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Radicals of the lightest group 13 element, boron, are well established and observed in numerous forms. In contrast to boron, radical chemistry involving the heavier group 13 elements (aluminum, gallium, indium, and thallium) remains largely underexplored, primarily attributed to the formidable synthetic challenges associated with these elements. Herein, we report the synthesis and isolation of planar and twisted conformers of a doubly CAAC (cyclic alkyl(amino)carbene)-radical-substituted dialane. Extensive characterization through spectroscopic analyses and X-ray crystallography confirms their identity, while quantum chemical calculations support their open-shell nature and provide further insights into their electronic structures. The dialane-connected diradicals exhibit high susceptibility to oxidation, as evidenced by electrochemical measurements and reactions with o-chloranil and a variety of organic azides. This study opens a previously uncharted class of dialuminum systems to study, broadening the scope of diradical chemistry and its potential applications., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The isolation of simple, fundamentally important, and highly reactive organometallic compounds remains among the most challenging tasks in synthetic chemistry. The detailed characterization of such compounds is key to the discovery of novel bonding scenarios and reactivity. The dimethylbismuth cation, [BiMe 2 (SbF 6 )] (1), has been isolated and characterized. Its reaction with BiMe 3 gives access to an unprecedented dative bond, a Bi→Bi donor-acceptor interaction. The exchange of methyl groups (arguably the simplest hydrocarbon moiety) between different metal atoms is among the most principal types of reactions in organometallic chemistry. The reaction of 1 with BiMe 3 enables an S E 2(back)-type methyl exchange, which is, for the first time, investigated in detail for isolable, (pseudo-)homoleptic main-group compounds., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The NHC-stabilised diboryne (B 2 (SIDep) 2 ; SIDep=1,3-bis(2,6-diethylphenyl)imidazolin-2-ylidene) undergoes a high-yielding P-P bond activation with tetraethyldiphosphine at room temperature to form a B 2 P 2 heterocycle via a diphosphoryldiborene by 1,2-diphosphination. The heterocycle can be oxidised to a radical cation and a dication, respectively, depending on the oxidant used and its counterion. Starting from the planar, neutral 1,3-bis(alkylidene)-1,3-diborata-2,4-diphosphoniocyclobutane, each oxidation step leads to decreased B-B distances and loss of planarity by cationisation. X-ray analyses in conjunction with DFT and CASSCF/NEVPT2 calculations reveal closed-shell singlet, butterfly-shaped structures for the NHC-stabilised dicationic B 2 P 2 rings, with their diradicaloid, planar-ring isomers lying close in energy., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation-state flexibility of the s-block metals has long stood in the way of their participation in sophisticated π-bonding arrangements, and truly antiaromatic systems containing s-block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis-base-coordination chemistry., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The one-electron reduction of a cyclic (alkyl)(amino)carbene (CAAC)-stabilized arylborylene carbonyl complex yields a dimeric borylketyl radical anion, resulting from an intramolecular aryl migration to the CO carbon atom. Computational analyses support the existence of a [(CAAC)B(CO)Ar] .- radical anion intermediate. Further reduction leads to a highly nucleophilic dianionic (boraneylidene)methanolate., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Narrow HOMO-LUMO gaps and high charge-carrier mobilities make larger acenes potentially high-efficient materials for organic electronic applications. The performance of such molecules was shown to significantly increase with increasing number of fused benzene rings. Bulk quantities, however, can only be obtained reliably for acenes up to heptacene. Theoretically, (oligo)acenes and (poly)acenes are predicted to have open-shell singlet biradical and polyradical ground states, respectively, for which experimental evidence is still scarce. We have now been able to dramatically lower the HOMO-LUMO gap of acenes without the necessity of unfavorable elongation of their conjugated π system, by incorporating two boron atoms into the anthracene skeleton. Stabilizing the boron centers with cyclic (alkyl)(amino)carbenes gives neutral 9,10-diboraanthracenes, which are shown to feature disjointed, open-shell singlet biradical ground states., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The reductive coupling of an N-heterocyclic carbene (NHC) stabilized (dibromo)vinylborane yields a 1,2-divinyldiborene, which, although isoelectronic to a 1,3,5-triene, displays no extended π conjugation because of twisting of the C 2 B 2 C 2 chain. While this divinyldiborene coordinates to copper(I) and platinum(0) in an η 2 -B 2 and η 4 -C 2 B 2 fashion, respectively, it undergoes a complex rearrangement to an η 4 -1,3-diborete upon complexation with nickel(0)., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Herein we describe the first examples of isolable electron-precise diboranes(4) that bear azide moieties: the acyclic 1,2-diazido-1,2-bis(dimethylamino)diborane(4) and the cyclic 1,4-diaryl-2,3-diazido-1,4-diaza-2,3-diborinines (aryl=mesityl, 2,6-xylyl, 4-tolyl). The reported examples are not only stable enough to be observed and isolated (putative transient diborane(4) azides previously reported by our group spontaneously decompose even below room temperature), but some of them are even robust enough to undergo controlled pyrolysis without explosive decomposition at temperatures well above 100 °C. In two cases, the controlled pyrolysis allows the isolation of complex diazaboretidines, which are the apparent dimerization products of endocyclic boryl-iminoboranes., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The absence