To explore plausible reaction pathways of the cross-coupling reaction between a haloalkane and an aryl metal reagent catalyzed by an iron-phosphine complex, we examine the reaction of FeBrPh(SciOPP) 1 and bromocycloheptane employing density functional theory (DFT) calculations. Besides the cross-coupling, we also examined the competitive pathways of β-hydrogen elimination to give the corresponding alkene byproduct. The DFT study on the reaction pathways explains the cross-coupling selectivity over the elimination in terms of FeI/FeII/FeIII mechanism which involves the generation of alkyl radical intermediates and their propagation in a chain reaction manner. The present study gives insight into the detailed molecular mechanic of the cross-coupling reaction and revises the FeII/FeII mechanisms previously proposed by us and others.
Keywords: FeI/FeII/FeIII mechanism; Grignard reagent; density functional theory; haloalkane coupling; iron catalysis.