NITRILE HYDROLYSIS INDUCED BY OXIDATION OF A DINUCLEAR DIRUTHENIUM COMPLEX

摘要

On oxidation of the dinuclear complex [(terpy)(bipy)Ru-II(4-pyCN)Ru-II (NH3)(5)](4+) (terpy = 2,2': 6',2 ''-terpyridine, bipy = 2,2'-bipyridine, 4-pyCN = 4-cyanopyridine) by excess S2O82- in an aqueous solution a mixed-valent species is formed, which undergoes nitrile hydrolysis according to the reaction: [(terpy)(bipy)Ru-II(4-pyCN)Ru-III (NH3)(5)](5+) + H2O --> [(terpy)(bipy)Ru-II(4-pyC(O)NH)Ru-III(NH3)(5)](4+) +H+ [with 4-pYC(O) NH = isonicotinamido]. The observed rate constant k(h) = 5.8 x 10(-3) s(-1) at 25.0 degrees C, pH = 3.3 (CF3COOH), mu = 0.1 M (KCl), is ca twice as high as that of the mononuclear complex [(4-pyCN)Ru-III(NH3)(5)](3+), but ca half that of the dinuclear species (CN)(5)Fe-II(4-pyCN)Ru-III (NH3)(5)and ca four times lower than that of the dinuclear complex [(NH3)(5)Ru-III(4-pyCN) Ru-III(NH3)(5)](6+), indicating that the catalytic effect of a Ru-III(NH3)(5) group on the rate of nitrile hydrolysis is somewhat enhanced by a Ru-II(terpy)(bipy) moiety, due to an inductive effect, although to a less extent than by a Fe-II(CN)(5) or a Ru-III(NH3)(5) group, probably because of the pi-back-bonding ability of Ru-II, which makes the nitrile carbon atom of 4-pyCN less susceptible to the nucleophilic attack of a water molecule. [References: 13]