Two Amphoteric Silver Carbene Clusters Tskhovrebov, Alexander G.; Goddard, Richard; Fürstner, Alois
Angewandte Chemie International Edition,
July 2, 2018, Letnik:
57, Številka:
27
Journal Article
Recenzirano
Two highly labile silver carbene cluster complexes are described, which are unique in that they mark the transition point at which the carbene center transmutes from a fairly common NHC‐like ...nucleophilic behavior to an electrophilic character befitting reactive silver carbene intermediates of relevance in various catalytic transformations. This amphoteric character is the distinguishing attribute of a μ‐bridged donor/donor carbene entity that connects two silver atoms of triangular or tetrahedral metallic core units.
Transmutation: Two fragile silver carbene cluster complexes have been fully characterized. They mark the point at which the nature of the carbene ligand transitions from a common nucleophilic NHC‐like character (see scheme, left) to an electrophilic reactivity mode (see scheme, right).
Gold carbenes of the general type LAu=CR2+ are sufficiently long‐lived for spectroscopic inspection only if the substituents compensate for the largely missing stabilization of the carbene center by ...the LAu+ fragment. π‐Donation by two fluorine substituents (R=F) is insufficient; rather, difluorocarbene complexes are so deprived in electron density that they sequester even “weakly coordinating” anions such as triflate or triflimide. This particular bonding situation translates into unmistakable carbenium ion chemistry upon reaction with stilbene as a model substrate.
(Dis)Integrate: Gold carbenoids generated by Lewis‐acid‐mediated α‐fluoride elimination from LAuCF3 are so deprived in electron density that they even retain “weakly coordinating” counteranions (triflate, triflimide); they disintegrate, however, on reaction with (E)‐ or (Z)‐stilbene to give a carbenium intermediate that accounts for the observed downstream chemistry.
Novel halogenated aromatic dichlorodiazadienes were prepared via copper-mediated oxidative coupling between the corresponding hydrazones and CCl
. These rare azo-dyes were characterized using
H and
C ...NMR techniques and X-ray diffraction analysis for five halogenated dichlorodiazadienes. Multiple non-covalent halogen···halogen interactions were detected in the solid state and studied by DFT calculations and topological analysis of the electron density distribution within the framework of Bader's theory (QTAIM method). Theoretical studies demonstrated that non-covalent halogen···halogen interactions play crucial role in self-assembly of highly polarizable dichlorodiazadienes. Thus, halogen bonding can dictate a packing preference in the solid state for this class of dichloro-substituted heterodienes, which could be a convenient tool for a fine tuning of the properties of this novel class of dyes.
Chalcogenodiazoles have been intensively studied in recent years in the context of their supramolecular chemistry. In contrast, the newly discovered cationic 1,2,4-selenodiazole supramolecular ...building blocks, which can be obtained via coupling between 2-pyridylselenyl halides and nitriles, are virtually unexplored. A significant advantage of the latter is their facile structural tunability via the variation of nitriles, which could allow a fine tuning of their self-assembly in the solid state. Here, we explore the influence of the substituent (which derives from the nitrile) and counterions on the supramolecular assembly of cationic 1,2,4-selenodiazoles via chalcogen bonding.
Antibacterial chitosan films, versatile and eco-friendly materials, have garnered significant attention in both the food industry and medicine due to their unique properties, including ...biodegradability, biocompatibility, and antimicrobial activity. This review delves into the various types of chitosan films and their distinct applications. The categories of films discussed span from pure chitosan films to those enhanced with additives such as metal nanoparticles, metal oxide nanoparticles, graphene, fullerene and its derivatives, and plant extracts. Each type of film is examined in terms of its synthesis methods and unique properties, establishing a clear understanding of its potential utility. In the food industry, these films have shown promise in extending shelf life and maintaining food quality. In the medical field, they have been utilized for wound dressings, drug delivery systems, and as antibacterial coatings for medical devices. The review further suggests that the incorporation of different additives can significantly enhance the antibacterial properties of chitosan films. While the potential of antibacterial chitosan films is vast, the review underscores the need for future research focused on optimizing synthesis methods, understanding structure-property relationships, and rigorous evaluation of safety, biocompatibility, and long-term stability in real-world applications.
