Oxidative addition to triorganylbismuthines

Iodine usually cleaves one of the Bi-C bonds in triarylbismuthines to give diaryliodobismuthines. Although trialkylbismuthines are readily cleaved by chlorine and bromine, tri(l-propenyl)bismuthine can be brominated by molecular bromine at low temperatures to give tri(l-propenyl)bismuth dibromide [63IZV1507]. 

Tris(2,4,6-trimethylphenyl)bismuthine (1 g, 1.8 mmol) dissolved in dry benzene was treated with dry gaseous chlorine until an excess was evident. Partial evaporation of the solvent, followed by addition of methanol, gave tris(2,4,6-trimethylphenyl)bismuth dichloride as a pale green solid (0.85 g, 76%), m.p. 149-150°C [41JA207]. 

This method is convenient because the reagents are easier to handle compared with molecular chlorine or fluorine. Trimethylbismuth dichloride is obtainable by using sulfuryl chloride at low temperatures [94AG(E)976]. However, an attempt to synthesize trimethylbismuth difluoride by using xenon difluoride has failed. 

Freshly degassed sulfuryl chloride (1.22 g, 9.0 mmol) was condensed into a dry ethereal solution (10 ml) of trimethylbismuthine (2.3 g, 9.1 mmol) at - 196°C. The mixture was stirred at - 100°C, then warmed to -78°C over 2 h, and the solvent together with sulfur dioxide was pumped off at 10 mbar to give trimethylbismuth dichloride as a colorless solid (2.9 g, 95%) [94AG(E)976]. 

The carboxyl ligands introduced are derived from the solvent employed. When this reaction is performed in dichloromethane, triarylbismuth dichloride is isolated in good yield. 

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