Die verschiedenartigen Konformationen <i>N</i>‐Trimethylsilyl‐substituierter <i>p</i>‐Phenylendiamin‐Derivate: Untersuchungen an Einkristallen sowie in der Gasphase

Abstract

Structures of Sterically Overcrowded and Charge‐Perturbed Molecules, 38 [1] . — The Different Conformations of N ‐Trimethylsilyl‐Substituted p ‐Phenylenediamine Derivatives: Investigation of Single Crystals and in the Gas Phase The ESR‐proven generation of a Wurster's Blue radical anion by one‐electron reduction of N,N,N′,N′ ‐tetrakis(trimethylsilyl)‐ p ‐phenylenediamine is rationalized by a posterior singlecrystal structure determination of the neutral molecule, which demonstrates inter alia that the bulky [(H 3 C) 3 Si] 2 N substituents are twisted out of the benzene plane by 83°. In contrast, the skeleton of the sterically congested N,N′ ‐bis(trimethylsilyl)‐ p ‐phenylenediamine remains almost planar and, accordingly, allows n N /π interaction between the p‐type nitrogen electron pairs of the also flattened [(H 3 C) 3 Si]HN groups and the benzene π system. These conformational differences are reflected in the gas‐phase photoelectron spectra, in which n N /π ionisation bands are split by less than 1 eV or more than 3 eV, respectively. The evidence for analogous structures of the two organosilicon p ‐phenylenediamine derivatives in solution is confirmed by geometry‐optimized AM1 calculations, which readily explain the surprising insertion of an extra electron into an already electron‐rich molecule.