Laddersiloxanes: Silsesquioxanes with Defined Ladder Structure
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1007-S01-05
Laddersiloxanes: Silsesquioxanes with Defined Ladder Structure Masafumi Unno Gunma University, Kiryu, 376-8515, Japan
ABSTRACT A series of structurally-defined laddersiloxanes [1] are presented. Pentacyclic laddersiloxanes were prepared by a stepwise procedure from all-cistetraisopropylcyclotetrasiloxanetetraol. All-anti pentacyclic, tetracyclic, tricyclic, and bicyclic laddersiloxanes were obtained by oxidation from respecting all-anti pentacyclic ladder polysilane. Stereocontrolled approach using RS-disiloxanediol as an expanding unit enabled the synthesis of longer laddersiloxanes. Finally, methyl-substituted ladder polysilsesquioxane was obtained by the stepwise transformation from (MePhSiO) 4. The X-ray crystal structures, NMR and IR spectra, and thermal stability of these laddersiloxanes are summarized. INTRODUCTION Highly-regular silsesquioxanes, especially those with ladder structures, have received considerable attention since 1960, when Brown and coworker proposed a ladder structure for phenylsilsesquioxanes (PhSiO1.5)n obtained by treatment of the hydrolysate of trichlorophenysilane with 0.1% KOH in toluene [2]. Evidence from IR and 29Si-NMR spectra as well as X-ray powder diffraction [3], has suggested the formation of ladder-type polysilsesquioxanes under certain conditions. However, such evidence is not universally accepted [4]. Thus it is worthwhile to prepare ladder polysiloxanes with defined structure (laddersiloxanes) since they can serve as models for ladder polysilsesquioxanes. In this paper, we will summarize our recent work related to the synthesis of tricyclic, pentacyclic, heptacyclic, and polycyclic laddersiloxanes. EXPERIMENTAL DETAILS Analytical HPLC was performed in a JASCO 875UV / 880PU with Chemco 4.6 mm x 250 mm 5-ODS-H column. Preparative recycle-type HPLC was carried out using JAI LC-908 with Chemco 20 mm x 250 mm 7-ODS-H column. Fourier transform nuclear magnetic resonance spectra were obtained by a JEOL Model α-500 (1H at 500.00MHz, 13C at 125.65 MHz, and 29Si at 99.25 MHz). Chemical shift were reported as δ units (ppm) relative to SiMe4, and residual solvents peaks were used for standard. Electron impact mass spectrometry was performed with a JEOL JMS-DX302. Infrared spectra were measured with a SHIMADZU FTIR-8700. Tricyclic laddersiloxanes Dichlorodiisopropyldiphenyldisiloxane 2 (7.36 g, 19.2 mmol) was added dropwise to a solution of all-cis-tetraisopropylcyclotetrasiloxanetetraol 1 (4.0 g, 9.60 mmol) in pyridine (90
mL) at 0 °C for 20 min. Then the mixture was warmed to room temperature and stirred for 2 h. Hexane was added to the reaction mixture and the organic phase was washed with water. The aqueous phase was extracted three times with hexane. The combined organic phase was dried over anhydrous magnesium sulfate and concentrated. The residue was triturated from methanol to give tricyclic laddersiloxanes as a mixture of isomers (8.52 g, 85%). The isomeric mixture was separated by recycle-type HPLC, and determined their structures (3a–3e) by X-ray crystallograp
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