Selective Hydrogenation of Amides using Ruthenium/Molybdenum Catalysts

Recyclable, heterogeneous bimetallic ruthenium/molybdenum catalysts, formed in situ from triruthenium dodecacarbonyl [Ru-3(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 degrees 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).