Chloride-Induced Aufbau of Perchlorinated Cyclohexasilanes from Si2Cl6: A Mechanistic Scenario

• Published in: Chemistry : a European journal 2014-07, Vol.20 (30), p.9234-9239
• Main Authors: Tillmann, Jan, Meyer, Lioba, Schweizer, Julia I., Bolte, Michael, Lerner, Hans-Wolfram, Wagner, Matthias, Holthausen, Max C.
• Format: Article
• Language: English
• Subjects: Catalysis; Chemistry; Chlorides - chemistry; density functional calculations; inverse sandwich complexes; Models, Molecular; Molecular Structure; perchlorinated silanes; reaction mechanisms; reactive intermediates; Silanes - chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201402655

A surprisingly simple preparative procedure, addition of Si2Cl6 to a solution of [nBu4N]Cl in CH2Cl2, leads to the formation of the chloride‐complexed cyclic dianions [Si6Cl12⋅2Cl]2−, [(SiCl3)Si6Cl11⋅2Cl]2−, or [1,y‐(SiCl3)2Si6Cl10⋅2Cl]2− (y=1, 3, 4), depending on the stoichiometric ratio of the reactants and the reaction temperature (25–85 °C). Below −40 °C the open‐chain oligosilane chloride adducts [Si3Cl9]−, [Si3Cl10]2−, [Si4Cl11]−, and [Si6Cl15]− are formed, again depending on the reaction conditions chosen. All species were characterized by X‐ray crystallography. The underlying reaction mechanism is elucidated by DFT calculations. It incorporates all experimental findings and involves a few key elementary steps: 1) chloride‐induced liberation of SiCl3− or higher silanides, 2) their addition to neutral silanes yielding larger oligosilane chloride adducts, 3) dimerization of larger silanides to (substituted) cyclohexasilane dichloride adducts with inverse sandwich structure. As simple as this: Chloride addition to Si2Cl6 provides efficient synthetic access to perchlorocyclohexasilane dichloride adducts (see scheme). The reaction mechanism has been elucidated in a combined theoretical and experimental study: chloride‐induced SiCl3− liberation from Si2Cl6 triggers the formation of higher silanide anions, which dimerize in a head‐to‐tail fashion to the cyclic final products.