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Author: Knorke, Harald × End date: 2024 × Start date: 2020 × DDC: 540 × DDC: 660 × WGL Institute: IOM ×

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    Relevance of π-Backbonding for the Reactivity of Electrophilic Anions [B12X11]− (X=F, Cl, Br, I, CN)
    (Weinheim : Wiley-VCH, 2021) Mayer, Martin; Rohdenburg, Markus; Kawa, Sebastian; Horn, Francine; Knorke, Harald; Jenne, Carsten; Tonner, Ralf; Asmis, Knut R.; Warneke, Jonas
    Electrophilic anions of type [B12X11]− posses a vacant positive boron binding site within the anion. In a comparatitve experimental and theoretical study, the reactivity of [B12X11]− with X=F, Cl, Br, I, CN is characterized towards different nucleophiles: (i) noble gases (NGs) as σ-donors and (ii) CO/N2 as σ-donor-π-acceptors. Temperature-dependent formation of [B12X11NG]− indicates the enthalpy order (X=CN)>(X=Cl)≈(X=Br)>(X=I)≈(X=F) almost independent of the NG in good agreement with calculated trends. The observed order is explained by an interplay of the electron deficiency of the vacant boron site in [B12X11]− and steric effects. The binding of CO and N2 to [B12X11]− is significantly stronger. The B3LYP 0 K attachment enthapies follow the order (X=F)>(X=CN)>(X=Cl)>(X=Br)>(X=I), in contrast to the NG series. The bonding motifs of [B12X11CO]− and [B12X11N2]− were characterized using cryogenic ion trap vibrational spectroscopy by focusing on the CO and N2 stretching frequencies (Formula presented.) and (Formula presented.), respectively. Observed shifts of (Formula presented.) and (Formula presented.) are explained by an interplay between electrostatic effects (blue shift), due to the positive partial charge, and by π-backdonation (red shift). Energy decomposition analysis and analysis of natural orbitals for chemical valence support all conclusions based on the experimental results. This establishes a rational understanding of [B12X11]− reactivety dependent on the substituent X and provides first systematic data on π-backdonation from delocalized σ-electron systems of closo-borate anions. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
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    Synthesis, Electronic Properties and Reactivity of [B12X11(NO2)]2− (X=F–I) Dianions
    (Weinheim : Wiley-VCH, 2020) Asmis, Knut R.; Beele, Björn B.; Jenne, Carsten; Kawa, Sebastian; Knorke, Harald; Nierstenhöfer, Marc C.; Wang, Xue-Bin; Warneke, Jonas; Warneke, Ziyan; Yuan, Qinqin
    Nitro-functionalized undecahalogenated closo-dodecaborates [B12X11(NO2)]2− were synthesized in high purities and characterized by NMR, IR, and Raman spectroscopy, single crystal X-diffraction, mass spectrometry, and gas-phase ion vibrational spectroscopy. The NO2 substituent leads to an enhanced electronic and electrochemical stability compared to the parent perhalogenated [B12X12]2− (X=F–I) dianions evidenced by photoelectron spectroscopy, cyclic voltammetry, and quantum-chemical calculations. The stabilizing effect decreases from X=F to X=I. Thermogravimetric measurements of the salts indicate the loss of the nitric oxide radical (NO.). The homolytic NO. elimination from the dianion under very soft collisional excitation in gas-phase ion experiments results in the formation of the radical [B12X11O]2−.. Theoretical investigations suggest that the loss of NO. proceeds via the rearrangement product [B12X11(ONO)]2−. The O-bonded nitrosooxy structure is thermodynamically more stable than the N-bonded nitro structure and its formation by radical recombination of [B12X11O]2−. and NO. is demonstrated. © 2020 The Authors. Published by Wiley-VCH GmbH