Iron-Catalyzed Homogeneous Hydrogenation with Precise Temperature-Governed Chemoselectivity.

The chemoselective hydrogenation of unsaturated compounds has been a powerful tool for both synthetic chemistry and chemical industry. The achievement of chemoselectivity among different functionalities with a single catalyst has been a challenge for transition metal-catalyzed hydrogenation. In this paper, iron tetraphosphine complexes show high catalytic efficiency for a variety of polar unsaturated substrates such as aldehydes, ketones, enones, nitroarenes and N-heteroaromatics. Without an N-H group on the catalyst, the chemoselectivity was controlled precisely by the reaction temperature. The catalytic efficiency, chemoselectivity and robustness of this Fe/P4N2 catalyst found its merit in the preparation of several important drug intermediates. A diamagnetic trans-iron dihydride complex, formed under the reaction conditions, was supposed to be an on-cycle catalytically active species.