Vanadium Phenolates as Models for Vanadium in Biological Systems. 1. Synthesis, Spectroscopy, and Electrochemistry of Vanadium Complexes of Ethylenebis and Its Derivatives

Article abstract of DOI:10.1021/ja00274a038

The ligand ethylenebis<(o-hydroxyphenyl)glycine> (EHPG) and its derivatives have been studied as models for vanadium binding sites in biomolecules.A series of vanadium complexes are presented which elucidate the behavior of oxovanadium-phenolate coordination.Vanadium-phenolate chemistry is shown to be quite diverse with stable complexes involving the VO²⁺, VO³⁺, VOOH²⁺, and VO2⁺ moieties being isolated and characterized by NMR, UV-visible, EPR, and infrared spectroscopy.Several of these forms of vanadium are seldom observed in chelate chemistry.The electrochemical behavior of these species is also described.In the pentavalent state, vanadium is seen to promote an unusual, stepwise, metal-assisted, oxidative decarboxylation of the EHPG ligand to yield oxovanadium(IV) complexes of N-<2-(o-salicylideneamino)ethyl>(o-hydroxyphenyl)glycine (EHGS) and N,N'-disalicylideneethylenediamine (SALEN).This reaction has been investigated and a mechanism is proposed.The results of this work should be of value in elucidating the coordination chemistry of vanadium in a variety of biological systems.