Ag-S Type Quantum Dots versus Superatom Nanocatalyst: A Single Sulfur Atom Modulated Decarboxylative Radical Cascade Reaction.

The preparation of high-nuclearity silver nanoclusters in quantitative yield remains exclusive and their potential applications in the catalysis of organic reactions are still undeveloped. Here, we have synthesized a quantum dot (QD)-based catalyst, AgS(SBu) (denoted as AgS-S) in excellent yield that enables the direct synthesis of pharmaceutically precious 3,4-dihydroquinolinone in 92% via a decarboxylative radical cascade reaction of cinnamamide with α-oxocarboxylic acid under mild reaction conditions. In comparison, a superatom AgS(SBu) (denoted as AgS) with identical surface anatomy and size, but without a central S atom in the core, gives an improved yield (95%) in a short time and exhibits higher reactivity. Multiple characterization techniques (single-crystal X-ray diffraction, nuclear magnetic resonance (H and P), electrospray ionization mass spectrometry, energy dispersive X-ray spectroscopy, Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis) confirm the formation of AgS-S. The BET results expose the total active surface area in supporting a single e transfer reaction mechanism. Density functional theory reveals that leaving the central S atom of AgS-S leads to higher charge transfer from AgS to the reactant, accelerates the decarboxylation process, and correlates the catalytic properties with the structure of the nanocatalyst.