Phosphine‐mediated Highly Enantioselective Spirocyclization with Ketimines as Substrates

Phosphine‐catalyzed enantioselective annulation reactions involving ketimines are a daunting synthetic challenge owing to the intrinsic low reactivity of ketimine substrates. A highly enantioselective [3+2] cycloaddition reaction that makes use of isatin‐derived ketimines as reaction partners was developed. Notably, both simple and γ‐substituted allenoates could be utilized, and various 3,2′‐pyrrolidinyl spirooxindoles with a tetrasubstituted stereocenter were obtained in excellent yields and with nearly perfect enantioselectivity (>98 % ee in all cases).     

A Single Excitation‐Duplexed Imaging Strategy for Profiling Cell Surface Protein‐Specific Glycoforms

This work develops a site‐specific duplexed luminescence resonance energy transfer system on cell surface for simultaneous imaging of two kinds of monosaccharides on a specific protein by single near‐infrared excitation. The single excitation‐duplexed imaging system utilizes aptamer modified upconversion luminescent nanoparticles as an energy donor to target the protein, and two fluorescent dye acceptors to tag two kinds of cell surface monosaccharides by a dual metabolic labeling technique. Upon excitation at 980 nm, only the dyes linked to protein‐specific glycans can be lit up by the donor by two parallel energy transfer processes, for in situ duplexed imaging of glycoforms on specific protein. Using MUC1 as the model, this strategy can visualize distinct glycoforms of MUC1 on various cell types and quantitatively track terminal monosaccharide pattern. This approach provides a versatile platform for profiling protein‐specific glycoforms, thus contributing to the study of the regulation mechanisms of protein functions by glycosylation.     

Radical Hydrodeiodination of Aryl,Alkenyl, Alkynyl,and Alkyl Iodides with an Alcoholate as Organic Chain Reductant through Electron Catalysis

A simple and efficient method for radical hydrodeiodination is reported. The novel approach uses electron catalysis. In situ generated Na‐alcoholates are introduced as radical chain reducing reagents and reactions work with O₂ as cheap initiator. Hydrodeiodination works on aryl, alkenyl, alkynyl iodides and a tert‐alkyl iodide also gets reduced applying the method. Albeit less general, the method is also applicable to the reduction of aryl bromides. The novel reagent is successfully used to conduct typical reductive radical cyclization reactions and mechanistic studies are reported.     

Asymmetric Organocatalysis: The Emerging Utility of α,β‐Unsaturated Acylammonium Salts

Although acylammonium salts are well‐studied, chiral α,β‐unsaturated acylammonium salts have received much less attention. While these intermediates are convenient synthons, which are readily available from several commodity unsaturated acids and acid chlorides, and possess three reactive sites, their application in organic synthesis has been limited because of the lack of appropriate chiral Lewis bases for their generation. In recent years, the utility of chiral, unsaturated acylammonium salts has expanded considerably, thus demonstrating the unique reactivity of this intermediate leading to the development of a diverse array of catalytic, asymmetric transformations including organocascade processes. This Minireview highlights the recent and growing interest in these intermediates which might spark further research into their untapped potential for asymmetric organocascade catalysis. A cursory comparison is made to related unsaturated iminium and acylazolium intermediates.     

Dry Reforming of Methane on a Highly‐Active Ni‐CeO2 Catalyst: Effects of Metal‐Support Interactions on C−H Bond Breaking

Ni‐CeO₂ is a highly efficient, stable and non‐expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO₂ at temperatures as low as 300 K, generating CH_x and CO_x species on the surface of the catalyst. Strong metal–support interactions activate Ni for the dissociation of methane. The results of density‐functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO_2?x(111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CH_x or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way.     

The Nanoparticle Size Effect in Graphene Cutting: A “Pac‐Man” Mechanism

Metal‐nanoparticle‐catalyzed cutting is a promising way to produce graphene nanostructures with smooth and well‐aligned edges. Using a multiscale simulation approach, we unambiguously identified a “Pac‐Man” cutting mechanism, characterized by the metal nanoparticle “biting off” edge carbon atoms through a synergetic effect of multiple metal atoms. By comparing the reaction rates at different types of edge sites, we found that etching of an entire edge carbon row could be triggered by a single zigzag‐site etching event, which explains the puzzling linear dependence of the overall carbon‐atom etching rate on the nanoparticle surface area observed experimentally. With incorporation of the nanoparticle size effect, the mechanisms revealed herein open a new avenue to improve controllability in graphene cutting.     

