Complexes of CO2, COS, and CS2 with the super Lewis acid BH4+ contrasted with extremely weak complexations with BH3: Theoretical calculations and experimental relevance

Structures and energies of the complexes of CO2, COS, and CS2 with BH4+, a super Lewis acid (1-4a), were calculated with the density functional theory (DFT) at the B3LYP/6-311+G** level. Each of the complexes 1-4a contains a hypercoordinate boron with a three-center two-electron (3c-2e) bond. Format ion of 1-4a from the complexation of CO2, COS, and CS2 with BH4+ was calcul ated to be exothermic by 26-42 kcal/mol. At the same B3LYP/6-311+G** level calculations indicate that complexation of CO2, COS, and CS2 with neutral B H3 leads only to very weak complexes (1-4c) with relatively long B-O or B-S bonds. The computational results shed new light on related experimental st udies of the ready and extremely mild superacid induced ionic hydrogenation of CO2, COS, and CS2 with NaBH4 to methane.