University of St Andrews. School of Chemistry, University of St Andrews. Centre of Magnetic Resonance, University of St Andrews. Biomedical Sciences Research Complex, University of St Andrews. EaSTCHEM
This work was supported by Sasol Ltd. SC is grateful for a St Leonard’s postgraduate fellowship by the University of St Andrews. The presence of multiple paramagnetic species can lead to overlapping electron paramagnetic resonance (EPR) signals. This complication can be a critical obstacle for the use of EPR to unravel mechanisms and aid the understanding of earth abundant metal catalysis. Furthermore, redox or spin-crossover processes can result in the simultaneous presence of metal centres in different oxidation or spin states. In this contribution, pulse EPR experiments on model systems containing discrete mixtures of Cr(I) and Cr(III) or Cu(II) and Mn(II) complexes demonstrate the feasibility of the separation of the EPR spectra of these species by inversion recovery filters and the identification of the relevant spin states by transient nutation experiments. We demonstrate the isolation of component spectra and identification of spin states in a mixture of catalyst precursors. The usefulness of the approach is emphasised by monitoring the fate of the chromium species upon activation of an industrially used precatalyst system. Postprint