Add time:08/12/2019         Source:sciencedirect.com

All-cis-2,4,6,8-tetramethyl-2,4,6,8-tetrakis(triphenylsiloxy)cyclotetrasiloxane (4) and syn-1,3,9,11-tetramethyl-5,5,7,7,13,13,15,15-octaphenyltricyclo[9.5.1.13,9]octasiloxane (5) were synthesized by the reaction of cis,trans,cis-[MeSi(NCO)O]4 (1) with Ph3SiOH (2) and [Ph2Si(OH)]2O (3), respectively, in the presence of pyridine for the sake of investigating the synthesis of ladder polysilsesquioxanes with perfect siloxane frameworks. Their stereostructures were confirmed by nuclear magnetic resonance spectra and X-ray crystallography, which revealed that 4 and 5 did not retain the stereostructure of the precursor 1. This result was caused by the racemization of 1 with pyridine, and a subsequent nucleophilic substitution reaction of 1 with 2 or 3, including inversion and retention of the configuration at the silicon atoms.

► Isocyanatosilane transformed its conformation in the presence of pyridine. ► Isocyanatosilane transformed its conformation via hyper coordinated intermediate. ► All-cis-tetrakis(triphenylsiloxy)tetramethyltetrasiloxane was synthesized. ► Ladder oligosilsesquioxane with tricyclic system was synthesized. ► Ladder oligosilsesquioxane was arranged in syn-form.

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