Active Cp∗Iridium(III) Complex with ortho-Hydroxyl Group Functionalized Bipyridine Ligand Containing an Electron-Donating Group for the Production of Diketone from 5-HMF

Diketones are ubiquitous blocks for organic synthesis. This work shows a highly active catalyst for the production of diketone 1-hydroxyhexane-2,5-dione (HHD) by hydrogenation of 5-hydroxymethylfurfural (5-HMF), a biobased platform chemical. Half-sandwich Cp∗Ir complexes with ortho-hydroxyl group functionalized bipyridine ligands were synthesized and found to exhibit remarkably high catalytic activity for this reaction in acidic water. The HHD formation rate was further increased when the bipyridine ligands of Cp∗Ir complexes were modified by an electron-donating group. A bipyridine ligand with both dimethylamino and ortho-hydroxyl groups achieved a HHD formation turnover frequency (TOF) of 31 560 h-1 by H2 and a TOF of 6140 h-1 by formic acid, representing 180-fold and 3 000-fold over the activities of the best reported results, respectively.