Oxidative coupling of 2-naphthol catalyzed by a new methoxido bridged dinuclear oxidovanadium(V) complex

Abstract

A new dinuclear oxidovanadium(V) complex, [(VO)2(μ-L-κ4O,N,N,O)(μ-OCH3)2(OMe)2]·CH3OH (1), is synthesized by the reaction of V2O5 with 1,1′-((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene))bis(naphthalen-2-ol) (H2L) in methanol. H2L is synthesized by two different methods: (i) from the reaction of hydrazine hydrate with 2-hydroxy-1-naphthaldehyde and (ii) from the reaction of hydrazine hydrate with 2-naphthol in the presence of formaldehyde (Mannich condensation). The ligand and its vanadium complex are characterized by elemental analysis, spectroscopic methods (FT-IR, NMR and UV–Vis) and their structures are determined by single crystal X-ray analysis. X-ray studies show that 1 is a neutral dinuclear complex of oxidovanadium(V) in which two vanadium(V) ions are connected by two methoxido bridging groups. The Schiff base ligand is coordinated to both vanadium centers by two NO-donor sets. Complex 1 is employed as initiator for oxidative coupling of 2-naphthol to produce BINOL. The effect of temperature, reaction atmosphere and solvent in catalytic reaction is studied. According to the obtained results, a mechanism is proposed for catalytic oxidative coupling reaction in the presence of complex 1.