Pentamethylantimony or pentamethylstiborane is an
organometalllic compound containing five
methyl group
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...
s bound to an
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient time ...
atom with formula Sb(CH
3)
5. It is an example of a
hypervalent
In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded Octet rule, octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. P ...
compound. The molecular shape is
trigonal bipyramid
In geometry, the triangular bipyramid (or dipyramid) is a type of hexahedron, being the first in the infinite set of face-transitive bipyramids. It is the dual of the triangular prism with 6 isosceles triangle faces.
As the name suggests, i ...
. Some other antimony(V) organometallic compounds include pentapropynylantimony (Sb(CCCH
3)
5) and pentaphenyl antimony (Sb(C
6H
5)
5).
[ Other known pentamethyl-pnictides include ]pentamethylbismuth
Pentamethylbismuth (or pentamethylbismuthorane) is an organometalllic compound containing five methyl groups bound to a bismuth atom with formula Bi(CH3)5. It is an example of a hypervalent compound. The molecular shape is trigonal bipyramid.
P ...
and pentamethylarsenic.
Production
Pentamethylantimony can be made by reacting Sb(CH3)3Br2 with two equivalents of methyl lithium
Methyllithium is the simplest organolithium reagent with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used in s ...
. Another production route is to convert trimethylstibine
Trimethylstibine is an organoantimony compound with the formula Sb(CH3)3. It is a colorless pyrophoric and toxic liquid.
It is synthesized by treatment of antimony trichloride and methyl Grignard reagent.Sabina C. Grund, Kunibert Hanusch, Hans J ...
to the trimethyl antimony dichloride, and then replace the chlorine with methyl groups with methyl lithium.[
:Sb(CH3)3 + Cl2 → Sb(CH3)3Cl2
:Sb(CH3)3Cl2 + 2LiCH3 → Sb(CH3)5 + 2LiCl
]
Properties
Pentamethylantimony is colourless. At -143 °C it crystallizes in the orthorhombic
In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...
system with space group
In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...
''Ccmm''. Unit cell dimensions are a=6.630 Å b=11.004 Å c=11.090 Å. There are four formula per unit cell. Unit cell volume is 809.1 Å3. The trigonal bipyramid shape has three equatorial positions for carbon, and two axial positions at the peaks of the pyramids. The length of the antimony-carbon bond is around 214 pm for equatorial methyl groups and 222 pm for the axial positions. The bond angles are 120° for ∠C-Sb-C across the equator, and 90° for ∠C-Sb-C between equator and axis. The molecules rapidly change carbon atom position, so that in NMR spectrum as low as −100 °C, there is only one kind of hydrogen position.
Pentamethylantimony is more stable than pentamethylbismuth
Pentamethylbismuth (or pentamethylbismuthorane) is an organometalllic compound containing five methyl groups bound to a bismuth atom with formula Bi(CH3)5. It is an example of a hypervalent compound. The molecular shape is trigonal bipyramid.
P ...
, because in lower energy trimethylbismuth, the non-bonding pair of electrons is more shielded due to the f-electrons and the lanthanoid contraction. Trimethylantimony
Trimethylstibine is an organoantimony compound with the formula Sb(CH3)3. It is a colorless pyrophoric and toxic liquid.
It is synthesized by treatment of antimony trichloride and methyl Grignard reagent.Sabina C. Grund, Kunibert Hanusch, Hans J. ...
is higher in energy, and thus less is released in a decomposition of pentamethylantimony. Pentamethylantimony can be stored as a liquid in clean glass at room temperature.[
Pentamethylantimony melts at -19 °C. Although it decomposes when boiling is attempted and can explode, it has a high vapour pressure at 8 mmHg at 25 °C.]
There are two absorption bands in the ultraviolet at 2380 and 2500 Å.[
]
Reactions
Pentamethylantimony reacts with methyl lithium to yield a colourless lithium hexamethylantimonate in tetrahydrofuran
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 ma ...
.
:Sb(CH3)5 + LiCH3 → Li(thf)Sb(CH3)6
Pentamethylantimony reacts with silsesquioxanes to yield tetramethylstibonium silsesquioxanes. eg (''cyclo''-C6H11)7Si7O9(OH)3 yields (''cyclo''-C6H11)7Si7O9(OSB(CH3)4)3. The reaction happens quickly when there are more than two OH groups.
Phosphonic acids and phosphinic acid
Hypophosphorous acid (HPA), or phosphinic acid, is a phosphorus oxyacid and a powerful reducing agent with molecular formula H3PO2. It is a colorless low-melting compound, which is soluble in water, dioxane
and alcohols. The formula for this ...
s combine with pentamethylantimony to yield compounds like (CH3)4SbOP(O)Ph2, (CH3)4SbOP(O)(OH)Ph and (CH3)4SbOP(O)(OH)3, eliminating methane.
Stannocene Sn(C5H5)2 combines with pentamethylantimony to produce bis(tetramethylstibonium)tetracyclopentadienylstannate ( 3)4Sb">CH3)4Sbsub>2Sn(C5H5)4).
Pentamethylantimony reacts with many very weak acids to form a tetramethylstibonium salt or tetramethylstibonium derivative with the acid. Such acids include water (H2O), alcohol
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
s, thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
s, phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...
, carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...
s, hydrogen fluoride
Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock i ...
, thiocyanic acid
Thiocyanic acid is a chemical compound with the formula HSCN and structure , which exists as a tautomer with isothiocyanic acid (HNCS). The iso- form tends to dominate with the material being about 95% isothiocyanic acid in the vapor phase.
:
...
, hydrazoic acid
Hydrazoic acid, also known as hydrogen azide or azoimide, This also contains a detailed description of the contemporaneous production process. is a compound with the chemical formula . It is a colorless, volatile, and explosive liquid at room tem ...
, difluorophosphoric acid
Difluorophosphoric acid is an inorganic compound with the formula HPO2F2. It is a colorless liquid. The acid has limited applications, in part because it is thermally and hydrolytically unstable.
It is prepared by hydrolysis of phosphorus oxyflu ...
, thiophosphinic acids, and alkylsilols.
With halogens, pentamethylantimony has one or two methyl groups replaced by the halogen atoms.[ Lewis acids also react to form tetramethyl stibonium salts, including 3)4Sb">CH3)4SblBr4, 3)4Sb">CH3)4SbCH3SbCl5],][
Pentamethylantimony reacts with the surface of ]silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
to coat it with Si-O-Sb(CH3)4 groups. Over 250 °C this decomposes to Sb(CH3) and leaves methyl groups attached to the silica surface.
References
{{antimony compounds
Organoantimony compounds
Hypervalent molecules
Methyl complexes