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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. 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. The first reported use of bismuth in organic chemistry was in oxidation of alcohols by Challenger in 1934 (using Ph3Bi(OH)2). Knowledge about methylated species of bismuth in environmental and biological media is very limited. Organobismuth heterocycles are bismole and bismabenzene.
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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. Compounds such as Ph5Bi and Ph3BiCl2 have been used in the arylation of arene compounds and 1,3-dicarbonyl compounds:
Bi(V) compounds can be accessed through Bi(III) compounds for example:
Me3Bi + SO2Cl2 → Me3BiCl2 Me3BiCl2 + 2 MeLi → Me5BiBi(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.
Structure and properties
Pentaphenylbismuth, Ph5Bi is square pyramidal like pentaphenylantimony, whereas pentamethybismuth is, as expected from VSEPR theory, trigonal bipyramidal. Both compounds have a violet colour.
Organobismuth(III) chemistry
Compounds of the type R3Bi can be accessed by reaction of bismuth chloride with organolithium compounds or Grignards:
BiCl3 + 3 RLi (or RMgCl) → R3Bi + 3 MgCl2 (or LiCl)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).
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.
Salicylates
Bismuth subsalicylate, commonly known as Pepto-Bismol or pink bismuth is used to treat a variety of ailments. However, while it involves an organic functional group (see salicylic acid), the bismuth is not bonded directly to any carbon atoms.