Chirally modified cobalt-vanadate grafted on battery waste derived layered reduced graphene oxide for enantioselective photooxidation of 2-naphthol: Asymmetric induction through non-covalent interaction

Abstract

The cobalt oxide-vanadium oxide (Co3O4-V2O5) combined with reduced graphene oxide (rGO) having band gap of ∼ 3.3 eV appeared as a suitable photocatalyst for selective oxidation of 2-naphthol to BINOL. C2-symmetric BINOL was achieved with good yield using hydrogen peroxide as the oxidant under UV-light irradiation. The same catalyst was chirally modified with cinchonidine and a newly synthesized chiral Schiff base ligand having a sigma-hole center. The strong interaction of the chiral modifiers with the cobalt-vanadium oxide was truly evident from various spectroscopic studies and DFT calculations. The chirally modified mixed metal oxide transformed the oxidative CC coupling reaction with high enantioselectivity. High enantiomeric excess upto 92 % of R-BINOL was obtained in acetonitrile solvent and hydrogen peroxide as the oxidant. A significant achievement was the formation of S-BINOL in the case of the cinchonidine modified catalyst and R-BINOL with the Schiff base ligand anchored chiral catalyst. The UV-light induced catalytic reaction was found to involve hydroxyl radical as the active reactive species. The spin trapping ESR and fluorescence experiment provided relevant evidence for the formation of such species through photodecomposition of hydrogen peroxide on the catalyst surface. The chiral induction to the resultant product was found to induce through supramolecular interaction like OH…π, H…Br interaction. The presence of sigma hole center was believed to play significant role in naphtholate ion recognition during the catalytic cycle.