Formylation with supercritical carbon dioxide over Ru/Al2O3 modified by phosphines: heterogeneous or homogeneous catalysis?

The formylation of 3-methoxypropylamine with hydrogen and “supercritical” carbon dioxide over Ru-based catalysts was studied. In this solventless process, carbon dioxide acts as both reactant and solvent. Interestingly, Ru/Al2O3 modified by the phosphine 1,2-bis(diphenylphosphino)ethane (dppe) showed a high formylation activity at 100% selectivity, comparable to those of the homogeneous catalysts RuCl2(dppe)2 and RuCl2(PPh3)3. Analysis of the reaction mixture by ICP-OES and structural studies by in situ X-ray absorption spectroscopy discovered that the presence of the phosphine modifier led to the formation of a homogeneous ruthenium catalyst.