Organoantimony chemistry

Organoantimony chemistry is the chemistry of compounds containing a carbon to antimony (Sb) chemical bond. Relevant oxidation states are SbV and SbIII. Few applications have been reported for this class of compounds. They are of interest as heavy analogues of organophosphorus compounds.

Antimony(III) derivatives

Synthesis

Stibines are typically prepared by alkylation of antimony trichloride with organolithium or Grignard reagents:[1]

SbCl3 + 3 RLi (or RMgCl) → R3Sb

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:

LiCH=CH−CH=CHLi + PhSbCl2 → H4C4SbPh + 2 LiCl (Ph = C6H5)

It is yellow oil that resinifies (polymerizes in an ill-defined manner) at room temperature.[2]

Antimony metallocenes are known as well:

14SbI3 + 3 (Cp*Al)4 → [Cp∗
2Sb]+[AlI4]− + 8Sb + 6 AlI3

The Cp*-Sb-Cp* angle is 154°.

Reactions

As soft Lewis donors, stibines form some coordination compounds.[3]: 348 . Stibines can be oxidized with halogens:

R3Sb + Br2 → R3SbBr2

The resulting dihalides, when heated, release the organic bromide:[4]

R3SbX2 → R2SbX + RX

Up treatment with metallic sodium, one C-Sb bond breaks:[3]: 443 

Ph3Sb + Na → Ph2SbNa + PhNa

The stibine Sb(C6F5)3 is Lewis acidic. It forms an adduct with triphenylphosphine oxide, indicating a donor-acceptor interaction between the lone pair on oxygen and the σ* level assicuated with an Sb–C bond.[5] 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 = C6H5):

Ph3Sb + Cl2 → Ph3SbCl2

As confirmed by X-ray crystallography, dichlorostiboranes feature pentacoordinate Sb(V) with trans-diaxial chloride ligands.[6] The dichlorostiborane reacts with phenyl lithium to give pentaphenylantimony:

Ph3SbCl2 + 2 PhLi → Ph5Sb

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 C6H5)3Sb(OH)2, not C6H5)3SbO. This observation contrasts with the behavior of phosphorus compounds where C6H5)3P(OH)2 is not observed and C6H5)3PO is robust.[7] C6H5)3SbO is claimed to exist as a dimer.[4]

Reactions

Lewis acidic antimony(V) compounds have long been exploited in the form of SbF5, which forms stable conjugate non-coordinating anions (SbF−
6 and Sb
2F−
11).[8] Some organoSb(V) derivatives indeed are Lewis acidic.[9]

A 9-anthracenylltriphenylstibonium cation binds fluoride to give a luminescent adduct.[10]

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.[12][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 

Compounds with multiple bonds to Sb

Stibabenzene, a planar ring akin to benzene, can be prepared by dehydrohalogenation of an stibacyclohexadiene.[13] Compounds have been made with the core structure C-Sb=Sb-C, the main requirement being that the organic substituent must be bulky.[14]

Safety

Antimony compounds are toxic. Organoantimony compounds occur in nature. Their biogenesis and structures are proposed to be similar to some organoarsenic derivatives.[15]

Further reading

  • Organoantimony-based Lewis acids
  • C. Elschenbroich, A. Salzer Organometallics : A Concise Introduction (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7

