A silylenoid in
organosilicon chemistry
Organosilicon compounds are organometallic compounds containing carbon–silicon bonds. Organosilicon chemistry is the corresponding science of their preparation and properties. Most organosilicon compounds are similar to the ordinary organic c ...
is a type of
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the general structure where R is any organic residue, X a
halogen and M a
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
. Silylenoids are the silicon pendants of
carbenoid In chemistry a carbenoid is a reactive intermediate that shares reaction characteristics with a carbene. In the Simmons–Smith reaction the carbenoid intermediate is a zinc / iodine complex that takes the form of
:I-CH2-Zn-I
This complex reacts w ...
and both compounds have
carbene
In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms.
The term "carbene" ma ...
or
silylene like properties.
Silylenoids are encountered as
reactive intermediates in
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
s. A stable silylenoid can be prepared by reaction of a fluorobromosilane with a silyllithium compound in
THF
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...
:
:(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 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) 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
Disilene is an inorganic compound with the chemical formula . The name ''disilene'', referring to the structure of a particular prototropic tautomer of the molecule. It is the simplest silene.
Properties and bonding
Disilene is a molecule with ...
forms probably via a
silylene intermediate. With
electrophiles
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carri ...
it reacts as an anion and with
organolithium
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom ...
compounds it reacts as a
silylene.
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
Yitzhak Apeloig (יצחק אפלויג; born 1 September 1944 in Uzbekistan) is a pioneer in the computational chemistry field of the Ab initio quantum chemistry methods for predicting and preparing the physical and chemical properties of mater ...
J. Am. Chem. Soc.; 2006; 128(9) pp 2784 – 2785
Abstract
Organosilicon compounds