Search

A series of LH[Z–I–Z] halogen(I) complexes, where Z = saccharinato or phthalimido anions and LH = pyridinium, pyrazinium, tetrabutyl (TBA)- or tetramethylammonium (TMA) cations, were prepared, structurally characterized, and discussed as complexes consisting of a [N–I–N]− anion with a three-center–four-electron (3c-4e) halogen bond, and a hydrogen-bonding (pyridinium or pyrazinium) or inert (TBA or TMA) cation. The symmetric [N–I–N]− anion, reminiscent of the triiodide [I–I–I]− anion, is found to be structurally equivalent to its cationic analogue [N–I–N]+ with N–I bond lengths of 2.26 Å. In contrast to the homoleptic [N–I–N]+ complexes, asymmetry of the N–I bond lengths (2.21 and 2.28 Å) was observed for those [N–I–N]− complexes which manifested a hydrogen bond to only one saccharinato moiety, thus being structurally analogous to the asymmetric heteroleptic [N–I–N]+ complexes. The results show that the 3c-4e [N–I–N] halogen bond, being either positively or negatively charged, can be asymmetrized by an external hydrogen bond ([N–I–N]−) or by using two different ligands (heteroleptic [N–I–N]+). peerReviewed

Introducing biobased polymers from renewable sources for use as high-performance thermoplastics with high demands on mechanical rigidity, transparency, thermal stability, as well as good processability, is a significant challenge. In the present work we have designed and prepared a rigid biobased bis-spirocylic diol by di-cycloketalization of a bicyclic diketone (cis-bicyclo[3.3.0]octane-3,7-dione, obtained from citric acid) using trimethylolpropane. This spiro-diol monomer has two reactive primary hydroxyl groups and the synthesis from inexpensive biobased starting materials is straightforward and readily upscalable, involving no chromatographic purification. In order to explore the usefulness of the new monomer, it was employed in melt polycondensations with diphenylcarbonate at up to 280 °C to form rigid fully amorphous polycarbonates (PCs). Molecular weights (MWs) up to Mn = 28 kg mol−1 were achieved, and thermal and dynamic mechanical measurements showed glass transitions up to Tg = 100 °C, with no thermal decomposition until Td ∼350 °C. Solvent cast films had excellent mechanical flexibility and strength, as well as a high transparency with only slight coloration. Results by dynamic melt rheology implied that the high-MW PCs had a good processability at 170 °C, with a stable shear modulus over time, but started to degrade via chain scission reactions when the temperature approached 200 °C. In conclusion, the present work demonstrates the straightforward preparation of the citric acid-based spiro-diol, and indicates that it is an efficient building block for the preparation of rigid biobased PCs and other condensation polymers.

Six bile acid alkyl amide derivatives were studied with respect to their gelation properties. The derivatives were composed of three different bile acids with hexyl or cyclohexyl side chains. The gelation behaviour of all six compounds were studied for 36 solvents with varying polarities. Gelation was observed mainly in aromatic solvents, which is characteristic for bile‐acid‐based low molecular weight gelators. Out of 108 bile acid‐solvent combinations, a total of 44 gel systems were formed, 28 of which from lithocholic acid derivatives, only two from deoxycholic acid derivatives, and 14 from cholic acid derivatives. The majority of the gel systems were formed from bile acids with hexyl side chains, contrary to the cyclohexyl group, which seems to be a poor gelation moiety. These results indicate that the spatial demand of the side chain is the key feature for the gelation properties of the bile acid amides., The gelation abilities of a series of six bile acid alkyl amides were studied. Gelation was observed mainly in aromatic solvents by lithocholyl derivatives. One of the cholyl derivatives formed exclusively flawless gels, speculated to stem from its ability to form H‐bonded 2D polymers contrary to 1D bilayered structures of the other derivatives. The shape of the side chain (linear vs. cyclic) clearly had an impact on the self‐assembly properties.

