| Abstract
| - A systematic theoretical study shows that the energy barriers for water additon to silenes, which denote the kinetic stability of the silene, strongly depend on the substituents; polar silenes exhibit negative or low activation energies (−3 to 8 kcal/mol), while substituents that strongly reduce the polarity of the silene increase significantly this activation energy, to ca. 16 kcal/mol.
- The addition of water to nine silenes (H2SiCH2 (1), Me2SiC(SiH3)2 (2), Cl2SiCH2 (3),Me2SiCMe2 (4), (H3Si)2SiCMe2 (5), (H3Si)2SiC(Me)OSiH3 (6), Me2SiC(SiMe3)H (7), Me(HCC)SiCH2 (8), and Me(Me3Si)SiCH2 (9)) was studied with ab initio (MP4/6-31+G(d,p))and DFT (B3LYP/6-31G(d)) methods. The energy barriers for addition, which denote thekinetic stability of the silene, strongly depend on the substituents. Silenes (1−4) exhibitlow and even negative activation energies (−3 to 8 kcal/mol). Substituents that stronglyreduce the polarity of the silene, as in 5 and 6, increase significantly the activation energyfor the nucleophilic addition of H2O to ca. 16 kcal/mol. The calculated activation energiesshow a good correlation with Δt (Δt = the difference in the total NBO charge between Siand C), i.e., the higher the polarity of the silene the lower is the activation barrier for wateraddition.
|
