocatalysts and their recycling potential. These studies provide important clues on the mechanism of the reactions we studied and also can be very useful in the process of designing better catalysts in the future.     

Palladium complexes of N-heterocyclic carbenes as catalysts for cross-coupling reactions--a synthetic chemist's perspective

Palladium-catalyzed C-C and C-N bond-forming reactions are among the most versatile and powerful synthetic methods. For the last 15 years, N-heterocyclic carbenes (NHCs) have enjoyed increasing popularity as ligands in Pd-mediated cross-coupling and related transformations because of their superior performance compared to the more traditional tertiary phosphanes. The strong sigma-electron-donating ability of NHCs renders oxidative insertion even in challenging substrates facile, while their steric bulk and particular topology is responsible for fast reductive elimination. The strong Pd-NHC bonds contribute to the high stability of the active species, even at low ligand/Pd ratios and high temperatures. With a number of commercially available, stable, user-friendly, and powerful NHC-Pd precatalysts, the goal of a universal cross-coupling catalyst is within reach. This Review discusses the basics of Pd-NHC chemistry to understand the peculiarities of these catalysts and then gives a critical discussion on their application in C-C and C-N cross-coupling as well as carbopalladation reactions.     

Hollow nanoshell-sphere Fe@Fe/Pd reactors: a magnetically recoverable catalyst for the C<Subscript>sp</Subscript>–S cross-coupling reactions in water

The hollow Pd–PVP–Fe nanosphere and Fe–PVP nanoparticle catalysts were synthesized by thermal method. Mixing of two metallic nanocatalysts was applied in the C_sp–S cross-coupling reactions between diphenyl disulfide and phenylacetylene under mild conditions in water. Results show that bi-catalytic system has higher catalytic efficiencies than their monocatalytic systems due to synergy between two catalysts. Order of adding two metallic catalysts were adjusted into the coupling reaction medium. Therefore, various bi-catalytic systems were obtained and characterized by XRD, SEM, EBSD, EDX, UV–Vis spectra, and particle size analyzer. Under special order of adding, the obtained hollow nanoshell-sphere Fe@Fe/Pd reactor showed higher catalytic activity in the coupling reaction compared to other bi-catalytic systems. The C_sp–S coupling products obtained of various diaryl disulfides and phenylacetylene at presence Fe@Fe/Pd (only 7.3?×?10^?5 mmol Pd) catalyst with moderate to high yields in water solvent and mild reaction conditions. After the reaction, the catalyst/product(s) separation could be easily achieved with an external magnet and more than 95% of catalyst could be recovered. The recovered catalyst was characterized by XRD, SEM, EBSD, EDX, and UV–Vis spectra. The Fe@Fe/Pd was reused at least six repeating cycles without any loss of its high catalytic activity. Tuning morphology and chemical composition of bi-catalytic system are key mainstays of high activity of Fe@Fe/Pd in repeating cycles of cross-coupling reactions.     

Prospects and Applications of Palladium Nanoparticles in the Cross-coupling of (hetero)aryl Halides and Related Analogues

Discovering efficient methods for the formation of carbon-carbon bonds is a central ongoing theme in organic synthesis. Cross-coupling reactions catalysed by metal nanoparticles are attractive alternatives to the traditional use of metal counterparts due to the catalytic tunability, selectivity, recyclability and reusability of the nanoparticles. The ongoing search for sustainable processes demands that reusable and environmentally benign catalysts are used. While the advantages of nanoparticles catalysts over bulk catalysts cannot be overemphasised, the problem of sintering, agglomeration and leaching are drawbacks to their full industrial applications. Hence, efforts are being made towards advancing the efficiency of the catalytic nanoparticle systems over the years. This review presents the progress, the challenges and the prospects of palladium nanoparticle with focus on Heck, Suzuki, Hiyama and Sonogashira cross-coupling reactions involving (hetero) aryl halides and the analogues.     

Robust acenaphthoimidazolylidene palladium complexes: highly efficient catalysts for suzuki-miyaura couplings with sterically hindered substrates

Robust acenaphthoimidazolylidene palladium complexes have been demonstrated as highly efficient and general catalysts for the sterically hindered Suzuki-Miyaura cross-coupling reactions in excellent yields even with low catalyst loadings under mild reaction conditions. The high catalytic activity of these complexes highlights that, besides the "flexible steric bulky" concept, σ-donor properties of the NHC ligands are also crucial to accelerate the transformations.     

Carbon-Based Material-Supported Palladium Nanocatalysts in Coupling Reactions: Discussion on their Stability and Heterogeneity

Scientific interest in carbon-based materials (CBMs) has grown dramatically over the past few decades. Due to a variety of atomic orbital hybrid forms (sp, sp² and sp³ hybridization), carbon can form a variety of materials with diverse structures and characteristics. CBMs used as efficient catalyst supports show extensive promise in organic reactions, which is attributed to their structural similarity with organics, large specific surface area, chemical stability, and photocatalytic properties. This review presents the synthesis of CBM-supported palladium nanocatalysts based on impregnation, template methods, etc. The CBMs include activated carbon (AC), graphene, carbon nanotubes (CNTs), and their functionalized products, as supports for improving the activity and recyclability of simple Pd nanocatalysts. After surveying the literature where these catalysts have been utilized for carbon–carbon coupling reactions, there is a particular emphasis on Suzuki, Heck, and Sonogashira reactions. The catalytic mechanism of these Pd nanocatalysts (surface heterogeneous catalysis or homogeneous catalysis caused by Pd leaching) is discussed in detail, especially the effect of Pd leaching on the stability of the catalyst.     

Novel in situ fabrication of chestnut-like carbon nanotube spheres from polypropylene and nickel formate

A novel in situ approach to mass fabrication of carbon nanotubes was reported. Composites of polypropylene (PP)/organomontmorillonite (OMMT)/nickel formate (NF) were prepared by mixing these components in a Brabender mixer at an elevated temperature. Chestnut-like carbon nanotube (CNT) spheres were in situ fabricated in high yields by heating the PP/OMMT/NF composites at 900 degrees C without adding any additional pre-synthesized nickel nanocatalysts. The products were studied by X-ray diffractometer (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, and N2 adsorption-desorption measurements. The results showed that nickel nanoparticles were in situ produced, which catalyzed the formation of multiwalled carbon nanotubes (MWNTs) in an autoclave-like microreactor formed by OMMT. These in situ formed nickel nanoparticles were found to be more catalytically active than pre-synthesized nickel nanocatalysts, resulting in higher yields of CNTs. The obtained CNT spheres have a high surface area, which makes them a good catalyst support. Loading of metal nanoparticles was preliminarily tried, and Pt nanoparticles of ca. 2.65 nm in size were successfully deposited on CNTs. The applications of these nanocatalysts in chemical reactions are currently being studied in our laboratory.     

Recent advances on iron-catalyzed coupling reactions involving organolithium reagents

Several iron-catalyzed cross- and homo-coupling reactions involving organolithiums were developed to form diverse carbon-carbon bonds. The usefulness of this protocol was demonstrated by producing gram-scale products in good yields.