Isolating Reactions at the Picoliter Scale: Parallel Control of Reaction Kinetics at the Liquid–Liquid Interface

Miniaturized liquid–liquid interfacial reactors offer enhanced surface area and rapid confinement of compounds of opposite solubility, yet they are unable to provide in situ reaction monitoring at a molecular level at the interface. A picoreactor operative at the liquid–liquid interface is described, comprising plasmonic colloidosomes containing Ag octahedra strategically assembled at the water‐in‐decane emulsion interface. The plasmonic colloidosomes isolate ultrasmall amounts of solutions (<200 pL), allowing parallel monitoring of multiple reactions simultaneously. Using the surface‐enhanced Raman spectroscopy (SERS) technique, in situ monitoring of the interfacial protonation of dimethyl yellow (p‐dimethylaminoazobenzene (DY)) is performed, revealing an apparent rate constant of 0.09 min^?1 for the first‐order reaction. The presence of isomeric products with similar physical properties is resolved, which would otherwise be indiscernible by other analytical methods.     

A Supramolecularly Activated Radical Cation for Accelerated Catalytic Oxidation

Tuning the activity of radicals is crucial for radical reactions and radical‐based materials. Herein, we report a supramolecular strategy to accelerate the Fenton reaction through the construction of supramolecularly activated radical cations. As a proof of the concept, cucurbit[7]uril (CB[7]) was introduced, through host–guest interactions, onto each side of a derivative of 1,4‐diketopyrrolo[3,4‐c]pyrrole (DPP), a model dye for Fenton oxidation. The DPP radical cation, the key intermediate in the oxidation process, was activated by the electrostatically negative carbonyl groups of CB[7]. The activation induced a drastic decrease in the apparent activation energy and greatly increased the reaction rate. This facile supramolecular strategy is a promising method for promoting radical reactions. It may also open up a new route for the catalytic oxidation of organic pollutants for water purification and widen the realm of supramolecular catalysis.     

Manganese(II) Complexes with Bridging Selenidoarsenate(III) Anions [AsSe2(Se2)]3− and [(AsSe2)2(μ‐Se2)]4−

Solvothermal reaction of [MnCl₂(terpy)] with elemental As and Se at a 1:1:2 molar ratio in H₂O/trien (10:1) at 150 °C affords the linear trimanganese(II) complex [{Mn(terpy)}₃(μ‐AsSe₄)₂] ( 1 ). The tridentate [AsSe₂(Se₂)]^3? anions of 1 chelate the terminal {Mn(terpy)}²⁺ fragments and bridge these through their remaining Se atom to the central {Mn(terpy)}²⁺ moiety. Weak interactions of Mn1···Se and Mn3···Se bonds with length 2.914(7) and 3.000(7) Å link the molecules of 1 into infinite chains. Treatment of [MnCl₂(cyclam)]Cl with As and Se at a 1:1:2 molar ratio in superheated H₂O/CH₃OH (1:1) at 150 °C yields the dinuclear complex [{Mn(cyclam)}₂ (μ‐As₂Se₆)] ( 2 ), whose novel [(AsSe₂)₂(μ‐Se₂)]^4? ligands bridge the Mn^II atoms in a μ‐1κ²Se¹, Se²: 2κ²Se⁵,Se⁶ manner.     

Syntheses and Crystal Structures of Two Chloro‐Bridged Coordination Polymers [Cd(BIM)Cl2]n and [Pb(BIM)Cl2]n

Two novel coordination polymers, [Cd(BIM)Cl₂]_n ( 1 ) and [Pb(BIM)Cl₂]_n ( 2 ) [wherein BIM = bis(imidazol‐1‐yl)methane], were synthesized by the reactions of the BIM ligand with CdCl₂ and PbCl₂, respectively. They were characterized by elemental analyses, IR, TGA and X‐ray single‐crystal diffraction techniques. Single‐crystal X‐ray structure analyses showed there is a pseudooctahedral arrangement around the cadmium atom in the complex 1 . It has a three‐dimensional network which contains one‐dimensional inorganic‐organic hybrid chains and μ₂‐bridging chloride ligands. A rare pentacoordinate square‐pyramidal arrangement was adopted for the lead(II) atom in the complex 2 , which has an unusual two‐dimensional layer structure of macrometallacycles crosslinked with the bridging Pb₂Cl₂ units. The metal atoms in both complexes were coordinated with two BIM ligands in cis arrangement and bridged by μ₂‐bridging chloride ligands.