Abstract

A new approach to the study of reactions between vanadate and monosaccharide derivatives by introducing them into an acetonitrile medium has been elaborated. Based on this approach, a crystalline product of the reaction of [NBun4][H2VO4] with methyl O-4,6-benzylidene-α-D-mannopyranoside (H2L1) has been obtained, [NBun4]2[(VO2L1)2], and its structure has been determined by X-ray crystallography. The anion comprises a dinuclear V2(µ-O)2 centre and two deprotonated H2L1 molecules. Each vanadium atom is bound to the deprotonated vicinal cis-diol of one mannopyranoside ring resulting in a five-membered ring cyclic complex. The geometry of the two five-co-ordinated vanadium(V) atoms is intermediate between a square pyramid and a trigonal bipyramid. A complex with a similar formula [NBun4]2[(VO2L3)2]{H2L3= 5′-O-[(p-methoxyphenyl)diphenylmethyl]uridine}, has also been prepared and spectroscopically characterized. Multinuclear NMR studies and conductivity measurements in acetonitrile provided strong evidence that the dimeric structure of both complexes is maintained in solution. Vanadium-51 NMR titration studies in acetonitrile solutions showed that the chelation ability follows the order L3 > L1 > L2(H2L2= methyl O-4,6-benzylidene-α-D-glucopyranoside). Molecular modelling suggested that the O–⋯ O– distance and dihedral angle between the adjacent hydroxyl groups in a sugar ring are the determining factors for vanadium chelation.

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