Coming of age: sustainable iron-catalyzed cross-coupling reactions.

Iron-catalyzed cross-coupling reactions have, over the past years, developed to maturity and today are an integral part of the organic chemist's toolkit. They benefit from low costs, operational simplicity, and high reactivity and thus constitute the "green" sister of the palladium and nickel establishment. This timely Review traces back major achievements, discusses their mechanistic background, and highlights numerous applications to molecular synthesis.Iron-catalyzed carbon-carbon bond-forming reactions have matured to an indispensable class of reactions in organic synthesis. The advent of economically and ecologically attractive iron catalysts in the past years has stepped up the competition with the established palladium and nickel catalyst systems that have dominated the field for more than 30 years, but suffer from high costs, toxicity, and sometimes low reactivity. Iron-catalyzed protocols do not merely benefit from economic advantages but entertain a rich manifold of reactivity patterns and tolerate various functional groups. The past years have witnessed a rapid development with ever-more-efficient protocols for the cross-coupling between alkyl, alkenyl, alkynyl, aryl, and acyl moieties becoming available to organic chemists. This Review intends to shed light onto the versatility that iron-catalyzed cross-coupling reactions offer, summarize major achievements, and clear the way for further use of such superior methodologies in the synthesis of fine chemicals, bioactive molecules, and materials.