Langlebige α-metallierte methylradikale und deren dimere

Abstract

Persistent radicals R' 2C .MR 3(I), R'C .(MR 3) 2 (II) and RC???(MR 3)OMR 3 (III), R'  mostly Ph but also t-Bu, H, R' 2  also 9-fluorenyl or 9-xanthenyl, M  Si, Ge, Sn, have been generated from the corresponding CH or CHal compounds or by addition of R 3M . to ketones. Radicals I, II and III are investigated by ESR spectroscopy. A temperature-dependent equilibrium has been found between these radicals and their dimers (IV), of, as far as investigated, quinonoid structure. Dimers IV rearrange with acids giving diaryl methanes. Autoxidation of radicals I at 80°C gives the benzpinacol derivatives, whose radicals are oxidized again, undergoing different fragmentations. At room temperature, however, the dimers IV are attacked by O 2 forming the metalated benzophenone derivatives via fragmentation, which are split by UV light into the radicals R 3M . (M  Si, Ge, Sn) and the oxyl radicals, which are highly stabilised by mesomerism.