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

摘要

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 H-1 and V-51 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. (C) 2006 Elsevier Ltd. All rights reserved.