In the presence of KOH, NH-sulfoximines react with pentafluoropyridine to give N-(tetrafluoropyridyl)sulfoximines (NTFP-sulfoximines) in moderate to excellent yields. Either a solution-based or a superior solvent-free mechanochemical protocol can be followed. X-Ray diffraction analyses of 26 products provided insight into the bond parameters and conformational rigidity of the molecular scaffold. In solid-state structures, sulfoximines with halo substituents on the S-bound arene are intermolecularly linked by C–X⋯O[double bond, length as m-dash]S (X = Cl, Br) halogen bonds. Hirshfeld surface analysis is used to assess the type of non-covalent contacts present in molecules. For mixtures of three different S-pyridyl-substituted NTFP-sulfoximines and N-iodosuccinimide (NIS) in CDCl3, association constants were determined by 1H NMR spectroscopy. The data revealed a dependence of the halogen bond strength on the position of the pyridyl nitrogen indicating the presence of N–I⋯N(S-pyridyl) interactions. Neither the S[double bond, length as m-dash]O oxygen nor the tetrafluoropyridyl-substituted nitrogen of the sulfoximine appeared to be involved in halogen bonding. peerReviewed

At elevated temperatures, N-cyanosulfoximines react with Meldrum’s acid derivatives to give sulfoximines with N-bound 5-carbonyl-1,3-oxazine-2,4-dione groups. A representative product was characterized by single-crystal X-ray structure analysis. The product formation involves an unexpected molecular reorientation requiring several sequential bond-forming and -cleaving processes. peerReviewed

A catalytic approach for the preparation of indolines by dearomatizing cyclization is presented. FeCl3 acts as a catalyst to afford tetracyclic 5a,6-dihydro-12H-indolo[2,1-b][1,3]benzoxazin-12-ones in good yields. The cyclization also proceeds with tosylamides forming C-N bonds in 53 % yield. peerReviewed

The nature of C–I⋯⁻O–N⁺ interactions, first of its kind, between non-fluorinated tetraiodoethylene XB-donor and pyridine N-oxides (PyNO) are studied by single-crystal X-ray diffraction (SCXRD) and Density Functional Theory (DFT) calculations. Despite the non-fluorinated nature of the C2I4, the I⋯O halogen bond distances are similar to well-known perfluorohaloalkane/-arene donor-PyNO analogues. With C2I4, oxygens of the N-oxides adopt exclusively 2-XB-coordination in contrast to the versatile bonding modes observed with perfluorinated XB-donors. The C2I4 as the XB donor forms with PyNO’s one-dimensional chain polymer structures in which the C2I4⋯(μ-PyNO)2⋯C2I4 segments manifesting two bonding motifs, namely, side-by-side (vicinal di-iodo) and head-to-head (geminal di-iodo), due to the nearly symmetric square planar structure of the C2I4. While the attractive nature between I- and O-atoms is mainly electrostatic, the narrow range of C⋯O bond parameters demonstrate that the -bond between four iodine atoms also plays an important role in enhancing the -hole strength. DFT-based monodentate XB interaction energies, ΔEint, in thirteen 1:1 XB complexes vary between 31.9 – 46.5 kJ mol–1, the strongest remarkably exceeding the value reported for I–I⋯⁻O–N⁺ = 42.0 kJ mol–1. In case of C2I4･(pyridine N-oxide) [31.9 kJ mol–1], the monodentate XB energy is on a par with perfluorinated donor complexes, namely, CF3I･(pyridine N-oxide) [31.1 kJ mol–1] and C6F5I･(pyridine N-oxide) [32.3 kJ mol–1]. peerReviewed

