Exchange of Anionic Groups at Tin

Thus the chlorides R SnCl4 can be converted into the corresponding bromides or iodides by heating them with the appropriate sodium halide in acetone, after which the sodium chloride which is formed can be filtered off. 

In organic syntheses using organotin reagents such as tributyltin hydride, the resulting tin compounds are often separated as the insoluble organotin fluorides. The trialkyltin chloride or bromide can then be recovered by heating the fluoride with sodium chloride or bromide under reflux in THF for 3-5 days.31 

A general method for the interhalide conversions, including those from a heavier halide to a lighter halide, is to heat the tin halide in a saturated solution of the required ammonium halide in ether conversions are essentially quantitative in 2 h. The reaction of tin fluorides requires a rather different technique the fluoride, suspended in tetrahy-drofuran, is mixed with an aqueous solution of the ammonium halide, and heated under reflux until the solution is clear.32 

ButSn(NEt2)3 + 3Me3SiCI —43% ButSnCI3 2Qh ButCI + SnCI2 (11-17) 

Tributyltin bromide or iodide and dibutyltin dibromide or diiodide can be prepared from the corresponding chlorides by reaction with alkyl bromides or iodides in the presence of a tetrabutylammonium halide catalyst. It is suggested that the reaction involves the coordination of halide ion to the tin, then nucleophilic substitution by the chloride ligand at the carbon centre (equations 11-18,11-19 and 11-20).35 

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