Apart from that, the hydrogenation of CO 2 to methanol was reported. The stepwise
reduction preceded via formamide intermediates. The consecutive hydrogenation of
the amide intermediates resulted in the formation of methanol and generation of
amines (Scheme 20). Turnover numbers of up to 36 were reported [37].
Apart from direct CO 2 hydrogenation, carbon dioxide-derived substances such as
(cyclic) carbonates, carbamates, or urea derivatives may be used in an indirect route
of CO 2 reduction to methanol. In fact, Milstein and coworkers were the first ones to
Scheme 19 Hydrogenation of CO 2 to formate catalyzed by Mn4
Scheme 20 Hydrogenation of CO 2 to formate, amides, and methanol catalyzed by Mn1 and Mn19
240
S. Weber and K. Kirchner