The molecular recognition of nine quaternary alkyl- and aryl-ammonium halides (Bn) by two different receptors, Calkyl-tetrasodiumsulfonatomethyleneresorcinarene (An), were studied in solution using 1H NMR spectroscopy. Substitution of methylenesulfonate groups at 2-positions of resorcinol units resulted in an increase of cavity depth by ∼2.80 Å and a narrow cavity aperture compared to Calkyl-2-H-resorcinarenes. The effect of alkyl chain lengths on the endo-complexation, that is the ability to incorporate other than N-methyl chains inside the cavities, were investigated using ammonium cations of the type ⁺NH2(R1)(R2), (R1 = Me, Et, Bu, R2 = Bu, Ph, Bz ). The C−H⋯ interactions between guests and hosts are the key driving forces for 14 out of 16 observed endo-complexes. In case of N-butyl-N-benzylammonium cation, the hydrogen bonding between -NH2 and sulfonate oxygens and the larger size hamper the N-butyl and N-benzyl groups from entering the host cavity. Association constants derived from isothermal calorimetry titrations confirm 1:1 host-guest complexes highlighting guest affinity, based on size and orientation. X-Ray crystallographic analysis revealed two types of complexes viz sodium-containing co-crystals, [(An)4⁻･m(Bn)⁺･qNa⁺], and sodium-free, [(An)4⁻･4(Bn)⁺]. Both types accommodate (Bn⁺) guests in their cavities. The N-methylated heterocycle guests and host form capsule-like structures in which the two-halves were joined by O−Na coordination bonds and self-assembles in to 2-D polymeric sheets. From the crystal structures, different conformations of methylenesulfonate groups with respect to cavity arising due to tetrahedral geometry of methylene linker were observed. Density Functional Theory (DFT) computations were used to analyze the effects of endo-guests on host conformations and to estimate the relative strengths of host-guest interactions. peerReviewed

