Formation of a Donor-Stabilized Tetrasilacyclobutadiene Dication by a Lewis Acid Assisted Reaction of an N-Heterocyclic Chloro Silylene

The first donor-stabilized tetrasilacyclobutadiene dication species has been synthesized and fully characterized. Its unexpected formation occurs by the Lewis acid assisted reaction of the N-heterocyclic chloro silylene [L(Si:)Cl] (L = PhC(NtBu)(2); amidinate) with Cp*ZrCl3 (Cp* = pentamethylcyclopentadienyl) in the molar ratio of 3:2. Remarkably, the four-membered Si-4 core consists of two N-donor stabilized silylium subunits and two silylene-like moieties. The dicationic charge is somewhat delocalized on the Si-4, core, which is supported by DFT calculations.