The cyclopropanation reaction of ethylene with samarium(II) carbenoid was studied by means of the B3LYP hybrid density functional method. The geometries for the reactants, the transition states and the products were completely optimized, and all the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate calculations. The effect of solvent THF was investigated by explicit coordination of the solvent THF molecules to the Sm(II) center of the carbenoid. The results show that all CH₃SmCH₂I/(THF)_n (n＝0, 1, 2) can react with ethylene fast, and both methylene transfer and carbometalation pathways are the same as those of lithium carbenoid, but the reaction barrier to cyclopropanation via methylene transfer pathway is lower than carbometalation pathway. The cyclopropanation reactions are able to occur at low temperatures because of the lower barrier. CH₃SmCH₂I/(THF)_n (n＝0, 1, 2) carbenoid carbometalation barrier to reaction became systematically higher as more solvent THF was added (from 24.36 kJ/mol without THF molecule to 58.44 kJ/mol with two THF molecules). In contrast, the barrier to the methylene transfer pathways remained low.

Key words: samarium carbenoid, cyclopropanation reaction, Simmons-Smith reaction, density functional theory