The scarcity of precious metals has led to the development of sustainable strategies for metal-catalyzed cross-coupling reactions. The establishment of new catalytic methods using iron is attractive owing to the low cost, abundance, ready availability, and very low toxicity of iron. In the last few years, sustainable methods for iron-catalyzed cross-couplings have entered the critical area of pharmaceutical research. Most notably, iron is one of the very few metals that have been successfully field-tested as highly effective base-metal catalysts in practical, kilogram-scale industrial cross-couplings. In this Minireview, we critically discuss the strategic benefits of using iron catalysts as green and sustainable alternatives to precious metals in cross-coupling applications for the synthesis of pharmaceuticals. The Minireview provides an essential introduction to the fundamental aspects of practical iron catalysis, highlights areas for improvement, and identifies new fields to be explored.

The iron‐catalyzed cross‐coupling of polyaromatic tosylates with alkyl Grignard reagents controlled by O‐coordinating ligand is reported. The reaction operates under very mild, operationally practical conditions to furnish alkylated polyaromatics that are a common motif in a wide range of electronic‐material, pharmaceutical and high‐performance fluid applications. The challenging C(sp2)–C(sp3) cross‐coupling products are obtained in good to excellent yields obviating the problems associated with β‐hydride elimination. For the first time the coupling of polyaromatic tosylates can be achieved in the presence of sensitive carboxylic acid derived functional groups. Mechanistic studies suggest that the reaction selectivity can be correlated with the reduction potential of polyaromatic hydrocarbons. The method represents a rare example of sustainable C–O bond alkylation of polyarenes at room temperature.

An operationally-simple protocol for the selective C(sp2)–C(sp3) iron-catalyzed cross-coupling of aryl chlorides with Grignard reagents at low catalyst loading is reported.

Aryl tosylates are an attractive class of electrophiles for cross-coupling reactions due to ease of synthesis, low price, and the employment of CÀ O electrophiles, however, the reactivity of aryl tosylates is low. Herein, we report the Ni-catalyzed C(sp 2 )À C(sp 3 ) Kumada cross-coupling of aryl tosylates with primary and secondary alkyl Grignard reagents. The method delivers valuable alkyl arenes by cross-coupling with challenging alkyl organometallics possessing β-hydrogens that are prone to β-hydride elimination and homocoupling. The reaction is catalyzed by an air-and moisture stable-Ni(II) precatalyst. A broad range of electronically-varied aryl tosylates, including bis-tosylates, underwent this transformation, and many examples are suitable at mild room temperature conditions. The combination of ArÀ X cross-coupling with the facile ArÀ OH activation/cross-coupling strategy permits for orthogonal cross-coupling with challenging alkyl organometallics. Furthermore, we demonstrate that the method operates with TON reaching 2000, which is one of the highest turnovers observed to date in Ni-catalyzed cross-couplings.

Der Mangel an Edelmetallen hat eine Suche nach nachhaltigen Strategien für metallkatalysierte Kreuzkupplungen ausgelöst. Die Entwicklung neuer Katalysemethoden unter Verwendung von Eisen ist wegen der geringen Kosten, leichten Verfügbarkeit und sehr geringen Toxizität von Eisen hoch attraktiv. In den letzten Jahren haben nachhaltige Methoden für eisenkatalysierte Kreuzkupplungen den kritischen Bereich der pharmazeutischen Forschung erreicht. Insbesondere ist Eisen eines der sehr wenigen unedlen Metalle, deren praktischer Einsatz in industriellen Kreuzkupplungen im Kilogrammmaßstab erfolgreich erprobt wurde. In diesem Kurzaufsatz wollen wir die strategischen Vorteile der Verwendung von Eisenkatalysatoren als umweltfreundliche und nachhaltige Alternative zu Edelmetallen in Kreuzkupplungen für die Synthese von Pharmazeutika kritisch beleuchten. Wir bieten eine Einführung in die grundlegenden Aspekte der Eisenkatalyse, heben Bereiche mit Verbesserungspotenzial hervor und zeigen neue Richtungen auf, die in Zukunft erforscht werden sollten.