A biologically inspired iron complex for the homogeneous reduction of Cr(VI) to Cr(III)

Hexavalent chromium (Cr^VI) is a toxic and carcinogenic pollutant commonly found in industrial waste, posing significant environmental and health risks. In contrast, trivalent chromium (Cr^III) is significantly less toxic and less mobile in water. This study presents the efficient reduction of Cr^VI to Cr^III using a biologically inspired non-heme iron complex, [N(afa^Cy)₃Fe^IIOTf]OTf. The reaction achieves near-quantitative conversion as calculated by a paramagnetic ¹H NMR calibration method for direct quantification of the iron(III)-oxo species formed during reduction. X-ray photoelectron spectroscopy (XPS) confirms Cr^III as the final chromium containing product. This work provides a highly effective and selective approach to chromium detoxification, with potential applications in water remediation while demonstrating the utility of a ¹H NMR calibration curve for quantifying paramagnetic species in reaction mixtures.