Catalysis with Palladium(I) Dimers.

Dinuclear Pd complexes have found widespread applications as diverse catalysts for a multitude of transformations. Initially their ability to function as pre-catalysts for low-coordinated Pd species was harnessed in cross-coupling. Such Pd dimers are inherently labile and relatively sensitive to oxygen. In recent years, more stable dinuclear Pd -Pd frameworks, which feature bench-stability and robustness towards nucleophiles as well as recoverability in reactions, were explored and shown to trigger privileged reactivities via dinuclear catalysis. This includes the predictable and substrate-independent, selective C-C and C-heteroatom bond formations of poly(pseudo)halogenated arenes as well as couplings of arenes with relatively weak nucleophiles, which would not engage in Pd /Pd catalysis. This Minireview highlights the use of dinuclear Pd  complexes as both pre-catalysts for the formation of highly active Pd and Pd -H species as well as direct dinuclear catalysts. Focus is set on the mechanistic intricacies, the speciation and the impacts on reactivity.