A Self‐Assembled Superhydrophobic Electrospun Carbon–Silica Nanofiber Sponge for Selective Removal and Recovery of Oils and Organic Solvents

An oil spill needs timely cleanup before it spreads and poses serious environmental threat to the polluted area. This always requires the cleanup techniques to be efficient and cost‐effective. In this work, a lightweight and compressible sponge made of carbon–silica nanofibers is derived from electrospinning nanotechnology that is low‐cost, versatile, and readily scalable. The fabricated sponge has high porosity (>99 %) and displays ultra‐hydrophobicity and superoleophilicity, thus making it a suitable material as an oil adsorbent. Owing to its high porosity and low density, the sponge is capable of adsorbing oil up to 140 times its own weight with its sorption rate showing solution viscosity dependence. Furthermore, sponge regeneration and oil recovery are feasible by using either cyclic distillation or mechanical squeezing.     

Vanadium(V) Oxo and Imido Calix[8]arene Complexes: Synthesis,Structural Studies,and Ethylene Homo/Copolymerisation Capability

Interaction of p‐tert‐butylcalix[8]areneH₈ (L⁸H₈) with [NaVO(OtBu)₄] (formed in situ from VOCl₃) afforded the complex [Na(NCMe)₅][(VO)₂L⁸H]?4 MeCN ( 1 ?4 MeCN). Increasing [NaVO(OtBu)₄] to 4 equiv led to [Na(NCMe)₆]₂[(Na(VO)₄L⁸)(Na(NCMe))₃]₂?10 MeCN ( 2 ?10 MeCN). With adventitious oxygen, reaction of 4 equiv of [VO(OtBu)₃] with L⁸H₈ afforded the alkali‐metal‐free complex [(VO)₄L⁸(μ³‐O)₂] ( 3 ); solvates 3 ?3 MeCN and 3 ?3 CH₂Cl₂ were isolated. For the lithium analogue, the order of addition had to be reversed such that lithium tert‐butoxide was added to L⁸H₈ and then treated with 2 equiv of VOCl₃; crystallisation afforded [(VO₂)₂Li₆[L⁸](thf)₂(OtBu)₂(Et₂O)₂]?Et₂O ( 4 ?Et₂O). Upon extraction into acetonitrile, [Li(NCMe)₄][(VO)₂L⁸H]?8 MeCN ( 5 ?8 MeCN) was formed. Use of the imido precursors [V(NtBu)(OtBu)₃] and [V(Np‐tolyl)(OtBu)₃] and L⁸H₈, afforded [tBuNH₃][{V(p‐tolylN)}₂L⁸H]?3 1/2 MeCN ( 6 ?3 1/2 MeCN). The molecular structures of 1 to 6 are reported. Complexes 1 , 3 , and 4 were screened as precatalysts for the polymerisation of ethylene in the presence of cocatalysts at various temperatures and for the copolymerisation of ethylene with propylene. Activities as high as 136 000 g (mmol(V) h)^?1 were sometimes achieved; higher molecular weight polymers could be obtained versus the benchmark [VO(OEt)Cl₂]. For copolymerisation, incorporation of propylene was 7.1–10.9 mol % (compare 10 mol % for [VO(OEt)Cl₂]), although catalytic activities were lower than [VO(OEt)Cl₂].     

Konzertierte nukleophile aromatische Substitutionen

Jüngste Entwicklungen in der experimentellen und theoretischen Chemie haben zur Identifizierung einer schnell wachsenden Klasse von nukleophilen aromatischen Substitutionsreaktionen geführt, die einem konzertierten Mechanismus (cS_NAr) folgen, und nicht dem klassischen, zweistufigen S_NAr‐Mechanismus. Während klassische S_NAr‐Reaktionen auf die substantielle Aktivierung des aromatischen Ringes durch elektronenziehende Substituenten angewiesen sind, ist eine solche Aktivierung für den konzertierten Reaktionsverlauf nicht zwingend nötig.     

