Transamidation of Amides and Amidation of Esters by Selective N–C(O)/O–C(O) Cleavage Mediated by Air- and Moisture-Stable Half-Sandwich Nickel(II)–NHC Complexes

The formation of amide bonds represents one of the most fundamental processes in organic synthesis. Transition-metal-catalyzed activation of acyclic twisted amides has emerged as an increasingly powerful platform in synthesis. Herein, we report the transamidation of N-activated twisted amides by selective N–C(O) cleavage mediated by air- and moisture-stable half-sandwich Ni(II)–NHC (NHC = N-heterocyclic carbenes) complexes. We demonstrate that the readily available cyclopentadienyl complex, [CpNi(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), promotes highly selective transamidation of the N–C(O) bond in twisted N-Boc amides with non-nucleophilic anilines. The reaction provides access to secondary anilides via the non-conventional amide bond-forming pathway. Furthermore, the amidation of activated phenolic and unactivated methyl esters mediated by [CpNi(IPr)Cl] is reported. This study sets the stage for the broad utilization of well-defined, air- and moisture-stable Ni(II)–NHC complexes in catalytic amide bond-forming protocols by unconventional C(acyl)–N and C(acyl)–O bond cleavage reactions.     

Coulomb analogy for non-Hermitian degeneracies near quantum phase transitions

Degeneracies near the real axis in a complex-extended parameter space of a Hermitian Hamiltonian are studied. We present a method to measure distributions of such degeneracies on the Riemann sheet of a selected level and apply it in classification of quantum phase transitions. The degeneracies are shown to behave similarly as complex zeros of a partition function.     

Experimental and four‐component relativistic DFT studies of tungsten carbonyl complexes

We present a theoretical and experimental study of the structure and nuclear magnetic resonance (NMR) parameters of the pentacarbonyltungsten complexes of η¹‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine, η²‐norbornene, and imidazolidine‐2‐thione. The three complexes have a pseudo‐octahedral molecular structure with the six ligands bonded to the tungsten atom. The η¹‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine‐pentacarbonyl tungsten complex was synthesized for the first time. For all compounds, we present four‐component relativistic calculations of the NMR parameters at the Dirac–Kohn–Sham density functional level of theory using hybrid functionals. These large‐scale relativistic calculations of NMR chemical shifts and spin–spin coupling constants were compared with available experimental data, either taken from the literature or measured in this work. The inclusion of solvent effects modeled using a conductor‐like screening model was found to improve agreement between the calculated and experimental NMR parameters, and our best estimates for the NMR parameters are generally in good agreement with available experimental results. The present work demonstrates that four‐component relativistic theory has reached a level of maturity that makes it a convenient and accurate tool for modeling and understanding chemical shifts and indirect spin–spin coupling constants of organometallic compounds containing heavy elements, for which conventional non‐relativistic theory breaks down. Copyright © 2015 John Wiley & Sons, Ltd.     

Dielectric Spectroscopy of Ferronematics Based on 6CHBT Liquid Crystal

In our study, the dielectric behaviour of the rod-like liquid crystal (6CHBT) doped with magnetic nanoparticles of spherical shape was investigated by means of dielectric spectroscopy in the frequency range from 20 Hz to 2 MHz. A low frequency dielectric dispersion in the nematic and isotropic phases of the pure liquid crystal (LC) has been assigned to the space charge polarization. After doping the host LC with the magnetic nano particles, a nearly Debye-like relaxation process was observed with the temperature dependence obeying the Arrhenius law. Considering a possible electric double layer formation on the particle surfaces, the detected relaxation process in the doped LC can be associated with the electric double layer polarization. The experimental results point out that in the measured frequency range the space charge and interfacial effects constitute the main dielectric response. Any anchoring effects were not observed and are therefore expected to appear in higher frequencies.     

