Ligand Modification of Cyclometalated Ruthenium Complexes in the Aerobic Oxidative Dehydrogenation of Imidazolines

New
cyclometalated ruthenium­(III) complexes bearing 2-phenylpyridine derivatives
were synthesized and characterized. Chemical modification of the cyclometalating
ligand affected its σ-donor character and resulted in regulation
of the redox potential of the ruthenium metal center, which was elucidated
by X-ray crystallography and cyclic voltammetry. The increase in the
electron-donating ability of the cyclometalating ligand improved the
catalytic activity of the ruthenium complexes in the aerobic oxidative
dehydrogenation of 2-phenylimidazoline, and enabled the catalytic
dehydrogenation of 2-phenylimidazoline in air at room temperature.
The effect of the ligand structure on the catalytic activity was also
elucidated by density functional theory (DFT) calculations and titration
experiments.