Reactivity of the Bicyclic Amido‐Substituted Silicon(I) Ring Compound Si<sub>4</sub>{N(SiMe<sub>3</sub>)Mes}<sub>4</sub> with FLP‐Type Character
Kevin Schwedtmann, Michael Quest, Benedikt J. Guddorf, Jan Keuter, Alexander Hepp, Milica Feldt, Jörn Droste, Michael Ryan Hansen, Felicitas Lips
Abstract
Abstract 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 (1,3,4,5‐tetramethyl‐imidazol‐2‐ylidene), we observe adduct formation to give Si 4 {N(SiMe 3 )Mes} 4 ⋅ NHC ( 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 ⋅ 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 .