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

The first regioselective oxidative coupling of 2-hydroxycarbazoles is described. With a vanadium catalyst and oxygen as the terminal oxidant, dimers with an ortho–ortho′ coupling pattern were obtained with high selectivity. Further oxidation led to ortho′–ortho′ coupling to generate a tetramer, which provided insight that the atropisomerization barriers of the unsymmetrical biaryl bonds are much lower than expected.

Design and implementation of the first (asymmetric) Fe-catalyzed intra- and intermolecular difunctionalization of vinyl cyclopropanes (VCPs) with alkyl halides and aryl Grignard reagents has been realized via a mechanistically driven approach.

The simple and cheap chiral catalyst, heteroarylidene-tethered Ph-bis(oxazoline)-Cu(OTf)(2), can efficiently catalyze the asymmetric F-C alkylation of indoles and pyrrole with β,γ-unsaturated α-ketoesters. The 3-indolyl adducts were obtained in up to >99% ee. Moreover, the 2-pyrrolyl adducts were achieved in up to 92% ee for the first time.

A highly selective iron-catalyzed three-component dicarbofunctionalization of unactivated alkenes with alkyl halides and sp2-hybridized Grignard reagents is reported.

Iron−bisphosphines have attracted broad interest as highly effective and versatile catalytic systems for two-and threecomponent cross-coupling strategies. While recent mechanistic studies have defined the role of organoiron(II)−bisphosphine species as key intermediates for selective cross-coupled product formation in these systems, mechanistic features that are essential for catalytic performance remain undefined. Specifically, key questions include the following: what is the generality of iron(II) intermediates for radical initiation in cross-couplings? What factors control reactivity toward homocoupled biaryl side-products in these systems? Finally, what are the solvent effects in these reactions that enable high catalytic performance? Herein, we address these key questions by examining the mechanism of enantioselective coupling between α-chloroand α-bromoalkanoates and aryl Grignard reagents catalyzed by chiral bisphosphine−iron complexes. By employing freeze-trapped 57 Fe Mossbauer and EPR studies combined with inorganic synthesis, X-ray crystallography, reactivity studies, and quantum mechanical calculations, we define the key in situ iron speciation as well as their catalytic roles. In contrast to iron−SciOPP aryl−alkyl couplings, where monophenylated species were found to be the predominant reactive intermediate or prior proposals of reduced iron species to initiate catalysis, the enantioselective system utilizes an iron(II)-(R,R)-BenzP* bisphenylated intermediate to initiate the catalytic cycle. A profound consequence of this radical initiation process is that halogen abstraction and subsequent reductive elimination result in considerable amounts of biphenyl side products, limiting the efficiency of this method. Overall, this study offers key insights into the broader role of iron(II)− bisphosphine species for radical initiation, factors contributing to biphenyl side product generation, and protocol effects (solvent, Grignard reagent addition rate) that are critical to minimizing biphenyl generation to obtain more selective cross-coupling methods.

A series of cheap and easily accessible heteroarylidenemalonate-derived bis(oxazoline) ligands 1 and 2 were synthesized and their copper(II) complexes were applied to the catalytic FriedelCrafts reaction between indoles and diethyl alkylidenemalonates, Excellent asymmetric enantioselectivities were afforded for the S-enantiomer (up to > 99% ee) in isobutyl alcohol, and the R-enantiomer (up to 96.5% ee) in dichloromethane.

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