A family of (N-salicylidene-alpha-amino acidato)vanadate esters incorporating chelated propane-1,3-diol and glycerol: Synthesis, structure, and reaction

摘要

The brown colored title complexes, (VO)-O-V(Asal)(Hpd) and (VO)-O-V(Asal)(H(2)pt), have been synthesized in excellent yields by reacting (VO)-O-IV(Asal)(H2O) with propane-1,3-diol (H(2)pd) and glycerol (H(3)pt), respectively, in methanol. Here Asal(2-) is the deprotonated salicylaldimine of glycine (A = g), L-alanine (A = a), L-valine (A = v), or L-phenylalanine (A = p). The complexes have relatively low oxovanadium(V)-oxovanadium(IV) reduction potentials (-0.2 V vs SCE in dimethyl sulfoxide). The X-ray structures of VO(gsal)(Hpd) and VO(gsal)(H(2)pt) have revealed distorted octahedral VO5-N coordination. Six-membered and five-membered O,O chelation occur for Hpd(-) and H(2)pt(-), respectively. an undissociated alcohol function lying trans to the oxo oxygen atom. The tridentate salicylaldimine ligand spans meridionally and has a folded structure consisting of two planar parts intersecting along a C-N bond. The V-O(alkoxide) bond in the complexes is similar to 0.6 Angstrom shorter than the V-O(alcohol) bond. The alkoxidic chelate ring partially hydrolyzes in moist solvents-the six-membered ring in VO(Asal)(Hpd) more easily than the five-membered ring in VO(Asal)(H(2)pt). The hydrolysis is suppressed in the presence of the relevant free alcohol. The V-51 NMR chemical shifts differ by similar to 20 ppm between VO(Asal)(Hpd) and VO(Asal)(H(2)pt) and are diagnostic of the alkoxidic chelate ring size. Species with chiral Asal(2-) ligands display diastereoisomeric equilibria in solution, and the equilibrium constants K = [endo]/[exo] have been determined from the V-51 NMR signal intensity. The trend in K values is L-alanine < L-phenylalanine < L-valine (for given alkoxidic chelation) and Hpd(-) H2Pt- (for given amino acid residue). These trends are consistent with size effects. Crystal data are as follows. VO(gsal)(Hpd): chemical formula, C12H14NO6V: crystal system, monoclinic; space group, P2(1); a = 9.229(5), b = 12.655(6), c = 11.478(4) Angstrom; beta = 99.61(4)degrees; Z = 4. VO(gsal)(H(2)pt): chemical formula, C12H13NO7V; crystal system. monoclinic; space group, P2(1)/c; a = 10.962(6), b = 9.544(4), c = 13.323(5) Angstrom; beta = 102.67(4)degrees; Z = 4. [References: 50]