DEHYDROCOUPLING REACTIONS OF ORGANOSILANES WITH HYDRAZINES

Phenylsilane reacts spontaneously with hydrazine to give a soluble oligomer, [PhSi(NHNH)2SiPhNHNH]n, 1, while in the presence of dimethyltitanocene (DMT) as catalyst, rapid coupling took place to give an insoluble gel. The dehydrocoupling reactions of phenylsilane with methylhydrazines (1-methyl-, 1,1-dimethyl-, and 1,2-dimethylhydrazine) are effectively catalyzed by DMT. Phenylsilane reacts with 1-methylhydrazine to give poly((phenylsilyl)-N-(methylamino)azane), 2, and poly[phenyl(methylhydrazyl)silane], 3. In the reaction with 1,1-dimethylhydrazine, homocoupling of phenylsilane competes effectively with the cross-coupling reaction with the hydrazine, to give diphenyldisilane and triphenyltrisilane in about the same amount as the oligomeric silylhydrazines (4 and 5, the analogs of 2 and 3, respectively). The reaction with 1,2-dimethylhydrazine gives simple silylhydrazines PhSiH2(NMeNHMe), 6, and PhSiH(NMeNHMe)2, 7, without homocoupling. The cyclic compound Ph2Si(NHNH)2SiPh2, 8, was obtained in 40 % yield from the reaction of diphenylsilane with hydrazine. The reaction of diphenylsilane with 2 equiv of methylhydrazine gave Ph2Si(NHNHMe)2, 13, in 70 % yield, by the stepwise replacement of the Si-H groups of diphenylsilane with hydrazyl groups. A strong inhibiting effect of methyl substitution was evident in the reactions of diphenylsilane with 1,1-dimethyl- and 1,2-dimethylhydrazine. The crystal structure of 8 reveals a chairlike conformation of the Si2N4 ring [a = 29.683(5) angstrom, b = 5.8972(17) angstrom, c = 39.038(7) angstrom, beta = 105.492(14)-degrees; monoclinic, A2/a; two independent molecules in one unit cell, Z = 12], in which each NHNH unit contains one planar nitrogen and one pyramidal nitrogen atom. The structure of 13 [a = 7.7725(5) angstrom, b = 9.1289(9) angstrom, c = 21.2624(17) angstrom, beta = 91.814(7)-degrees; monoclinic, P2(1)/c; Z = 4] is also reported.