The synthesis and structural characterization of a series of supramolecular complexes of bicyclic cationic pyridine-fused 1,2,4-selenodiazoles with various anions is reported. The binding of ...trifluoroacetate, tetrachloroaurate, tetraphenylborate, perrhenate, and pertechnetate anions in the solid state is regarded. All the anions interact with selenodiazolium cations exclusively via a pair of “chelating” Se⋯O and H⋯O non-covalent interactions, which make them an attractive, novel, non-classical supramolecular recognition unit or a synthon. Trifluoroacetate salts were conveniently generated via novel oxidation reaction of 2,2′-dipyridyl diselenide with bis(trifluoroacetoxy)iodo)benzene in the presence of corresponding nitriles. Isolation and structural characterization of transient 2-pyridylselenyl trifluoroacetate was achieved. X-ray analysis has demonstrated that the latter forms dimers in the solid state featuring very short and strong Se⋯O and Se⋯N ChB contacts. 1,2,4-Selenodiazolium trifluoroacetates or halides show good solubility in water. In contrast, (AuCl4)−, (ReO4)−, or (TcO4)− derivatives immediately precipitate from aqueous solutions. Structural features of these supramolecular complexes in the solid state are discussed. The nature and energies of the non-covalent interactions in novel assembles were studied by the theoretical methods. To the best of our knowledge, this is the first study that regards perrhenate and pertechnetate as acceptors in ChB interactions. The results presented here will be useful for further developments in anion recognition and precipitation involving cationic 1,2,4-selenodiazoles.
N-Heterocyclic carbenes (NHCs) react at ambient conditions with nitrous oxide to give covalent adducts. In the crystal, all compounds show a bent N2O group connected via the N-atom to the former ...carbene carbon atom. Most adducts are stable at room temperature, but heating induces decomposition into the corresponding ureas. Kinetic experiments show that the thermal stability of the NHC–N2O adducts depends on steric as well as electronic effects. The coordination of N2O to NHCs weakens the N–N bond substantially, and facile N–N bond rupture was observed in reactions with acid or acetyl chloride. On the other hand, reaction with tritylium tetrafluoroborate resulted in a covalent modification of the terminal O-atom, and cleavage of the C–N2O bond was observed in a reaction with thionyl chloride. The coordination chemistry of IMes–N2O (IMes = 1,3-dimesitylimidazol-2-ylidene) was explored in reactions with the complexes CuOTf, Fe(OTf)2, PhSnCl3, CuCl2, and Zn(C6F5)2. Structural analyses show that IMes–N2O is able to act as a N-donor, as an O-donor, or as a chelating N,O-donor. The different coordination modes go along with pronounced electronic changes as evidenced by a bond length analysis.
The synthesis and structural characterization of α-haloalkyl-substituted pyridinium-fused 1,2,4-selenadiazoles with various counterions is reported herein, demonstrating a strategy for directed ...supramolecular dimerization in the solid state. The compounds were obtained through a recently discovered 1,3-dipolar cycloaddition reaction between nitriles and bifunctional 2-pyridylselenyl reagents, and their structures were confirmed by the X-ray crystallography. α-Haloalkyl-substituted pyridinium-fused 1,2,4-selenadiazoles exclusively formed supramolecular dimers via four-center Se···N chalcogen bonding, supported by additional halogen bonding involving α-haloalkyl substituents. The introduction of halogens at the α-position of the substituent R in the selenadiazole core proved effective in promoting supramolecular dimerization, which was unaffected by variation of counterions. Additionally, the impact of cocrystallization with a classical halogen bond donor C6F3I3 on the supramolecular assembly was investigated. Non-covalent interactions were studied using density functional theory calculations and topological analysis of the electron density distribution, which indicated that all ChB, XB and HB interactions are purely non-covalent and attractive in nature. This study underscores the potential of halogen and chalcogen bonding in directing the self-assembly of functional supramolecular materials employing 1,2,4-selenadiazoles derived from recently discovered cycloaddition between nitriles and bifunctional 2-pyridylselenyl reagents.
This comprehensive review illuminates the various methods of chitosan extraction, its antibacterial properties, and its multifarious applications in diverse sectors. We delve into chemical, physical, ...biological, hybrid, and green extraction techniques, each of which presents unique advantages and disadvantages. The choice of method is dictated by multiple variables, including the desired properties of chitosan, resource availability, cost, and environmental footprint. We explore the intricate relationship between chitosan’s antibacterial activity and its properties, such as cationic density, molecular weight, water solubility, and pH. Furthermore, we spotlight the burgeoning applications of chitosan-based materials like films, nanoparticles, nonwoven materials, and hydrogels across the food, biomedical, and agricultural sectors. The review concludes by highlighting the promising future of chitosan, underpinned by technological advancements and growing sustainability consciousness. However, the critical challenges of optimizing chitosan’s production for sustainability and efficiency remain to be tackled.
Nitro functionalized dibromodiazadiene dyes were prepared and fully characterized including X-ray single crystal analysis. Electron deficient dibromodiazadienes were found to be able to act as donors ...of halogen bonding (XB), while the nitro group acted as an acceptor of the XB. Depending on the substituents, the Br···O XB competed with other weak interactions, and for some of the dyes, they even outcompeted the XB involving the nitro group. However, the nitro functionalized dibromoalkenes 6a and 10a, which had only the nitro moiety as the most plausible acceptor of the XB, reliably formed 1D chains via Br⋯O XB. Experimental work was supported by the DFT calculations and topological analysis of the electron density distribution within the framework of Bader’s theory (QTAIM method).
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