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Metal-Promoted Hydrolysis of a Coordinated Nitrile Group in a Dinuclear Ruthenium Complex
FAGALDE, FLORENCIA; MELLACE, MARÍA G.; LIS DE KATZ, NOEMÍ D.; KATZ, NÉSTOR E.
Congreso; FIGIPAS; 2007
Vienna University of Tecnology
Continuing our previous works on metal-promoted hydrolysis in dinuclear species [1,2], we report in this communication some results on the effects brought about by the electronic interaction between two metallic centers in a dinuclear unsymmetric ruthenium complex on the hydrolysis rate constants of a coordinated nitrile group. The already described dinuclear complex [(bpy)2RuII(5-CNphen)RuII(NH3)5]4+ (with bpy = 2,2´-bipyridine, 5-CNphen = 5-cyano-1,10-phenanthroline) , when oxidized by S2O82- to form the mixed-valent species [(bpy)2RuII(5-CNphen)RuIII(NH3)5]5+ , undergoes an hydrolysis reaction at pH @ 4 to generate the hydrolyzed product [(bpy)2RuII(5-C(O)NH2-phen)RuIII(NH3)5]5+ with a rate constant kh = 5 x 10-5 s-1. At pH @ 13, this rate is increased to kh = 4 x 10-4 s-1. Although these rates are higher than those of the free ligand, when comparing the former value to that of the related complex [RuIII(NH3)5(4-CNpy)]3+ (4-CNpy = 4-cyanopyridine) , a decrease in kh of ca. two orders of magnitude is disclosed. This latter effect results not only from the fact that the nitrile group in 5-CNphen is less susceptible to nucleophilic attack than the nitrile group in 4-CNpy, as confirmed by ab initio calculations, but also from the increased charge density at the C atom induced by p-backbonding of the polypyridyl RuII center. We conclude that reaction rates of formation of coordinated amides from nitriles can be efficiently modulated by introducing additional metal centers to remote positions of the coordinated ligand. ____  Lis de Katz, N. D.; Fagalde, F.; Katz, N. E. Polyhedron 1995, 14, 3111.  Fagalde, F. ; Mellace, M. G.; Lis de Katz, N. D. ; Katz, N. E. J. Coord. Chem. 2004, 57, 635.  Mellace, M. G. ; Fagalde, F. ; Katz, N. E. ; Crivelli, I. G.; Delgadillo, A.; Leiva, A. M.; Loeb, B. ; Garland, M. T. ; Baggio, R. Inorg. Chem. 2004, 43, 1100.  da Rocha, Z. N.; Chiericato Jr., G.; Tfouni, E. Adv. Chem. Ser. ACS 1997, 297.