Organoantimony chemistry

Synthesis Stibines are typically prepared by alkylation of antimony trichloride with organolithium or Grignard reagents: : Triphenylstibine (triphenylantimony) is one of the best studied organoantimony compounds and representative of the entire class of stibines. 1-Phenylstibole, a relative of pyrrole, can be prepared by treating 1,4-dilithiobutadiene with phenyldichlorostibine: : (Ph = C6H5) It is yellow oil that resinifies (polymerizes in an ill-defined manner) at room temperature. Antimony metallocenes are known as well: :14SbI3 + 3 (Cp*Al)4 → [CpSb]+[AlI4]− + 8Sb + 6 AlI3 The Cp*-Sb-Cp* angle is 154°. Reactions As soft Lewis donors, stibines form some coordination compounds. : Up treatment with metallic sodium, one C-Sb bond breaks: Sb(C6H5)3 is a weaker Lewis acid than its fluorinated analogue. == Antimony(V) derivatives ==

Major families of Sb(V) compounds are of the type SbR4+ (stibonium ions), which are tetrahedral, and pentacoordinate antimony compounds called stiboranes. Stiboranes are synthesised from stibines and halogens (Ph = ): :Ph3Sb + Cl2 → Ph3SbCl2 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: : Pentaphenylantimony decomposes at 200 °C to triphenylstibine and biphenyl. 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 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. Antimony resists forming multiple bonds, as anticipated by the double bond rule. Thus, it forms , not . This observation contrasts with the behavior of phosphorus compounds where is not observed and is robust. is claimed to exist as a dimer. Some organoSb(V) derivatives indeed are Lewis acidic. A 9-anthracenylltriphenylstibonium cation binds fluoride to give a luminescent adduct. == Distibines and antimony(I) compounds ==

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. A typical synthesis first displaces an SbIII halide with an alkali metal and then reduces the resulting anion with ethylene dichloride. Like its lighter congener, arsenic, organoantimony compounds can be reduced to cyclic oligomers that are formally antimony(I) compounds. ==Compounds with multiple bonds to Sb==

Stibabenzene, a planar ring akin to benzene, can be prepared by dehydrohalogenation of an stibacyclohexadiene. Compounds have been made with the core structure C-Sb=Sb-C, the main requirement being that the organic substituent must be bulky. Ph3Sb=NSO2Ar + PhC=O → Ph3Sb=O + PhC=NSO2ArThe effect may extend vinylically: R2C=O{} + HBrCHCO2R ->[\ce{Bu3Sb}] R2C=CHCO2R{} + HBrIn contrast, unstabilized ylides (R3Sb=CR'2; R' not electron-withdrawing) form only with difficulty (e.g. diazo reagents). 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: :Ph2SbCH2CH(OH)Ph → CH2=CHPh + Ph2SbOH As tertiary stibines also insert into haloalkyl bonds, tertiary stibines are powerful dehalogenating agents. However, stibanes poorly imitate active metal organometallics: only with difficulty do their ligands add to carbonyls or they power noble-metal cross couplings. Stiboranes are gentle oxidants, converting acyloins to diketones and thiols to disulfides. In air, tris(thiophenyl)stibine catalyzes a Hunsdiecker-like decarboxylative oxidation of anhydrides to alcohols. In ultraviolet light, distibines radicalize; the resulting radicals can displace iodide. --> ==Safety==

Antimony compounds are toxic. Organoantimony compounds occur in nature. Their biogenesis and structures are proposed to be similar to some organoarsenic derivatives. ==Further reading==