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Organoantimony chemistry is the chemistry of compounds containing a carbon to antimony (Sb) chemical bond. Relevant oxidation states are SbV and SbIII. The toxicity of antimony[1] limits practical application in organic chemistry.[2]
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 R3Sb:
Stibines are weak Lewis acids and do not form ate complexes. As soft Lewis donors, they see wide use in coordination chemistry[3]: 348 and typically react through oxidative addition:
This property also sensitizes them to air.
If reduced instead, stibanes typically release substituents (ligands):[3]: 443
The cyclic compound stibole, a structural analog of pyrrole, has not been isolated, but substituted derivatives have. Antimony metallocenes are known as well:
The Cp*-Sb-Cp* angle is 154°.
Pentacoordinate antimony compounds are called stiboranes, and can be synthesised from stibines and halogens:
Like their heavier congeners, the organobismuth compounds, stiboranes form onium compounds and ate complexes. Asymmetric compounds can also be obtained through the stibonium ion:
Stibonium halides (R4SbX) tend to dimerize.
Trigonal-bipyramidal molecule pentaphenylantimony decomposes at 200 °C to triphenylstibine and biphenyl. In the related Me5Sb, proton NMR at -100 °C cannot resolve different methyl protons.
Distibines are formally SbII 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.[4][3]: 442 A typical synthesis first displaces an SbIII halide with an alkali metal and then reduces the resulting anion with ethylene dichloride.[3]: 781–783
Like its lighter congener, arsenic, organoantimony compounds can be reduced to cyclic oligomers that are formally antimony(I) compounds.[3]: 563–577
SbV-N bonds are unstable, except where the N is also bonded to other electron-withdrawing substituents.[5]
Stibine oxides undergo a sort of polarized-olefin metathesis. For example, they mediate a carbonyl-imine exchange (Ar is any activated arene):[6]: 399
Ph3Sb=NSO2Ar + PhC=O → Ph3Sb=O + PhC=NSO2Ar
The effect may extend vinylically:[7] In contrast, unstabilized ylides (R3Sb=CR'2; R' not electron-withdrawing) form only with difficulty (e.g. diazo reagents).[6]: 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:[6]: 400–402
As tertiary stibines also insert into haloalkyl bonds, tertiary stibines are powerful dehalogenating agents.[6]: 403 However, stibanes poorly imitate active metal organometallics: only with difficulty do their ligands add to carbonyls or they power noble-metal cross couplings.[6]: 403–405
Stiboranes are gentle oxidants, converting acyloins to diketones and thiols to disulfides.[6]: 406–408 In air, tris(thiophenyl)stibine catalyzes a Hunsdiecker-like decarboxylative oxidation of anhydrides to alcohols.[6]: 411
In ultraviolet light, distibines radicalize; the resulting radicals can displace iodide.[3]: 766
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