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    Air and moisture stable para- and ortho-quinodimethane derivatives derived from bis-N-Heterocyclic olefins
    (American Chemical Society, 2023) Jana, Subhadip; Elvers, Benedict J.; Patsch, Sebastian; Sarkar, Pallavi; Krummenacher, Ivo; Nayak, Mithilesh Kumar; Maiti, Avijit; Chrysochos, Nicolas; Pati, Swapan K.; Schulzke, Carola; Braunschweig, Holger; Yıldız, Cem Bural
    Herein we report the development of a new methodology for the synthesis of various quinodimethane derivatives under two-electron oxidation of bis-Nheterocyclic olefins linked by different pi-conjugated aromatic spacers. In case of paraand ortho-phenylene bridge, we obtained air and moisture stable diimidazolium paraand ortho-quinodimethane derivatives. Analogues of the para-phenylene spacer such as tetrafluoro-p-phenylene and p-anthracene also led to the corresponding air and moisture stable quinodimethane derivatives. This emphasizes the influence of imidazolium substituents which facilitate the air and moisture stability of the quinodimethane derivatives. Differences were observed for the electron transfer processes: two one-electron vs one two-electron redox transitions between bis-N-heterocyclic olefins and diimidazolium-quinodimethanes depending on the employed pi-conjugated aromatic spacer. The formation of the pi-conjugated radical-cations, transient redox intermediates between bis-N-heterocyclic olefins and diimidazolium-quinodimethanes, was addressed by an EPR investigation.
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    Comment on "Disclosing Cyclic(Alkyl)(Amino)Carbenes as a One-Electron Reductant: Synthesis of Acyclic(Amino)(Aryl)Carbene-Based Kekulé Diradicaloids"
    (Wiley-VCH - Home, 2023) Maiti, Avijit; Elvers, Benedict J.; Bera, Sachinath; Lindl, Felix; Krummenacher, Ivo; Ghosh, Prasanta; Braunschweig, Holger; Yıldız, Cem B.; Schulzke, Carola
    The authors would like to correct a misassignment of an EPR spectrum in the title paper (https://doi.org/10.1002/chem. 202104567). The authors of the original paper reported the one-electron oxidation of the cyclic(alkyl)(amino)carbene (CAAC) 1 to produce the intermediate iminium radical cation 2, as deduced from the high isolated yield of the hydrogen abstraction product 3 (Figure 1). By low-temperature (200 K) EPR spectroscopy, we observed a weak transient, three-line EPR spectrum with a g-factor of 2.0043 and a 14N hyperfine splitting (hfs) of a( 14N)=5.9 G, which we attributed to the radical cation 2 (the spectrum was depicted as Figure 1b, in the TOC cover image, in the Cover Feature (https://doi.org/10.1002/chem. 202201219), and as Figure S46 of the original paper). However, as one of the present authors (H.G.K.) later pointed out, the foregoing EPR parameters, in particular the g-factor, would not be in agreement with the proposed vinyl-type ?-radical cation.
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    ?,??-diamino- p-tetrafluoroquinodimethane: stability of one- and two-electron oxidized species and fixation of molecular oxygen
    (American Chemical Society, 2021) Mahata, Alok; Chrysochos, Nikolas; Krummenacher, Ivo; Chandra, S.; Braunschweig, H.; Schulzke, C.; Sarkar, B.; Yıldız, Cem Burak; Jana, A.
    Herein, we report the synthesis, characterization, and reactivity of ?,??-diamino-p-tetrafluoroquinodimethane, a p-tetrafluorophenylene-bridged monosubstituted carbene-based Thiele's hydrocarbon A. The compound exhibits a reversible two-step one-electron oxidation with a marginally stable radical cation state B. The in situ formation of the radical cation could be confirmed by electron paramagnetic resonance spectroscopy.
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    Disclosing Cyclic(Alkyl)(Amino)Carbenes as a One-Electron Reductant: Synthesis of Acyclic(Amino)(Aryl)Carbene-Based Kekulé Diradicaloids
    (Wiley, 2023) Maiti, Avijit; Elver, Benedict J.; Bera, Sachinath; Lindl, Felix; I-Krummenacher, Ivo; Krummenacher, Ivo; Ghosh, Prasanta; Yıldız, Cem Burak; Braunschweig, Holger; Schulzke, Carola; Jana, Anukul
    Herein we disclose cyclic(alkyl)(amino)carbenes (CAACs) as a one-electron reductant under the formation of a transient radical cation as indicated by EPR spectroscopy. Subsequently, the disclosed CAAC reducing reactivity was utilized for the synthesis of acyclic(amino)(aryl)carbene-based Thiele and Chichibabin hydrocarbons, a new class of Kekulé diradicaloids. The results demonstrate the CAAC to be a potent organic reductant. Notably, the acyclic(amino)(aryl)carbene-based Chichibabin's hydrocarbon shows an appreciable population of the triplet state at room temperature, as evidenced by both variable temperature NMR and EPR spectroscopy.