Dissertation, RWTH Aachen University, 2018; Aachen 1 Online-Ressource (XVIII, 204 Seiten) : Illustrationen (2018). = Dissertation, RWTH Aachen University, 2018, Die Dissertation unter dem Titel „Design von Bimetallischen Koordinationsnetzwerken: Synthese, Strukturelle Charakterisierung, und Thermische Zersetzung“ beschäftigt sich mit der Herstellung von metall-organischen Gerüsten (engl. Metal-Organic Frameworks, MOFs) und die darauffolgende Zersetzungsreaktion zu einem potentiellen Katalysatormaterial für den deNOx Prozess. In dieser Arbeit liegt der Schwerpunkt auf der Synthese von Systemen mit zwei verschiedenen Metallen, beispielsweise ytterbium- und silberhaltigen Verbindungen, die über nicht kommerziell-erhältlich, sogenannte ditope Liganden verknüpft werden. N-substituierte Acetylaceton-Derivate stellt eine beliebte Gruppe innerhalb der ditopen Liganden dar. Sie besitzen zwei Koordinationsseiten mit verschiedenen Pearson-Härten: eine harte, chelatisierende O,O’-Koordinationsseite sowie eine weiche N-Donorseite. Schwerpunkt dieser Dissertation liegt in der Syntheseoptimierung von den noch nicht viel untersuchten, ditopen Liganden und ihre Reaktivität mit verschiedenen Metallsalzen. Folgende N-substituierte Acetylacetone, wie 3-(Pyridin-4-yl)pentan-2,4-dion (HacacPy, A), 3-(2-(Pyridin-4-yl)ethyl)pentan-2,4-dion (HacacPyen, B), und/oder 4-Acetyl-5-oxohexanenitril (HacacCNen, C) wurden untersucht. Zunächst soll möglichst einfach und in wenigen Syntheseschritten das bimetallische Koordinationspolymer (Precursormaterial) hergestellt und charakterisiert werden. Idealerweise erfolgt die Synthese in einem Schritt. Vorangegangene Arbeiten haben jedoch gezeigt, dass meist mehrere Syntheseschritte bis zum gewünschten Endprodukt vonnöten sind. Grundlagenforschung in den Punkten Optimierung der Ligandsynthese, strukturelle Charakterisierung aller Verbindungen mittels hauptsächlich Einkristallröntgendiffraktion, Herstellung der metallischen Knotenpunkten (Secondary Building Units, SBUs) sowie den bimetallischen Netzwerke, thermische Zersetzungsstudien und Eignung als Katalysatoren werden in dieser Arbeit angesprochen. Die beiden letztgenannten Punkte erfolgen in Kooperation mit Kollegen aus dem New Chemical Syntheses Institute (INS) in Pulawy, Polen. Die Synthese von dem Liganden aus der ersten Generation, HacacPy, sowie seine Nutzung als verbrückenden Liganden zwischen zwei Metallkationen, Al(III) and Zn(II), sind seit 1995 bekannt. Sein Koordinationsverhalten zu harten zwei- und dreiwertigen Metallsalzen wurde ausführlich untersucht. Systematische Untersuchung zur direkten N-Koordination sowie eine strukturelle Charakterisierung des Liganden wurden bis dato nicht durchgeführt. Neben der Isolierung von zwei Nebenprodukten und einem Zersetzungsprodukt, nämlich (4-Pyridyl)-aceton (acPy, Aa), zeigten Röntgen- und Neutronendiffraktionsstudien an HacacPy, dass ein reversibler, struktureller Phasenübergang vorliegt. Systematische Untersuchungen der weichen N-Donorseite zu Zinkgruppenhalogeniden resultierte in eindimensionale Kettenpolymeren und Komplexen mit HacacPy als terminalen Liganden. Deprotonierung der Acetylacetonseite und Vernetzung der SBUs mit einem zweiten Metallkation führte zur Bildung von multidimensionalen Netzwerkstrukturen. Liganden aus der ersten Generation besitzen jedoch folgende Nachteile: giftige und nicht gerade billige Startmaterialien, relativ viele Syntheseschritte, geringe Ausbeute und Anfälligkeit des Liganden zur Zersetzung. Im Rahmen von potentieller industrieller Anwendung der bimetallischen Verbindungen als deNOx Katalysator müssen diese Punkte idealerweise entfallen. Liganden aus der zweiten Generation, HacacPyen, B, and HacacCNen, C, erfüllen alle oben genannten Punkte, jedoch sind diese Liganden wenig erforscht. Strukturell gesehen sind sie den Liganden aus der ersten Generation sehr ähnlich; die funktionellen Gruppen sind hier durch eine Ethylen-Gruppe getrennt, wodurch die Liganden beweglicher sind. Mittels Einkristalldiffraktion konnte nachgewiesen werden, dass die Liganden als Enol-Tautomer und als antiperiplanare Konformere auskristallisieren. Die Flexibilität des Liganden macht sich erst nach erfolgreicher N-, O,O’- oder N/O,O’-Koordination bemerkbar, je nach dem welches Metallsalz, welche Temperatur und welches Lösungsgemisch verwendet wurde, findet man verschiedene Konformationen (gauche und/oder antiperiplanar) und Tautomere des Liganden (Enol und Diketo) in den SBUs und bimetallische Netzwerkstrukturen. Durch die Flexibilität wurde ebenfalls beobachtet, dass Kristallisationsansätze in der Regel länger brauchen als beispielsweise analoge Reaktionen mit HacacPy. Zusätzlich sind hier auch härtere Bedingungen für die Deprotonierung notwendig. Highlight dieser Arbeit sind die Verbindungen B-16 und C-13. B-16 ist eine dimere Ytterbium(III)-Verbindung mit den zum allerersten Mal beobachteten gauche-Konformationen des acacPyen- Liganden. C-13 ist eine acht-kerniger Anderson-Typ Cluster basierend auf Al(acacCNen)3 and Ag(I) mit einem relativ geringen Silberanteil (Al-zu-Ag-Verhältnis: 3:1). Diese Verbindung wird in Kürze von den Kollegen aus Polen bezüglich ihrer potentiellen katalytischen Aktivität zur N2O-Zersetzung getestet., Published by Aachen