Comparative chemistry of unsaturated compounds of Group 14 elements*
Mitsuo Kira
Department of Chemistry, Graduate School of Science,
Tohoku University, Aoba-ku Sendai, 980-8578, Japan
Abstract: Structures and reactions of a stable dialkylsilylene
and various cyclic and acyclic disilenes, which we have recently synthesized,
are discussed in detail. The stable silylene was found to be well protected
sterically from dimerization but least perturbed electronically as evidenced
by UVvis and NMR spectroscopy. Persilylated acyclic and cyclic
disilenes have shown interesting features in the Si=Si bond distances,
electronic spectra, and reactions, due to the remarkable electronic
and steric effects of trialkylsilyl substituents. Detailed theoretical
calculations for the addition of water to disilene has shown that the
intramolecular anti-addition pathway is rationalized using the orbital
symmetry rule. The reactions of disilenes with haloalkanes were judged
to proceed via the rate-determining halogen abstraction of disilenes
from haloalkanes. The biradical character of disilenes may be related
to the small p bond energy.
*Plenary lecture presented at the 15th
International Conference on Physical Organic Chemistry (ICPOC 15), Göteborg,
Sweden, 8 –13 July 2000. Other presentations are published in this
issue, pp. 2219 –2358.
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