Silylenoid
Encyclopedia
A Silylenoid in organosilicon chemistry
is a type of chemical compound
with the general structure R2SiXM where R is any organic residue, X a halogen
and M a metal
. Silylenoids are the silicon pendants of carbenoid
and both compounds have carbene
or silylene
like properties.
Silylenoids are encountered as reactive intermediate
s in chemical reaction
s. A stable silylenoid can be prepared by reaction of a fluorobromosilane with a silyllithium compound in THF :
2SiFBr + t-Bu2MeSiLi/THF → (t-Bu2MeSi)2SiFLi.3THF + t-Bu2MeSiBr
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-Bu2MeSi)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
intermediate. With electrophiles it reacts as an anion and with organolithium compounds it reacts as a silylene
.
Organosilicon
Organosilicon compounds are organic compounds containing carbon silicon bonds. Organosilicon chemistry is the corresponding science exploring their properties and reactivity.Like carbon, the organically bound silicon is tetravalent and tetrahedral...
is a type of chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the general structure R2SiXM where R is any organic residue, X a halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
and M a metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
. Silylenoids are the silicon pendants of carbenoid
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...
and both compounds have carbene
Carbene
In 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 RR'C:, but the carbon can instead be double-bonded to one group. The term "carbene" may also merely refer to the compound H2C:, also called...
or silylene
Silylene
Silylenes are chemical compounds containing a divalent silicon atom without any electrical charge. Both dicoordinate and tricoordinate silylenes are reported in the literature. They are considered to be heavier analogues of carbene. In earlier times, they were called silene, but this is a mistake,...
like properties.
Silylenoids are encountered as reactive intermediate
Reactive intermediate
In chemistry a reactive 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 compounds be isolated and stored, e.g. low temperatures, matrix isolation...
s in chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
s. A stable silylenoid can be prepared by reaction of a fluorobromosilane with a silyllithium compound in THF :
2SiFBr + t-Bu2MeSiLi/THF → (t-Bu2MeSi)2SiFLi.3THF + t-Bu2MeSiBr
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
Ionic bond
An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some...
with an estimated (in silico
In silico
In silico is an expression used to mean "performed on computer or via computer simulation." The phrase was coined in 1989 as an analogy to the Latin phrases in vivo and in vitro which are commonly used in biology and refer to experiments done in living organisms and outside of living organisms,...
) positive charge of 0.88 residing on lithium and a negative charge of 0.74 on fluorine making it a t-Bu2MeSi)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
Disilenes are compounds containing a silicon–silicon double bond and are considered to be heavier analogues of alkenes. They are sometimes also called disilaalkenes.-History:...
forms probably via a silylene
Silylene
Silylenes are chemical compounds containing a divalent silicon atom without any electrical charge. Both dicoordinate and tricoordinate silylenes are reported in the literature. They are considered to be heavier analogues of carbene. In earlier times, they were called silene, but this is a mistake,...
intermediate. With electrophiles it reacts as an anion and with organolithium compounds it reacts as a silylene
Silylene
Silylenes are chemical compounds containing a divalent silicon atom without any electrical charge. Both dicoordinate and tricoordinate silylenes are reported in the literature. They are considered to be heavier analogues of carbene. In earlier times, they were called silene, but this is a mistake,...
.