# Organoantimony chemistry

Organoantimony chemistry is the chemistry of compounds containing a carbon to antimony (Sb) chemical bond. Relevant oxidation states are Sb$^V$ and Sb$^{III}$. The toxicity of antimony limits practical application in organic chemistry.

## Syntheses
### Stibines

An organoantimony synthesis typically begins with tricoordinate antimony compounds, called stibines. Antimony trichloride reacts with organolithium or Grignard reagents to give compounds of the form R$_3$Sb:
    SbCl$_3$ + 3 RLi (or RMgCl) → R$_3$Sb
Stibines are weak Lewis acids and do not form ate complexes. As soft Lewis donors, they see wide use in coordination chemistry$^{:348}$ and typically react through oxidative addition:
    R$_3$Sb + Br$_2$ → R$_3$SbBr$_2$
    R$_3$Sb + O$_2$ → R$_3$SbO
    R$_3$Sb + B$_2$H$_6$ → R$_3$Sb·BH$_3$
This property also sensitizes them to air.
If reduced instead, stibanes typically release substituents (ligands):$^{:443}$
    R$_3$Sb + Na + NH$_3$ → R$_2$SbNa
    R$_2$SbBr + Mg → (R$_2$Sb)$_2$ + MgBr$_2$
The cyclic compound stibole, a structural analog of pyrrole, has not been isolated, but substituted derivatives have. Antimony metallocenes are known as well:
    14SbI$_3$ + 3 (Cp*Al)$_4$ → [Cp$^∗$ $_2$Sb]$^+$[AlI$_4$]$^−$ + 8Sb + 6 AlI$_3$
The Cp*-Sb-Cp* angle is 154°.

### Stiboranes

Pentacoordinate antimony compounds are called stiboranes. They can be synthesised from stibines and halogens (Ph = C$_6$H$_5$):
    Ph$_3$Sb + Cl$_2$ → Ph$_3$SbCl$_2$
As confirmed by X-ray crystallography, dichlorostiboranes feature pentacoordinate Sb(V) with trans-diaxial chloride ligands. The dichlorostiborane reacts with phenyl lithium to give pentaphenylantimony:
    Ph$_3$SbCl$_2$ + 2 PhLi → Ph$_5$Sb
Like the organobismuth compounds, stiboranes form onium compounds and ate complexes. Unsymmetrical stiboranes can also be obtained through the stibonium ions:
    R$_5$Sb + X$_2$ → [R$_4$Sb]$^+$[X]$^−$ + RX
    [R$_4$Sb]$^+$[X]$^−$ + R'MgX → R$_4$R'Sb
Pentaphenylantimony decomposes at 200 °C to triphenylstibine and biphenyl.
In the related Me$_5$Sb, proton NMR spectra recorded at -100 °C cannot resolve the two types of methyl protons. This observation is consistent with rapid Berry pseudorotation.

### Distibines and antimony(I) compounds

Distibines are formally Sb$^{II}$ compounds, but feature tricoordinate Sb atoms with a single Sb-Sb bond. They may have interest as thermochromes. For example, tetramethyldistibine is colorless when gas, yellow when liquid, red when solid just below the melting point of 18.5 °C, shiny-blue when cooler, and again yellow at cryogenic temperatures.$^{:442}$ A typical synthesis first displaces an Sb$^{III}$ halide with an alkali metal and then reduces the resulting anion with ethylene dichloride.$^{:781–783}$
Like its lighter congener, arsenic, organoantimony compounds can be reduced to cyclic oligomers that are formally antimony(I) compounds.$^{:563–577}$

### With other substituents

Sb$^V$-N bonds are unstable, except where the N is also bonded to other electron-withdrawing substituents.

## Reactions

Stibine oxides undergo a sort of polarized-olefin metathesis. For example, they mediate a carbonyl-imine exchange (Ar is any activated arene):$^{:399}$
   Ph$_3$Sb=NSO$_2$Ar + PhC=O → Ph$_3$Sb=O + PhC=NSO$_2$Ar
The effect may extend vinylically: ${\ce {R2C=O+HBrCHCO2R->[ \atop {\ce {Bu3Sb}}]R2C=CHCO2R+HBr}}$In contrast, unstabilized ylides (R$_3$Sb=CR'$_2$; R' not electron-withdrawing) form only with difficulty (e.g. diazo reagents).$^{:399–400}$
Like other metals, stibanes vicinal to a leaving group can eliminate before a proton. For example, diphenyl(β-hydroxyphenethyl)stibine decomposes in heat or acid to styrene:$^{:400–402}$
    Ph$_2$SbCH$_2$CH(OH)Ph → CH$_2$=CHPh + Ph$_2$SbOH
As tertiary stibines also insert into haloalkyl bonds, tertiary stibines are powerful dehalogenating agents.$^{:403}$ However, stibanes poorly imitate active metal organometallics: only with difficulty do their ligands add to carbonyls or they power noble-metal cross couplings.$^{:403–405}$
Stiboranes are gentle oxidants, converting acyloins to diketones and thiols to disulfides.$^{:406–408}$ In air, tris(thiophenyl)stibine catalyzes a Hunsdiecker-like decarboxylative oxidation of anhydrides to alcohols.$^{:411}$
In ultraviolet light, distibines radicalize; the resulting radicals can displace iodide.$^{:766}$