Cyclometalated Half-Sandwich Iridium Complex for Catalytic Hydrogenation of Imines and Quinolines

Several C,N-chelate cyclometalated half-sandwich iridium-based catalysts for imines and quinoline derivatives reduction have been prepared through metal-mediated C–H bond activation based on benzothiazole ligands. These iridium complexes exhibited high catalytic activity for hydrogenation of various types of imines with high yields. The most active catalyst was obtained from methoxyl substituted complex 2, showing the catalytic TOF value of 975 h–1 for the reduction of imine 6a. Additionally, these half-sandwich complexes also showed high efficiency for the catalytic hydrogenation of N-heterocyclic quinoline derivatives. Good catalytic activity was displayed for various kinds of substrates with either electron-donating or electron-withdrawing groups. Complexes 1–5 were fully characterized by NMR, IR, and elemental analysis. Molecular structures of complexes 1 and 4 were further confirmed by X-ray diffraction analysis.