Nanostructured Intermetallic Nickel Silicide (Pre)Catalyst for Anodic Oxygen Evolution Reaction and Selective Dehydrogenation of Primary Amines

The development of novel earth-abundant metal-based catalysts to accelerate the sluggish oxygen evolution reaction (OER) is crucial for the process of large-scale production of green hydrogen. To solve this bottleneck, herein, a simple one-pot colloidal approach is reported to yield crystalline intermetallic nickel silicide (Ni2Si), which results in a promising precatalyst for anodic OER. Subsequently, an anodic-coupled electrosynthesis for the selective oxidation of organic amines (as sacrificial proton donating agents) to value-added organocyanides is established to boost the cathodic reaction. A partial transformation of the Ni2Si intermetallic precatalyst generates a porous nickel(oxy)hydroxide phase modified with oxidic silicon species as unequivocally demonstrated by a combination of quasi in situ Raman and X-ray absorption spectroscopy as well as ex situ methods. The activated form of the catalyst generates a geometric current density of 100 mA cm−2 at an overpotential (η100) of 348 mV displaying long-term durability over a week and high efficiency in paired electrolysis

In‐Liquid Plasma Modified Nickel Foam: NiOOH/NiFeOOH Active Site Multiplication for Electrocatalytic Alcohol, Aldehyde, and Water Oxidation

The oxygen evolution reaction (OER) and the value-added oxidation of renewable organic substrates are critical to supply electrons and protons for the synthesis of sustainable fuels. To meet industrial requirements, new methods for a simple, fast, environmental-friendly and cheap synthesis of robust, self-supported and high surface area electrodes are required. Herein, a novel in-liquid plasma (plasma electrolysis) approach for the growth of hierarchical nanostructures on nickel foam is reported on. Under morphology retention, iron can be doped into this high surface area electrode. For the oxidation of 5-(hydroxymethyl)furfural and benzyl alcohol, the iron-free, plasma-treated electrode is more suitable reaching current densities up to 800 mA cm$^{-2}$ with Faradaic efficiencies above 95%. For the OER, the iron-doped nickel foam electrode reaches the industrially relevant current density of 500 mA cm$^{-2}$ at 1.473 ± 0.013$_{VRHE}$ (60 °C) and shows no activity decrease over 140 h. The different effects of iron doping are rationalized using methanol probing and in situ Raman spectroscopy. Furthermore, the intrinsic activity is separated from the number of active sites, and, for the organic oxidation reactions, diffusion limitations are revealed. The authors anticipate that the plasma modified nickel foam will be suitable for various (electro)catalytic processes

Linking PO43- and HAsO42- anions with a dinuclear Zn-2(II)] complex: Formation and stabilization of novel decanuclear metallomacrocyclic Zn-10(II)] and tetranuclear Zn-4(II)] clusters

The linkage of PO43- and HAsO42--anions with a newly synthesized five-coordinate dinuclear zinc complex, Zn-2(cpdp)(H2O)(2)]Cl (1) H(3)cpdp =N,N'-bis2-carboxybenzomethyl]-N,N'-bis2-pyridylmethyl]-1,3diamino propan-2-ol], has been explored. In methanol-water, the reaction of 1 with Na2HPO4 center dot 2H(2)O and Na2HAsO4 center dot 7H(2)O/NaBr separately, at ambient temperature, yielded the novel phosphate-bridged decanuclear zinc cluster, (H3O)(4)Zn-10(cPdP)(4)(mu(5)-PO4)(2)(H2O)(6)](6 center dot Cl)center dot 53H(2)O (2) and hydrogen arsenate bridged tetranuclear zinc cluster, Na-2Zn-4(cpdp)(2)(mu(4)-HAsO4)]ClBr center dot 13H(2)O (3), respectively. Analysis of the single crystal X-ray structure discloses that the metallic core of cluster 2 entails eight distorted trigonal bipyramidal and two distorted octahedral zinc ions, displaying a mu(5):eta(2):eta(1):eta(1):eta 1 bridging mode of two POi-groups. The metallic core of cluster 3 holds four distorted trigonal bipyramidal zinc ions, showing a mu(4):eta(1):eta(1):eta(1):eta 1 bridging mode of the HAsO42- group. In solution, UV-Vis titration spectra of complex 1 upon increasing the concentration of the PO43- and HAsO(4)(2-)anions show a significant binding-induced increase in the absorption intensities of 1, accompanied by a substantial red shift. Additionally, the integrity of all three zinc assemblies has been confirmed by H-1 and C-13 NMR spectroscopic data in solution. The thermal behaviors of 1, 2 and 3 have been studied by thermogravimetric analysis (TGA). (C) 2016 Elsevier Ltd. All rights reserved

