Highly Efficient and Stable Palladium Nanoparticles Supported on an Ionic Liquid Silica Sol?Gel Modified Electrode

A carbon ionic liquid electrode modified with a thin layer of silica sol? gel containing phosphinite ionic liquid was prepared for deposition of palladium nanoparticles. Palladium nanoparticles were formed easily by simple contact of the modified electrode with palladium chloride solution. The novel material overcomes the shortcomings of conventionally modified electrodes with a thin layer of silica sol? gel, due to the existence of ionic liquid in silica matrix. A crack‐free sol? gel matrix was obtained and also, the uniform porous structure of the ionic liquid‐sol? gel matrix resulted in a fast mass transport and increased ionic conductivity. The electrode exhibits high electrocatalytic effects towards hydrazine and ascorbic acid. It is very stable against repetitive cycling in the applied potential window.     

Dendron‐Functionalized Core–Shell Superparamagnetic Nanoparticles: Magnetically Recoverable and Reusable Catalysts for Suzuki C?C Cross‐Coupling Reactions

A metallodendron functionalized with dicyclohexyldiphosphino palladium complex was synthesized. The metallodendron was grafted onto core–shell superparamagnetic nanoparticles (γ‐Fe₂O₃/polymer, 200–500 nm) to give optimal catalytic reactivity in cross‐coupling reactions. The grafted nanoparticles were used as recoverable and reusable catalysts for Suzuki C? C cross‐coupling reactions. They showed remarkable reactivity towards iodo‐ and bromoarenes under mild conditions, and unprecedented reactivity towards chloroarenes. On completion of the catalytic reaction, the catalysts were readily recovered by using a simple magnet to attract the superparamagnetic grafted nanoparticles. Catalysts were recovered more than 25 times with almost no discernable loss of reactivity.     

Palladium(II)‐Catalyzed C?H Activation/C?C Cross‐Coupling Reactions: Versatility and Practicality

Pick your Pd partners : A number of catalytic systems have been developed for palladium‐catalyzed C? H activation/C? C bond formation. Recent studies concerning the palladium(II)‐catalyzed coupling of C? H bonds with organometallic reagents through a Pd^II/Pd⁰ catalytic cycle are discussed (see scheme), and the versatility and practicality of this new mode of catalysis are presented. Unaddressed questions and the potential for development in the field are also addressed.

     

Amide‐Directed Tandem C?C/C?N Bond Formation through C?H Activation

The transformation of C? H bonds into other chemical bonds is of great significance in synthetic chemistry. C? H bond‐activation processes provide a straightforward and atom‐economic strategy for the construction of complex structures; as such, they have attracted widespread interest over the past decade. As a prevalent directing group in the field of C? H activation, the amide group not only offers excellent regiodirecting ability, but is also a potential C? N bond precursor. As a consequence, a variety of nitrogen‐containing heterocycles have been obtained by using these reactions. This Focus Review addresses the recent research into the amide‐directed tandem C? C/C? N bond‐formation process through C? H activation. The large body of research in this field over the past three years has established it as one of the most‐important topics in organic chemistry.     

Palladium Nanoparticles on Graphite Oxide as Catalyst for Suzuki?Miyaura,Mizoroki?Heck,and Sonogashira Reactions

Pd²⁺‐Exchanged graphite oxide (GO) serves as a precatalyst for the formation of Pd‐nanoparticles which are then deposited on the highly functionalized carbonaceous support. This versatile, air‐stable, and ligand‐free system was applied successfully to Suzuki? Miyaura couplings of some aryl chlorides and to the Mizoroki? Heck as well as the Sonogashira reaction showing relatively high activities and good selectivities. Like with other ligand‐free supported systems, the reaction proceeded dominantly by a homogeneous mechanism, but attack of an aryl iodide to Pd‐nanoparticles can be excluded as substantial contribution to the entire catalytic process. Beside its straightforward preparation and its stability in air, the system combines the advantages of both homogeneous and heterogeneous catalysis.     

