A silylenoid in
organosilicon chemistry is a type of
chemical compound with the general structure where R is any organic residue, X a
halogen
The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...
and M a
metal. Silylenoids are the silicon pendants of
carbenoid and both compounds have
carbene or
silylene
Silylene is a chemical compound with the formula SiH2. It is the silicon analog of methylene, the simplest carbene. Silylene is a stable molecule as a gas but rapidly reacts in a bimolecular manner when condensed. Unlike carbenes, which can exis ...
like properties.
Silylenoids are encountered as
reactive intermediate
In chemistry, a reactive intermediate or an intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these comp ...
s in
chemical reactions. A stable silylenoid can be prepared by reaction of a fluorobromosilane with a silyllithium compound in
THF :
:(t-Bu
2MeSi)
2SiFBr + t-Bu
2MeSiLi/THF → (t-Bu
2MeSi)
2SiFLi.3THF + t-Bu
2MeSiBr
In this silylenoid the silicon atom is bonded with three substituents and not the usual four.
X-ray diffraction
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
shows that the Si-F bond with 170
pm is longer than usual for fluorosilanes. The F-Li bond is
ionic with an estimated (
in silico
In biology and other experimental sciences, an ''in silico'' experiment is one performed on computer or via computer simulation. The phrase is pseudo-Latin for 'in silicon' (correct la, in silicio), referring to silicon in computer chips. It ...
) positive charge of 0.88 residing on lithium and a negative charge of 0.74 on fluorine making it a (t-Bu
2MeSi)
2SiF
−, Li
+.3THF salt. The Si-F bond is likewise polarized with only 10% of the charge on silicon.
When the silylenoid is irradiated or heated a
disilene forms probably via a
silylene
Silylene is a chemical compound with the formula SiH2. It is the silicon analog of methylene, the simplest carbene. Silylene is a stable molecule as a gas but rapidly reacts in a bimolecular manner when condensed. Unlike carbenes, which can exis ...
intermediate. With
electrophiles it reacts as an anion and with
organolithium compounds it reacts as a
silylene
Silylene is a chemical compound with the formula SiH2. It is the silicon analog of methylene, the simplest carbene. Silylene is a stable molecule as a gas but rapidly reacts in a bimolecular manner when condensed. Unlike carbenes, which can exis ...
.
References
# {{Note, Molev ''Synthesis, Molecular Structure, and Reactivity of the Isolable Silylenoid with a Tricoordinate Silicon'' Gregory Molev, Dmitry Bravo-Zhivotovskii, Miriam Karni, Boris Tumanskii, Mark Botoshansky, and
Yitzhak Apeloig J. Am. Chem. Soc.; 2006; 128(9) pp 2784 – 2785
Abstract
Organosilicon compounds