Stereoisomers of 1,3,5,7-Tetrahydroxy-1,3,5,7-tetraisopropylcyclotetrasiloxane:  Synthesis and Structures in the Crystal

Abstract

The first synthesis of all four stereoisomers of 1,3,5,7-tetrahydroxy-1,3,5,7-tetraisopropylcyclotetrasiloxane, [i-PrSiO(OH)]4 (all-trans-, cis-cis-trans-, cis-trans-cis-, and all-cis-1), is presented. The starting compounds, all-trans-, cis-cis-trans-, cis-trans-cis-, and all-cis-1,3,5,7-tetraaryl-1,3,5,7-tetraisopropylcyclotetrasiloxanes, were prepared by the hydrolysis of the corresponding arylisopropyldichlorosilanes, i-PrArSiCl2 (Ar = Ph, p-tolyl), and subsequent separation of isomers. A combination of dephenylchlorination of tetraarylcyclotetrasiloxanes and the following hydrolysis proved to be an efficient method for the stereospecific transformation of aryl-substituted cyclotetrasiloxanes into (i-PrSiO(OH))4. For example, treatment of cis-trans-cis-1,3,5,7-tetraphenyl-1,3,5,7-tetraisopropylcyclotetrasilane with HCl and AlCl3, followed by hydrolysis in the presence of pyridine, resulted in the exclusive formation of cis-trans-cis-1 in 92% yield. The structures of cis-cis-trans-1, cis-trans-cis-1, and all-cis-1 were determined by X-ray crystallography. All isomers were found to construct unique packing structures by intermolecular hydrogen bonding; cis-trans-cis-1 composed an infinite antiladder structure, and cis-cis-trans-1 formed a sheetlike structure.

Synthesis and characterization of heptacyclic laddersiloxanes and ladder polysilsesquioxane

“…These temperatures are significantly higher than the Td 5 temperatures of cage silsesquioxane, (i-PrSi) 8 …”

“…[8] However, the methyl groups are not large enough for Similar to a few methyl-substituted silsesquioxanes, ladder polysilsesquioxane 6 is insoluble in organic solvents. Therefore, we identified this compound by IR and solid-state NMR spectroscopy.…”

Synthesis of macrocyclic tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane in carbonic acid solution

“…As for the macrocyclic siloxanols they could not be synthesized by traditional reaction routes used in siloxane chemistry. Successful efforts in synthesis of stereoregular organosiloxanols by means of different synthetic approaches (6)(7)(8)(9)(10)(11) have attracted much attention because of high potential usage of these unique synthons in synthesis of well-defined siloxane structures.…”

Alkali-Metal-Directed Hydrolytic Condensation of 3-Mercaptopropyltrimethoxysilane

“…However, the most promising method for the preparation of defect-free LPSQs is hydrolytic condensation of monomers containing cyclic siloxane units [11][12][13][14][15][16][17][18][19]. The most popular method for preparation of cyclic siloxane monomers is hydrolytic condensation of trialkoxyorganosilanes (Scheme 1) in the presence of water and an alkali metal hydroxide.…”

“…The syntheses of cyclotetrasiloxanolates functionalized at the Si atom with simple alkyl [34][35][36][37] and aryl [30,33,34] [33,34], iBu [33,34,36], Me [37], Vi [37], Et [37], iPr [37] tions. The presence of thiol groups in side chains would enable their functionalization by thiol-ene and thiol-yne addition, and thereby preparation of LPSQs with a large variety of functional groups.…”