Sydnone methides - a forgotten class of mesoionic compounds for the generation of anionic N-heterocyclic carbenes

Sydnone methides are described from which only one single example has been mentioned in the literature so far. Their deprotonation gave anions which can be formulated as π-electron rich anionic N-heterocyclic carbenes. Sulfur and selenium adducts were stabilized as their methyl ethers, and mercury, gold as well as rhodium complexes of the sydnone methide carbenes were prepared. Sydnone methide anions also undergo C−C coupling reactions with 1-fluoro-4-iodobenzene under Pd(PPh3)4 and CuBr catalysis. 77Se NMR resonance frequencies and 1JC4-Se as well as 1JC4-H coupling constants have been determined to gain knowledge about the electronic properties of the anionic N-heterocyclic carbenes. The carbene carbon atom of the sydnone methide anion 3 j resonates at δ=155.2 ppm in 13C NMR spectroscopy at −40 °C which is extremely shifted upfield in comparison to classical N-heterocyclic carbenes

Customizing the appearance of sparks with binary metal alloys

Long-flying sparks are an essential part of several pyrotechnic effects. Unfortunately, and in contrast to colored flames, the color space of sparks is basically limited to the black-body curve. With low-boiling metals, vapor phase combustion and bright colorful flashes are achievable. In 1999, alloys of rare-earth elements have been proposed for colorful spark genera-tion. To the best of our knowledge, here we present the first investigation of such alloys to change the color of sparks be-yond the black-body limit. Alloys consisting of >65 at.-% of a brightly emitting and low-boiling metal and a carrier metal allow achieving long-flying deeply colored sparks. Besides the color, branching of sparks is crucial for the visual appear-ance. Rare-earth metals were found to promote branching of different alloys. Finally, fountains ejecting golden/green sparks based on a stable eutectic Yb-Cu alloy and continuously branching sparks based on Nd2Fe14B are presented

Formation of titanium nitride, titanium carbide, and silicon carbide surfaces by high power femtosecond laser treatment

Coatings based on titanium nitrides, titanium carbides and silicon carbides can optimize the surface properties of titanium or silicon for various applications ranging from biocompatibility to chemical stability and durability. Here, we investigated a high power (100 W) high pulse repetition rate femtosecond laser process (λ=1030 nm, τ=750 fs, f=1 MHz) for the treatment of titanium and silicon in atmospheres of argon, nitrogen, methane, ethene and acetylene. In a nitrogen atmosphere, a homogeneous coating of TiON is formed on titanium. In an ethene/argon atmosphere coatings of TiOC and SiC are formed on Ti and Si, respectively. The process allows a fast surface transformation with a process rate of 0.33 cm2 s−1 and a high spatial resolution below 0.5 mm with a minimal heat affected zone at the same time. In contrast to low repetition rate femtosecond laser processed samples, the surfaces are more robust against mechanical impact. At the same time, the surfaces reveal a distinct microstructure in comparison to coatings obtained by vapor deposition techniques

3D-Printing inside the glovebox: a versatile tool for inert-gas chemistry combined with spectroscopy

3D-Printing with the well-established ‘Fused Deposition Modeling’ technology was used to print totally gas-tight reaction vessels, combined with printed cuvettes, inside the inert-gas atmosphere of a glovebox. During pauses of the print, the reaction flasks out of acrylonitrile butadiene styrene were filled with various reactants. After the basic test reactions to proof the oxygen tightness and investigations of the influence of printing within an inert-gas atmosphere, scope and limitations of the method are presented by syntheses of new compounds with highly reactive reagents, such as trimethylaluminium, and reaction monitoring via UV/VIS, IR, and NMR spectroscopy. The applicable temperature range, the choice of solvents, the reaction times, and the analytical methods have been investigated in detail. A set of reaction flasks is presented, which allow routine inert-gas syntheses and combined spectroscopy without modifications of the glovebox, the 3D-printer, or the spectrometers. Overall, this demonstrates the potential of 3D-printed reaction cuvettes to become a complementary standard method in inert-gas chemistry

Sydnone anions and abnormal N-heterocyclic carbenes of O-ethylsydnones : Characterizations, calculations and catalyses

Peer reviewe

Switchable mesomeric betaines derived from pyridinium-phenolates and bis(thienyl)ethane

Syntheses of push–pull substituted non-symmetric bis(thienyl)ethenes (BTEs) possessing a central perfluorocyclopentene core are described. The substituent effects of anisole, phenole, and phenolate as well as pyridine, pyridinium, and N-methylpyridinium substituents, joined through their 3- or 4-positions to the central BTE core, respectively, cover the range from very strongly electron-donating [σ(4-phenolate)=−1.00] to extremely strongly electron-withdrawing [σ(pyridinium-4-yl)=+2.57] in the title mesomeric betaines. The different isomers possessing 4-yl/4-yl, 4-yl/3-yl and 3-yl/3-yl substituents represent different combinations of conjugated and cross-conjugated partial structures and cause different spectroscopic properties. In addition, through-space conjugation between the 2- and 2′-position of the thiophenes can be observed which circumvents the charge-separation of through-bond cross-conjugation. The BTE possessing the push–pull chromophore consisting of 3-anisole and 4-pyridinium substituents (24) displays the best extinction coefficients within the series of compounds described here (ϵ=33.8/15.7 L/mol ⋅ cm), while the mesomeric betaine possessing an N-methylpyridinium-4-yl and a 4-phenolate substituent (29) displays considerable bathochromic shifts to λmax=724 nm in its closed form

