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On the possible formation of Si=O, Si=S, and Si=Se double bonds via the reaction of silylenes

Summary: On the possible formation of Si=O, Si=S, and
Si=Se double bonds via the reaction of silylenes
with oxirane, thiirane, and selenirane,
respectively. An ab initio theoretical study
Yitzhak Apeloig and Stepan Sklenak
Abstract: The reactions between silylene, H2Si, and the three-membered ring compounds, oxirane (9), thiirane (10),
and selenirane (11), which provide possible routes to Si=X (X = O, S, Se) double bonds were studied by ab initio cal-
culations at the MP2 and QCISD correlated levels of theory employing the polarized 6-31G** basis set. The calcula-
tions show that the three reactions are all highly exothermic, (­61.8, ­45.2, ­52.9 kcal/mol at MP2/6-31G**//MP2/6-
31G** for X = O, S, Se, respectively). In the gas phase, at 0 K, these reactions are predicted to be also spontaneous
(i.e., the calculated transition states are lower in energy than the reactants). At 298 K, entropy contributions result in
small barriers on the G surface for X = O, S (7.4 kcal/mol for both reactions at QCISD (full)/6-31G**), but for X =
Se the reaction remains spontaneous. Thus, the calculations suggest that these reactions are viable routes for the prepa-
ration of compounds with Si=X (X = O, S, Se) double bonds. The first step in all the reactions is the barrier-less for-
mation of an encounter-complex between the silylene and the X atom of the precursor. For X = O, S, these complexes
are predicted to be sufficiently stable to be observed in a matrix. The reaction steps which follow depend on X; for
X = O fragmentation of the silylene­XC2H4 complex proceeds in two steps via a biradical intermediate, while for
X = S and X = Se the fragmentation occurs in a single step. The first ab initio calculations for H2Si=Se are reported.
Key words: silylene, silanone, silanethione, silaneselone.
Résumé : Faisant appel à des calculs ab initio aux niveaux MP2 et QCISD apparentés de la théorie et utilisant


Source: Apeloig, Yitzhak - Department of Chemistry, Technion, Israel Institute of Technology
Sklenak, Stepan - Department of Chemical Physics, Jaroslav Heyrovsky Institute of Physical Chemistry


Collections: Chemistry