One-Pot Microwave-Assisted Olefin Hydroaminomethylation Over Bifunctional Heterogeneous Rh Catalysts

Abstract

Commercial Rh/C and lab-made Rh/CNTs catalysts were compared in the one-pot microwave-assisted hydroaminomethylation of olefins to amines using EtOAc as the solvent. This reaction accounts for two steps: hydroformylation from the alkene, followed by aldehyde reductive amination. Acid sites exposed at the surface of the support promote the formation of a metal-alkene coordination complex to preferentially form the linear aldehyde. Synthetic and natural olefins were converted with yields up to 99% under mild conditions (120 °C, 40 bar of syngas, 4 h). With the addition of catalytic amounts of acetic acid, the hydroformylation step proceeded with a 99% yield over both catalysts. The catalysts were recovered and reused, maintaining their activity for three reaction cycles (12 h). The hydroaminomethylation step again gave yields up to 99%, using 1-hexene as substrate (120 °C, 4 h, 40 bar of N2/H2 1:1). Subsequent tests with different nitrogen sources resulted in amine yields ranging from 56% to 99%, even with ammonia. FESEM, XRD, and XPS were employed for an exhaustive surface characterization and structure-to-activity correlation of the catalysts.