Catalytic Hydrogenation of Cyclic Carbonates using Manganese Complexes

Catalytic hydrogenation of cyclic carbonates to diols and methanol was achieved using a molecular catalyst based on earth-abundant manganese. The complex [Mn(CO)(2)(Br)-[HN((C2H4PPr2)-Pr-i)(2)] 1 comprising commercially available MACHO ligand is an effective pre-catalyst operating under relatively mild conditions (T = 120 degrees C, p(H-2) = 30-60 bar). Upon activation with (NaOBu)-Bu-t, the formation of coordinatively unsaturated complex [Mn(CO)(2)[N((C2H4PPr2)-Pr-i)(2))] 5 was spectroscopically verified, which confirmed a kinetically competent intermediate. With the pre-activated complex, turnover numbers up to 620 and 400 were achieved for the formation of the diol and methanol, respectively. Stoichiometric reactions under catalytically relevant conditions provide insight into the stepwise reduction form the CO2 level in carbonates to methanol as final product.