Use of Supported Organotins in Organic Synthesis

In principle, if no further complications arise, the organotin residues should remain on the support and can be removed by filtration, so that the organic product can be recovered uncontamined by tin residues. Unfortunately, this expectation is too optimistic. When examined at trace level, variable amounts of tin 

The reduction of simple alkyl halides is generally achieved with good yields and low levels of tin contamination when the conversion of the Sn—X function into an Sn—H function is efficient. Conversion of Sn—X to give Sn—H is generally best achieved using di-n-butylaluminium hydride or sodium borohydride, but lithium aluminium hydride can also be used under appropriate experimental conditions. 

It is worth noting that the recycling of supported hydrides may be problematic because they may be transformed into ditin species. Furthermore, the radical processes that they promote can lead to hydrogen atom abstraction, particularly of benzylic hydrogens, a reaction which can contribute significantly to cleavage (p-elimination) of the organotin from the polymer, when two carbon spacers are used, as, for instance, in polymer B or copolymer E. 

A few general trends are given in Table 5.5.1 and provide a primary evaluation of the stannylated polymers which can be used either directly as a source of stoichiometric tin hydride or catalytically as the tin chloride, with in situ reduction using a metal hydride. 

Even allowing disparities due to the variation in reaction conditions used with the different polymers (temperature, stirring mode), this table highlights the following points  

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