ELECTROCHEMICAL OXIDATION OF [1.1.1.1]PAGODANES, BISSECODODECAHEDRA(DI)ENES, SECODODECAHEDRA(DI)ENES AND DODECAHEDRA(DI)ENES - STABILITY OFCAGED 4C 3E RADICAL CATIONS AND 4C/2E DICATIONS/

The anodic oxidation of variously functionalized [1.1.1.1]pagodanes A and bissecododecahedradienes B (pi,pi-distance, ca. 2.8 Angstrom) has been studied by cyclic voltammetry (CV). For nine out of ten pagodanes A, independent of their functionalization and of the scan rate, an ir reversible two-electron oxidation wave (E(p) = 1.20-2.23 V) was observ ed in line with the sequence A --> A(.+) --> B-.+ --> B2+ (ECE) in whi ch the chemical step C is very fast on the CV timescale. For seven of the corresponding valence isomeric dienes B, the first one-electron ox idation wave (B --> B-.+), was found to be reversible (E(o)' = 0.66-1- 39 V) whilst the second one-electron oxidation wave (B-.+ --> B2+) was found to be irreversible (E(p) = 1.20-1.80 V). The standard half-wave potentials allowed a thermodynamically meaningful estimate of the con jugative stabilization of the unusually persistent caged, non-classica l 4c/3e radical cations B-.+ (Delta E(o)' = 0.91 V for the parent dien e B and the monoene reference) and of the destabilization by various f unctionalization patterns (0.40-0.73 V). For the secododecahedradienes D (pi pi-distance ca. 2.85/3.2 Angstrom) and the dodecahedradienes E (pi pi-distance ca. 3.5 Angstrom), only irreversible one-electron oxid ation waves were recorded [E(p) = (0.8)-1.46 V and (1.0)-1.39 V, respe ctively]. The degree of conjugative stabilization, in the increasingly spherical, yet still non-classical 4c/3e radical cations D-.+ and E(. +) is approximated Delta E(p) = 0.62 and 0.39 V, respectively.