Transition metal anion exchanged layered double hydroxides as a bioinspired model of vanadium bromoperoxidase

Tungstate-exchanged layered double hydroxides (LDHs) and V-bromoperoxidase enzymes perform oxidative brominations in a highly similar way: first H2O2 binds on the metal to form a peroxometal complex; next the peroxometal oxidizes Br− to “Br+”; this electrophilic “Br+” halogenates an organic compound, or oxidizes a second H2O2 molecule to form excited state singlet oxygen. Full evidence for this similarity is given, based on spectroscopic observation of peroxotungstate and 1O2 and on identification of the organic bromination products. In comparison with the homogeneous oxometallates, or with heterogeneous Ti-catalysts, the bioinspired LDH–WO42− catalyst displays much higher rates of Br− oxidation; this rate enhancement is explained. The activity of LDH–WO42− can be enhanced by changing the elemental composition of the octahedral layer of the LDH structure. Since LDH–WO42− is stable toward leaching and high H2O2 concentrations, it is a practical catalyst for oxidative bromination.