Supramolecular system composed of B₁₂ model complex and organic photosensitizer: impact of the corrin framework of B₁₂ on the visible-light-driven dechlorination without the use of noble metals

Abstract

The visible-light-driven dechlorination system without the use of a noble metal has been developed. We screened the combination of cobalt catalysts having square-planar monoanionic ligands (hydrophobic B₁₂ model complex 1/imine-oxime type complex 2) and typical red dyes (Rose Bengal 3/Rhodamine B 4/Nile Red 5) for the construction of a dehalogenation system via a noble-metal-free and visible-light-driven process. The combination of the hydrophobic B₁₂ model complex 1 and Rose Bengal 3 exhibited the highest catalytic activity to 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) to form the monodechlorinated compound, 1,1-bis(4-chlorophenyl)-2,2-dichloroethane, as the major product. The prolonged photocatalysis of DDT by the B₁₂–Rose Bengal system afforded the tri-dechlorinated compound, trans-4,4′-dichlorostilbene, as the major product. Furthermore, we investigated the mechanism of the dehalogenation cycle using various methods such as UV–vis spectroscopy and laser flash photolysis. Finally, we clarified the advantage of using the hydrophobic B₁₂ model complex 1 as an electron acceptor as well as a cobalt catalyst in the organic dye-involved photocatalysis.

Keywords:

• vitamin B₁₂
• dechlorination
• DDT
• visible-light-driven
• organic dye
• Rose Bengal

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. RBH^3- would be the active species for the background dehalogenation of DDT in the absence of 1 (Entry 7 in Table 1). The RBH^3- species did not contribute to the dechlorination result of DDT by the B₁₂-Rose Bengal system (Entry 4 in Table 1) because the oxidative quenching favorably proceeds over the reductive quenching during the photocatalysis.