CHEMISTRY OF ORGANOSILICON COMPOUNDS .263. SYNTHESIS, PROPERTIES, AND MOLECULAR-STRUCTURE OF HIGHLY DISTORTED HEXAKIS(TRIMETHYLSILYL)BENZENE

Hexakis(trimethylsilyl)benzene (2), the most distorted benzene to a chair form, has been prepared as yellow crystals by methylation of hexakis(bromodimethylsilyl)benzene. The structure of 2 has been determined by X-ray crystallography. Crystals of 2 are orthorhombic, space group P212121 a = 14.579 (3) Å, b = 18.927 (4) Å, c = 12.069 (9) Å, V = 3330.3 (10) Å3, Dc = 1.02 g/cm3, Z = 4. The benzene ring is remarkably deformed to a chair form with torsion angles of 9.8° (average) for Car-Car-Car-Car, and the six Si atoms are located up and down alternately from the benzene ring with torsion angles of 60.5° (average) for Si-Car-Car-Si. In solution, 2 exists as an equilibrium mixture of chair and boat forms. The quite unique chemical features of 2 are also demonstrated, for example, by photolysis with a0, light (» > 300 nm) to afford hexakis(trimethylsilyl)bicyclo[2.2.0]hexa-2,5-diene (Dewar benzene), whereas thermolysis led to the formation of 1,1,3,4,6,6-hexakis-(trimethylsilyl)-1,2,4,5-hexatetraene. © 1990, American Chemical Society. All rights reserved.