Borohydride salts as high efficiency reducing reagents for carbon dioxide transformation to methanol: Theoretical approach

• In this work, the reduction of carbon dioxide to methanol by borohydride salts was studied, theoretically.
• The steps of the overall reaction classified into three phases affected by substituting groups of borohydride salts.
• The electronic interactions and charge density of boron atom affect the Gibbs free energy of activations.
• Li[MeBH3] as the best reductive reagent has been proposed for the reaction, thermodynamically and kinetically.

In this work, the mechanism of CO2 reduction to methanol using the borohydride salts of M [RBH3] (M = Li+, Na+ and R = Ph, CH3, CN and H) as the reduction reagents, has been investigated, theoretically. In spite of expensive and less reactive boranes such as pinacolborane, borohydride salts have unique properties such as simplicity of use, low cost, and high chemoselectivity. Previously, the production of Methoxyborane (MeOBO)3 by using the boron molecule, carbon dioxide and sodium borohydride was reported, experimentally. But, in addition to sodium borohydride, we investigated the effects of three other types of borohydride salts. The studied steps of the overall reaction have been divided into three phases, and the effects of the substituted groups (R = Ph, CH3, CN and H) on the kinetics have been fully investigated. Two considered phases have been affected by R group which their effects have been justified by the electronic interactions of the substituted groups and electron density of boron atom. Finally, it has been concluded that Li[MeBH3] and Li[PhBH3] are the best reduction reagents for the reaction, thermodynamically and kinetically.

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