The Combination of Cross‐Hyperconjugation and σ‐Conjugation in 2,5‐Oligosilanyl Substituted Siloles

Reaction of a 2,5‐dilithiated silole with excess dichlorodimethylsilane gives the respective 2,5‐bis(chlorodimethylsilyl) substituted silole. This compound can be converted to 2,5‐bis(oligosilanyl) substituted siloles by addition of a suitable oligosilanide. In the UV spectra of the thus obtained compounds the lowest energy absorptions are bathochromically shifted compared to the absorptions of the two constituents, namely the 2,5‐disilyl substituted silole and a trisilane. The bathochromic shift is interpreted as being caused by a mixed σ‐conjugation/cross‐hyperconjugation. This assumption is supported by TD‐DFT calculations, which show a significant contribution from Si−Si bonds to the HOMO of the molecule.