Addition of Nucleophiles to Silenes. A Theoretical Study of the Effect of Substituents on Their Kinetic Stability
2002-08-13T00:00:00Z (GMT) by
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 the kinetic stability of the silene, strongly depend on the substituents. Silenes (1−4) exhibit low and even negative activation energies (−3 to 8 kcal/mol). Substituents that strongly reduce the polarity of the silene, as in 5 and 6, increase significantly the activation energy for the nucleophilic addition of H2O to ca. 16 kcal/mol. The calculated activation energies show a good correlation with Δt (Δt = the difference in the total NBO charge between Si and C), i.e., the higher the polarity of the silene the lower is the activation barrier for water addition.
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