PUB - Publikationen an der Universität Bielefeld

The crystal structures of (H3C)(2)O, H2SiCl2 and an adduct of these were determined by low-temperature X-ray crystallography on crystals grown in situ at low temperatures on a diffractometer. The adduct of (H3C)(2)O and H2SiCl2 has the composition [(H3C)(2)O.H2SiCl2](2) and contains a four-membered Si2O2 ring, with the Cl atoms pointing to the outside and the Si-H functions pointing to the inner side of the ring. The Si2O2 ring has two longer and two shorter Si...O bonds and thus deviates from a square. Quantum chemical calculations give a geometry for [(H3C)(2)O.H2SiCl2](2) which has D-2h symmetry and allow to obtain an estimate for the adduct formation energies, which are -13.4 kJ mol(-1) for the formation of the mono adduct [(H3C)(2)O + H2SiCl2 --> (H3C)(2)O.H2SiCl2], -14.4 kJ mol(-1) for the dimerization of two mono adducts {(H3C)(2)O.H2SiCl2 --> [((HC)-C-3)(2)O.H2SiCl2](2)} and -41.2 kJ mol(-1) for the reaction 2 (H3C)(2)O + 2 H2SiCl2 --> [(H3C)(2)O.H2SiCl2](2). The results are used to rationalize the strongly reduced reactivity of H2SiCl2 towards nucleophilic substitution reactions in (H3C)(2)O at low temperatures.