Crystal and Molecular Structures of Mononuclear Coordinated Copper(I) Complexes with Thio-triazole and Thio-triazine based Schiff base Ligands

Reaction of 4-amino-5-methyl-1,2,4-triazol-3(2H)-thione (AMTT) and 4-amino-6-methyl-3-thio-3,4-dihydro-1,2,4-triazin-5(2H)-one (AMTTO) with 2-hydroxybenzaldehyde led to the synthesis of corresponding Schiff base ligands [(Z)-4-((2-hydroxybenzylidene)amino)-3-methyl-1H-1,2,4-triazole-5(4H)-thione ( L1 ) and (Z)-4-((2-hydroxybenzylidene)amino)-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one ( L2 )]. Treatment of synthesized Schiff base ligands with CuCl provided the complexes [Cu(L1)₃Cl] ( 1 ) and [Cu(L2)₂Cl] ( 2 ). Synthesized complexes were characterized by elemental analyses, IR spectroscopy and X-ray diffraction studies. Complex 1 consists of a metal ion coordinated with one chloride ion and three Schiff base ligands via sulfur atoms in a distorted tetrahedral environment, whereas 2 consists of a metal ion coordinated with one chloride ion and two sulfur atoms from two different Schiff base ligands in a trigonal planar arrangement. Crystal data for 1 at –153 °C revealed an orthorhombic space group Fdd2, a = 34.8088(7), b = 33.8156(8), c = 11.6142(2) Å, Z = 16, R₁ = 0.0357; for 2 at –178 °C the symmetry was triclinic, space group P1 , a = 7.27520(10), b = 15.4620(2), c = 23.7985(4) Å, α = 72.1964(13), β = 86.5208(12), γ = 89.8597(11)°, Z = 4, R₁ = 0.0359.     

Bifunctional Nanoscale Assemblies: Multistate Electrochromics Coupled with Charge Trapping and Release

We demonstrate controlled charge trapping and release, accompanied by multiple color changes in a metallo‐organic bilayer. The dual functionality of the metallo‐organic materials provides fundamental insight into the metal‐mediated electron transport pathways. The electrochemical processes are visualized by distinct, four color‐to‐color transitions: red, transparent, orange, and brown. The bilayer is composed of two elements: 1) a nanoscale gate consisting of a layer of well‐defined polypyridyl ruthenium complexes bound to a flexible transparent electrode, and 2) a charge storage layer consisting of isostructural iron complexes attached to the surface of the gate. This gate mediates or blocks electron transport in response to an applied voltage. The charge storage and release depend on the oxidation state of the layer of ruthenium complexes (=gate). Combining electrochemistry with optical data revealed mechanistic information: the brown coloration of the bilayer directly relates to the formation of intermediate ruthenium species, providing evidence for catalytic positive charge release mediated through the gate.     

Polymer Lamellae as Reaction Intermediates in the Formation of Copper Nanospheres as Evidenced by In Situ X‐ray Studies

The classical nucleation theory (CNT) is the most common theoretical framework used to explain particle formation. However, nucleation is a complex process with reaction pathways which are often not covered by the CNT. Herein, we study the formation mechanism of copper nanospheres using in situ X‐ray absorption and scattering measurements. We reveal that their nucleation involves coordination polymer lamellae as pre‐nucleation structures occupying a local minimum in the reaction energy landscape. Having learned this, we achieved a superior monodispersity for Cu nanospheres of different sizes. This report exemplifies the importance of developing a more realistic picture of the mechanism involved in the formation of inorganic nanoparticles to develop a rational approach to their synthesis.     

A Photochemical/Thermal Switch Based on 4,4′-Bis(benzimidazolio)stilbene: Synthesis and Supramolecular Properties.

Stilbene derivatives are well-recognised substructures of molecular switches based on photochemically and/or thermally induced (E)/(Z) isomerisation. We combined a stilbene motif with two benzimidazolium arms to prepare new sorts of supramolecular building blocks and examined their binding properties towards cucurbit[n]urils (n=7, 8) and cyclodextrins (β-CD, γ-CD) in water. Based on the ¹H NMR data and molecular dynamics simulations, we found that two distinct complexes with different stoichiometry, i. e., guest@β-CD and guest@β-CD₂, coexist in equilibrium in a water solution of the (Z)-stilbene-based guests. We also demonstrated that the bis(benzimidazolio)stilbene guests can be transformed from the (E) into the (Z) form via UV irradiation and back via thermal treatment in DMSO.