Synthesis, structure and metal redox of alkoxide bound oxovanadium(V) complexes incorporating N-salicylidene/N-naphthalidene-α-aminoalcohols

Abstract

In the title families the ONO ligands are deprotonated forms of N-(1-hydroxyethyl) salicylaldimine(H2L1), N-(1-hydroxy-2-methylpropyl)salicylaldimine (H2L2), N-(1-hydroxyethyl)naptthaldimine(H2L3), N-(1-hydroxy-2-methylpropyl) naphthaldimine(H2L4). The ON ligand is deprotonated 8-quinolino(Hhq). The complexes VO(L) (hq) (L = L1-L4) have been synthesized in excellent yields from VO(L)x and 8-quinolinol in methanol (oxidant is aerial oxygen). The crystal structure of VO(L2)(hq) has revealed tridentate ONO and bidentate ON binding by [L2]2− and hq−, respectively. The Vsingle bondO(phenolate) bond length is longer than Vsingle bondO(alkoxidic) by ∼ 0.09Å. In CDCl3 solution the1H NMR spectrum of the VOL2(hq) shows that the binding nature in solid state is also retained in solution. The complexes display the quasi-reversible one-electron couple VO(L)(hq)-VO(L)(hq)− near −0.43 V vs saturated calomel electrode. This lowering of potentials indicate considerable VO3+ stabilization due to alkoxide binding. Electrogenerated solution of VO(L)(hq)− are EPR-active corresponding to a dxy1 configuration.