Cyclometalated Half‐Sandwich Ruthenium(II) Complexes: Synthesis, Structure, and Catalytic Activity in Imine Synthesis

ABSTRACT Four kinds of cyclometalated half‐sandwich ruthenium(II) complexes 1 – 4 with air stability were synthesized, which were supported by C,N‐donor Schiff base ligands as raw materials by C‐H activation. These newly synthesized ruthenium(II) complexes were characterized and studied by infrared (IR), ultraviolet (UV), nuclear magnetic resonance (NMR), and other analytical or spectroscopic techniques, and their exact structures of ruthenium(II) complexes were confirmed by single‐crystal X‐ray analysis. Cyclometalated half‐sandwich ruthenium(II) complexes 1 – 4 exhibited good catalytic activity in catalyzing the oxidative homo‐coupling of primary amines, dehydrogenation of secondary amines, and cross‐coupling reaction of amines with alcohols to synthesize imines, all of which were conducted in an open flask with air as oxidant. There was little effect of different substituents on ruthenium complexes ligands on catalytic efficiency. Ruthenium catalysts had the characteristics of mild reaction conditions, strong universality of substrate, good stability, and high catalytic efficiency, which had potential application in industrial production.