Radicals stannyl-centred

Homolytic substitution reactions including homolytic allylation, radical [2,3]-migrations and stereochemical reactions been reviewed. The review also highlights the possible applications of homolytic substitution reactions. ni reactions at silicon (by carbon-centred radicals in the a-position of stannylated silyl ethers) are efficient UMCT reactions producing cyclized alkoxysilanes. Bimolecular reactions can also be facilitated in good yield (Schemes 32 and 33). ... 

Posner and coworkers concluded that the low activity of the stannyl-substituted tri-oxanes indicated that the killing species must be an intermediate somewhere along the route after the 1,5-H shift has generated a C4-centred radical. 

A number of the stannyl radicals, R3Sn have been characterised by ESR spectroscopy,5 and their reaction kinetics have been determined, and used in interpreting and designing the radical chain syntheses. Radical ions R SnX4. +, R SnX4. and R2Sn have also been identified, again principally by ESR spectroscopy, and there is some spectroscopic evidence for the species RnSnX Y" which are postulated to be formed in the course of some SH2 reactions at tin centres. 

This pyramidal structure of stannyl radicals is supported by the negative temperature dependence of a(119Sn) and by the fact that optically active organotin compounds with the asymmetry centred on the tin can react through the intermediate stannyl radical and show retention of optical activity. Again, the fact that the trineophyltin radical (PhMc2CCII2)3Sn shows non-equivalent methylene protons in the ESR spectrum below -20 °C is most readily explained by the fact that the radicals are non-planar at tin.53... 

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