Chloride-induced aufbau of perchlorinated cyclohexasilanes from Si2Cl6: a mechanistic scenario

Abstract

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.

Keywords: density functional calculations; inverse sandwich complexes; perchlorinated silanes; reaction mechanisms; reactive intermediates.