Manganese is found in the active center of numerous enzymes that operate by an outer-sphere homolytic C−H cleavage. Thus, a plethora of bioinspired radical-based C−H functionalizations by manganese catalysis have been devised during the past decades. In contrast, organometallic C−H activation by means of manganese catalysis has emerged only recently as an increasingly viable tool in organic synthesis. These manganese(I)-catalyzed processes enabled a variety of C− H functionalizations with ample scope, which very recently set the stage for substitutive C−H functionalizations. The versatile manganese catalysis largely operates by an isohypsic, thus redox-neutral, mode of action through chelation assistance, and provided step-economical access to structurally divers compounds of relevance to inter alia bioorganic, agrochemical, and medicinal chemistry as well as the material sciences.

Synthetically useful functional groups, including ketones, amides, carbamates, carboxylic acids, aldehydes or ethers, have been identified as weakly coordinating directing groups in efficient ruthenium(II)-catalyzed C À H functionalizations. This strategy set the stage for versatile C À H bond olefinations, oxygenations, nitrogenations and oxidative alkyne annulations among others. Thereby, step-economical access to diversely decorated arenes and heteroarenes was provided in a sustainable fashion.

The first manganese(I)-catalyzed C-H allylations with ample scope were achieved by carboxylate assistance. The highly selective C-H/C-O functionalizations proved viable with densely substituted allyl carbonates, and the organometallic C-H allylation strategy set the stage for expedient late-stage diversification with excellent levels of positional selectivity.

Direct cyanations of arenes and heteroarenes bearing only weakly coordinating amides were accomplished using a robust ruthenium(II) catalyst. The user-friendly C(sp(2))-H activation occurred with the assistance of carboxylate with high site-selectivity, excellent functional group tolerance and ample scope.

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