Silicon Chalcogenide Cage Compounds: New Structures Derived from the Bicyclic Silicon(I) Ring Compound Si4 {N(SiMe3 )Mes}4.

The bicyclic silicon(I) ring compound Si4 {N(SiMe3 )Mes}4 (2) was used as starting material in reactions with chalcogens and chalcogen transfer agents at low temperatures. This resulted in the selective formation of new cage compounds. With Me3 NO, a silicon oxide with adamantane-type cage 3 was isolated that represents the first isolated T4 silsesquioxane. Reactions with propylenesulfide and red selenium gave direct access to defect heterocubane-type cages 4 and 5 with three Si-Si bonds wherein the silicon atoms adopt different low oxidation states of +I and +III. A reaction with elemental tellurium even occurs below room temperature to provide ditelluro-tetrasila-tricyclohexane 6.

Reactivity of the Bicyclic Amido-Substituted Silicon(I) Ring Compound Si4 {N(SiMe3 )Mes}4 with FLP-Type Character.

The bicyclic amido-substituted silicon(I) ring compound Si4 {N(SiMe3 )Mes}4 2 (Mes=Mesityl=2,4,6-Me3 C6 H2 ) features enhanced zwitterionic character and different reactivity from the analogous compound Si4 {N(SiMe3 )Dipp}4 1 (Dipp=2,6-i Pr2 C6 H3 ) due to the smaller mesityl substituents. In a reaction with the N-heterocyclic carbene NHC Me 4 (1,3,4,5-tetramethyl-imidazol-2-ylidene), we observe adduct formation to give Si4 {N(SiMe3 )Mes}4 ⋅ NHC Me 4 (3). This adduct reacts further with the Lewis acid BH3 to yield the Lewis acid-base complex Si4 {N(SiMe3 )Mes}4 ⋅ NHC Me 4 ⋅ BH3 (4). Coordination of AlBr3 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.