Stannylenes, Distannenes, and Stannenes

Studies of the organotin(II) compounds have frequently been preceded or accompanied by work on the corresponding silicon(II) and germanium (II) compounds, and a number of reviews (e.g. references1-4) illustrate the symbiotic development of these topics. 

Stannyl radicals R3Sn can be identified by ESR spectroscopy, but there is no equivalent sensitive and selective technique for observing the transient simple (singlet) stannylenes, R2Sn . Their formation usually has to be inferred from their reactions, and it is not always unambiguous as to whether monomeric R2Sn has existed as a kinetically free entity the same problem of course occurs with the carbenes R2C . 

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Recent years have seen important developments in the chemistry of tin(II) compounds and compounds with multiple bonds to tin (Scheme 1-3). The cyclopentadi-enyltin(II) compounds, which are formed from CpM and SnCL, are pentahapto monomers. When R is a simple alkyl or aryl group, the stannylenes R2Sn(II) are known only as short-lived reactive intermediates, but when the organic group is bulky [e.g. bis(trimethylsilyl)methyl or 2,4,6-trisubstituted aryl], as indicated by R in Scheme 1-3, the monomeric stannylenes, R 2Sn , have been isolated, and have provided routes to the stannenes (R 2Sn=CR.2) and distannenes (R 2Sn=SnR 2), and other compounds with a multiple bond to tin. 

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