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

Abstract

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, [Ag62S13(SBu t )32]­(PF6)4 (denoted as Ag62S12-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 [Ag62S12(SBu t )32]­(PF6)2 (denoted as Ag62S12) with identical surface anatomy and size, but without a central S2– 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 (1H and 31P), 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 Ag62S12-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 Ag62S12-S leads to higher charge transfer from Ag62S12 to the reactant, accelerates the decarboxylation process, and correlates the catalytic properties with the structure of the nanocatalyst.

Dithiophosphonate-Protected Eight-Electron Superatomic Ag21 Nanocluster: Synthesis, Isomerism, Luminescence, and Catalytic Activity

“…The catalytic activity of NCs depends on a high-surface area-to-volume ratio, incorporation of heteroatoms, engineering of ligands, steric interference, etc. , For example, the decarboxylative cascade reaction using [Ag 62 S 13 (SBu t ) 32 ] 4+ and [Ag 62 S 12 (SBu t ) 32 ] 2+ NCs demonstrated the role of a single interstitial sulfur (S 2– ) atom in catalytic activity . Herein, synthesized NCs 1 and 2 were used as catalysts for the synthesis of bioactive oxindole via a decarboxylative acylarylation reaction (Scheme and Table ).…”

“…As indicated by XPS results, 1 and 2 are mixed valence NCs, and Ag­(I) atoms are usually presented on the surface to neutralize the charge of stapled ligands. Based on the experimental and literature reports, a possible free-radical mechanism for the reaction using these silver NCs is proposed in Scheme . First, Ag + at the surface of silver NCs is oxidized to Ag 2+ by potassium persulfate (K 2 S 2 O 8 ) to facilitate coordination of silver NCs with phenyl glyoxylic acid 2a , which upon single electron oxidation produces the carboxyl radical A .…”

“…The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations support their structure, isomerism, and optical properties and compared with DTP-stabilized congener [Ag 21 {S 2 P­(O i Pr) 2 } 12 ]­PF 6 , ( 3 ) . Subsequently, 1 and 2 were investigated as catalysts in the production of oxindole from the acrylamide reaction with α-oxocarboxylic acid under ambient conditions (Scheme ) with a possible reaction pathway.…”