De-Saturation of Single-Atom Copper Catalysts for Accelerating Propargylic Substitution Reactions

Rational design of proximal coordination microenvironments surrounding catalytic sites to achieve optimal reaction kinetics represents a paramount pursuit in single-atom catalysts (SACs), yet continues to pose substantial synthetic challenges. Developing innovative strategies that simultaneously stabilize low-coordinated single-metal species on solid supports, while ensuring atomic precision and high activity, remains imperative. Herein, a de-saturation strategy for SACs is demonstrated (denoted as De-sat SACs) using a top-down approach based on a KOH-mediated Joule thermal shock to obtain under-coordinated and asymmetric SACs for efficient organic synthesis. Using copper-based SACs as a proof-of-concept, the de-saturation strategy effectively converts the CuN₄ to CuN₃ configuration. The De-sat Cu SACs exhibit remarkable catalytic activity in propargylic substitution reactions, tolerating a broad range of nucleophiles (N-, C-, and O-), as well as diverse aryl, alkyl, tertiary, and cyclic propargylic carbonates. The coordination reduction in these De-sat SACs not only breaks the structural symmetry to enhance site accessibility but also elevates the energy of the $d_{z^2}$ orbital of Cu atom, thereby facilitating the formation of copper-alkynyl intermediates and boosting their catalytic performance. These findings establish a new platform for the rational design and synthesis of de-saturated yet stable SACs, facilitating challenging catalytic transformations toward sustainable chemical manufacturing.