Highly Active Carbene Potassium Complexes for the Ring-Opening Polymerization of ε‑Caprolactone

Herein we report the synthesis of two complexes of potassium employing strongly nucleophilic carbenes, such as cyclic “(alkyl)­(amino)­carbene (<i>c</i>AAC) and abnormal N-heterocyclic carbene (<i>a</i>NHC). Both complexes are dimeric in the solid state and the two potassium centers are bridged by trimethylsilylamide. In these complexes, the carbene- - -K interaction is predominantly electrostatic in character, which has been probed thoroughly by NBO and AIM analyses. Indeed, the delocalization energy of the <i>c</i>AAC lone pair calculated from the second-order perturbation theory was only 5.21 kcal mol^–1, supporting a very weak interaction. The solution-state behavior of these molecules, as inferred from NOESY spectra, hints that the weak carbene- - -K interaction is retained in nonpolar solvents, and the bond is not dissociated at least on the NMR time scale. We took advantage of such a weak interaction to develop highly effective ring-opening polymerization catalysts for ε-caprolactone and <i>rac</i>-lactide. The efficacy of these catalysts is prominent from a very high substrate/metal-initiator ratio as well as very low dispersity index of the obtained polymer chains, reflecting significant control over polymerization

ICT–Isomerization-Induced Turn-On Fluorescence Probe with a Large Emission Shift for Mercury Ion: Application in Combinational Molecular Logic

A unique turn-on fluorescent device based on a ferrocene–aminonaphtholate derivative specific for Hg²⁺ cation was developed. Upon binding with Hg²⁺ ion, the probe shows a dramatic fluorescence enhancement (the fluorescence quantum yield increases 58-fold) along with a large red shift of 68 nm in the emission spectrum. The fluorescence enhancement with a red shift may be ascribed to the combinational effect of CN isomerization and an extended intramolecular charge transfer (ICT) mechanism. The response was instantaneous with a detection limit of 2.7 × 10^–9 M. Upon Hg²⁺ recognition, the ferrocene/ferrocenium redox peak was anodically shifted by Δ<i>E</i>_1/2 = 72 mV along with a “naked eye” color change from faint yellow to pale orange for this metal cation. Further, upon protonation of the imine nitrogen, the present probe displays a high fluorescence output due to suppression of the CN isomerization process. Upon deprotonation using strong base, the fluorescence steadily decreases, which indicates that H⁺ and OH^– can be used to regulate the off–on–off fluorescence switching of the present probe. Density functional theory studies revealed that the addition of acid leads to protonation of the imine N (according to natural bond orbital analysis), and the resulting iminium proton forms a strong H-bond (2.307 Å) with one of the triazole N atoms to form a five-membered ring, which makes the molecule rigid; hence, enhancement of the ICT process takes place, thereby leading to a fluorescence enhancement with a red shift. The unprecedented combination of H⁺, OH^–, and Hg²⁺ ions has been used to generate a molecular system exhibiting the INHIBIT–OR combinational logic operation

An Efficient Molecular Tool with Ferrocene Backbone: Discriminating Fe³⁺ from Fe²⁺ in Aqueous Media