A modular and divergent approach to spirocyclic pyrrolidines

An efficient three-step sequence to afford a valuable class of spirocyclic pyrrolidines is reported. A reductive cleavage/Horner–Wadsworth–Emmons cascade facilitates the spirocyclisation of a range of isoxazolines bearing a distal β-ketophosphonate. The spirocyclisation precursors are elaborated in a facile and modular fashion, via a [3 + 2]-cycloaddition followed by the condensation of a phosphonate ester, introducing multiple points of divergence. The synthetic utility of this protocol has been demonstrated in the synthesis of a broad family of 1-azaspiro[4,4]nonanes and in a concise formal synthesis of the natural product (±)-cephalotaxine.

A three-step, modular and divergent sequence accessing challenging spirocyclic pyrrolidines has been developed, featuring a novel reductive spirocyclization cascade.     

A Multi‐Component Sensor System for Detection of Amphiphilic Compounds

Many biologically important compounds are amphiphilic in character. Glycolipids, for example, represent a biologically important class of amphiphiles. Receptors and sensors for such compounds must also be amphiphilic making them a challenge to prepare. Here, a cucurbit[8]uril (CB[8])‐based sensor system has been prepared and tested for detection of amphiphilic compounds. This multi‐component system consists: a CB[8], which acts as a hydrophobic lipid receptor, a hydrophilic pyridinium‐based carbohydrate receptor, and a fluorescent indicator. The system self‐assembles in aqueous solution. The pyridinium quenches the fluorescence of the indicator giving a strong turn‐on response when it is displaced by the analyte. The sensor system was characterized by NMR, X‐ray crystallography, and fluorescence titrations.     

Bifunctional iminophosphorane superbases: Potent organocatalysts for enantio- and diastereoselective Michael addition reactions

Bifunctional iminophosphorane (BIMP) organocatalysts catalyze the enantio- and diastereoselective Michael additions of high pK_a cyclic malonamate ester pro-nucleophiles to nitroalkenes with reactivity profiles of up to 3 orders of magnitude greater than tertiary amine bifunctional Brønsted base/(thio)urea organocatalysts. The unrivalled performance of the BIMPs allows reaction times of challenging reactions to be slashed from weeks to minutes and has enabled new flow chemistry applications using polystyrene-supported versions contained within a flow reactor.     

Multiple weak supramolecular interactions stabilize a surprisingly twisted As2L3 assembly

A combined crystallographic, DFT and NMR spectroscopic study of a flexible As(2)(3) assembly reveals temperature dependent conformational behavior in solution and a highly asymmetric structure stabilized by As-pi and edge-to-face aromatic interactions.     

Bifunctional Iminophosphorane-Catalyzed Enantioselective Nitroalkane Addition to Unactivated α,β-Unsaturated Esters**

Herein we describe the enantioselective intermolecular conjugate addition of nitroalkanes to unactivated α,β-unsaturated esters, catalyzed by a bifunctional iminophosphorane (BIMP) superbase. The transformation provides the most direct access to pharmaceutically relevant enantioenriched γ-nitroesters, utilizing feedstock chemicals, with unprecedented selectivity. The methodology exhibits a broad substrate scope, including β-(fluoro)alkyl, aryl and heteroaryl substituted electrophiles, and was successfully applied on a gram scale with reduced catalyst loading, and, additionally, catalyst recovery was carried out. The formal synthesis of a range of drug molecules, and an enantioselective synthesis of (S)-rolipram were achieved. Additionally, computational studies revealed key reaction intermediates and transition state structures, and provided rationale for high enantioselectivities, in good agreement with experimental results.     

Control of porosity geometry in amino acid derived nanoporous materials

Substitution of the pillaring ligand in the homochiral open-framework [Ni(2)(L-asp)(2)(bipy)] by extended bipy-type ligands leads to a family of layer-structured, homochiral metal-organic frameworks. The 1D channel topology can be modified by the nature of the organic linker, with shape, cross-section and the chemical functionality tuneable. In addition, the volume of these channels can be increased by up to 36 % compared to the parent [Ni(2)(L-asp)(2)(bipy)]. The linker 1,4-dipyridylbenzene (3rbp) gives access to a new layered homochiral framework [Ni(2)(L-asp)(2)(3rbp)] with channels of a different shape. In specific cases, non-porous analogues with the linker also present as a guest can be activated to give porous materials after sublimation. Their CO(2) uptake shows an increase of up to 30 % with respect to the parent [Ni(2)(L-asp)(2)(bipy)] framework.