Asymmetric Aldol Reactions in Caprolactam?Quaternary Ammonium Salt Coordination Ionic Liquid Catalyzed by L‐Pro‐L‐Trp

A direct asymmetric aldol reaction of aldehydes and acetone catalyzed by L ‐Pro‐L ‐Trp was performed in β‐caprolactam? quaternary ammonium salt coordination ionic liquid media in the presence of N‐methylmorpholine (NMM) in high yield and with good enantioselectivity. The approach has the advantages of simple product isolation, and reusable catalyst and coordination ion liquids.     

Gold for C?C Coupling Reactions: A Swiss‐Army‐Knife Catalyst?

For organic chemists, the construction of C C bonds is the most essential aspect of the assembly of molecules. Transition‐metal‐catalyzed coupling reactions have evolved as one of the key tools for this task. Lately, gold has also emerged as a catalyst for this kind of transformation. Gold, with its special properties as a mild carbophilic π Lewis acid, its ability to insert into C H bonds, and, as discovered recently, its ability to undergo redox transformations, offers the opportunity to apply all this potent proficiency for the construction of compounds in an efficient and economical way. This Minireview critically presents the C C coupling reactions enabled by gold catalysts to encourage further research activities in this promising area of oxidation/reduction gold catalysts.     

Influence of Guanidinium Salts and Other Ionic Liquids on the Three‐Component Aza‐Diels?Alder Reaction

The three‐component reaction of aniline, benzaldehyde, and dienophiles such as 2,3‐dihydrofuran, ethyl vinyl ether, 2,3‐dihydropyran, and cyclopentadiene can be promoted by ionic liquids like imidazolium salts and guanidinium salts under thermal as well as microwave conditions. The chemical yield as well as the diastereoselectivity of the Povarov reaction strongly depend on the ionic liquid employed. The guanidinium salts can be recycled and reused several times without loss of reactivity.     

Catalytic C?C,C?N,and C?O Ullmann‐Type Coupling Reactions

Copper‐catalyzed Ullmann condensations are key reactions for the formation of carbon–heteroatom and carbon–carbon bonds in organic synthesis. These reactions can lead to structural moieties that are prevalent in building blocks of active molecules in the life sciences and in many material precursors. An increasing number of publications have appeared concerning Ullmann‐type intermolecular reactions for the coupling of aryl and vinyl halides with N, O, and C nucleophiles, and this Minireview highlights recent and major developments in this topic since 2004.     

Direct Borylation of Primary C?H Bonds in Functionalized Molecules by Palladium Catalysis

Organoborane compounds are among the most commonly employed intermediates in organic synthesis and serve as crucial precursors to alcohols, amines, and various functionalized molecules. A simple palladium‐based system catalyzes the conversion of primary C(sp³) H bonds in functionalized complex organic molecules into alkyl boronate esters. Amino acids, amino alcohols, alkyl amines, and a series of bioactive molecules can be functionalized with the use of readily available and removable directing groups in the presence of commercially available additives, simple ligands, and oxygen (O₂) as the terminal oxidant. This approach represents an economic and environmentally friendly method that could find broad applications.     

meso‐Tritolylcorrole‐Functionalized Single‐walled Carbon Nanotube Donor?Acceptor Nanocomposites for NO2 Detection

meso‐Tritolylcorrole‐functionalized single‐walled carbon nanotubes (TTC‐SWNT) donor‐acceptor (D–A) heterojunction nanocomposite film was fabricated on a polycarbonate membrane through filtration and non‐covalent functionalization, providing an excellent sensing platform with low‐cost, high flexibility and good gas accessibility. The TTC‐SWNTs nanocomposite displays a fast and sensitive response to nitrogen dioxide with a limit of detection of 10 ppb (S/N=3). The sensing response was significantly amplified compared to the unmodified one, which was ascribed to a D–A heterojunction at the interface between electron donor TTC and electron acceptor SWNTs. This study provides a simple route to fabricate low‐cost and highly sensitive donor‐acceptor nanocomposite‐based gas sensors.     

