Diradicaloid or Zwitterionic Character: The Non-Tetrahedral Unsaturated Compound [Si4 {N(SiMe3 )Dipp}4 ] with a Butterfly-type Si4 Substructure.

The reduction of the tribromoamidosilane {N(SiMe3 )Dipp}SiBr3 (Dipp=2,6-iPr2 C6 H3 ) with potassium graphite or magnesium resulted in the formation of [Si4 {N(SiMe3 )Dipp}4 ] (1), a bicyclo[1.1.0]tetrasilatetraamide. The Si4 motif in 1 does not adopt a tetrahedral substructure and exhibits two three-coordinate and two four-coordinate silicon atoms. The electronic situation on the three-coordinate silicon atoms is rationalized with positive and negative polarization based on EPR analysis, magnetization measurements, and DFT calculations as well as 29 Si CP MAS NMR and multinuclear NMR spectroscopy in solution. Reactivity studies with 1 and radical scavengers confirmed the partial charge separation. Compound 1 reacts with sulfur to give a novel type of silicon sulfur cage compound substituted with an amido ligand, [Si4 S3 {N(SiMe3 )Dipp}4 ] (2).