Olefins hydrostannation

The hydrostannation of olefinic compounds in the presence of azobisisobutyronitrile AIBN is quite a well known reaction in organotin chemistry. Its mechanism is given below... 

Results of a chemical activation induced by ultrasound have been reported by Nakamura et al. in the initiation of radical chain reactions with tin radicals [59]. When an aerated solution of R3SnH and an olefin is sonicated at low temperatures (0 to 10 °C), hydroxystannation of the double bond occurs and not the conventional hydrostannation achieved under silent conditions (Scheme 3.10). This point evidences the differences between radical sonochemistry and the classical free radical chemistry. The result was interpreted on the basis of the generation of tin and peroxy radicals in the region of hot cavities, which then undergo synthetic reactions in the bulk liquid phase. These findings also enable the sonochemical synthesis of alkyl hydroperoxides by aerobic reductive oxygenation of alkyl halides [60], and the aerobic catalytic conversion of alkyl halides into alcohols by trialkyltin halides [61]. 

Table 2. Representative Hydrogermylation and Hydrostannation Reactions OF Olefins ...

The synthesis of alkyltins from olefins and organic tin halides becomes particularly smooth in the presence of compounds that decompose to radicals at relatively low temperatures use of azoisobutyronitrile and azoisobutyric esters have proved valuable. Many different types of terminal alkene can be hydrostannated at 30-80° in a very short time by hydrides of types R3SnH, R2SnH2, and RSnH3 443... 

It has been shown447 that hydrostannation of terminal and non-terminal olefins and of acetylenes occurs by a radical and not by a polar mechanism. 

As is true for hydrostannation, acetylenes are also more reactive than the olefins toward hydroplumbation. Acetylenedicarboxylic acid dimethyl ester and ethyl propiolate 152) add Bu3PbH at — 50° C (used as a pure substance, or made in situ from organotin hydrides) spontaneously and without side reactions. Me3PbH adds in the same smooth manner to cyanoacetylene and methyl propiolate 165). Phenylacetylene reacts under the same conditions but in a side reaction Pb is precipitated and H2 evolves. After a short while starting materials disappear if excess of lead hydride is used. The IR spectrum shows absorption at 990 cm , which is in accordance with a trans adduct 152,194). 

Similarly, the reactions of olefins with metal hydrides, such as silicon hydrides, germanium hydrides, tin hydrides and lead hydrides, were also found. These reactions are called hydrosilylation, hydrogeimanation, hydrostannation and hydroplumbylation, respectively. These reactions easily proceed even if the R in eq. (2.28) are functional groups. Then these reactions are conveniently used for syntheses of organometallic compounds having a functional group by a one-stage reaction. 

There appears to be no significant indication of polymerization of the olefin, or of telomerization in hydrostannation. This is not unexpected, since the polymerization step, Eq. (29), involves the breaking of the second... 

Although the above discussion regarding hydrostannation of olefins should be valid for the reactions initiated by free radical sources, it may not be applicable to the thermal reaction. However, all of the information currently available is consistent with a free radical mechanism in this case also. 

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