Lutz Ruwisch

Synthesis of silyl substituted organoboranes by hydroboration of vinylsilanes

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.

Solid-state NMR investigations of the polymer route to SiBCN ceramics

Silicon based polymers obtained by ammonolysis of organochlorosilylboranes and their pyrolytic transformation into Si-B-C-N ceramics were studied by a detailed solid-state NMR investigation. Sol–gel polymerisation/pyrolysis routes were applied to form Si-B-C-N materials with exceptional high-temperature stability. The polymer to ceramic conversion was analyzed by 11B, 13C, 15N, and 29Si MAS NMR spectroscopy as well as by thermal analysis measurements coupled with mass spectroscopy (TGA–MS). The results showed that a significant change in the carbon-, silicon-, and boron-coordination environments occurs during pyrolysis. An evolution of cleavage of silcon–carbon–boron bridges and the formation of new BN3 sites was observed. The NMR data obtained suggest the presence of a rather homogeneous dispersion of the boron atoms in the as synthesized silicon carbonitride phase, supporting the high thermal stability with respect to decomposition found in these compounds.Key words: organosilicon polymers, polymer pyro...

Synthese und Molekülstruktur des [α-(Dichlormethylsilyl)ethyl]- dichlorboran-dimethylsulfid / Synthesis and Molecular Structure of [α-(Dichloromethylsilyl)ethyl]- dichloroborane-dimethylsulfide

[α-(Dichloromethylsilyl)ethyl]-dichloroborane-dimethylsulfide has been synthesized by the reaction of dichloromethylvinylsilane with dichloroborane-dimethylsulfide and its molecular structure determined by single crystal X-ray diffraction and by spectroscopic methods. Following the Markovnikov rule, a chiral methine group is formed as a bridge between silicon and boron.