Borane adducts of punicine and of its dehydroxy derivatives (pyridinium-1-yl)-2-and 3-phenolates

The natural product punicine (Punica granatum) exists in two tautomeric forms, the cross-conjugated mesomeric betaine 1-(pyridinium-1-yl)-2-hydroxy-phenyl-5-olate and the conjugated mesomeric betaine 1-(pyridinium-1-yl)-5-hydroxy-phenyl-2-olate. Punicine as well as its picoline derivatives reacted with tris(pentafluorophenyl)borane exclusively at the 2'-olate group to form zwitterionic borates. Correspondingly, the 5'-dehydroxy derivate of punicine, the conjugated heterocyclic mesomeric betaine 1-(pyridinium-1-yl)-phenyl-2-olate and its picoline derivatives also gave borates, whereas analogous reactions of the cross-conjugated isomer 2'-dehydroxypunicine [1-(pyridinium-1-yl)-phenyl-3-olatel did not result in the formation of stable adducts. (C) 2020 Elsevier Ltd. All rights reserved.Peer reviewe

Sydnonmethide - fast vergessene Mesoionen als Vorläufermoleküle von anionischen N-heterocyclischen Carbenen

Wir beschreiben Sydnonmethide, von denen bisher nur ein einziges Beispiel in der Literatur erwähnt worden war. Sydnonmethide können zu Anionen deprotoniert werden, die als π-elektronenreiche anionische N-heterocyclische Carbene formulierbar sind. Schwefel- und Selenaddukte konnten wir als ihre Methylether stabilisieren sowie Quecksilber-, Gold- und Rhodiumkomplexe von Sydnonmethiden herstellen. Die Anionen von Sydnonmethiden gehen zudem C-C-Kupplungsreaktionen mit 1-Fluor-4-iodbenzol unter Pd(PPh3)4- und CuBr-Katalyse ein. Zur Abschätzung der elektronischen Eigenschaften dieser anionischen N-heterocyclischen Carbene bestimmten wir die 77Se-NMR-Resonanzfrequenzen und die 1JC4-Se-Kopplungskonstanten der Selen-Addukte sowie die 1JC4-H-Kopplungskonstanten der mesoionischen Vorläufermoleküle. Im Vergleich zu klassischen N-heterocyclischen Carbenen erscheint das Carben-Kohlenstoffatom des Sydnonmethid-Anions 3 j in den bei −40 °C gemessenen 13C-NMR-Spektren mit δ=155.2 ppm bei extrem hohem Feld

Immobilisation of monoanionic N,N,O-ligands aswell as complexes thereof and DFT calculations

Im Rahmen dieser Dissertation wurden monoanionische N,N,O-Liganden mit unterschiedlichen Methoden auf verschiedenen Festphasen immobilisiert. Komplexe mit monoanionischen N,N,O-Liganden sind als Modellverbindungen für zahlreiche zink- und eisenhaltige Metalloenzyme von Bedeutung. Aufgrund der hohen Affinität der N,N,O-Liganden zu den Metall-Zentren liegt jedoch eine Tendenz zur Ausbildung von katalytisch inaktiven Bisligandverbindungen mit Zink(II) und Eisen(II) vor. Die Immobilisierung erlaubt es, ohne die Einführung sterisch anspruchsvoller Reste die Koordination zweier N,N,O-Liganden an ein Metall-Zentrum zu unterbinden.Darüber hinaus wird der Aufbau eines Rechenclusters für DFT-Rechnungen und dessen Anwendung für zahlreiche Rechnungen aus dem Themengebiet der monoanionischen N,N,O-Liganden beschrieben

Color‐changing sparks from rare earth metal powders

Commonly, sparks emit light according to the well-known black (gray) body radiation. Recently, we reported on color‐changing sparks based on erbium powder, which switch their light emission between black body emission (surface combustion) and element‐specific emission (vapor phase combustion). Herein, we investigated the spark formation from the adjacent rare‐earth elements. The corresponding boiling points are significantly below (Yb, Sm, Tm) or above (Y, Lu) the boiling point of Er. While Yb and Sm evaporate too fast to form longer sparks, Y, Lu and Tm form color‐changing sparks with varying length of the element‐specific emission phase. The sparks were investigated by time‐resolved emission spectroscopy, long‐time exposures, and NIR/MIR imaging. The same basic pyrotechnic formulation containing one of these metal powders reveals a strongly differing burning behavior depending on the boiling point of the metal. The burning characteristics change from a green strobe (Yb) to intense colorful crackling (Tm) and finally a sparkling fountain with long‐flying sparks (Lu, Y, Er)