Non-oxo vanadium(IV) complexes of aminebis(phenolate) [O,N,O] donor ligands and solution studies of isostructural VIV and MnIV complexes

Mononuclear non-oxo vanadium(IV) complexes, [(VL2Me)-L-IV] (1) and [V(IV)LtBu(2)] (2), with a tridentate bis(phenol) ligand H2L bearing the O2N donor atoms and with either dimethyl or ditert-butyl substituents have been synthesized and the X-ray structures of 1 and 2 are reported. Additionally, 3, an Mn-IV complex [(MnL2Me)-L-IV], and 4, the anion containing the MnIII center (MnL2Me)-L-III](-), are discussed. The X-ray structure of 4 present as an anion in 4a, [{Me(3)tacn)(2)Mn-2(II)(mu OOCCH3)(3)][(MnLMe2)-L-III], where Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, confirms the magnetic susceptibility results of the high-spin d(4) nature of the manganese center in 4. The compounds were characterized by elemental analysis, IR, UV/Vis, mass spectrometry, EPR spectroscopy, electrochemical and variable-temperature (2-295 K) magnetic susceptibility measurements. The electrochemical results of I and 2 suggest the metal-centered oxidation, i.e. the generation of a V-V-phenolate species, prior to the second oxidation attributable to the formation of a V-V-phenoxyl radical species. Isomerization of the meridional form for the bis(ligand)metal species to the facial form has been observed for 1 and 3 in solution. The EPR spectroscopic data of 1 and 2 clearly show a considerable increase in the in-plane pi bonding, as is expected for a phenolate ligand. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim., Germany, 2003)