Palladium–Borane Cooperation: Evidence for an Anionic Pathway and Its Application to Catalytic Hydro‐/Deutero‐dechlorination

Metal–Lewis acid cooperation provides new opportunities in catalysis. In this work, we report a new type of palladium–borane cooperation involving anionic Pd0 species. The air‐stable DPB palladium complex 1 (DPB=diphosphine‐borane) was prepared and reacted with KH to give the Pd0 borohydride 2, the first monomeric anionic Pd0 species to be structurally characterized. The boron moiety acts as an acceptor towards Pd in 1 via Pd→B interaction, but as a donor in 2 thanks to B‐H‐Pd bridging. This enables the activation of C−Cl bonds and the system is amenable to catalysis, as demonstrated by the hydro‐/deutero‐dehalogenation of a variety of (hetero)aryl chlorides (20 examples, average yield 85 %). A palladium–borane dance: An anionic reaction pathway involving hydride insertion into a Pd→B bond, C−Cl bond activation by an anionic Pd0 species, and B‐assisted C−H bond formation has been discovered and leveraged into catalysis of hydro‐/deutero‐dechlorination. The boron acts as an acceptor towards Pd via the Pd→B interaction (see figure), but as a donor in the Pd0 borohydride thanks to B‐H‐Pd bridging.