Reduction of CO2 to Trimethoxyboroxine with BH3 in THF

Commercially available THF solutions of BH3·THF, which contain 0.5 mol % of NaBH4 as a stabilizing reagent for BH3·THF, react with 1 atm of CO2 at room temperature to form trimethoxyboroxine, (MeOBO)3, in 87% yield after 12 h. Since no reaction took place in the absence of NaBH4, NaBH4 was found to work as a promoter or catalyst for the reduction of CO2 with BH3 to the methoxy compound. A similar reaction using HCOONa in place of NaBH4 also gave (MeOBO)3 in comparable yield.