Recently, chalcogen bonding has been investigated in more detail in organocatalysis and the scope of activated functionalities continues to increase. Herein, the activation of imines in a Povarov [4+2] cycloaddition reaction with bidentate cationic chalcogen bond donors is presented. Tellurium-based Lewis acids show superior properties compared to selenium-based catalysts and inactive sulfur-based analogues. The catalytic activity of the chalcogen bonding donors increases with weaker binding anions. Triflate, however, is not suitable due to its participation in the catalytic pathway. A solvent screening revealed a more efficient activation in less polar solvents and a pronounced effect of solvent (and catalyst) on endo : exo diastereomeric ratio. Finally, new chiral chalcogen bonding catalysts were applied but provided only racemic mixtures of the product.

Noncovalent interactions such as halogen bonding (XB) and chalcogen bonding (ChB) have gained increased interest over the last decade. Whereas XB-based organocatalysis has been studied in some detail by now, intermolecular ChB catalysis only emerged quite recently. Herein, bidentate cationic tellurium-based chalcogen bond donors are employed in the catalytic chloride abstraction of 1-chloroisochroman. While selenium-based ChB catalysts showed only minor activity in this given benchmark reaction, tellurium-based variants exhibited strong activity, with rate accelerations of up to 40 relative to non-chalogenated reference compounds. In general, the activity of the catalysts improved with weaker coordinating counterions, but tetrafluoroborate took part in a fluoride transfer side reaction. Catalyst stability was confirmed via a fluoro-tagged variant.

Preorganization is a powerful tool in supramolecular chemistry which has been utilized successfully in intra- and intermolecular halogen bonding. In previous work, we had developed a bidentate bis(iodobenzimidazolium)-based halogen bond donor which featured a central trifluoromethyl substituent. This compound showed a markedly increased catalytic activity compared to unsubstituted bis(iodoimidazolium)-based Lewis acids, which could be explained either by electronic effects (the electron withdrawal by the fluorinated substituent) or by preorganization (the hindered rotation of the halogen bonding moieties). Herein, we systematically investigate the origin of this increased Lewis acidity via a comparison of the two types of compounds and their respective derivatives with or without the central trifluoromethyl group. Calorimetric measurements of halide complexations indicated that preorganization is the main reason for the higher halogen bonding strength. The performance of the catalysts in a series of benchmark reactions corroborates this finding.

Chalcogen bonding is the non-covalent interaction between Lewis acidic chalcogen substituents and Lewis bases. Herein, we present the first application of dicationic tellurium-based chalcogen bond donors in the nitro-Michael reaction between trans-beta-nitrostyrene and indoles. This also constitutes the first activation of nitro derivatives by chalcogen bonding (and halogen bonding). The catalysts showed rate accelerations of more than a factor of 300 compared to strongly Lewis acidic hydrogen bond donors. Several comparison experiments, titrations, and DFT calculations support a chalcogen-bonding-based mode of activation of beta-nitrostyrene.

Chalcogen bonding is a noncovalent interaction between electrophilic chalcogen substituents and Lewis bases. In their Communication on page 16923 ff., S. M. Huber and co-workers show that dicationic tellurium compounds can act as strong catalysts in a nitro-Michael reaction. This is the first time that a nitro compound has been reported to be activated by halogen bonding or chalcogen bonding. The crucial role of chalcogen bonding was confirmed by comparison experiments.

Abstract In the last years the use of chalcogen bonding—the noncovalent interaction involving electrophilic chalcogen centers—in noncovalent organocatalysis has received increased interest, particularly regarding the use of intermolecular Lewis acids. Herein, we present the first use of tellurium‐based catalysts for the activation of a carbonyl compound (and only the second such activation by chalcogen bonding in general). As benchmark reaction, the Michael‐type addition between trans‐crotonophenone and 1‐methylindole (and its derivatives) was investigated in the presence of various catalyst candidates. Whereas non‐chalcogen‐bonding reference compounds were inactive, strong rate accelerations of up to 1000 could be achieved by bidentate triazolium‐based chalcogen bond donors, with product yields of >90 % within 2 h of reaction time. Organotellurium derivatives were markedly more active than their selenium and sulphur analogues and non‐coordinating counterions like BArF 4 provide the strongest dicationic catalysts.

