Stable and Storable N(CF3)2 Transfer Reagents

Fluorinated groups are essential for drug design, agrochemicals, and materials science. The bis(trifluoromethyl)amino group is an example of a stable group that has a high potential. While the number of molecules containing perfluoroalkyl, perfluoroalkoxy, and other fluorinated groups is steadily increasing, examples with the N(CF₃)₂ group are rare. One reason is that transfer reagents are scarce and metal-based storable reagents are unknown. Herein, a set of Cu^I and Ag^I bis(trifluoromethyl)amido complexes stabilized by N- and P-donor ligands with unprecedented stability are presented. The complexes are stable solids that can even be manipulated in air for a short time. They are bis(trifluoromethyl)amination reagents as shown by nucleophilic substitution and Sandmeyer reactions. In addition to a series of benzylbis(trifluoromethyl)amines, 2-bis(trifluoromethyl)amino acetate was obtained, which, upon hydrolysis, gives the fluorinated amino acid N,N-bis(trifluoromethyl)glycine.     

Fluorinated Azobenzenes Switchable with Red Light

Molecular photoswitches triggered with red or NIR light are optimal for photomodulation of complex biological systems, including efficient penetration of the human body for therapeutic purposes (“therapeutic window”). Yet, they are rarely reported, and even more rarely functional under aqueous conditions. In this work, fluorinated azobenzenes are shown to exhibit efficient E→Z photoisomerization with red light (PSS_660nm >75 % Z) upon conjugation with unsaturated substituents. Initially demonstrated for aldehyde groups, this effect was also observed in a more complex structure by incorporating the chromophore into a cyclic dipeptide with propensity for self-assembly. Under physiological conditions, the latter molecule formed a supramolecular material that reversibly changed its viscosity upon irradiation with red light. Our observation can lead to design of new photopharmacology agents or phototriggered materials for in vivo use.     

Bis(4-benzhydryl-benzoxazol-2-yl)methane – from a Bulky NacNac Alternative to a Trianion in Alkali Metal Complexes

A novel sterically demanding bis(4-benzhydryl-benzoxazol-2-yl)methane ligand 6 (^4−BzhH2BoxCH₂) was gained in a straightforward six-step synthesis. Starting from this ligand monomeric [M(^4-BzhH2BoxCH)] (M=Na ( 7 ), K ( 8₁ )) and dimeric [{M(^4-BzhH2BoxCH)}₂] (M=K ( 8₂ ), Rb ( 9 ), Cs ( 10 )) alkali metal complexes were synthesised by deprotonation. Abstraction of the potassium ion of 8 by reaction with 18-crown-6 resulted in the solvent separated ion pair [{(THF)₂K@(18-crown-6)}{bis(4-benzhydryl-benzoxazol-2-yl)methanide}] ( 11 ), including the energetically favoured monoanionic (E,E)-(^4-BzhH2BoxCH) ligand. Further reaction of ^4−BzhH2BoxCH₂ with three equivalents KH and two equivalents 18-crown-6 yielded polymeric [{(THF)₂K@(18-crown-6)}{K@(18-crown-6)K(^4-BzhBoxCH)}]_n (n→∞) ( 12 ) containing a trianionic ligand. The neutral ligand and herein reported alkali complexes were characterised by single X-ray analyses identifying the latter as a promising precursor for low-valent main group complexes.     

The Rayleigh law in silicon doped hafnium oxide ferroelectric thin films

A wealth of studies have confirmed that the low‐field hysteresis behaviour of ferroelectric bulk ceramics and thin films can be described using Rayleigh relations, and irreversible domain wall motion across the array of pining defects has been commonly accepted as the underlying micro‐mechanism. Recently, HfO₂ thin films incorporated with various dopants were reported to show pronounced ferroelectricity, however, their microscopic domain structure remains unclear till now. In this work, the effects of the applied electric field amplitude, frequency and temperature on the sub‐coercive polarization reversal properties were investigated for 10 nm thick Si‐doped HfO₂ thin films. The applicability of the Rayleigh law to ultra‐thin ferroelectric films was first confirmed, indicating the existence of a multi‐domain structure. Since the grain size is about 20–30 nm, a direct observation of domain walls within the grains is rather challenging and this indirect method is a feasible approach to resolve the domain structure. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Following Solid‐Acid‐Catalyzed Reactions by MAS NMR Spectroscopy in Liquid Phase—Zeolite‐Catalyzed Conversion of Cyclohexanol in Water

A microautoclave magic angle spinning NMR rotor is developed enabling in situ monitoring of solid–liquid–gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130 °C water. The ¹³C spectra show that dehydration of 1‐¹³C‐cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the ¹³C label. A simplified kinetic model shows the E1‐type elimination fully accounts for the initial rates of 1‐¹³C‐cyclohexanol disappearance and the appearance of the differently labeled products, thus suggesting that the cyclohexyl cation undergoes a 1,2‐hydride shift competitive with rehydration and deprotonation. Concurrent with the dehydration, trace amounts of dicyclohexyl ether are observed, and in approaching equilibrium, a secondary product, cyclohexyl‐1‐cyclohexene is formed. Compared to phosphoric acid, HBEA is shown to be a more active catalyst exhibiting a dehydration rate that is 100‐fold faster per proton.     

