Selective hydrogenation of amides using Rh/Mo catalysts

Rh/Mo catalysts formed in situ from Rh6(CO)16 and Mo(CO)6 are effective for the liquid phase hydrogenation of CyCONH2 to CyCH2NH2 in up to 87% selectivity, without the requirement for ammonia to inhibit secondary amine formation. Use of in situ HP-FTIR spectroscopy has shown that decomposition of metal carbonyl precursors occurs during an extended induction period, with the generation of recyclable, heterogeneous, bimetallic catalysts. Variations in Mo:Rh content have revealed significant synergistic effects on catalysis, with optimum performance at values of ca. 0.6, and substantially reduced selectivities at ⩾1. Good amide conversions are noted within the reaction condition regimes 50–100 bar H2 and 130–160 °C. Ex situ characterization of the catalysts, using XRD, XPS and EDX-STEM, has provided evidence for intimately mixed (ca. 2–4 nm) particles that contain metallic Rh and reduced Mo oxides, together with MoO3. Silica-supported Rh/Mo analogues, although active, perform poorly at <150 °C and deactivate during recycle.

Graphical abstractSelective reduction of amides to the corresponding amines has been achieved using recyclable, bimetallic heterogeneous Rh/Mo catalysts derived from Rh6(CO)16 and Mo(CO)6. Primary amide substrates do not require the addition of ammonia to inhibit secondary amine formation.Figure optionsDownload full-size imageDownload high-quality image (80 K)Download as PowerPoint slide