Dioxovanadium(V) complexes of Schiff bases derived from S-(+)-2-(aminomethyl)pyrrolidine and aromatic o-hydroxycarbonyl compounds: Synthesis, characterization and structure

Ten new dioxovanadium(V) complexes incorporating Schiff bases derived from (S)-(+)-2-(aminomethyl)pyrrolidine and aromatic o-hydroxycarbonyl compounds were synthesized and investigated by spectroscopic methods. The X-ray experiment on N-(methylsalicylidene)-(S)-(2-pyrrolidinylmethyl)amine dioxovanadium(V) monohydrate shows that the crystal of that compound is a solid solution of two diastereomers, which differ in conformation of five-membered rings and in absolute configuration of the chiral centre containing the asymmetric carbon atom. The weak predominance in content of S-diastereomer over R-diastereomer in the crystal (55:45) increases strongly in DMSO solution (75:25), as evidenced by 1H and 51V NMR studies, indicating that the crystallization induces the asymmetric transformation of S-diastereomer. The free energy of transformation of S-diastereomer into its R analog in DMSO solution is particularly low for complexes containing ethylidene substituent attached to the aromatic ring.

Graphical abstractTwo diastereomers, which differ in absolute configurations of chiral centres and in conformation of five-membered rings, in one crystal of N-(7-methylsalicylidene)-(S)-(2-pyrrolidynylmethyl)amine dioxovanadium(V).Figure optionsDownload full-size imageDownload as PowerPoint slide