Non‐Oxo Vanadium( IV ) Complexes of Aminebis(phenolate) [O,N,O] Donor Ligands and Solution Studies of Isostructural V IV and Mn IV Complexes

Mononuclear non‐oxo vanadium( IV ) complexes, [V IV L Me 2 ] ( 1 ) and [V IV L t Bu 2 ] ( 2 ), with a tridentate bis(phenol) ligand H 2 L bearing the O 2 N donor atoms and with either dimethyl or di‐ tert ‐butyl substituents have been synthesized and the X‐ray structures of 1 and 2 are reported. Additionally, 3 , an Mn IV complex [Mn IV L Me 2 ], and 4 , the anion containing the Mn III center [Mn III L Me 2 ] − , are discussed. The X‐ray structure of 4 present as an anion in 4a , [(Me 3 tacn) 2 M n II 2 (μ‐OOCCH 3 ) 3 ][Mn III L Me 2 ], where Me 3 tacn = 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 1 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 π bonding, as is expected for a phenolate ligand. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)