Direct structural and mechanistic insights into fast bimolecular chemical reactions in solution through a coupled XAS/UV–Vis multivariate statistical analysis

Abstract

In this work, we obtain detailed mechanistic and structural information on bimolecular chemical reactions occurring in solution on the second to millisecond time scales through the combination of a statistical, multivariate and theoretical analysis of time-resolved coupled X-ray Absorption Spectroscopy (XAS) and UV–Vis data. We apply this innovative method to investigate the sulfoxidation of p-cyanothioanisole and p-methoxythioanisole by the nonheme Fe^IV oxo complex [N4Py·Fe^IV(O)]²⁺ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) in acetonitrile at room temperature. By employing statistical and multivariate techniques we determine the number of key chemical species involved along the reaction paths and derive spectral and concentration profiles for the reaction intermediates. From the quantitative analysis of the XAS spectra we obtain accurate structural information for all reaction intermediates and provide the first structural characterization in solution of complex [N4Py·Fe^III(OH)]²⁺. The employed strategy is promising for the spectroscopic characterization of transient species formed in redox reactions.