Bypassing Oxidative Addition: Steric Control in Aryl Iodide Activation at Rh(I) Promotes an Open‐Shell Rh(II) Pathway

Abstract

The activation of aryl halides by second‐row late transition metals usually follows the classical two‐electron oxidative addition pathway to yield closed‐shell species. Departing from this reactivity pattern, we report that a square‐planar Rh(I) complex supported by a bulky PCPtBu pincer ligand activates an aryl iodide through an one‐electron radical pathway, yielding a paramagnetic RhIII complex, rather than the expected RhIII(Ar)(I) oxidative addition product. This open‐shell RhIII complex was independently synthesized and characterized. The less hindered (PCPⁱPr) analog instead undergoes the conventional two‐electron oxidative addition to form the expected RhIII(Ar)(I) product. DFT calculations confirm that steric hindrance in the PCPtBu ligand destabilizes the concerted transition state and favors homolytic CI bond cleavage. This study provides the first experimental evidence of radical aryl halide activation by a second‐row Rh(I) complex and highlights how ligand design can divert oxidative addition from a classical to a single‐electron mechanism. Moreover, the generated aryl radical reacted with the benzene solvent to yield the corresponding biphenyl, opening new opportunities for controlled single‐electron transformations and CH arylation processes mediated by late transition metal centers.