Organobismuth chemistry

Organobismuth chemistry is the chemistry of organometallic compounds containing a carbon to bismuth chemical bond. According to one reviewer, applications are rare even though bismuth and bismuth compounds are the least toxic among the heavy metals and are relatively cheap.[1] The main bismuth oxidation states are Bi(III) and Bi(V) as in all higher group 15 elements. The energy of a bond to carbon in this group decreases in the order P > As > Sb > Bi.[2] The first reported use of bismuth in organic chemistry was in oxidation of alcohols by Challenger in 1934 (using Ph₃Bi(OH)₂).[3] Knowledge about methylated species of bismuth in environmental and biological media is very limited.[4] Organobismuth heterocycles are bismole and bismabenzene. For reviews, see the cited articles[5]

Preparation of Organobismuth(III) Compounds

Organobismuth(III) compounds can be prepared from BiCl₃ by substitution with the corresponding carbon nucleophiles (generally of the form of a Grignard reagent or alkyl/aryl lithium species). Triaryl bismuth(III) compounds are typically crystalline solids that are not air and moisture sensitive and can easily be purified by recrystallization or chromatography, thus making them attractive reagents for organic synthesis[6].

Since formation of organobismuth (III) complexes require the formation of highly basic coupling partners, a limited number of functional groups (especially those that are base sensitive) can be incorporated on the bismuth center through alkyl metal addition. Recently, the Gagnon group has demonstrated that chemical modification of the substituents on the bismuth center can be achieved after formation of the organobismuth(III) center with aryl Grignards to form triaryl bismuth(III) complexes with sensitive functionalities such as alcohols, aldehydes, and ketones.[7]

Synthesis of Organobismuth(V) compounds

Organobismuth(V) complexes may be accessed directly from organobismuth(III) through oxidative addition to a halogen then displacement of the newly formed bismuth-halogen bond for a bismuth-carbon bond with an alkyl or aryl lithium or Grignard reagent. Alternatively, treatment of the organobismuth(III) with thionyl chloride also affords the dihalo-oranobismuth(V) complex.

Bi(V) easily forms an onium ion for example:

Ph₅Bi + BPh₃ → Ph₄Bi⁺[BPh₄]⁻

or an ate complex for example:

Ph₅Bi + PhLi → Li⁺[Ph₆Bi⁻]

The thermal stability of R₅M compounds decrease in the order As > Sb > Bi and aryl compounds are more stable than alkyl compounds. Me₅Bi decomposes explosively at 20 °C.

Organobismuth(III) Chemistry

The most common synthetic use of Bi(III) complexes is to transmetallate one of its substituents onto a different metal center such as palladium. One early example of this comes from the Barton group where triaryl bismuth(III) were shown to react with acylchlorides under Pd(0) catalysis to form a variety of phenyl ketones.[8]

More recently, the Barabe group demonstrated that tricyclopropylbismuth(III) reagents can react with aryl halides and triflates under Pd(0) catalysis in a similar fashion to afford a variety of aryl and heteroaryl cyclopropanes.[9]

Examples of Bi(III) transferring carbon to a new metal center

Triphenylbismuth, unlike the related phosphorus, arsenic, and antimony compounds, undergoes mild redistribution with its trihalide to give the mixed derivatives such as diphenylbismuth chloride (Ph₂BiCl).[10] Bismuth(III) iodide is a catalyst in the Mukaiyama aldol reaction. Bi(III) is also used in a Barbier type allylation of carbonyl compounds in combination with a reducing agent such as zinc or magnesium, possibly forming the active Bi(0) catalyst in situ. The cyclic compound bismole, a structural analog of pyrrole, has not been isolated, but substituted bismoles are known.[11]

Triaryl bismuth(III) compounds may also be employed in C-N bond forming transformations with an appropriate metal co-catalyst. For instance, Barton and coworkers demonstrated that amines could be N-arylated with a bismuth(III) reagent in the presence of copper(II) salt.[12]

Organobismuth(V) chemistry

Bi(V) compounds are strongly oxidizing due to the inert pair effect and relativistic effects. Oxidizing agents are Ph₃Bi(OOtBu)₂, Ph₃BiCO₃ and (Ph₃BiCl)₂O. Substrates for oxidation are oximes, thiols, phenols and phosphines.[13] Compounds such as Ph₅Bi and Ph₃BiCl₂ have been used in the arylation of arene compounds and 1,3-dicarbonyl compounds:[14]

The above transformation proceeds through in an asynchronous concerted fashion from the O-bound organobismuth(V) reagent after loss of an aryl group. A triarylbismuth(III) complex forms concomitantly[15]. Regioselectivity of this transformation is guided by the directing ability of adjacent lewis basic functionalities. It is important to note that in the above arylation, a full equivalent of the pentavalent bismuth compound is required for the arylation reaction therefore leaving four ligands on bismuth inactive for further arylations. Catalytic manifolds of this chemistry are challenging due in part to the reoxidation of Bi(III) to Bi(V). For more examples of bismuth mediated arylations, see the cited review.[16]

