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Summary: Addition of Nucleophiles to Silenes. A Theoretical Study
of the Effect of Substituents on Their Kinetic Stability
Michael Bendikov, Sabine Ruth Quadt, Oded Rabin, and Yitzhak Apeloig*
Department of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum
Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel
Received April 2, 2002
The addition of water to nine silenes (H2SidCH2 (1), Me2SidC(SiH3)2 (2), Cl2SidCH2 (3),
Me2SidCMe2 (4), (H3Si)2SidCMe2 (5), (H3Si)2SidC(Me)OSiH3 (6), Me2SidC(SiMe3)H (7), Me-
(HCC)SidCH2 (8), and Me(Me3Si)SidCH2 (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 t (t ) 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.
Introduction
Following the synthesis of the first stable silene in
1981,1 many reactions of silenes have been reported.2,3
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