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

Abstract

The reaction of [V^IVO(L)(H₂O)] with ethane-1,2-diol (H₂ed) in methanol in air afforded complexes of type [V^VO(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 [V^VO(L)(Hed)] complexes represent authentic examples of the very rare mononuclear oxovanadium species incorporating ethane-1,2-diol as a ligand.