Remarkable efficiency of bifunctional ligand-metal catalysts continues to attract the attention of synthetic chemists. The ligand-associated activation of a substrate enhances a rate and a selectivity of a transfomation of organic molecules. Recently, we reported a dramatic rate enhancement by a diphenyl-2-pyridylphosphine (PPh_2py) ligand in the hydration of nitriles catalyzed by Ru(acac)_2 complexes. In the reactions, the nucleophilic addition of water to the coordinated nitrile was assisted by the PPh_2py ligand. Thus, the ruthenium-PPh_2py complexes have dual functionalities, the Lewis acidic ruthenium center activates the nitrile and the nitrogen atom of the PPh_2py ligand ehnances the nucleophilicity of water. The extremely high activity (TOF = 20900 h~(-1)) was observed in cis-Ru(acac)_2(PPh_2py)_2 catalyzed the hydration of benzonitrile; however, the reaction required high temperature (180 °C) compared to those in the conventional homogeneous catalysts for the hydration of nitriles. Here we report new bifunctional pyridylphosphine-ruthenium and iridium catalysts which catalyze the hydration of nitriles below 100 °C.
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