LAUSR

Description Iron links a trio Iron holds particular appeal as a catalytic metal—it is safe and abundant, as well as a mainstay of enzymatic reactivity. Nonetheless, in synthetic construction of carbon-carbon bonds, modern chemists have largely had to rely on rarer metals such as palladium. Liu et al. now report that coordination of iron by a bulky chelating phosphine ligand enables efficient mutual coupling of three different reactants—an alkyl halide, an aryl Grignard, and an olefin—to form two carbon-carbon bonds (see the Perspective by Lefèvre). A combination of Mössbauer spectroscopy, crystallography, and computational simulations illuminates the mechanism. —JSY Iron coordinated by a chelating phosphine can catalyze formation of two carbon-carbon bonds between three reactants. Transition metal–catalyzed cross-coupling reactions are some of the most widely used methods in chemical synthesis. However, despite notable advantages of iron (Fe) as a potentially cheaper, more abundant, and less toxic transition metal catalyst, its practical application in multicomponent cross-couplings remains largely unsuccessful. We demonstrate 1,2-bis(dicyclohexylphosphino)ethane Fe–catalyzed coupling of α-boryl radicals (generated from selective radical addition to vinyl boronates) with Grignard reagents. Then, we extended the scope of these radical cascades by developing a general and broadly applicable Fe-catalyzed multicomponent annulation–cross-coupling protocol that engages a wide range of π-systems and permits the practical synthesis of cyclic fluorous compounds. Mechanistic studies are consistent with a bisarylated Fe(II) species being responsible for alkyl radical generation to initiate catalysis, while carbon-carbon bond formation proceeds between a monoarylated Fe(II) center and a transient alkyl radical.