Six-coordinated oxovanadium(V) complexes of reduced Schiff bases derived from amino acids: synthesis, reactivity and redox studies

Abstract

New oxovanadium(V) complexes, [VOL(hq)] (1)–(4) have been prepared by the reaction of [VO(acac)2] with ligands LH2 in the presence of 8-hydroxyquinoline (Hhq). LH2 is the dibasic tridentate ONO Mannich base [(S)-H2glysal, (S)-H2alasal, (S)-H2leusal and (S)-H2ileusal; S represents the S-enantiomer] obtained by the reduction of the Schiff bases of salicylaldehyde (sal) and the amino acids: glycine (gly), DL-alanine (ala), leucine (leu) and isoleucine (ileu), respectively. Spectral studies suggest an octahedral structure for these complexes. The complexes exhibit a single 51V-n.m.r. signal at −464.6 to −468.0 p.p.m. due to the existence of a single isomeric species in solution. In the presence of L-ascorbic acid under aerobic conditions [VO(S-glysal)(hq)] (1) and [VO(S-isoleusal)(hq)] (4) are converted into the corresponding dioxo species possible via intermediate reduction. A time- dependent 51V-n.m.r. study has also been carried out in order to investigate the possible isomerisation and/or further reaction in solution.