Various neutral, mono- and dicationic halogen bond donors were screened for their ability to act as catalysts in a Nazarov cyclisation reaction. Using a highly preorganized dicationic catalyst with a noncoordinating counterion proved essential for high activity.

AbstractChalkogenbrücken sind nicht‐kovalente Wechselwirkungen zwischen Lewis‐aziden Chalkogensubstituenten und Lewis‐Basen. Hierin präsentieren wir die erste Anwendung dikationischer, Tellur‐basierter Chalkogenbrückendonoren als Katalysatoren in einer Nitro‐Michael‐Reaktion zwischen trans‐β‐Nitrostyrol und Indolen. Dies ist außerdem die erste Aktivierung einer Nitro‐Gruppe durch Chalkogenbrücken (und Halogenbrücken). Die Katalysatoren zeigten eine mehr als 300‐fache Beschleunigung der Reaktionsgeschwindigkeit im Vergleich zu stark Lewis‐sauren Wasserstoffbrückendonoren. Durch mehrere Vergleichsexperimente, Titrationen und DFT‐Rechnungen konnte die Aktivierung des Nitrostyrols durch Chalkogenbrücken nachgewiesen werden.

Chalkogenbrücken sind nichtkovalente Wechselwirkungen zwischen elektrophilen Chalkogensubstituenten und Lewis-Basen. In ihrer Zuschrift auf S. 17079 zeigen S. M. Huber und Mitarbeiter, dass dikationische Tellurverbindungen eine Nitro-Michael-Reaktion katalysieren können, indem sie die Nitroverbindung aktivieren. Die entscheidende Rolle der Chalkogenbrücken wurde durch Vergleichsexperimente bestätigt.

In the last few decades, "unusual" noncovalent interactions like anion-pi and halogen bonding have emerged as interesting alternatives to the ubiquitous hydrogen bonding in many research areas. This is also true, to a somewhat lesser extent, for chalcogen bonding, the noncovalent interaction involving Lewis acidic chalcogen centers. Herein, we aim to provide an overview on the use of chalcogen bonding in crystal engineering and in solution, with a focus on the recent developments concerning intermolecular chalcogen bonding in solution-phase applications. In the solid phase, chalcogen bonding has been used for the construction of nano-sized structures and the self-assembly of sophisticated self-complementary arrays. In solution, until very recently applications mostly focused on intramolecular interactions which stabilized the conformation of intermediates or reagents. In the last few years, intermolecular chalcogen bonding has increasingly also been exploited in solution, most notably in anion recognition and transport as well as in organic synthesis and organocatalysis.

AbstractIn den letzten Jahrzehnten haben sich “unübliche” nichtkovalente Wechselwirkungen wie Anion‐π oder Halogenbrücken in vielen Forschungsbereichen zu interessanten Alternativen zu den allgegenwärtigen Wasserstoffbrücken entwickelt. Dies trifft – zu einem etwas geringeren Grad – auch auf Chalkogenbrücken zu, die nichtkovalenten Wechselwirkungen Lewis‐acider Chalkogenzentren. Dieser Kurzaufsatz soll einen Überblick über den Einsatz von Chalkogenbrücken in der kondensierten Phase geben, mit einem Fokus auf den neuesten Entwicklungen bei der Anwendung intermolekularer Chalkogenbrücken in Lösung. Im Festkörper wurden Chalkogenbrücken zum Aufbau nanoskaliger Strukturen und für die Selbstorganisation ausgefeilter selbstkomplementärer Komplexe verwendet. Bis vor kurzem konzentrierten sich die Anwendungen in Lösung vor allem auf intramolekulare Wechselwirkungen, welche die Konformation von Intermediaten oder Reagentien stabilisierten. In den letzten Jahren wurden nun aber auch intermolekulare Chalkogenbrücken zunehmend in Lösung eingesetzt, besonders für Anionenerkennung und ‐transport sowie in der organischen Synthese und der Organokatalyse.

