Base-free transfer hydrogenation of aryl-ketones, alkyl-ketones and alkenones catalyzed by an (IrCp)-Cp-III* complex bearing a triazenide ligand functionalized with pyrazole

摘要

An (IrCp)-Cp-III* complex (2) bearing a triazenide ligand functionalized with pyrazole was synthesized and fully characterized by spectroscopic methods and the structure confirmed by X-ray diffraction studies. The catalytic activity of 2 and the control complex 3, which lacks of pyrazole in its structure, was evaluated in the reduction of aryl-ketones, alkyl-ketones, alpha,beta-unsaturated and gamma, delta-unsaturated ketones. The catalytic system, using either 2 or 3, exhibited good to excellent selectivity when tested with ketones and alkenones at 90 degrees C in 2-propanol as hydrogen source under base-free conditions. Reactivity of 2 in 2-propanol and NaH gave a neutral metal hydride (4) while in the absence of base gave two major cationic hydrides species (5 and 6).