The reduction of the tribromoamidosilane {N(SiMe )Dipp}SiBr (Dipp=2,6-iPr C H ) with potassium graphite or magnesium resulted in the formation of [Si {N(SiMe )Dipp} ] (1), a bicyclo[1.1.0]tetrasilatetraamide. The Si 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 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, [Si S {N(SiMe )Dipp} ] (2).

Reaction of the bicyclo[1.1.0]tetrasilatetraamide Si4{N(SiMe3)Dipp}4 1 (Dipp=2,6‐diisopropylphenyl) with 5 equiv of the N‐heterocyclic carbene NHCMe4 (1,3,4,5‐tetramethylimidazol‐2‐ylidene) affords a bifunctional carbene‐coordinated four‐membered‐ring compound with a Si=N group and a two‐coordinate silicon atom Si4{N(SiMe3)Dipp}2(NHCMe4)2(NDipp) 2. When 2 reacts with 0.25 equiv sulfur (S8), two sulfur atoms add to the divalent silicon atom in plane and perpendicular to the plane of the Si4 ring, which confirms the silylone character of the two‐coordinate silicon atom in 2.

Thermal treatment of the bicyclo[1.1.0]tetrasilatetraamide [Si4{N(SiMe3)Dipp}4] 1 resulted in the formation of a highly unsaturated six-vertex silicon cluster [Si6{N(SiMe3)Dipp}4] 2 with only four amine-substituents and two ligand-free silicon atoms.

The bicyclic amido-substituted silicon(I) ring compound Si 4 {N(SiMe 3 )Mes} 4 2 (Mes = Mesityl = 2,4,6-Me 3 C 6 H 2 ) features enhanced zwitterionic character and different reactivity from the analogous compound Si 4 {N(SiMe 3 )Dipp} 4 1 (Dipp = 2,6-i Pr 2 C 6 H 3 ) due to the smaller mesityl substituents. In a reaction with the N-heterocyclic carbene NHC Me 4 (1,3,4,5tetramethyl-imidazol-2-ylidene), we observe adduct formation to give Si 4 {N(SiMe 3 )Mes} 4 • NHC Me 4 (3). This adduct reacts further with the Lewis acid BH 3 to yield the Lewis acid-base complex Si 4 {N(SiMe 3 )Mes} 4 • NHC Me 4 • BH 3 (4). Coordination of AlBr 3 to 2 leads to the adduct 5. Calculated proton affinities and fluoride ion affinities reveal highly Lewis basic and very weak Lewis acidic character of the low-valent silicon atoms in 1 and 2. This is confirmed by protonation of 1 and 2 with Brookharts acid yielding 6 and 7. Reaction with diphenylacetylene only occurs at 111 °C with 2 in toluene and is accompanied by fragmentation of 2 to afford the silacyclopropene 8 and the trisilanorbornadiene species 9.

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