Stereospecific Formation of Dinuclear Vanadium(V) Tartrato Complexes

The first dinuclear nonperoxido tartrato complexes of vanadium(V), (NMe4)2[V2O4((2R,3R)-H2tart)2]·6H2O (1), (NMe4)2[V2O2((2R,3R)-tart)((2S,3S)-tart)] (2), (NEt4)2[V2O2((2R,3R)-tart)((2S,3S)-tart)] (3) (tart = tartrato(4−) = C4H2O64−) have been prepared from water−ethanol medium and characterized by X-ray structure analysis and spectral methods. The formation of the complexes has been found to be stereospecific; the composition and structure of anions containing one or both enantiomers of the ligand are profoundly different. The structure of anions in 1−3 also differs significantly from the structure of other dinuclear vanadium(V) α-hydroxycarboxylato complexes, but, interestingly, the geometry of the [V2O2((2R,3R)-tart)((2S,3S)-tart)]2− ion resembles the structure of the [(VO)2((2R,3R)-tart)((2S,3S)-tart)]4− ion which has a vanadium(IV) center. Using Raman and 51V NMR spectroscopy the solvent dependent mutual transformations of [V4O8((2R,3R)-tart)2]4− (V4L2-RR), [V4O8((2S,3S)-tart)2]4− (V4L2-SS), [V2O4((2R,3R)-H2tart)2]2− (V2L2-RR), [V2O4((2S,3S)-H2tart)2]2− (V2L2-SS), and [V2O2((2R,3R)-tart)((2S,3S)-tart)]2− (V2L2-rac) have been established. In aqueous solution the following reactions take place; 2 V2L2-rac → V2L2-RR + V2L2-SS followed by partial decomposition, V2L2-RR → V4L2-RR + 2 L (V2L2-SS → V4L2-SS + 2 L). On the other hand V2L2-rac is stable in CH3CN solution while V2L2-RR (V2L2-SS) decomposes into several species.