of fluorine from most biomolecules renders it an excellent probe for NMR spectroscopy to monitor inhibitor-protein interactions. However, predicting the binding mode of a fluorinated ligand from a chemical shift (or vice versa) has been challenging due to the high electron density of the fluorine atom. Nonetheless, reliable 19 F chemical-shift predictions to deduce ligand-binding modes hold great potential for in silico drug design. Herein, we present a systematic QM/MM study to predict the 19 F NMR chemical shifts of a covalently bound fluorinated inhibitor to the essential oxidoreductase tryparedoxin (Tpx) from African trypanosomes, the causative agent of African sleeping sickness. We include many protein-inhibitor conformations as well as monomeric and dimeric inhibitor-protein complexes, thus rendering it the largest computational study on chemical shifts of 19 F nuclei in a biological context to date. Our predicted shifts agree well with those obtained experimentally and pave the way for future work in this area., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Singly NHC-coordinated (aminoboryl)aminoborenium salts react with Na 2 [Fe(CO) 4 ] to yield stable coordination complexes of aminoborylene-stabilized aminoborylenes, which exhibit exceptional σ-donor properties. Upon photolytic CO extrusion from the metal center, the diboron ligand adopts a novel η 3 -BBN coordination mode, where bond-strengthening backdonation from the metal center into the vacant B-B π-orbital is observed. This bonding situation can be alternatively described as a Fe-diaminodiborene complex. In a related reduction of CAAC-stabilized (aminoboryl)aminoborenium with KC 8 , the reduced species can be captured with nucleophiles to form three-coordinate (diaminoboryl)borylenes, where both amino groups have migrated to the distal boron atom. Collectively, these reactions illustrate the isomeric flexibility imparted by amino groups on this reduced diboron system, thus opening multiple avenues of novel reactivity., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Trypanosomal and leishmanial infections claim tens of thousands of lives each year. The metabolism of these unicellular eukaryotic parasites differs from the human host and their enzymes thus constitute promising drug targets. Tryparedoxin (Tpx) from Trypanosoma brucei is the essential oxidoreductase in the parasite's hydroperoxide-clearance cascade. In vitro and in vivo functional assays show that a small, selective inhibitor efficiently inhibits Tpx. With X-ray crystallography, SAXS, analytical SEC, SEC-MALS, MD simulations, ITC, and NMR spectroscopy, we show how covalent binding of this monofunctional inhibitor leads to Tpx dimerization. Intra- and intermolecular inhibitor-inhibitor, protein-protein, and inhibitor-protein interactions stabilize the dimer. The behavior of this efficient antitrypanosomal molecule thus constitutes an exquisite example of chemically induced dimerization with a small, monovalent ligand that can be exploited for future drug design., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new structural class of boron-based diradicals is prepared by Lewis base addition to and reduction of singly cyclic (alkyl)(amino)carbene (CAAC) stabilised diborylalkenes. The diradicals feature a perpendicular olefinic bridge preventing delocalization between the B(CAAC) π systems, making the coupling between the spin centres very weak. DFT calculations indicate that the compounds are ground-state (open-shell) singlets, with triplet states negligibly higher in energy, thus making the triplet states easily populated thermally., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Diaryldihalodiboranes(4) were reacted with bis(amidinato)- and bis(guanidinato)silylenes to generate the first neutral diborane-centered radicals. These formally non-aromatic 5π electron systems are stable in the solid state as well as in solution and were characterized by solid-state structure determination, high-resolution mass spectrometry, and EPR spectroscopy. The reactivity of one of these radicals with the oxidant 1,4-benzoquinone led to ring-opening and B-O bond formation., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The 2,5-bis(borolyl)thiophene 2, a conjugated acceptor-π-acceptor system, can be reduced to the monoradical anion [2](.-) , the dianion [2](2-) , and the tetraanion [2](4-) . The dianion [2](2-) was also prepared by a comproportionation reaction and features an absorption maximum in the near-IR region (λmax =800 nm), which is characteristic of a bipolaron with a quinoidal structure., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

While the general course of the mode of action of the antitumor agent neocarzinostatin (NCS) is clarified, it is still unclear which structural elements are relevant for the high efficacy of NCS. This question and the role of alternatively possible biradicals are addressed., (© 2001 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

A terra incognita of chemistry is represented by the phosphorus suboxides owing to their high reactivity. The present computational study provides the first insights into this interesting class of compound. The picture shows the most stable isomer of P 4 O 2 (the smaller, darker centers denote oxygen atoms)., (© 2001 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

The regioselectivity of the biradical cyclization of enyne-carbodiimides 1 can easily be controlled by variation of R 1 at the alkyne terminus. Attachment of a hydrogen atom (R 1 =H) leads to C 2 -C 7 cyclization and formation of biradical 2, whereas C 2 -C 6 cyclization to provide biradical 3 is observed with R 1 =Me 3 Si or Ph., (© 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

Both benzocarbazoles and quinolines can be synthesized from enyne ketenimines 1 generated in situ via biradical intermediates (see reaction below). Which of the heterocyclic ring systems is formed depends on the choice of the substituent R 1 at the alkyne terminus., (© 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)