Self-Condensation Reaction of Lithium (Alkoxy)silylenoid: A Model Study by ab Initio Calculation

A theoretical study on the reaction mechanism of the self-condensation reaction of lithium (methoxy)silylenoid (MeO)H 2 SiLi ( 4 ) has been performed using MP2//HF/6-31G**. Stable geometries of the unsolvated 4, bis-solvated 4 ·(H 2 O) 2, and tris-solvated species 4 ·(H 2 O) 3 are found. A stable geometry of 4 ·(Me 2 O) 2 is also investigated. The self-condensation reaction path is followed using two molecules of 4 ·(H 2 O) 2 to yield the reactive intermediate, the transition state, and the product. In the transition state, one silicon center functions as a nucleophile and the other as an electrophile. In the electrophilic part the lithium-assisted ionization of the Si−O bond lowers the energy of the σ*(Si−O) orbital. The interaction between the lobe of the HOMO which localizes on the silicon atom in the nucleophilic part and the backside lobe of the σ*(Si−O) orbital in the electrophilic part leads to the formation of the Si−Si bond and the breaking of the Si−O bond. Finally, the (disilanyl)lithium (MeO)H 2 SiSiH 2 Li and lithium methoxide are obtained. The reaction proceeds via an S N 2 type displacement with retention of the configuration of silicon in the nucleophilic part but with inversion of the configuration of silicon in the electrophilic part.