Flipped Spin‐State Resists Cobalt Poisoning for the Durable Electrocatalytic Deuteration of <i>N</i> ‐Heterocyclic Compounds

ABSTRACT Electrocatalytic deuteration represents a sustainable method for synthesizing deuterated N ‐heterocycles, which are scaffolds for drug development. However, the utility of this transformation is severely restrained by strong orbital interactions between metal sites and the lone pairs of N atoms that lead to irreversible catalyst deactivation. Here, we propose a Mn 3 Co 7 alloy electrocatalyst that triggers a high‐spin‐to‐low‐spin transition in Co. The flipped spin state originates from tuned d ‐electron pairing, promoting electron occupation in antibonding orbitals and weakening the Co–N bond. The reduced adsorption energy that facilitates the desorption of N ‐heterocycles is revealed to be the key factor driving the improved catalytic durability. This strategy enables a scaled‐up electrosynthesis with a yield of 92.5% at 1.25 A to obtain 10 g of deuterated piperazine hydrochloride. The methodological universality of diverse unsaturated N ‐heterocycles highlights the application potential.