The Silaguanidinium Cation and the Search for a Stable Silylium Cation in Condensed Phases

✍ Scribed by Ulrich Pidun; Martin Stahl; Gernot Frenking

• Book ID: 102793065
• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 871 KB
• Volume: 2
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.19960020719

✦ Synopsis

Quantum mechanical calculations at the MP2/6-31 G(d) level are reported for the silaguanidinium cation Si(NH,): (1) and derivatives thereof. The equilibrium structure 1 a has D, symmetry with planar amino groups rotated out of the SIN, plane by 19.6". The Si-N bond length of 1 a (1.658 A) is intermediate between a single and a double bond. Isodesmic reactions show that the stabilization of the silylium cation l a by the amino groups (63.5 kcalmol-') is about 40 % of the resonance stabilization of the guanidinium cation (1 59.3 kcal mol -I ) , but l a is clearly better stabilized than alkyl-substituted silylium cations. The electronic stabilization of 1 a by the amino groups is also made obvious by the calculated complexation energy with one molecule of water. The calculated stabilization through complexation of water at HF/6-31 G(d) is markedly lower for Si(NH,),-(H,O)+ (6) (28.8 kcalmol-') than for SiMe,(H,O)+ (40.6 kcalmol-I ) . The tris-(dimethylamino) silylium cation Si(N-Me,): (8) is even more stable than l a . The complexation energy of Si(NMe,),-(H,O)+ (10) is only 17.3 kcalmol-'.