Siloxides are
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 ...
s with the formula R
3SiOM, where R is usually an organic group and M is usually 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 ...
cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
. Also called silanoates, they are derived by
deprotonation
Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.ed ...
of
silanols
A silanol is a functional group in silicon chemistry with the connectivity Si–O–H. It is related to the hydroxy functional group (C–O–H) found in all alcohols. Silanols are often invoked as intermediates in organosilicon c ...
. They also arise by the degradation of
siloxanes
A siloxane is a functional group in organosilicon chemistry with the Si−O−Si linkage. The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2)''n''OH and (OSiH2)n. Siloxanes also include branched compou ...
by base:
[
:R3SiOSiR3 + 2 NaOH → 2 R3SiONa + H2O
Cleavage of cyclic siloxanes affords siloxides:
:(Me2SiO)3 + MeLi → Me3SiOSiMe2OSiMe2OLi
These anions function as ]ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
s for metal ions, forming complexes similar to metal alkoxide
In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organic substituent. Alkoxides are strong bases and, whe ...
s. Sodium trimethylsiloxide
Sodium trimethylsiloxide is an organosilicon compound with the formula NaOSi(CH3)3. It is the sodium salt of the conjugate base derived from trimethylsilanol. A white solid, its molecular structure consists of a cluster with Na-O-Na linkages on t ...
is useful for generating metal complexes by salt metathesis reaction
A salt metathesis reaction, sometimes called a double displacement reaction, is a chemical process involving the exchange of bonds between two reacting chemical species which results in the creation of products with similar or identical bonding a ...
s. A very bulky siloxide is tert-butyl
In organic chemistry, butyl is a four-carbon alkyl radical or substituent group with general chemical formula , derived from either of the two isomers (''n''-butane and isobutane) of butane.
The isomer ''n''-butane can connect in two ways, givi ...
3SiO−, sometimes called silox
Sodium silox is the name for an organosilicon compound that serves as a source of the siloxide anion CH3)3CSiO−. Complexes of this bulky anionic ligand often adopt with low coordination numbers. Examples include Ti(silox)3, Nb(silox)3(PMe3) ...
.
Siloxides are weaker net donors than alkoxides
In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organic substituent. Alkoxides are strong bases and, w ...
because pπ-d donation has to compete with backbonding from the oxygen atom into the low-lying Si-C σ* orbitals.[{{cite journal , last1=Krempner , first1=Clemens , title=Role of Siloxides in Transition Metal Chemistry and Homogeneous Catalysis , journal=Eur. J. Inorg. Chem. , year=2011 , volume=2011 , issue=11 , page=1689 , doi=10.1002/ejic.201100044 , url=https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/ejic.201100044]
References
Organosilicon compounds