We present herein an in-depth study of complexes in which a molecule containing a boron-boron triple bond is bound to tellurate cations. The analysis allows the description of these salts as true pi complexes between the B-B triple bond and the tellurium center. These complexes thus extend the well-known Dewar-Chatt-Duncanson model of bonding to compounds made up solely of p block elements. Structural, spectroscopic and computational evidence is offered to argue that a set of recently reported heterocycles consisting of phenyltellurium cations complexed to diborynes bear all the hallmarks of pi-complexes in the pi-complex/metallacycle continuum envisioned by Joseph Chatt. Described as such, these compounds are unique in representing the extreme of a metal-free continuum with conventional unsaturated three-membered rings (cyclopropenes, azirenes, borirenes) occupying the opposite end.

The first spontaneous, metal-free, room-temperature hydrogen transfer from ammonia borane to an iminoborane is reported. Mechanistic studies of the reaction indicate a concerted transfer of H+ and H- from donor to acceptor with an activation energy far below those of comparable concerted transfer hydrogenations. This reaction was employed in the syntheses and isolation of new B,N-disubstituted aminoboranes, a comparatively rare subset within the aminoborane family. This successful transfer hydrogenation to a highly dehydrogenated BN system may serve as a starting point for the design of new systems capable of reversible dehydrogenation/rehydrogenation.

1 Institute for Inorganic Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany. 2 Institute for Sustainable Chemistry & Catalysis with Boron, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany. 3 Institute for Physical and Theoretical Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany. 4 Institut für Anorganische Chemie, Universität Göttingen, Tammanstraße 4, 37077 Göttingen, Germany 5 Max-Planck-Institut für Chemische Energiekonversion, Stiftstrasse 34–36, 45470 Mülheim an der Ruhr, Germany

Molecules containing multiple bonds between atoms-most often in the form of olefins-are ubiquitous in nature, commerce, and science, and as such have a huge impact on everyday life. Given their prominence, over the last few decades, frequent attempts have been made to perturb the structure and reactivity of multiply-bound species through bending and twisting. However, only modest success has been achieved in the quest to completely twist double bonds in order to homolytically cleave the associated π bond. Here, we present the isolation of double-bond-containing species based on boron, as well as their fully twisted diradical congeners, by the incorporation of attached groups with different electronic properties. The compounds comprise a structurally authenticated set of diamagnetic multiply-bound and diradical singly-bound congeners of the same class of compound.

Wir berichten hier über den ersten spontanen und metallfreien Wasserstofftransfer zwischen Amminboran (NH 3 BH 3 ) und Iminoboranen bei Raumtemperatur. DFT‐Rechnungen belegen einen konzertierten H + /H − ‐Transfer von NH 3 BH 3 mit einer Aktivierungsenergie weit unter der vergleichbarer Wasserstoffübertragungsreaktionen. Zudem konnten durch Umsetzung von Iminoboranen mit Amminboranen neue B,N‐disubstituierte Aminoborane isoliert werden, von denen bisher nur wenige Vertreter bekannt sind. Dieser erfolgreiche Wasserstofftransfer zu einem dehydrierten BN‐System könnte ein Ansatzpunkt für die Entwicklung neuartiger Systeme für Dehydrierungs‐ bzw. Rehydrierungsprozesse sein.

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.

A remarkably mild, catalyst-free cyclopropanation reaction is confirmed by low-temperature isolation of a fused bicyclic cyclopropane intermediate. This intermediate is one of two that were isolated and fully characterised in a three-step temperature-controllable reaction cascade.

Convenient solution-phase syntheses of tetrahalodiboranes(4) B2F4, B2Cl4 and B2I4 are presented herein from common precursor B2Br4. In addition, the dimethylsulfide adducts B2Cl4(SMe2)(2) and B2Br4(SMe2)(2) are conveniently prepared in one-step gram and multigram scale syntheses from the commercially-available starting material B-2(NMe2)(4). The results provide simple access to the full range of tetrahalodiboranes(4) for the exploration of their untapped synthetic potential.

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.

AbstractDie Reaktionen eines Diborens mit elementaren Selen oder Tellur führen zur Bildung eines Diboraselenirans bzw. eines Diboratellurirans. Diese Reaktionen erinnern an die Bindung von niedervalentem Sauerstoff und Stickstoff bei der Bildung von Oxiranen und Aziridinen. Eine solche Reaktivität wurde jedoch zwischen Alkenen und den höheren Homologen der Chalcogene bisher nicht beobachtet. Während die Elektronegativität von Kohlenstoff zu groß ist, um Elemente mit niedriger Elektronegativität zu reduzieren, ermöglicht das hohe Reduktionspotential der B‐B‐Doppelbindung eine Reaktion mit Se0 und Te0. Die Fähigkeit einer Bor‐Bor Mehrfachbindung, Elektronendichte zu donieren, wird durch Reaktionen verdeutlicht, in denen diese als Nukleophil an einem der beiden Tellurzentren von Diarylditelluriden angreift. Die entstehenden salzartigen Verbindungen bestehen aus einem Diboratellurirenium‐Kation und einem Aryltellurid‐Anion.

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.

Reactions of an aryldihydroborane with a Pt(0) complex lead to a range of novel products, including complexes with bridging diborene and diborane(3) ligands and a complex with both borylene and borane (M → B) ligands. The products imply varying degrees of dehydrogenation of the boron centers with concomitant formation of boron-boron bonds, which in one case is later broken. These reactions show that although the dehydrocoupling of dihydroboranes is not a straightforward process in this case, the reactions are capable of connecting boron atoms in unusual ways, leading to unprecedented bonding motifs.

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.

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.

The reaction of tert-butylisonitrile (tBuNC) with 1,2-dihalo-1,2-diduryldiborane leads initially to the formation of the mono-base adduct of the symmetrical diborane(4), which then undergoes an intramolecular cyclization resulting in the formation of a 1-boraindane. This result is in contrast to a previously reported cyclization of a mono-isonitrile adduct of an unsymmetrical 1,1-pinacol-2,2-diaryldiborane(4), which results in the formation of a 1-boraindane. This latter result is herein confirmed by the reaction of 1,1-difluoro-2,2-dimesityldiborane(4) with tBuNC, which yielded the 2-boraindane compound. The mechanism of the former reaction has been computationally elucidated, and the differences between this route and the pathway to 1-boraindanes is discussed. These reactions further the understanding of the chemistry of the increasingly popular mono-base adducts of diborane(4), demonstrate the versatility of isonitriles in comparison to standard two-electron donors, and elucidate selective routes to boron-containing polycyclics, such as those being proposed as analogues for conventional organic pharmaceuticals.

Among the numerous routes organic chemists have developed to synthesize benzene derivatives and heteroaromatic compounds, transition-metal-catalyzed cycloaddition reactions are the most elegant. In contrast, cycloaddition reactions of heavier alkene and alkyne analogues, though limited in scope, proceed uncatalyzed. In this work we present the first spontaneous cycloaddition reactions of lighter alkene and alkyne analogues. Selective addition of unactivated alkynes to boron-boron multiple bonds under ambient conditions yielded diborocarbon equivalents of simple aromatic hydrocarbons, including the first neutral 6 π-aromatic diborabenzene compound, a 2 π-aromatic triplet biradical 1,3-diborete, and a phosphine-stabilized 2 π-homoaromatic 1,3-dihydro-1,3-diborete. DFT calculations suggest that all three compounds are aromatic and show frontier molecular orbitals matching those of the related aromatic hydrocarbons, C6 H6 and C4 H4 (2+) , and homoaromatic C4 H5 (+) .