Synthesis of Novel Sila-Multi-Grignard Reagents Via Radical Activation of Si-H Bonds by RMgX or R₂Mg

Organomagnesium compounds play an important role in both organic and organometallic chemistry. In contrast, the chemistry of silylmagnesium compounds is very limited, most probably because reactions of elemental magnesium with silyl halides do not lead to the desired silylmagnesium compounds but rather to Wurtz-type silicon-silicon coupling products. Reaction of silyllithiums with magnesium halides is currently the most useful method for preparation of silylmagnesium compounds. However, the limited number of available silyllithium reagents is a major drawback. Moreover, there is almost no data on the synthesis and properties of geminal 1,1-di-Grignard compounds in organic or silicon chemistry.

Previously, we reported that organozinc reagents can activate Si-H bonds via a radical mechanism producing silylzinc compounds [1]. Here, we report the first examples of radical activation of Si-H bonds in R_(4-n)SiH_n (n=1-3) by R`MgX (R`= tBu, tBuMe₂Si; X= Cl, Br) and R``<sub>2</sub>Mg (R`` = nBu, tBu) leading to direct sila-metalation products. Using this reaction, we synthesized novel mono- and geminal- di-Grignard compounds from the di-hydrido silane 1 (Scheme, path a). Interestingly, when 1 is reacted with 2 equivalents of tBuMe₂SiMgBr under the same reaction conditions a quantitative formation of novel bis(Grignard)silane 2 is observed as well as MgBr₂ salt (Scheme, path b). Addition of 1,4-cyclohexadiene (radical inhibitor) inhibited these reactions completely, supporting a radical mechanism similar to reactions of silanes with organozinc reagents [1].

1. Dobrovetsky, Y. Kratish, B. Tumanskii, M. Botoshansky, D. Bravo-Zhivotovskii, Y. Apeloig, Angew. Chem. Int. Ed. 2012, 51, 4671.