References

  1. ^ Hiers, G. S. (1927). "Triphenylstibine". Organic Syntheses. 7: 80. doi:10.15227/orgsyn.007.0080.
  2. ^ Ashe, Arthur J.; Drone, Frederick J. (1985). "Synthesis of 1-phenylarsole and 1-phenylstibole". Organometallics. 4 (8): 1478–1480. doi:10.1021/om00127a038.
  3. ^ a b c d e Patai, Saul, ed. (1994). The Chemistry of Organic Arsenic, Antimony, and Bismuth Compounds. Chemistry of Functional Groups. Chichester, UK: Wiley. doi:10.1002/0470023473. ISBN 047193044X.
  4. ^ a b Grund, Sabina C.; Hanusch, Kunibert; Breunig, Hans J.; Wolf, Hans Uwe (2006). "Antimony and Antimony Compounds". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a03_055.pub2. ISBN 978-3-527-30385-4.
  5. ^ Yang, Mengxi; Tofan, Daniel; Chen, Chang-Hong; Jack, Kevin M.; Gabbaï, François P. (2018-10-15). "Digging the Sigma-Hole of Organoantimony Lewis Acids by Oxidation". Angewandte Chemie International Edition. 57 (42): 13868–13872. doi:10.1002/anie.201808551. ISSN 1433-7851. PMID 30151881. S2CID 52099143.
  6. ^ Begley, M. J.; Sowerby, D. B. (1993). "Structures of triphenylantimony(V) dibromide and dichloride". Acta Crystallographica Section C Crystal Structure Communications. 49 (6): 1044–1046. Bibcode:1993AcCrC..49.1044B. doi:10.1107/S0108270192011958.
  7. ^ Pankaj, S.; Rosas, N.; Espinosa-Pérez, G.; Cabrera, A. (1996). "Triphenylstibine Dihydroxide". Acta Crystallographica Section C Crystal Structure Communications. 52 (4): 889–891. doi:10.1107/S0108270195013898.
  8. ^ Krossing, Ingo; Raabe, Ines (2004-04-13). "Noncoordinating Anions—Fact or Fiction? A Survey of Likely Candidates". Angewandte Chemie International Edition. 43 (16): 2066–2090. doi:10.1002/anie.200300620. ISSN 1433-7851. PMID 5083452.
  9. ^ Marczenko, Katherine M.; Zurakowski, Joseph A.; Bamford, Karlee L.; MacMillan, Joshua W. M.; Chitnis, Saurabh S. (2019-12-09). "Hydrostibination". Angewandte Chemie International Edition. 58 (50): 18096–18101. doi:10.1002/anie.201911842. ISSN 1433-7851. PMID 31591801. S2CID 242968313.
  10. ^ Lee, Min Hyung; Agou, Tomohiro; Kobayashi, Junji; Kawashima, Takayuki; Gabba?, Fran?ois P. (2007). "Fluoride ion complexation by a cationic borane in aqueous solution". Chemical Communications (11): 1133–5. doi:10.1039/b616814k. ISSN 1359-7345. PMID 17347716.
  11. ^ Breunig, Hans Joachim; Häberle, Karl; Dräger, Martin; Severengiz, Tevfik (1985). "(C6H5Sb)6·(1,4-dioxane), the First Cyclohexastibane". Angewandte Chemie International Edition in English. 24: 72–73. doi:10.1002/anie.198500721.
  12. ^ Organoantimony compounds with element-element bonds H.J. Breunig, R. Rosler Coordination Chemistry Reviews 163 (1997) 33-53
  13. ^ Ashe, Arthur J. (February 2016). "The Route to Phosphabenzene and Beyond" (PDF). European Journal of Inorganic Chemistry. 2016 (5): 572–574. doi:10.1002/ejic.201600007. hdl:2027.42/117476. ISSN 1434-1948. S2CID 101713336.
  14. ^ Roller, Clara A.; Doler, Berenike; Steller, Beate G.; Saf, Robert; Fischer, Roland C. (2024). "A Distibene with Extremely Long Sb=Sb Distance and Related Heavier Dipnictenes from Salt-Free Metathesis Reactions". European Journal of Inorganic Chemistry. 27 (10) e202300586. doi:10.1002/ejic.202300586.
  15. ^ Filella, M. (2010). "Alkyl derivatives of antimony in the environment". Metal Ions in Life Sciences. 7. Cambridge: RSC publishing: 267–301. doi:10.1039/9781849730822-00267. ISBN 978-1-84755-177-1. PMID 20877810.
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