Anja Wiesner

The properties of the strong Lewis acid Ge(OTeF5)4 are investigated experimentally and quantum-chemically and compared to other germanes with electron-withdrawing ligands. It readily forms the octahedral germanate [NEt4]2[Ge(OTeF5)6] upon reaction with two equivalents of [NEt4][OTeF5]. Additionally, germanes with the formula RxGe(OTeF5)4–x with R = Me, Ph and x = 3, 2, 1 have been characterized. Ph3GeOTeF5 was utilized to generate the germylium ion [GePh3][Al(OTeF5)4] by –OTeF5 abstraction with one of the strongest Lewis acids available─Al(OTeF5)3.

In this work, we present the characterization of Si(OTeF ₅ ) ₄ and its utilization as a Lewis acid. Therefore, the adduct formation toward Si(OTeF ₅ ) ₄ L ₂ (L = 4‐(dimethylamino)pyridine)), Si(OTeF ₅ ) ₄ L (L = 2,2’‐bipyridine, 1,10‐phenanthroline) and [NEt ₄ ] ₂ [Si(OTeF ₅ ) ₆ ] was studied. Furthermore, we compare its Lewis acidity to that of other homoleptic silanes with electron‐withdrawing ligands.

The functionalization of a hexa-peri-benzocoronene–fluoranthene hybrid with a K-type bay region is investigated. Bromination proceeds regioselectively at two peripheral positions, which contradicts the electronic and structural predictions suggesting that substitution at the K-type bay region should be favored. Computational studies reveal that the transition state and intermediate energies for all substitution positions are comparable, though no substitution in the bay region is observed. To rationalize this unexpected regioselectivity, a model is proposed based on dynamic helical inversion, which prevents the corresponding Wheland intermediates from being stabilized. Subsequent conversion of the brominated compounds to nitrile derivatives affords compounds with photoluminescence quantum yields of up to 76% in solution. Organic light-emitting diodes with luminance values of up to 6,500 cd·m–2 are realized due to the effective energy level alignment by a hole-transport and electron-blocking layer, which was not possible with the related nonfunctionalized derivative.

A one‐pot synthesis of KOTeF ₅ without hazardous fluorosulfonic acid is presented. KOTeF ₅ can easily be protonated to HOTeF ₅ with sulfuric acid. The intermediate KOTeF ₄ Cl and the corresponding acid HOTeF ₄ Cl are fully characterized. A synthesis of the important OTeF ₅ transfer reagents AgOTeF ₅ and TMSOTeF ₅ , starting from the now readily available KOTeF ₅ is developed as well.

We report the synthesis, structural characterization, and optoelectronic properties of a highly electron‐deficient bi(cyclopropylidene)‐framework ( CN8CP2 ). The developed one‐pot synthesis gives access to the dianionic species via thermally induced homocoupling of an iodinated precursor. The controlled oxidation yields the radical anion, whereas the neutral molecule is accessible only as an electrochemically generated in situ species. Single‐crystal X‐ray diffraction studies of the dianion reveal molecular layers separated by counterions, thereby enabling fluorescence in the solid state. The structure of the radical anion reveals a highly ordered arrangement of π‐stacked molecules. Optical spectroscopy and quantum chemical calculations indicate that the vibronic fine structure is governed by the vibrational modes of the cyclopropane core. The analysis of the electronic structures confirms extensive spin delocalization for the radical anion and a pronounced σ‐aromatic character. The exceptionally low energy levels of the acceptor orbitals are determined as −5.66 eV for the radical anion and −6.18 eV for the neutral species. Consequently, charge transfer to the neutral molecule or the radical anion results in the formation of the closed‐shell dianion, which circumvents instabilities that are associated with open‐shell species formed for conventional electron acceptors. Thus, CN8CP2 appears as one of the strongest small‐molecule organic acceptors for advanced organic electronic materials.

Herein, the ionic liquid [NEt ₃ Me][Cl(SO ₂ ) _n ] is reported as a reversible sulfur dioxide storage medium and transfer reagent for organic synthesis. Vapor pressure measurements revealed that the ionic liquid can store up to 3.66 equivalents of SO ₂ at room temperature, which can be released in a controlled manner upon heating or depressurization. The physicochemical properties were investigated, and long‐term stability was demonstrated, as no decomposition was observed for more than six months. Based on its solid‐state structure, the bonding analysis indicated a covalent sulfur‐chlorine interaction, which is consistent with conducted Raman studies and quantum chemical calculations. Atom economy and cost estimates are compared with those of commonly used SO ₂ surrogates, highlighting the developed transfer reagent as an inexpensive and (atom‐)economic alternative for laboratory‐scale applications. The synthetic utility of [NEt ₃ Me][Cl(SO ₂ ) _n ] is further demonstrated, enabling the synthesis of valuable organosulfur compounds such as 3‐sulfolenes, sulfonamides, sulfones, and sulfonyl fluorides in good to excellent yields. Importantly, the incorporation of SO ₂ is scalable, rendering [NEt ₃ Me][Cl(SO ₂ ) _n ] as a safe and user‐friendly SO ₂ transfer reagent for synthetic applications.