Bi(V) compounds can be accessed through Bi(III) compounds for example:

Me₃Bi + SO₂Cl₂ → Me₃BiCl₂

Me₃BiCl₂ + 2 MeLi → Me₅Bi

Structure and properties

Pentaphenylbismuth, Ph₅Bi is square pyramidal like pentaphenylantimony, whereas pentamethybismuth is, as expected from VSEPR theory, trigonal bipyramidal.[17] Both compounds have a violet colour.[18]

1. "Bismuth-Mediated Organic Reactions", Ollevier, T. Ed., Topics in Current Chemistry, 2012, Springer Verlag, Berlin, vol. 311, 277 p. https://www.springer.com/chemistry/organic+chemistry/book/978-3-642-27238-7, Bismuth Reagents and Catalysts in Organic Synthesis Axel Jacobi von Wangelin in Transition Metals for Organic Synthesis Building Blocks and Fine Chemicals Beller, Matthias / Bolm, Carsten (eds.)
2. C. Elschenbroich, A. Salzer Organometallics : A Concise Introduction (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7
3. Organo-derivatives of bismuth and thallium Frederick Challenger and Oswald V. Richards, J. Chem. Soc., 1934, 405 doi:10.1039/JR9340000405
4. Filella, M. (2010-03-15). "Alkyl derivatives of bismuth in the environmental and biological media". Metal Ions in Life Sciences. Cambridge: RSC publishing. 7: 303–317. doi:10.1039/9781849730822-00303. ISBN 978-1-84755-177-1. PMID 20877811.
5. Gagnon, Alexandre (2017). "Organobismuth Reagents: Synthesis, Properties and Applications in Organic Synthesis". Synthesis. 49 (8): 1707–1745. doi:10.1055/s-0036-1589482.
6. Finet, Jean Pierre (1989). "Arylation reactions with organobismuth reagents". Chemical Reviews. 89 (7): 1487–1501. doi:10.1021/cr00097a005.
7. Hébert, Martin; Petiot, Pauline; Benoit, Emeline; Dansereau, Julien; Ahmad, Tabinda; Le Roch, Adrien; Ottenwaelder, Xavier; Gagnon, Alexandre (2016). "Synthesis of Highly Functionalized Triarylbismuthines by Functional Group Manipulation and Use in Palladium- and Copper-Catalyzed Arylation Reactions". The Journal of Organic Chemistry. 81 (13): 5401–5416. doi:10.1021/acs.joc.6b00767. PMID 27231755.
8. "ScienceDirect". www.sciencedirect.com. Retrieved 2019-05-08.
9. Gagnon, Alexandre; Duplessis, Martin; Alsabeh, Pamela; Barabé, Francis (2008). "Palladium-Catalyzed Cross-Coupling Reaction of Tricyclopropylbismuth with Aryl Halides and Triflates". The Journal of Organic Chemistry. 73 (9): 3604–3607. doi:10.1021/jo702377h. PMID 18363369.
10. Derek H.R. Barton, Neerja Yadav Bhatnagar, Jean-Pierre Finet, William B. Motherwell "Pentavalent organobismuth reagents. Part vi. Comparative migratory aptitudes of aryl groups in the arylation of phenols and enols by pentavalent bismuth reagents" Tetrahedron 1986, Volume 42, Pages 3111-3122 doi:10.1016/S0040-4020(01)87378-6
11. Caster, Kenneth C. "Arsoles, stiboles, and bismoles" Clive W. Bird, ed. Comprehensive Heterocyclic Chemistry II (1996), 2, 857-902.
12. Barton, Derek H. R. (1987). "Copper salts catalysis of N-phenylation of amines by trivalent organobismuth compounds". Tetrahedron Letters. 28 (8): 887–890. doi:10.1016/S0040-4039(01)81015-7.
13. Organobismuth Chemistry Hitomi Suzuki, Yoshihiro Matano Elsevier, 2001
14. Bismuth(V) reagents in organic synthesis Derek H.R. Barton and Jean-Pierre Finet Pure Appl. Chem., Vol. 59, No. 8, pp. 937—946, 1987.
15. "ScienceDirect". www.sciencedirect.com. Retrieved 2019-05-08.
16. Konopelski, Joseph P. (2001). "Arylation with organolead and organobismuth reagents". Tetrahedron. 57 (27): 5683–5705. doi:10.1016/S0040-4020(01)00385-4.
17. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 599. ISBN 978-0-08-037941-8.
18. Arnold F. Holleman, Nils Wiberg: Lehrbuch der Anorganischen Chemie, 102nd Edition, de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1, p. 857.