Ir-catalyzed hydroaminomethylation of olefins with formic acid as hydrogen source

Abstract

Formic acid (FA) is a neat and safe source of hydrogen storage. In this paper, PPh₃-based Ir catalyst was applied to the hydroaminomethylation of olefins with FA as the hydrogen source successfully. The conversion of 1-octene reached 99 % under the optimal reaction conditions (150 °C, 20 h, P/Ir = 1/1, CO 3.0 MPa, NMP as the solvent), and the product amine’s selectivity was 92 %. The catalytic system was also suitable for a variety of aliphatic, aromatic α-olefins and cycloolefins. It was demonstrated that the reaction system underwent the following steps: the dehydrogenation of FA to release H₂; the hydroformylation of olefins to aldehydes; the condensation of amines and aldehydes to enamines; and the reduction of enamines by H₂ to produce amines. In situ high-pressure ¹H NMR spectroscopy analyses proved that the Ir–H species were facilitated by the involving of FA, which played crucial roles in hydroaminomethylation. Additionally, mercury poisoning test indicated the homogeneous nature of the catalytic process.