Dinuclear Chiral Vanadium Catalysts for Oxidative Coupling of 2-Naphthols via a Dual Activation Mechanism

This review describes our recent efforts in the development of chiral dinuclear vanadium complexes that work as dual activation catalysts for the oxidative coupling of 2-naphthols. The dinuclear vanadium(IV) complex (Ra,S,S)-1a was prepared by complexation of VOSO4 with the Schiff base derived from (R)-3,3′-diformyl-2,2′-dihydroxy-1,1′-binaphthyl (15) and (S)-tert-leucine. Since the dinuclear vanadium(IV) complex was found to be readily oxidized to afford a corresponding vanadium(V) species during preparation in air, a new synthetic procedure using VOCl3 has been applied towards dinuclear vanadium(V) complexes (Ra,S,S)-2 and (Ra,S,S)-3. To the best of our knowledge, (Ra,S,S)-1a, 2 and 3 show considerably higher catalytic activity than previously reported vanadium complexes for the oxidative coupling of 2-naphthols.