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

Abstract

The first known trimercury and cyclic tetramercury organosilicon compounds containing the -(Hg-R 2 Si-Hg)-fragment, (t-BuHgSiR 2 ) 2 Hg [R ) i-Pr 3 Si (3a), R ) t-Bu 2 MeSi (3b)] and [(i-Pr 3 Si) 2 SiHg] 4 (6), were synthesized and characterized. Reactions of the corresponding H 2 SiR 2 silanes with t-Bu 2 Hg 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.

Radical Activation of SiH Bonds by Organozinc and Silylzinc Reagents: Synthesis of Geminal Dizinciosilanes and Zinciolithiosilanes

“…This reaction is analogous to the synthesis of silylmercury oligomers, obtained in the reaction between 11 and ( t BuMe 2 Si) 2 Hg 3a. The formation of 12 supports a radical mechanism for this reaction, similarly to that of the analogous silylmercury compounds 20 …”

Radical Activation of SiH Bonds by Organozinc and Silylzinc Reagents: Synthesis of Geminal Dizinciosilanes and Zinciolithiosilanes

“…This reaction is analogous to the synthesis of silylmercury oligomers, obtained in the reaction between 11 and ( t BuMe 2 Si) 2 Hg 3a. The formation of 12 supports a radical mechanism for this reaction, similarly to that of the analogous silylmercury compounds 20 …”

“…The above experiments and in particular the higher yields obtained in the presence of AIBN or t Bu 2 Hg (Scheme ) suggest that in analogy to R 2 Hg,2b, 3a,b R 2 Zn reacts with silanes by a radical mechanism.…”

“…9 Therefore, a single‐pot reaction leading to zinciosilanes by activation of SiH bonds has a great synthetic potential. Furthermore, in analogy to the synthesis of bismercuriosilanes,2b, 3a,b activation of dihydridosilanes by diorganozinc or disilylzinc compounds can lead, in a single‐step reaction, to new geminal dizinciosilanes. These interesting dimetallic reagents are potentially very attractive reagents, in a similar fashion to geminal dizinciomethanes, their organic analogues 10…”

“…radicals ( 13 a and 13 b ) were observed (Scheme ) 21. Radicals 13 a and 13 b were characterized by the relatively small hyperfine coupling constant with the 29 Si α nuclei (25.3 G and 31.1 G, respectively), which is typical for α‐metal‐substituted silyl radicals 3b. 22 13 a and 13 b differ in their R′′ substituents, which were not yet determined.…”