ADDITION-REACTIONS OF TRIS(TRIMETHYLSILYL) GERMYL RADICALS TO UNSATURATED-COMPOUNDS - AN EPR AND PRODUCT STUDY

Tris(trimethylsilyl)germyl radicals, (TMS)(3)Ge-., thermally or photoc hemically generated by means of suitable radical initiators, were reac ted with a number of unsaturated compounds. The preparative scale reac tion of (TMS)(3)GeH with a variety of alkynes proceeded stereo-and reg ioselectively affording exclusively 2-alkenylgermanes in excellent che mical yields. In the analogous reactions with alkenes, no addition pro ducts were obtained except in the case of 4-vinylpyridine. This behavi or is explained in terms of the reversibility of germyl radical additi on to olefines. The reaction with arylalkenes, ketones, quinones, azin es, and nitroalkanes was instead carried out in the cavity of an EPR s pectrometer. In most cases the corresponding radical adducts were obse rved; however, quite often the intensity of the spectra was lower than expected and with azines no EPR signals could be detected. These resu lts have been interpreted as an indication that the addition reaction of tris(trimethylsilyl)germyl radicals to multiple bonds is less exoth ermic than that of trialkylgermyl radicals. With some of the investiga ted compounds, the addition of (TMS)(3)Ge-. is; thermoneutral or even endothermic and is therefore readily reversible.