Organotin compounds disproportionation

The disproportionation reactions of organotin compounds may also be regarded as alkylations by organometallic compiounds, as they involve transfer of an alkyl group from one tin atom to another. An ingenious application of this has been described in which a,ct>-distannanes are caused to disproportionate into the corresponding tetraalkyltins and 1,1-dialkyIstannacycloalkanes (65). 

Industrial consumption of organotins, for example, rose from about 5000 tons in 1965 to about 35,000 tons in 1985. The uses of nontoxic organotin compounds (R2SnX2 and RSnXs types) account for about 67% of the total world production, although use of RsSnX types as selective biocides has increased disproportionately. Tin now has more of its organometallic derivatives in commercial use than any other element. 

The alkylation of tin tetrachloride with organolithium compounds, Grignard reagents, or organoaluminum compounds remains the most common route to tetraalkyltins, and thence, by the Kocheshkov disproportionation, to the various organotin halides. 

Decarboxylations of organotin and -lead propiolates do not yield the expected ethynyl compounds, R3MC=CH, but the dimetallated acetylenes R3MC=CMR3 (M = Sn or Pb, R = Ph) are obtained (53,54). The disproportionation reaction [Eq. (39)] is thought to follow decarboxylation [Eq. (38)]. Independently synthesized ethynyltriphenyltin has been observed to undergo disproportionation [Eq. (39), R = Ph, M = Sn] at room temperature (55). 

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