New VIVO2+ complexes containing biologically relevant ligands as synthetic models for the vanadium(IV) transferrins

Two new N,O-donor polyfunctional ligands, N,N′-bis-(2-hydroxybenzyl)-N-(1-methylimidazole-2-yl-methyl)-N′-(2-hydroxyethyl)ethylenediamine H3BIMETEN (1), C23H30N4O3, N,N′-bis-(2-hydroxybenzyl)-N-2-pyridylmethyl)-N′-(2-hydroxyethyl) ethylenediamine H3BPETEN (2), C24H29N3O3.2 C3H8O, and their first vanadium (IV)-oxo coordination compounds have been prepared in order to investigate and compare the coordination chemistry of the unsymmetrical hexadentate ligands derived from alkyldiamine containing phenolate-type, hydroxyethyl, and methylimidazolyl or methylpyridyl pendant arms. The ligands were characterized by CHN, IR, and 1H NMR spectroscopies and X-ray diffraction for (1), and the coordination compounds [OVIV(HBIMETEN)] (3) and [OVIV(HBPETEN)] (4) were characterized by IR, CHN, molar conductivity, electronic absorption and EPR spectroscopies, and electrochemical methods of analyses and X-ray diffraction only was used for (3). Spectroelectrochemical in the UV–Vis spectral region has been used to characterize the VVO3+ analogues of [OVIV(HBIMETEN)] and [OVIV(HBPETEN)]. The E1/2=−0.229 V vs. Fc+/Fc and −0.170 V vs. Fc+/Fc obtained from spectropotentiostatic data for (3) and (4), respectively, are consistent with the cyclic voltammetric results. The electronic spectra of the oxidized species show one intense LMCT transition at 485 nm for both, similar to the spectrum of the oxidized species obtained by chemical oxidation with nitric acid of the compounds (3) and (4) in acetonitrile. A comparison of the UV–Vis and EPR properties of (3) and (4) and those detected in VO2+-transferrins reveal that these compounds are potential models for the active site of these modified transferrins.