We report the synthesis of five new examples of ladder cyclohexasilanes, possessing up to three consecutive fused rings. The synthesis of ladder compounds is challenging for both organic and inorganic skeletons, but Si's tetrahedral geometry introduces the problem of diastereoisomerism: with each additional ring, the number of possible stereoisomers differing only in relative configuration at the ring fusion increases. By coupling a 1,4-dipotassiooligosilyl dianion to a central cyclohexasilane, we report the isolation of three of the five possible diastereomers of the ladder tricyclohexasilane. Combined experimental and theoretical studies suggest a kinetic selectivity for the cis diastereomer and a thermodynamic preference for the trans diastereomer that is also dependent on the structure of the dianion. Computational studies show that with each additional ring in the trans-diastereomeric series, the predicted onset of light absorption shifts to longer wavelengths.
Keywords: Annulation; Conjugation; Diastereoselectivity; Ladder polymers; Silanes.
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