Rhodium‐Catalyzed Tandem Cyclization/Si?C Activation Reaction for the Synthesis of Siloles

Siloles represent an important emerging class of photoluminescent materials. Reported herein is a new synthetic strategy involving a tandem cyclization/Si C activation reaction featuring high efficiency, wide substrate scope, and practical utility. This method enabled the first synthesis of benzofuran siloles as well as rapid access to conjugated siloles. During the course of the study we also uncovered an unusual yet general Si C(sp²) activation in the presence of π acids.     

Rare‐Earth‐Metal Alkylaluminates Supported by N‐Donor‐Functionalized Cyclopentadienyl Ligands: C?H Bond Activation and Performance in Isoprene Polymerization

Homoleptic tetramethylaluminate complexes [Ln(AlMe₄)₃] (Ln=La, Nd, Y) reacted with HCp^NMe2 (Cp^NMe2=1‐[2‐(N,N‐dimethylamino)‐ethyl]‐2,3,4,5‐tetramethyl‐cyclopentadienyl) in pentane at ?35 °C to yield half‐sandwich rare‐earth‐metal complexes, [{C₅Me₄CH₂CH₂NMe₂(AlMe₃)}Ln(AlMe₄)₂]. Removal of the N‐donor‐coordinated trimethylaluminum group through donor displacement by using an equimolar amount of Et₂O at ambient temperature only generated the methylene‐bridged complexes [{C₅Me₄CH₂CH₂NMe(μ‐CH₂)AlMe₃}Ln(AlMe₄)] with the larger rare‐earth‐metal ions lanthanum and neodymium. X‐ray diffraction analysis revealed the formation of isostructural complexes and the C? H bond activation of one aminomethyl group. The formation of Ln(μ‐CH₂)Al moieties was further corroborated by ¹³C and ¹H‐¹³C HSQC NMR spectroscopy. In the case of the largest metal center, lanthanum, this C? H bond activation could be suppressed at ?35 °C, thereby leading to the isolation of [(Cp^NMe2)La(AlMe₄)₂], which contains an intramolecularly coordinated amino group. The protonolysis reaction of [Ln(AlMe₄)₃] (Ln=La, Nd) with the anilinyl‐substituted cyclopentadiene HCp^AMe2 (Cp^AMe2=1‐[1‐(N,N‐dimethylanilinyl)]‐2,3,4,5‐tetramethylcyclopentadienyl) at ?35 °C generated the half‐sandwich complexes [(Cp^AMe2)Ln(AlMe₄)₂]. Heating these complexes at 75 °C resulted in the C? H bond activation of one of the anilinium methyl groups and the formation of [{C₅Me₄C₆H₄NMe(μ‐CH₂)AlMe₃}Ln(AlMe₄)] through the elimination of methane. In contrast, the smaller yttrium metal center already gave the aminomethyl‐activated complex at ?35 °C, which is isostructural to those of lanthanum and neodymium. The performance of complexes [{C₅Me₄CH₂CH₂NMe(μ‐CH₂)AlMe₃}‐ Ln(AlMe₄)], [(Cp^AMe2)Ln(AlMe₄)₂], and [{C₅Me₄C₆H₄NMe(μ‐CH₂)AlMe₃}Ln(AlMe₄)] in the polymerization of isoprene was investigated upon activation with [Ph₃C][B(C₆F₅)₄], [PhNMe₂H][B(C₆F₅)₄], and B(C₆F₅)₃. The highest stereoselectivities were observed with the lanthanum‐based pre‐catalysts, thereby producing polyisoprene with trans‐1,4 contents of up to 95.6 %. Narrow molecular‐weight distributions (M_w/M_n<1.1) and complete consumption of the monomer suggested a living‐polymerization mechanism.