Pd/C as a Catalyst for Completely Regioselective CH Functionalization of Thiophenes under Mild Conditions

The completely C3‐selective arylation of thiophenes and benzo[b]thiophenes was achieved by using Pd/C as a heterogeneous catalyst without ligands or additives under mild reaction conditions. The practicability of this transformation is demonstrated by notable functional group tolerance and the insensitivity of the reaction to H₂O and air. This method is also applicable to nitrogen‐ and oxygen‐containing heterocycles, yielding the corresponding C2‐arylated products. Three‐phase tests along with Hg‐poisoning and hot‐filtration tests suggest that the catalytically active species is heterogeneous in nature.     

The Electronic Ground State of [Fe(CO)3(NO)]−: A Spectroscopic and Theoretical Study

During the past 10 years iron‐catalyzed reactions have become established in the field of organic synthesis. For example, the complex anion [Fe(CO)₃(NO)]^?, which was originally described by Hogsed and Hieber, shows catalytic activity in various organic reactions. This anion is commonly regarded as being isoelectronic with [Fe(CO)₄]^2?, which, however, shows poor catalytic activity. The spectroscopic and quantum chemical investigations presented herein reveal that the complex ferrate [Fe(CO)₃(NO)]^? cannot be regarded as a Fe^?II species, but rather is predominantly a Fe⁰ species, in which the metal is covalently bonded to NO^? by two π‐bonds. A metal–N σ‐bond is not observed.     

A Molecular Placeholder Strategy To Access a Family of Transition‐Metal‐Functionalized Vanadium Oxide Clusters

Systematic access to metal‐functionalized polyoxometalates has thus far been limited to lacunary tungsten oxide and molybdenum oxide clusters. The first controlled, stepwise bottom‐up assembly route to metal‐functionalized molecular vanadium oxides is now presented. A di‐vacant vanadate cluster with two metal binding sites, (DMA)₂[V₁₂O₃₂Cl]^3? (DMA=dimethylammonium) is formed spontaneously in solution and characterized by single‐crystal X‐ray diffraction, ESI mass spectrometry, ⁵¹V NMR spectroscopy, and elemental analyses. In the cluster, the metal binding sites are selectively blocked by hydrogen‐bonded DMA placeholder cations. Reaction of the cluster with transition metals TM (Fe³⁺, Co²⁺, Cu²⁺, Zn²⁺) gives access to mono‐functionalized vanadate clusters (DMA)[{TM(L)}V₁₂O₃₂Cl]^n? (L=ligand). Metal binding is accomplished by significant distortions of the vanadium oxide framework reminiscent of a pincer movement. Cluster stability under technologically relevant conditions in the solid‐state and solution is demonstrated.     

Pyranoside‐into‐Furanoside Rearrangement: New Reaction in Carbohydrate Chemistry and Its Application in Oligosaccharide Synthesis

Great interest in natural furanoside‐containing compounds has challenged the development of preparative methods for their synthesis. Herein a novel reaction in carbohydrate chemistry, namely a pyranoside‐into‐furanoside (PIF) rearrangement permitting the transformation of selectively O‐substituted pyranosides into the corresponding furanosides is reported. The discovered process includes acid‐promoted sulfation accompanied by rearrangement of the pyranoside ring into a furanoside ring followed by solvolytic O‐desulfation. This process, which has no analogy in organic chemistry, was shown to be a very useful tool for the synthesis of furanoside‐containing complex oligosaccharides, which was demonstrated by synthesizing disaccharide derivatives α‐D ‐Galp‐(1→3)‐β‐D ‐ Galf ‐OPr, 3‐O‐s ‐lactyl‐β‐D ‐ Galf ‐(1→3)‐β‐D ‐Glcp‐OPr, and α‐L ‐ Fucf ‐(1→4)‐β‐D ‐GlcpA‐OPr related to polysaccharides from the bacteria Klebsiella pneumoniae and Enterococcus faecalis and the brown seaweed Chordaria flagelliformis.     

Is Electrostatics Sufficient to Describe Hydrogen‐Bonding Interactions?

The stability and geometry of a hydrogen‐bonded dimer is traditionally attributed mainly to the central moiety A?H???B, and is often discussed only in terms of electrostatic interactions. The influence of substituents and of interactions other than electrostatic ones on the stability and geometry of hydrogen‐bonded complexes has seldom been addressed. An analysis of the interaction energy in the water dimer and several alcohol dimers—performed in the present work by using symmetry‐adapted perturbation theory—shows that the size and shape of substituents strongly influence the stabilization of hydrogen‐bonded complexes. The larger and bulkier the substituents are, the more important the attractive dispersion interaction is, which eventually becomes of the same magnitude as the total stabilization energy. Electrostatics alone are a poor predictor of the hydrogen‐bond stability trends in the sequence of dimers investigated, and in fact, dispersion interactions predict these trends better.