The structures and stability of silylenoids RBrSiLi2 (R=CH3, C(SiH3)3).

The structures and stabilities of RBrSiLi2 (R=CH3, C(SiH3)3) have been studied using ab initio and DFT methods. CH3BrSiLi2 and C(SiH3)3BrSiLi2 have three possible structures, the p-complex, the plain, and the folded structures. The plain and the folded structures are different from those of known structures of silylenoids. The energy of the plain structure is the lowest and nearly equals to that of the folded structure. The plain and the folded structures, which can isomerize into each other, are the most stable and possibly detected ones in chemical reactions. The essential of the insertion reactions with Me3SiCl is the same. The insertion barriers are in the order of H2SiLiBr > C(SiH3)3BrSiLi2 > CH3BrSiLi2. The C(SiH3)3 group makes the insertion of C(SiH3)3BrSiLi2 more difficult.