Triorganylbismuthines

This class of compounds can be obtained by a variety of methods which include metathesis, oxidative addition, reduction, transmetallation, thermolysis, disproportionation, electrochemical coupling, and others. In this section, the syntheses of symmetrical and unsymmetrical triorganylbismuthines according to these methodologies are described. 

The most general method for the synthesis of diorganylbismuth compounds is the nucleophilic substitution of halo- or alkoxydiorganylbismuthines. Diorganylbismuth compounds are obtained by the action of an equimolar amount of an acidic compound on triorganylbismuthine. However, they are often aceompanied by a monoorganylbismuth or inorganic bismuth compound as a by-product. 

Mono- and dihalobismuthines of the type R2BiX and RBiX2 (X=C1, Br, I) are prepared best by a redistribution reaction between a triorganylbismuthine (R3Bi) and a bismuth halide (BiX ). 

Disproportionation reaction of halodiorganylbismuthines leads to a mixture of dihaloorganylbismuthines and triorganylbismuthines [62ZAAC(317)54, 22JCS(121)104]. 

In contrast with extensive works on lighter organylpnicogen oxides, little attention has hitherto been paid to the chemistry of organylbismuthine oxides. However, the oxides of triorganylbismuthines have potential as a versatile precursor for a variety of organobismuth(V) compounds. 

The physical properties of triorganylbismuthine oxides have not been examined quite so extensively. Goel et al. claim that triphenylbismuthine oxide has a five-coordinated bismuth center with a polymeric structure involving -Bi-O-Bi- units [72JOM(36)323]. 

Triorganylbismuthines can mediate such C-C bond forming reactions as shown in Scheme 5.38 in the presence or absence of a transition metal salt. Tributylbismuthine promotes the allylation of carbonyl compounds with allylic bromide [91HAC297] and the olefination of diazo compounds with carbonyl compounds in the presence of catalytic amounts of a copper(I) halide [90TL5897]. A combination of triphenylbismuthine and WCle promotes the metathesis of olefins, while a similar combination with TiC facilitates the stereoselective Diels-Alder reaction of unsaturated esters [76TMC183, 93JOC4783]. 

Scheme 5.38. Triorganylbismuthine-mediated C-C bond forming reactions.

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