ZUSAMMENFASSUNG: Hexacyanotrimethylencyclopropan ( CN6CP ) ist in seiner neutralen Form ein außergewöhnlich starker organischer Elektronenakzeptor und findet breite Anwendung bei der Dotierung von Materialien, um Ladungstransferprozesse zu induzieren und elektrochemische Systeme anzupassen. Dennoch sind seine grundlegenden molekularen Eigenschaften bislang weitgehend unbekannt geblieben. Hier präsentieren wir die erste umfassende strukturelle Charakterisierung von CN6CP . Möglich wurde dies durch eine verbesserte Synthese bei niedrigen Temperaturen. Auch die erste Festkörperstruktur der neutralen Verbindung wurde zugänglich. Das resultierende Verfahren liefert isolierbares, kristallines CN6CP , das bei –30°C über Wochen stabil ist. Über alle Redoxzustände hinweg zeigen kombinierte IR/Raman‐, UV/Vis‐ und NMR‐Untersuchungen zusammen mit NICS‐Berechnungen eine vom Oxidationszustand abhängige Umverteilung der Elektronendichte. Die Daten zeigen, dass CN6CP einen σ‐aromatischen Cyclopropan‐Kern mit abgestimmter π‐Delokalisierung besitzt, die bei der Reduktion verstärkt wird, während die zusätzliche Ladung überwiegend auf dem exocyclischen Akzeptorgerüst lokalisiert ist. Zyklische Voltammetrie‐Experimente zeigen zwei reversible Ein‐Elektronen‐Prozesse und eine außergewöhnlich niedrige LUMO‐Energie von –5,85 eV, die die niedrigste ist, die für kleine organische Moleküle berichtet wurde, und deutlich unter den Werten von Referenzakzeptoren wie F ₄ TCNQ oder F ₆ TCNNQ liegt. Insgesamt bestätigen diese Ergebnisse, dass CN6CP ein strukturell einzigartiger, extrem starker Elektronenakzeptor ist, und liefern die molekulare Grundlage für seine Leistungsfähigkeit in der organischen Elektronik und in redoxaktiven Materialien.

Hexacyanotrimethylenecyclopropane ( CN6CP ) is an exceptionally strong organic electron acceptor in its neutral form, and widely applied for molecular doping to induce charge transfer processes and enable electrochemical systems. Yet, its fundamental molecular properties have remained largely unknown. Here, we show the first comprehensive structure‐analytical characterization of CN6CP , enabled by an improved, low‐temperature synthesis and the first solid‐state structure of the neutral compound. The resulting procedure affords isolable, crystalline CN6CP that is stable for weeks at –30°C and can be recrystallised. Across all redox states, combined IR/Raman, UV–Vis and NMR measurements, together with NICS calculations, reveal an oxidation‐state‐dependent redistribution of electron density. These data show that CN6CP possesses a σ‐aromatic cyclopropane core with tunable π‐delocalisation, which is enhanced upon reduction while the additional charge is predominantly localised on the exocyclic acceptor framework. Cyclic voltammetry experiments unveil two reversible one‐electron processes and an exceptionally low LUMO energy of –5.85 eV, which is the lowest reported for small organic molecules being significantly lower than those of benchmark acceptors such as F ₄ TCNQ or F ₆ TCNNQ. All together, these findings establish CN6CP as a structurally unique, extremely strong electron acceptor and provide the molecular basis underlying its performance in organic electronics and redox‐active materials.

The reported syntheses of dipyrromethanes and tetrapyrroles suffer from accompanying polymerization processes lowering yields and necessitating a laborious workup. Here we present the reaction of geminal dimethoxyethers (i.e., acetals or ketals) with pyrrolic nucleophiles under mild conditions solving those problems. The observed minimal polymerization enables greatly simplified purification procedures. This is possible, because under anhydrous, mildly acidic conditions, geminal dimethoxyethers are more reactive than their carbonyl counterparts. The reaction of geminal dimethoxyethers with pyrrolic nucleophiles proceeds smoothly and selectively at 0°C. Computational studies suggest that geminal dimethoxyethers react readily, while unfeasibly high intermediate energies hamper the reaction of carbonyl compounds under the same conditions. We demonstrate a high functional group tolerance and high yields by the preparation of 27 dipyrromethanes, one porphyrin, and 20 calix[4]pyrroles, many of which include synthetic anchor points for facile postfunctionalization. The method was scaled up to a 500 mmol scale for a dipyrromethane and a 252 mmol scale for a two‐walled calix[4]pyrrole, without loss in yield or purity.

The preparation and characterization of R _x R′ _y SiOTeF ₅ (R = Me, Et, ⁱ Pr, Ph; x = 3, y = 0; R = Pr, ^t Bu, R′ = Me; x = 1, y = 2; 1a‐1f), R ₂ Si(OTeF ₅ ) ₂ (R = Me, Et, ⁱ Pr, Ph; 2a‐2d) and RSi(OTeF ₅ ) ₃ (R = Me, Et, ^t Bu, Ph; 3a‐3d) by reaction of the corresponding chlorosilane and an OTeF ₅ transfer reagent is presented. Molecular structures in the solid state were obtained for Ph ₃ SiOTeF ₅ (1f), Ph ₂ Si(OTeF ₅ ) ₂ (2d) and ^t BuSi(OTeF ₅ ) ₃ (3c). Furthermore, the Lewis acidity was assessed by calculating the fluoride ion affinity (FIA), leading to the observation that a higher number of pentafluoroorthotellurate groups results in an increased FIA.