Selective Hydrogenation of Amides using Ruthenium/ Molybdenum Catalysts

Recyclable, heterogeneous bimetallic ruthenium/molybdenum catalysts, formed in situ from triruthenium dodecacarbonyl [Ru₃(CO)₁₂] and molybdenum hexacarbonyl [Mo(CO)₆], are effective for the selective liquid phase hydrogenation of cyclohexylcarboxamide (CyCONH₂) to cyclohexanemethylamine (CyCH₂NH₂), with no secondary or tertiary amine by‐product formation. Variation of Mo:Ru composition reveals both synergistic and poisoning effects, with the optimum combination of conversion and selectivity at ca. 0.5, and total inhibition of catalysis evident at ≥1. Good amide conversions are noted within the reaction condition regimes 20–100 bar hydrogen and 145–160 °C. The order of reactivity of these catalysts towards reduction of different amide functional groups is primary>tertiary≫secondary. In situ HP‐FT‐IR spectroscopy confirms that catalyst genesis occurs during an induction period associated with decomposition of the organometallic precursors. Ex situ characterisation, using XRD, XPS and EDX‐STEM, for active Mo:Ru compositions, has provided evidence for intimately mixed ca. 2.5–4 nm particles that contain metallic ruthenium, and molybdenum (in several oxidation states, including zero).