In the last few decades, “unusual” noncovalent interactions like anion‐π and halogen bonding have emerged as interesting alternatives to the ubiquitous hydrogen bonding in many research areas. This is also true, to a somewhat lesser extent, for chalcogen bonding, the noncovalent interaction involving Lewis acidic chalcogen centers. Herein, we aim to provide an overview on the use of chalcogen bonding in crystal engineering and in solution, with a focus on the recent developments concerning intermolecular chalcogen bonding in solution‐phase applications. In the solid phase, chalcogen bonding has been used for the construction of nano‐sized structures and the self‐assembly of sophisticated self‐complementary arrays. In solution, until very recently applications mostly focused on intramolecular interactions which stabilized the conformation of intermediates or reagents. In the last few years, intermolecular chalcogen bonding has increasingly also been exploited in solution, most notably in anion recognition and transport as well as in organic synthesis and organocatalysis.

AbstractErst seit zwei Jahren nutzen Wissenschaftler intermolekulare Chalkogenbrücken als nichtkovalente Lewis‐Säuren in der Organokatalyse. Zunächst untersuchten sie nur schwefelbasierte, inzwischen auch selen‐ oder tellurhaltige Moleküle. Je nach Edukt lassen sich Reaktionen damit bis zum 34‐Fachen beschleunigen.

Chalkogenbrücken sind bisher wenig erforschte nichtkovalente Wechselwirkungen, welche vergleichbar mit Halogenbrücken sind. Diese Arbeit beschreibt die erste Anwendung selenbasierter Chalkogenbrückendonoren als Lewis‐Säuren in der organischen Synthese. Als Testreaktion zur Halogenidabstraktion diente die Solvolyse von Benzylhydrylbromid. Chalkogenbrückendonoren, welche auf einem Bis(benzimidazolium)‐Grundgerüst basieren, ergaben Reaktionsbeschleunigungen in einer Größenordnung von 20–30 im Vergleich zur Hintergrundreaktion. Mehrere Vergleichsexperimente lieferten klare Hinweise darauf, dass die beobachtete Aktivierung auf Chalkogenbrücken zurückgeführt werden kann. Zudem sind die eingesetzten Chalkogenbrückendonoren dem entsprechenden bromierten Halogenbrückendonor in ihrer Aktivität überlegen.

Chalcogen bonding is a noncovalent interaction based on electrophilic chalcogen substituents, which shares many similarities with the more well-known hydrogen and halogen bonding. Herein, the first application of selenium-based chalcogen bond donors in organocatalysis is described. Cationic bifunctionalized organoselenium compounds activate the carbon-chlorine bond of 1-chloroisochroman in a benchmark reaction. While imidazolium-based derivatives showed no noticeable activation, benzimidazolium backbones yielded potent catalysts. In all cases, syn-isomers were markedly more active, presumably due to bidentate coordination, which was confirmed by DFT calculations. Comparison experiments with the corresponding non-selenated as well as the non-cationic reference compounds clearly indicate that the catalytic activity can be ascribed to chalcogen bonding. The rate acceleration by the catalystcompared to the non-selenated derivativewas about 10 fold.

Selenverbindungen können nichtkovalente Wechselwirkungen (Chalkogenbrücken) mit Lewis-Basen eingehen. S. M. Huber und Mitarbeiter zeigen in ihrer Zuschrift auf S. 12172, dass solche Chalkogenbrückendonoren eine Testreaktion aktivieren. Kontrollexperimente mit nichtselenierten Referenzverbindungen bestätigen die entscheidende Rolle des Selensubstituenten. Der entsprechende bromierte Halogenbrückendonor war etwas weniger aktiv.

Chalcogen bonding is a little explored noncovalent interaction similar to halogen bonding. This manuscript describes the first application of selenium-based chalcogen bond donors as Lewis acids in organic synthesis. To this end, the solvolysis of benzhydryl bromide served as a halide abstraction benchmark reaction. Chalcogen bond donors based on a bis(benzimidazolium) core provided rate accelerations relative to the background reactivity by a factor of 20-30. Several comparative experiments provide clear indications that the observed activation is due to chalcogen bonding. The performance of the chalcogen bond donors is superior to that of a related brominated halogen bond donor.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.