Mercury-Substituted Silyl Radical Intermediates in Formation and Fragmentation of Geminal Dimercury Silyl Compounds^†

The first known trimercury and cyclic tetramercury organosilicon compounds containing the −(Hg−R2Si−Hg)− fragment, (t-BuHgSiR2)2Hg [R = i-Pr3Si (3a), R = t-Bu2MeSi (3b)] and [(i-Pr3Si)2SiHg]4 (6), were synthesized and characterized. Reactions of the corresponding H2SiR2 silanes with t-Bu2Hg yielded 3a and 3b. 6 was obtained from a hexane solution of 3a that was stored at room temperature for 6 months. The molecular structures of 3a, 3b, and 6 were determined by X-ray analysis. Photolysis and thermolysis of 3 leads to formation of mercury-substituted silyl radicals (previously unknown). Their structure was confirmed by a detailed EPR study and by trapping with 2,2,6,6,-tetramethyl-1-piperidinyloxyl (TEMPO) radical. A radical mechanism for the formation of 3 was evidenced by the observation of EPR signals in the reaction mixture of Hg-substituted silyl radicals.