Organoantimony chemistry

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:

:{{nowrap|SbCl₃ + 3 RLi (or RMgCl) → R₃Sb}}

Stibines are weak Lewis acids and do not form ate complexes. As soft Lewis donors, they see wide use in coordination chemistry{{rp|348}} and typically react through oxidative addition:

:R₃Sb + Br₂ → R₃SbBr₂

:R₃Sb + O₂ → R₃SbO

:R₃Sb + B₂H₆ → R₃Sb·BH₃

This property also sensitizes them to air.

If reduced instead, stibanes typically release substituents (ligands):{{rp|443}}

:{{nowrap|R₃Sb + Na + NH₃ → R₂SbNa}}

:{{nowrap|R₂SbBr + Mg → (R₂Sb)₂ + MgBr₂}}

The cyclic compound stibole, a structural analog of pyrrole, has not been isolated, but substituted derivatives have. Antimony metallocenes are known as well:

:14SbI₃ + 3 (Cp*Al)₄ → [Cp{{su|b=2|p=∗}}Sb]⁺[AlI₄]⁻ + 8Sb + 6 AlI₃

The Cp*-Sb-Cp* angle is 154°.

Pentacoordinate antimony compounds are called stiboranes. They can be synthesised from stibines and halogens (Ph = {{chem2|C6H5}}):

:Ph₃Sb + Cl₂ → Ph₃SbCl₂

As confirmed by X-ray crystallography, dichlorostiboranes feature pentacoordinate Sb(V) with trans-diaxial chloride ligands.{{cite journal |doi=10.1107/S0108270192011958 |title=Structures of triphenylantimony(V) dibromide and dichloride |date=1993 |last1=Begley |first1=M. J. |last2=Sowerby |first2=D. B. |journal=Acta Crystallographica Section C Crystal Structure Communications |volume=49 |issue=6 |pages=1044–1046 |bibcode=1993AcCrC..49.1044B }}

The dichlorostiborane reacts with phenyl lithium to give pentaphenylantimony:

:{{chem2|Ph3SbCl2 + 2 PhLi → Ph5Sb}}

Like the organobismuth compounds, stiboranes form onium compounds and ate complexes. Unsymmetrical stiboranes can also be obtained through the stibonium ions:

:R₅Sb + X₂ → [R₄Sb]⁺[X]⁻ + RX

:[R₄Sb]⁺[X]⁻ + R'MgX → R₄R'Sb

Pentaphenylantimony decomposes at 200 °C to triphenylstibine and biphenyl.

In the related Me₅Sb, proton NMR spectra recorded at -100 °C cannot resolve the two types of methyl protons. This observation is consistent with rapid Berry pseudorotation.

File:PhSbhexamer.svg

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.Organoantimony compounds with element-element bonds H.J. Breunig, R. Rosler Coordination Chemistry Reviews 163 (1997) 33-53{{Cite book |title=The Chemistry of Organic Arsenic, Antimony, and Bismuth Compounds |publisher=Wiley |year=1994 |isbn=047193044X |editor-last=Patai |editor-first=Saul |editor-link=Saul Patai |series=Chemistry of Functional Groups |location=Chichester, UK |doi=10.1002/0470023473}}{{Rp|page=442}} A typical synthesis first displaces an Sb^III halide with an alkali metal and then reduces the resulting anion with ethylene dichloride.{{rp|pp=781–783}}

Like its lighter congener, arsenic, organoantimony compounds can be reduced to cyclic oligomers that are formally antimony(I) compounds.{{rp|pp=563–577}}

Sb^V-N bonds are unstable, except where the N is also bonded to other electron-withdrawing substituents.{{harvnb|Patai|1994|p=340}}, which immediately undercuts itself by giving an example of an -SbCl₃-NMe-... complex.

Stibine oxides undergo a sort of polarized-olefin metathesis. For example, they mediate a carbonyl-imine exchange (Ar is any activated arene):{{Cite book |last1=Freedman |first1=Leon D. |title=The Chemistry of the Metal—Carbon Bond |last2=Doak |first2=George O. |publisher=Interscience |year=1989 |isbn=0471915564 |editor-last=Hartley |editor-first=Frank Robinson |series=(Patai's) Chemistry of Functional Groups |volume=5 |location=Chichester, UK |pages=397–413 |chapter=The use of organoantimony and organobismuth compounds in organic synthesis |doi=10.1002/9780470772263.ch9}}{{Rp|page=399}}

Ph₃Sb=NSO₂Ar + PhC=O → Ph₃Sb=O + PhC=NSO₂Ar

• Lewis acidic antimony compounds

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