Combining Low-Pressure CO₂ Capture and Hydrogenation To Form Methanol

This paper describes a novel approach to CO2 hydrogenation, in which CO2 capture with aminoethanols at low pressure is coupled with hydrogenation of the captured product, oxazolidinone, directly to MeOH. In particular, (2-methylamino)ethanol or valinol captures CO2 at 1–3 bar in the presence of catalytic Cs2CO3 to give the corresponding oxazolidinones in up to 65–70 and 90–95% yields, respectively. Efficient hydrogenation of oxazolidinones was achieved using PNN pincer Ru catalysts to give the corresponding aminoethanol (up to 95–100% yield) and MeOH (up to 78–92% yield). We also have shown that both CO2 capture and oxazolidinone hydrogenation can be performed in the same reaction mixture using a simple protocol that avoids intermediate isolation or purification steps. For example, CO2 can be captured by valinol at 1 bar with Cs2CO3 catalyst followed by 4-isopropyl-2-oxazolidinone hydrogenation in the presence of a bipy-based pincer Ru catalyst to produce MeOH in 50% yield after two steps.