“Click” Chemistry Mildly Stabilizes Bifunctional Gold Nanoparticles for Sensing and Catalysis

A large family of bifunctional 1,2,3‐triazole derivatives that contain both a polyethylene glycol (PEG) chain and another functional fragment (e.g., a polymer, dendron, alcohol, carboxylic acid, allyl, fluorescence dye, redox‐robust metal complex, or a β‐cyclodextrin unit) has been synthesized by facile “click” chemistry and mildly coordinated to nanogold particles, thus providing stable water‐soluble gold nanoparticles (AuNPs) in the size range 3.0–11.2 nm with various properties and applications. In particular, the sensing properties of these AuNPs are illustrated through the detection of an analogue of a warfare agent (i.e., sulfur mustard) by means of a fluorescence “turn‐on” assay, and the catalytic activity of the smallest triazole–AuNPs (core of 3.0 nm) is excellent for the reduction of 4‐nitrophenol in water.     

Acylzirconocene Chloride as an “Unmasked” Acyl Anion: Enantioselective 1,2-Addition to α,β-Unsaturated Ketone Derivatives

The chiral monodentate phosphane ligand ( R )-MOP facilitated the first enantioselective nucleophilic 1,2-addition of an “unmasked” acyl anion to a carbonyl group in the Pd^II-catalyzed reaction of α,β-unsaturated ketones with acylzirconocene chlorides [Eq. (1), 66 % ee, 88 % yield; (R)-MOP=(R)-2-(diphenylphosphanyl)-2′-methoxy-1,1′-binaphthyl].     

Diels–Alder “Click” Chemistry in Designing Dendritic Macromolecules

Simple, versatile and green : Diels–Alder “click” chemistry is a simple, versatile and “greener” approach in the design of a diverse range of dendritic macromolecules (see scheme).

     

A Mechanochemically Triggered “Click” Catalyst

“Click” chemistry represents one of the most powerful approaches for linking molecules in chemistry and materials science. Triggering this reaction by mechanical force would enable site‐ and stress‐specific “click” reactions—a hitherto unreported observation. We introduce the design and realization of a homogeneous Cu catalyst able to activate through mechanical force when attached to suitable polymer chains, acting as a lever to transmit the force to the central catalytic system. Activation of the subsequent copper‐catalyzed “click” reaction (CuAAC) is achieved either by ultrasonication or mechanical pressing of a polymeric material, using a fluorogenic dye to detect the activation of the catalyst. Based on an N‐heterocyclic copper(I) carbene with attached polymeric chains of different flexibility, the force is transmitted to the central catalyst, thereby activating a CuAAC in solution and in the solid state.     

Polysiloxane‐Based Luminescent Elastomers Prepared by Thiol–ene “Click” Chemistry

Side‐chain vinyl poly(dimethylsiloxane) has been modified with mercaptopropionic acid, methyl 3‐mercaptopropionate, and mercaptosuccinic acid. Coordinative bonding of Eu^III to the functionalized polysiloxanes was then carried out and crosslinked silicone elastomers were prepared by thiol–ene curing reactions of these composites. All these europium complexes could be cast to form transparent, uniform, thin elastomers with good flexibility and thermal stability. The networks were characterized by FTIR, NMR, UV/Vis, and luminescence spectroscopy as well as by scanning electron microscopy, thermogravimetric analysis, and X‐ray photoelectron spectroscopy. The europium elastomer luminophores exhibited intense red light at 617 nm under UV excitation at room temperature due to the ⁵D₀→⁷F₂ transition in Eu^III ions. The newly synthesized luminescent materials offer many advantages, including the desired mechanical flexibility. They cannot be dissolved or fused, and so they have potential for use in optical and electronic applications.     

Acylzirconocene Chloride as an “Unmasked” Acyl Anion

Under mild conditions the acyl group of acylzirconocene chloride 1 formed from an alkene or alkyne and [(C₅H₅)₂ZrHCl] reacts as an “unmasked” acyl anion. The Lewis acid mediated reactions with aldehydes that yield α-ketol products in high yields demonstrate the versatility of this reagent for C–C coupling.     

The Coordination Number – an “Inorganic Chameleon”

The purpose of the present article is to describe the changing ambiguous character of the term “coordination number” and its present-day definition in structural chemistry, particularly of typical solids (assemblies of particles with short-range and long-range order). An effort is made at the same time to describe the crystal structure of solids as simply as possible while also taking long-range order into account, i.e. by determining “effective” coordination numbers by the geometrical “polyhedron method” or from MAPLE (Madelung Part of Lattice Energy) values.     

Mesoporous Hybrid Materials Containing Nanoscopic “Binding Pockets” for Colorimetric Anion Signaling in Water by using Displacement Assays

