Acceptorless Dehydrogenation of Methanol to Carbon Monoxide and Hydrogen using Molecular Catalysts

• Published in: Angewandte Chemie International Edition Vol. 60; no. 51; pp. 26500 - 26505
• Main Authors: Kaithal, Akash, Chatterjee, Basujit, Werlé, Christophe, Leitner, Walter
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 13-12-2021; John Wiley and Sons Inc
• Edition: International ed. in English
• Subjects: carbon dioxide; Carbon monoxide; Catalysts; Communication; Communications; Coordination compounds; decarbonylation; Dehydrogenation; Gas mixtures; Hydrogen; Manganese; Methanol; Methyl formate; Ruthenium; Ruthenium compounds
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202110910

The acceptorless dehydrogenation of methanol to carbon monoxide and hydrogen was investigated using homogeneous molecular complexes. Complexes of ruthenium and manganese comprising the MACHO ligand framework showed promising activities for this reaction. The molecular ruthenium complex [RuH(CO)(BH4)(HN(C2H4PPh2)2)] (Ru‐MACHO‐BH) achieved up to 3150 turnovers for carbon monoxide and 9230 turnovers for hydrogen formation at 150 °C reaching pressures up to 12 bar when the decomposition was carried out in a closed vessel. Control experiments affirmed that the metal complex mediates the initial fast dehydrogenation of methanol to formaldehyde and methyl formate followed by subsequent slow decarbonylation. Depending on the catalyst and reaction conditions, the CO/H2 ratio in the gas mixture thus varies over a broad range from almost pure hydrogen to the stoichiometric limit of 1:2.
Homogeneous catalysts based on ruthenium and manganese enable the generation of gaseous CO and H2 (syngas) from conveniently storable and easily transportable methanol. Conversion/time profiles and kinetic isotope effects together with spectroscopically detected intermediates indicate rapid dehydrogenation followed by two possible catalytic pathways via formaldehyde or methyl formate for decarbonylation as mechanistic manifold.