Chemistry of oxovanadium(V) alkoxides: synthesis and structure of mononuclear complexes incorporating ethane-1,2-diol

Abstract

The reaction of [VIVO(L)(H2O)] with ethane-1,2-diol (H2ed) in methanol in air afforded complexes of type [VVO(L)(Hed)] in very good yields (H2L1=N-salicylideneglycine, H2L2=N-salicylidene-L-phenylalanine). The crystal structure of [VO(L2)(Hed)] has revealed the presence of tridentate [L2]2– and bidentate Hed–. In the latter the alcoholic oxygen lies trans to the oxo atom. In the VO5N co-ordination sphere the five vanadium–oxygen lengths follow the order: oxo < alkoxidic < phenoxidic < carboxylic < alcoholic. The absolute configuration of the complex is CS. The lattice consists of hydrogen-bonded (between alcoholic and carboxylic oxygen atoms) dimers having two-fold symmetry. The CD spectrum of [VO(L2)(Hed)] has revealed the composite nature of the O(alkoxide)→ V charge-transfer band in the visible region. In the 1H NMR spectra of the complexes the four methylene protons of co-ordinated Hed– are inequivalent. The [VVO(L)(Hed)] complexes represent authentic examples of the very rare mononuclear oxovanadium species incorporating ethane-1,2-diol as a ligand.