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.
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Organoantimony(V) chemistry
Antimony compounds of the type R5Sb (stiboranes) can be synthesised from trivalent Sb precursors:
Ph3Sb + Cl2 → Ph3SbCl2 Ph3SbCl2 + 2 PhLi → Ph5SbAsymmetric compounds can also be obtained through the stibonium ion:
R5Sb + X2 → [R4Sb]+[X] [R4Sb]+[X] + R'MgX → R4R'SbJust as in the related organobismuth compounds (same group 15), organoantimony(V) compounds form onium compounds and ate complexes.
Pentaphenylantimony decomposes at 200 °C to triphenylstibine and biphenyl. It forms a trigonal bipyramidal molecular geometry. In the related Me5Sb all methyl protons are equivalent at -100 °C in proton NMR. Compounds of the type R4SbX tend to form dimers.
Organoantimony(III) chemistry
Compounds of the type R3Sb (stibines) can be accessed by reaction of antimony trichloride with organolithium compounds or Grignards.
SbCl3 + 3 RLi (or RMgCl) → R3SbTypical reactions are:
R3Sb + Br2 → R3SbBr2 R3Sb + O2 → R3SbO R3Sb + Na + NH3 → R2SbNa R3Sb + B2H6 → R3Sb·BH3Stibanes are weak Lewis acids and therefore ate complexes are not encountered. On the other hand, they have good donor properties and are therefore widely used in coordination chemistry. R3Sb compounds are more air-sensitive than the R5Sb counterparts.
Antimony Metallocenes are known as well:
14SbI3 + 3 (Cp*Al)4 → [2Cp*Sb]+[AlI4]− + 8Sb + 6 AlI3The Cp*-Sb-Cp* angle is 154°.
The cyclic compound stibole, a structural analog of pyrrole, has not been isolated, but substituted derivatives known as stiboles are known.
Organoantimony(II) chemistry
Distibines have a Sb-Sb single bond and are of some interest as thermochromic materials. For example, tetramethyldistibine is a colorless as a gas, yellow as a liquid, red as solid just below the melting point of 18.5 °C and again yellow well below the melting point.