Of two very proximatesyn-periplanar bisdiazenes (1,2) mono-, di-, tri- and tetra-N-oxides were prepared, representing six combinations of the individual NN/NNO/ONNO chromophores. According to DFT calculations (B3LYP/6-31G*), [2+2]photocycloaddition to the respective oxidized tetrazetidines is significantly to moderately endothermic. The metathesis isomerization of the oxidized tetrazetidines is generally
Cyclic In-Plane Electron Delocalization (σ-Bishomoaromaticity) in 4N/5e Radical Anions and 4N/6e DianionsGeneration, Structures, Properties, Ion-Pairing, and Calculations
175−156°), short contact with alkali metals (Li, Na, K, Cs) generates turquoise to deeply green radical anions (λmax(DME) ≈ 700−900 nm). The character of these radical anions as cyclically in-plane delocalized bishomoconjugated 4N/5e species with a high concentration of spin density between the NN units is established by extensive UV/vis, electrochemical, and EPR measurements (CW, pulsed) at temperatures down
One- and two-electronoxidation of a caged, proximate, syn-periplanar bishydrazine leads to highly persistent, 4N/(7)6e (radical) cations—with dominant electron delocalisation along the cage bonds (CV, EPR, B3LYP). A NICS value of −20.6 is evidence for strong electron delocalisation in the caged dication.
By oxidation of (presumably) bislithiated, unusually proximate, syn-periplanar bishydrazines an alternative access to sigma-bis-homoaromatic 4N/6e dianions is realized. Formal N-alkylation/arylation of these 4N/6e dianions leads to novel, cyclically delocalized 4N/6e monoanions. Experimental realization is achieved by addition of metal organyls to proximate bisdiazenes as well as by deprotonation of the respective diazene/alkyl(aryl) hydrazines. The nature of the 4N/6e bonding motif is investigated by UV/Vis and NMR spectroscopy as well as by DFT calculations. (C) 2002 Elsevier Science Ltd. All rights reserved.