Two novel molecular probes with ferrocene backbone have been designed and synthesized for the first time, and they were subsequently found capable of distinguishing Fe³⁺ and Fe²⁺ ion in aqueous media. The discrimination of both the oxidation states (II/III) of iron by these receptors can be established either from a striking shift in redox potential (<b>1</b>: Δ<i>E</i>_1/2 ≈ 90 mV and <b>2</b>: Δ<i>E</i>_1/2 ≈ 59 mV) for Fe²⁺ ion or from UV–vis absorption studies (using light-absorption ratio variation approach (LARVA)). Moreover, the discrimination of Fe²⁺ and Fe³⁺ cations could be performed by naked-eye observation because of the development of different colors upon interaction with these probes which act as indicators for the in situ qualitative detection of Fe³⁺ and Fe²⁺. The limits of detection of Fe²⁺ and Fe³⁺ cations with receptor <b>2</b> were found to be as low as 30 and 15 parts per billion (ppb), respectively. The probable binding modes of these receptors with Fe²⁺ have also been suggested on the basis of the ¹H NMR spectroscopic titration, electrospray ionization mass spectrometry (ESI-MS), Job’s plot, and computational (DFT) studies along with electrochemical and spectro-photochemical data. Single crystal X-ray diffraction analysis of <b>1</b> revealed that its solid-state structure was stabilized via intermolecular C–H/O and O–H/N hydrogen bonds and by C–H/π interactions. Interestingly, detailed theoretical calculations (DFT) indicated that hydroxymethyl (−CH₂OH) group attached to naphthalene unit plays a pivotal role in sensing Fe²⁺/³⁺ ion selectively and in the stabilization of <b>2</b> in unusual eclipsed configuration through C–H···O type hydrogen bonding

Abnormal-NHC-Supported Nickel Catalysts for Hydroheteroarylation of Vinylarenes

Herein we report the hydroheteroarylation of vinylarenes with benzoxazole in the presence of a free abnormal N-heterocyclic carbene and Ni­(COD)₂, resulting in 1,1-diarylethane products exclusively. In an attempt to understand the mechanism of this catalytic reaction, two abnormal-NHC (<i>a</i>NHC)-coordinated Ni­(II) cyclooctenyl complexes were isolated and their solid-state structures were determined by X-ray crystallographic studies. These Ni­(II) cyclooctenyl complexes act as active catalyst precursors to generate in situ <i>a</i>NHC-Ni­(0) species, which undergo oxidative addition with heteroarene to form Ni­(II) hydride intermediates

A Highly Efficient Base-Metal Catalyst: Chemoselective Reduction of Imines to Amines Using An Abnormal-NHC–Fe(0) Complex

A base-metal, Fe(0)-catalyzed hydrosilylation of imines to obtain amines is reported here which outperforms its noble-metal congeners with the highest TON of 17000. The catalyst, (<i>a</i>NHC)­Fe­(CO)₄, works under very mild conditions, with extremely low catalyst loading (down to 0.005 mol %), and exhibits excellent chemoselectivity. The facile nature of the imine reduction under mild conditions has been further demonstrated by reducing imines towards expensive commercial amines and biologically important N-alkylated sugars, which are difficult to achieve otherwise. A mechanistic pathway and the source of chemoselectivity for imine hydrosilylation have been proposed on the basis of the well-defined catalyst and isolable intermediates along the catalytic cycle

Cyclic (Alkyl)amino Carbene Complex of Aluminum(III) in Catalytic Guanylation Reaction of Carbodiimides

Herein we report the synthesis of a cyclic (alkyl)­amino carbene (<i>c</i>AAC) complex of AlMe₃. This complex was used as an efficient catalyst for the guanyl­ation reaction of carbo­diimides with primary aryl­amines and secondary amines to deliver guanidine derivatives in good to excellent yields. This catalytic protocol can tolerate a wide range of functional groups. Furthermore, the longevity of the catalyst was tested in successive catalytic cycles, which indicated a sustained catalytic activity over a multiple cycles. The mechanistic pathway was well understood with the help of stoichiometric reaction and DFT study

Accessing Heterobiaryls through Transition-Metal-Free C–H Functionalization

Herein we report a transition-metal-free synthetic protocol for heterobiaryls, one of the most important pharmacophores in the modern drug industry, employing a new multidonor phenalenyl (PLY)-based ligand. The current procedure offers a wide substrate scope (24 examples) with a low catalyst loading resulting in an excellent product yield (up to 95%). The reaction mechanism involves a single electron transfer (SET) from a phenalenyl-based radical to generate a reactive heteroaryl radical. To establish the mechanism, we have isolated the catalytically active SET initiator, characterizing by a magnetic study