Paramagnetic species in catalysis research: A unified approach towards (the role of EPR in) heterogeneous, homogeneous and enzyme catalysis

Paramagnetic (open-shell) systems, including transition metal ions, radical intermediatesand defect centres, are often involved in catalytic transformations. Despite the prevalenceof such species in catalysis, there are relatively few studies devoted to their character-isation, compared to their diamagnetic counterparts. Electron Paramagnetic Resonance(EPR) is an ideal technique perfectly suited to characterise such reaction centres, providingvaluable insights into the molecular and supramolecular structure, the electronic struc-ture, the dynamics and even the concentration of the paramagnetic systems underinvestigation. Furthermore, as EPR is such a versatile technique, samples can be measuredas liquids, solids (frozen solutions and powders) and single crystals, making it ideal forstudies in heterogeneous, homogeneous and enzyme catalysis. Coupled with the higherresolving power of the pulsed, higher frequency and hyperfine techniques, unsurpasseddetail on the structure of these catalytic centres can be obtained. In this Chapter, weprovide an overview to demonstrate how advanced EPR methods can be successfullyexploited in the study of open-shell paramagnetic reaction centres in heterogeneous,homogeneous and enzymatic catalysts, including heme-based enzymes for use in bio-catalysts, polymerisation based catalysts, supported microporous heterogeneous catalyticcentres to homogeneous metal complexes for small molecule actions