Mesoporous solids functionalized with anion‐binding groups have proved to be suitable anion hosts and have been used in selective colorimetric displacement assays. The material UVM‐7, a mesoporous MCM41‐type support characterized by the presence of nanometric mesoporous particle conglomerates, was selected as inorganic scaffolding. Reaction of the template‐free UVM‐7 solid with 3‐aminopropyltriethoxysilane ( 1 ) yielded solid S1 , from which the derivatives S2 and S3 were obtained by reaction with 2‐methylthio‐2‐imidazoline hydroiodide ( 2 ) and butyl isocyanate ( 3 ), respectively. Solids S4 and S5 were prepared by reaction of the starting mesoporous UVM‐7 scaffolding with N‐methyl‐N′‐propyltrimethoxysilyl imidazolium chloride ( 4 ) and with 3‐(trimethoxysilyl)propyl‐N,N,N‐trimethylammonium chloride ( 5 ), respectively. The solids synthesized contain mesoporous binding pockets that can interact with anions through electrostatic attractive forces ( S1 , S2 , S4 , S5 ) and hydrogen‐bonding interactions ( S1 , S2 , S3 , S4 ). These functionalized solids were loaded with a dye ( d ) capable of interacting coordinatively with the anchored binding sites, in our case 5‐carboxyfluorescein, to yield the hybrid materials S1d, S2d , S3d , S4d and S5d . These dye‐containing solids are the signaling reporters. Their sensing ability towards a family of carboxylates, namely acetate, citrate, lactate, succinate, oxalate, tartrate, malate, mandelate, glutamate and certain nucleotides, has been studied in pure water at pH 7.5 (Hepes, 0.01 mol dm^?3). In the sensing protocol, a particular analyte may be bonded preferentially by the nanoscopic functionalized pocket, leading to delivery of the dye to the solution and resulting in colorimetric detection of the guest. The response to a given anion depends on the characteristics of the binding pockets and the specific interaction of the anion with the binding groups in the mesopores. We believe that the possibility of using a wide variety of mesoporous supports that can easily be functionalized with anion‐binding sites, combined with suitable dyes as indicators, make this approach significant for opening new perspectives in the design of chromogenic assays for anion detection in pure water.     

“Dumbbell”‐ and “Clackers”‐Shaped Dimeric Derivatives of Monocarba‐closo‐dodecaborate

We designed, synthesized, and characterized two types of dimeric forms of monocarba‐closo‐dodecaborate, namely, a “dumbbell”‐shaped dianion having a C?C bond and a “clackers”‐shaped monoanion having an iodonium linker. The unique architectures of these anionic molecules were established by X‐ray analysis. Spectroscopic analysis, DFT calculations, and reactivity experiments revealed high anionic and chemical stability of both anions, which are crucial properties for weakly coordinating anions.     

Variable Reactivity of a N‐Heterocyclic Phosphenium Complex: P−C Bond Activation or “Abnormal” Deprotonation

The reaction of an N‐heterocyclic phosphenium complex of manganese with MeLi/Et₃NHCl under formal addition of CH₄ to the Mn=P double bond can be reversed upon UV photolysis, providing a rare example for selective P−C(alkyl) bond activation. Action of LDA on the phosphenium complex does not proceed via attack at phosphorus but rather via C4‐deprotonation to yield a unique P‐analogue of an “abnormal” carbene. A transmetalation product of the original complex was fully characterized. The C‐metalation is also applicable to bis‐phosphenium complexes of other metals.     

Tellurium(II)‐Centered Dications from the Pseudohalide “Te(OTf)2”

Te for two : Supported by pyridine‐ or carbene‐based ligands, tellurium‐centered dications are prepared in high yield and include a dicationic tellurium analogue of the recently synthesized “carbodicarbene”. The key to accessing these compounds is the isolation of a base‐stabilized form of TeOTf₂ (see structure), a new highly electrophilic reagent for tellurium chemistry.

     

Synthesis,purification, and characterization of “perfect” star polymers via “Click” coupling

The copper (I)‐catalyzed azide‐alkyne cycloaddition “click” reaction was successfully applied to prepare well‐defined 3, 6, and 12‐arms polystyrene and polyethylene glycol stars. This study focused particularly on making “perfect” star polymers with an exact number of arms, as well as developing techniques for their purification. Various methods of characterization confirmed the star polymers high purity, and the structural uniformity of the generated star polymers. In particular, matrix‐assisted laser desorption ionization‐time‐of‐flight mass spectrometry revealed the quantitative transformation of the end groups on the linear polymer precursors and confirmed their quantitative coupling to the dendritic cores to yield star polymers with an exact number of arms. In addition to preparing well‐defined polystyrene and poly(ethylene glycol)homopolymer stars, this technique was also successfully applied to amphiphilic, PCL‐b‐PEG star polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

In Situ Hetero End‐Functionalized Polythiophene and Subsequent “Click” Chemistry With DNA

It is demonstrated that bifunctionalized polythiophenes involving thiol and azide end‐functional groups can be synthesized by chain‐growth Suzuki‐Miyaura type polymerization. The bifunctionalized polythiophenes are successfully characterized by 1H NMR, gel permeation chromatography (GPC), and matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF). Furthermore, the azide end‐group reacts with DNA via “click chemistry” to form a polythiophene/DNA hybrid structure, which is characterized by ESI‐MS. The described synthetic approaches will lead to the synthesis of novel multi‐block copolymers as well as biomolecule‐based conjugated polymer structures.     

“Click”‐Triggered Self‐Healing Graphene Nanocomposites

Strategies to compensate material fatigue are among the most challenging issues, being most prominently addressed by the use of nano‐ and microscaled fillers, or via new chemical concepts such as self‐healing materials. A capsule‐based self‐healing material is reported, where the adverse effect of reduced tensile strength due to the embedded capsules is counterbalanced by a graphene‐based filler, the latter additionally acting as a catalyst for the self‐healing reaction. The concept is based on “click”‐based chemistry, a universal methodology to efficiently link components at ambient reaction conditions, thus generating a “reactive glue” at the cracked site. A capsule‐based healing system via a graphene‐based Cu₂O (TRGO‐Cu₂O‐filler) is used, acting as both the catalytic species for crosslinking and the required reinforcement agent within the material, in turn compensating the reduction in tensile strength exerted by the embedded capsules. Room‐temperature self‐healing within 48 h is achieved, with the investigated specimen containing TRGO‐Cu₂O demonstrating significantly faster self‐healing compared to homogeneous (Cu(PPh₃)₃F, Cu(PPh₃)₃Br), and heterogeneous (Cu/C) copper(I) catalysts.