SYNTHESIS OF AN ORGANOSILICON DENDRIMER CONTAINING 324 SI-H BONDS

Starting with tetravinylsilane as the core molecule, a succession of alternate Pt-catalyzed hydrosilylations of all vinyl groups with HSiCl6 and vinylations of all of the SiCl groups thus introduced with CH2=CHMgBr in THF provided a divergent synthesis of four generations of polycarbosilane dendrimers in which the Si atoms are linked by CH2CH2 groups. The chlorosilane of each generation was reduced with LiAlH4 to the corresponding silicon hydride. The fourth generation hydride 4G-H, contains 324 Si-H bonds. The crystal structure of the second generation hydride, 2G-H, is described: space group P1BAR, a = 13.907 angstrom, b = 15.682 angstrom, c = 16.414 angstrom, alpha = 82.76-degrees, beta = 71.76-degrees, gamma = 82.49-degrees, Z = 2, R = 0.0996, R(w) = 0.1274. The high residuals result from the inherently high thermal activity at the ends of the dendrimer arms.