ABOUT THE SYNTHESIS OF TRIS(TRIMETHYLSILY L)SILYL POTASSIUM, RUBIDIUMAND CESIUM AND THE MOLECULAR-STRUCTURES OF 2 TOLUENE SOLVATES

Solventfree tris(trimethylsilyl)silyl potassium (1), rubidium (2) and cesium (3) are obtained by the reaction of the zink group bis[tris(tri methylsilyl)silyll derivatives with the appropriate alkali metal in n- pentane. Addition of benzene or toluene to the colourless powders yiel ds deeply coloured solutions. From these solutions single crystals of tris(trimethylsilyl)sily] rubidium-toluene (2/1) (2a) and tris(trimeth ylsilyl)silyl cesium-toluene (2/3) (3a) suitable for X-ray structure a nalysis are isolated [2a: orthorhombic; P2(1)2(1)2,; a = 1382.1(3); b = 1491.7(5); c = 2106.3(6) pm; Z = 4 (dimers); 3a: orthorhombic; P2(1) 2(1)2,; a = 2(1)31.0(6); b = 2 833.1(2); c = 925.2(2) pm; Z = 4 (dimer s)]. The central structure moieties are folded four-membered Rb2Si2 an d CS2Si2 rings, respectively. Small Si-Si-Si angles (100 to 104-degree s) on the one hand and extreme highfield Si-29-NMR shifts of the centr al silicon atoms on the other hand indicate a strong charge transfer f rom the alkali metal atoms to the tris(trimethylsilyl)silyl fragments, i.e. mainly ionic interactions between alkalimetal and silicon atoms.