Structures and fragmentations of organosilicon and organotin radical cations

Abstract

EPR spectroscopy has been used to study radical cations derived from organosilicon and organotin compounds, as isolated in solid trichlorofluoromethane matrices at low temperatures. For the organotin radical cations depletion of electron density occurs from a unique C–Sn bond, and leads to dissociation on annealing for allyl- and benzyl-tin species, yielding allyl and benzyl radicals, respectively: remarkably, the dissociation is reversible for p-MeOC₆H₄CH₂SnBu₃˙⁺ radical cations. No such fragmentation is observed for the corresponding organosilicon species, even on annealing to the melting point of the matrix (ca. 160 K) despite evidence that the C–Si bonds are similarly depleted on ionisation. The Me₂N(CH₂)₃SnBu₃˙⁺ radical cation is unstable at 77 K, and fragments to form butyl radicals as the only detectable paramagnetic species.