Organoantimony chemistry

Antimony compounds of the type R₅Sb (stiboranes) can be synthesised from trivalent Sb precursors:

Ph₃Sb + Cl₂ → Ph₃SbCl₂

Ph₃SbCl₂ + 2 PhLi → Ph₅Sb

Asymmetric compounds can also be obtained through the stibonium ion:

R₅Sb + X₂ → [R₄Sb]⁺[X]

[R₄Sb]⁺[X] + R'MgX → R₄R'Sb

Just 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.

Compounds of the type R₃Sb (stibines) can be accessed by reaction of antimony trichloride with organolithium or Grignard reagents.

SbCl₃ + 3 RLi (or RMgCl) → R₃Sb

Typical reactions are:

R₃Sb + Br₂ → R₃SbBr₂

R₃Sb + O₂ → R₃SbO

R₃Sb + Na + NH₃ → R₂SbNa

R₃Sb + B₂H₆ → R₃Sb·BH₃

Stibanes 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 AlI₃

The 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.

Distibines have a Sb-Sb single bond and are of some interest as thermochromic materials. For example, tetramethyldistibine is 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.[3]

• Lewis acidic antimony compounds