Ruwisch, Lutz M. ; Dürichen, P. ; Riedel, R. (2000):
Synthesis of silyl substituted organoboranes by hydroboration of vinylsilanes.
In: Polyhedron, 19 (3), pp. 323-330. Elsevier, [Article]

Abstract

Hydroboration reactions of dichloroborane-, monochloroborane- and borane-dimethylsulfide with dichloromethylvinylsilane and trichlorovinylsilane were investigated. The proposed structures of the produced organochlorosilylboranes 1–4 were verified by NMR spectroscopic measurements and in the case of [α-(dichloromethylsilyl)ethyl]dichloroborane-dimethylsulfide (4) the molecular structure was determined by single-crystal X-ray diffraction (L.M. Ruwisch, R. Riedel, U. Klingebiel, M. Noltemeyer, Z. Naturforsch., Teil B 54 (1999) 624). Following the Markovnikov rule, the first addition appears strictly regioselective in the α-position to silicon, producing one chiral methine group between silicon and dichloroborane in compound 4. The second addition of borane- or monochloroborane-dimethylsulfide at the vinyl groups of dichloromethylvinylsilane and trichlorovinylsilane also takes place in the α-position to silicon, forming a second chiral methine group. In the case of borane-dimethylsulfide the third addition occurs in the β-position (anti-Markovnikov) owing to steric hindrance to boron in tris[(dichloromethylsilyl)ethyl]borane (1). A stepwise substitution of chlorine bonded at boron in compounds 2 and 3 using hexamethyldisilazane produces bis[α-(dichloromethylsilyl)ethyl]boryl-trimethylsilylamine (5) and bis[α-(trichlorosilyl)ethyl]boryl-trimethylsilylamine (6), respectively, under release of chlorotrimethylsilane. The remaining trimethylsilylamine group in 6 can be replaced by further reaction with 3 forming tetrakis[α-(trichlorosilyl)ethyl]diborylamine (7). This reaction resembles a selective amino condensation at boron. In a similar condensation reaction of 4 with equivalent amounts of hexamethyldisilazane, tris[α-(dichloromethylsilyl)ethyl]borazine (8) can be obtained.

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