Síntese, caracterização e reatividade de complexos de rutênio com macrocíclico e ligantes heteroaromáticos nitrogenados.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The synthesis of the complexes cis-[RuCl2(cyclen)]Cl.2H2O (I) (cyclen = 1,4,7,10-tetraazacyclododecane), cis-[Ru(4-NCpyH+)2(cyclen)](BF4)4 (II) (4-NCpy = 4-cyanopyridine), cis-[Ru (cyclen)bpy](BF4)2 (III) (bpy = 2,2?-bipyridine) and cis-[Ru (cyclen)(phen)](BF4)2 (IV) (phen = 1,10-phenanthroline) are reported. The complexes were studied by of UV-visible infrared and 13C and 1H NMR spectroscopies, conductivity measurements and voltammetry.After reduction of the metallic center, the cis-[RuCl2(cyclen)]Cl.2H2O species undergoes an aquation reaction, forming cis-[Ru(OH2)2(cyclen)]2+, which in the presence of N-heterocyclic ligands results in the above mentioned ruthenium(II) complexes.These ruthenium(II) compounds display absorption bands in the UV-visible range. The UV bands can be assigned to p - p* transitions, mainly centered in the ligand and named internal-ligand (IL). The lowest energy bands were assigned as metal-to-ligand charge transfer (MLCT) for the ruthenium(II) complexes and as ligand-to-metal ligand charge transfer (LMCT) for cis-[RuCl2(cyclen)]Cl.2H2O. In the Ru(II) complexes the MLCT transitions are blue shifted when compared with the corresponding cis-[Ru(NH3)4L]2+ and cis-[Ru (cyclam)L]2+ (L = bpy or phen; cyclam = 1,4,8,11-tetraazacyclotetradecane) species.The presence of an imine stretching band (u = 1648 cm-1) in the infrared spectra of cis-[RuCl2(cyclen)]Cl.2H2O was indicative of an oxidative dehydrogenation reaction of the macrocycle, and also occurs in the Ru(II) complexes (u = 1630 cm-1). The number of bands in the 750-900 cm-1 range is consistent with a cis configuration. The IR data of (II), (III) and (IV) resemble closely to those of the corresponding free ligands, with minor shifts in position, splitting and intensities. There are also two bands around 530 cm-1 assigned to the Ru-N stretching (heterocyclic N and macrocyclic N). For the (II) complex the nitrile stretching band is shifted to lower energy when compared with the non-coordinated nitrile. The shift can been assigned to a bond-order lowering of the coordinated nitrile by population of the nitrile antibonding orbitals through Ru(II) back bonding. The 13C and 1H NMR spectra of these complexes (I-IV) showed one peak at d = 160,2-175 in the 13C spectrum which correlated with a peak at d = 8-9 in the 1H NMR spectrum, indicating the presence of an imine group. The E1/2 values of the complexes (III) and (IV) have been found to be more positive than the corresponding cis-[RuII(cyclam)L]2+ and cis-[RuII(NH3)4L]n+ (L = bpy, phen). These high values, along with the E1/2 value for the compound (II), are in agreement with the solvation effect and the presence of imine group.

ASSUNTO(S)

macrocíclico macrocycle ruthenium quimica inorganica rutenio

ACESSO AO ARTIGO

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