Iron Catalyzed Aryl–Aryl Kumada Cross‐Coupling: A Mechanistic and Computational Investigation

The widespread use of precious metal catalysts in C-C bond-forming reactions is increasingly challenged by concerns over toxicity, cost, and limited availability. As a sustainable alternative, iron offers distinct advantages in cross-coupling chemistry, but its broader application has been hindered by limited mechanistic understanding. Here, we report a mechanistically driven investigation of aryl-aryl Kumada cross-coupling catalyzed by our previously reported iron complex (PCNHCP)FeCl2 (2). Through a combination of multinuclear NMR, 57Fe Mössbauer spectroscopy, single-crystal X-ray diffraction, and reactivity studies, we identify and characterize key in situ formed intermediates, including mono- and bis-arylated iron species, along the catalytic pathway. While PCP-ligated Fe(II) complexes support two-electron chemistry, our findings uncover a distinct radical mechanism responsible for the efficient formation of the biaryl products. Furthermore, we demonstrate that small coordinating molecules, such as N2, significantly influence the speciation and reactivity of the iron catalyst. These insights advance fundamental understanding of iron-mediated cross-coupling and provide new design principles for sustainable C(sp2)-C(sp2) bond construction.