Transition metal catalyzed cross-coupling reactions are one of the most important synthetic methods for the production of fine chemicals. Iron has emerged as a great alternative compared to precious metals due to several advantages such as high abundance, low cost, and low toxicity, in addition to offering potential new reactive pathways. However, the development of new synthetic methods and their practical application have been limited. This is due to a lack of understanding with respect to reactivity and mechanistic details, which stem from the challenges associated with the characterization of paramagnetic iron species. In addition, the multiple oxidation and spin states iron can exhibit makes proposing a general mechanism difficult, as a small change in the catalytic conditions can lead to the formation of different iron speciation, resulting in uncontrolled reactivity. In this work, we address those challenges by applying a physical-inorganic approach that involves spectroscopic and analytical techniques (<sup>57</sup>Fe Mössbauer, EPR (electron paramagnetic resonance), MCD (magnetic circular dichroism), and GC (gas chromatography)) combined with X-ray crystallography to provide direct molecular-level insights into the speciation, mechanism, and reactivity pathways of two- and three-component cross coupling methods catalyzed by iron centers supported by bisphosphine ligands. These studies also rationalize required experimental protocols such as slow nucleophile addition and solvent effects to achieve high product yields. Upon combination with computational studies, further insight into ligand effects on iron reactivity for the radical generation that starts the catalytic cycle can be obtained.

Understanding the reactivity of iron-bisphosphine species in two- and three- component cross-coupling reactions

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