Dichlorosilane–dimethyl ether aggregation: a new motif in halosilane adduct formation

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The crystal structures of (H₃C)₂O, 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)₂O and H₂SiCl₂ has the composition [(H₃C)₂O·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)₂O·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)₂O + H₂SiCl₂ → (H₃C)₂O·H₂SiCl₂], −14.4 kJ mol⁻¹ for the dimerization of two mono adducts {(H₃C)₂O·H₂SiCl₂ → [(H₃C)₂O·H₂SiCl₂]₂} and −41.2 kJ mol⁻¹ for the reaction 2 (H₃C)₂O + 2 H₂SiCl₂ → [(H₃C)₂O·H₂SiCl₂]₂. The results are used to rationalize the strongly reduced reactivity of H₂SiCl₂ towards nucleophilic substitution reactions in (H₃C)₂O at low temperatures.