Redox-Reaktionen von Hexahydropyren: Kristallstrukturen seiner Radikalanion-Salze sowie von Trihydropyrenylium-tetrachloroaluminat und Dichtefunktionaltheorie-Berechnungen

摘要

Hexahydropyrene 1, a doubly propane-1,3-diyl-bridged peri-naphthalene derivative wtih 10 #PI#-electrons allows both oxidation to its cation as well as reduction to its radical-anion salts, which could be crystallized and structurally characterized -a rather rare case for small unsaturated hydrocarbons. The unexpected formally threefold dehydrogenation by the oxidizing system AlCI_2H_2CCl_2 (Bock's reagent) generated the hitherto unknown 1,2,3-trihydropyrene cation in two polymorphic crystals, which contain 12#PI#-electrons delocalized over three anellated six-membered rings comprising 13 #PI#-centers. Structural comparison of the altogether four crystallized redox products [K+_(solv)[M'-] 28, [K+_(solv)[M.-]infinity 2b, [Na+_(solv)[M.-] 2c, and [(M-3H)+][AlCl-4] 3 with the neutral hydrocarbon 1 reveals only small differences in bond lengths and angles, but establishes solvation contacts, #PI#(#eta#~6)…K~+coordination in the polymer 2b, the flattening of one molecular half in the trihydropyren cation of 3 and ten H-bonds CH …Cl to the AlCl_4~- counter anion of 3. DFf/NBO Charge distributions, calculated based on the experimental structural parameters, show charge accumulation in the propanediyl bridges as well as in the peripheral naphthalene C-C bonds of the radical anions. The largest changes result expectedly for the formally triply dehydrogenated 1, i.e. the trihydropyren ~ation of 3, with two slightly positive and partly considerably less negative #PI#-centers.