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

Abstract

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.

Radicals and Anions of Siloles and Germoles

“…Progress in the chemistry of tetroles I , the heavier analogs of cyclopentadiene, is driven by the favorable photophysical properties of these compounds (Figure 1). [1–4] The cross‐hyperconjugation between the butadiene part and the tetrylene unit lowers their absorption energy and promotes their application in optoelectronic devices [5–8] . The discovery of the aggregation induced emission effect in perarylated siloles additionally fueled the interest in this class of compounds [9–12] .…”

“…[ 1 , 2 , 3 , 4 ] The cross‐hyperconjugation between the butadiene part and the tetrylene unit lowers their absorption energy and promotes their application in optoelectronic devices. [ 5 , 6 , 7 , 8 ] The discovery of the aggregation induced emission effect in perarylated siloles additionally fueled the interest in this class of compounds. [ 9 , 10 , 11 , 12 ] The second mainspring for the development of the chemistry of tetroles was the possible occurrence of aromaticity in the negatively charged ions, II and III , and their applications as ligands in transition metal chemistry.…”

One-Pot Direct Synthesis of Siloles from 1-Bromo-2-silylethynylbenzenes or 1-Bromo-4-silyl-1,3-enynes

“…Siloles and benzosiloles have garnered increasing attention because of their specific physical and chemical properties. − Therefore, several methodologies for preparing siloles, including benzosiloles and dibenzosiloles, have been reported thus far. − Most synthetic methodologies for preparing siloles are limited to symmetrically substituted siloles bearing the same substituents, and there have been few reports on the preparation of unsymmetrically substituted siloles bearing different substituents with complete regioselectivity. To this end, we reported the synthetic methodology that enables the synthesis of benzosiloles and unsymmetrically substituted siloles bearing different substituents in good to excellent yields from starting materials 2 (Scheme (a), eq 2). , However, this method has a critical defect because it is necessary to synthesize the starting materials 2 , which are difficult to get access and purify (Scheme (a), eq 1).…”

Silole allylic anions instead of silanides

“…This is indeed the case and we recently reported on the synthesis and conjugational properties of 2,5-di(oligosilanylated) 1,1-dimethyl-3,4-diphenylsilole 1a, which constitutes a first example of the combination of crosshyperconjugation and σ-conjugation in 2,5-oligosilanylated siloles. 12 The current account deals with experiments to modify the oligosilanyl parts of siloles like 1a. The possibility of converting oligosilanyl groups to silanides would reveal their potential to serve as building blocks for the construction of more complex molecular architectures.…”

“…This is indeed the case and we recently reported on the synthesis and conjugational properties of 2,5-di(oligosilanylated) 1,1-dimethyl-3,4-diphenylsilole 1a , which constitutes a first example of the combination of cross-hyperconjugation and σ-conjugation in 2,5-oligosilanylated siloles. 12 …”