Ruthenium-Catalyzed Reduction of Carbon Dioxide to Formaldehyde

Functionalization of CO2 is a challenging goal and precedents
exist for the generation of HCOOH, CO, CH3OH, and CH4 in mild conditions. In this series, CH2O, a very
reactive molecule, remains an elementary C1 building block
to be observed. Herein we report the direct observation of free formaldehyde
from the borane reduction of CO2 catalyzed by a polyhydride
ruthenium complex. Guided by mechanistic studies, we disclose the
selective trapping of formaldehyde by in situ condensation with a
primary amine into the corresponding imine in very mild conditions.
Subsequent hydrolysis into amine and a formalin solution demonstrates
for the first time that CO2 can be used as a C1 feedstock to produce formaldehyde.