Síntese, caracterização e estudo de reatividade dos complexos cis-[Ru(bpy)2(TU)(H2O)](PF6)2 E cis-[Ru(bpy)2(TU)(NO)](PF6)3

Abstract

In this work, it was carried out the synthesis and characterization of the complexes cis-[Ru(bpy)2(TU)(H2O)](PF6)2 and cis-[Ru(bpy)2(TU)(NO)](PF6)3, where TU = thiourea and bpy = 2,2 '-bipyridine, and preliminary studies of the photoreactivity of the nitrosyl complex and its reaction with cysteine, a biological reductant agent. The aqua-complex contains the thiourea ligand coordinated to the metal center through the sulfur atom, according to the data obtained by infrared vibrational spectroscopy and reinforced by theoretical study using DFT. The complex showed a half-wave potential (E1/2) for the RuIII/II redox couple at 415 mV vs Ag | AgCl and a pHdependent electronic spectrum, due to acid-base equilibrium of the proton released from the NH2 group of thiourea that presents a pKa = 10.11. The nitrosyl complex, which also contains the thiourea ligand coordinated to the metal center through the sulfur atom, showed NO stretching frequency at 1932 cm-1, which is also consistent with the half-wave potential (E1/2) for the NO+/0 redox couple at 37.5 mV. Additionally, it was measured the equilibrium constant for the interconversion reaction of nitrosyl to nitro complex at K = 1.26 x 1015. These data were further supported by empirical calculations carried out by DFT, where the energy of the LUMO orbital and the electronic density on the nitrosyl ligand were in agreement with the previous data. The nitrosyl complex has exhibited efficient release of NO in solution whether upon electrochemical or photochemical reduction. Curiously, the mechanism for the photochemical release of NO was different from other similar complexes. The chemical reduction of the nitrosyl complex with cysteine has efficiently released NO but again it followed a different mechanism from that found in other related systems.