Surface Menshutkin S_N2 Reaction on Basic Gold Clusters Provides Novel Opportunities for the Cationization and Functionalization of Molecular Metal Clusters

Abstract

Surface chemical reactions on atomically precise metal clusters have considerable attention for opening a new platform for cluster functionalization. In this study, basic Au25(4-PyET)18 (4-PyET = −SCH2CH2Py; Py = pyridyl) clusters were successfully transformed into cationized Au25(4-PyET-CH3 +) x (4-PyET)18‑x clusters, without altering their Au25 cores, through the Menshutkin SN2 reaction of their surface Py moieties. This study offers not only a simple cationization method but also a protocol for modifying the surface functionalities of molecular metal clusters via a synthetic reaction.

Unexpected Reactivity of Cationic-to-Cationic Thiolate Ligand-Exchange Reaction on Au25 Clusters

“…Thiolate-protected molecular gold (Au) clusters have been extensively investigated because of their interesting physicochemical properties based on the well-defined structures, which make them applicable in diverse fields, such as catalysis, , sensing, , and bio-applications. , Thus far, many thiolate-protected Au clusters having various core sizes and thiolate ligands have been synthesized; − however, Au clusters protected by cationic thiolate ligands are rarely reported, except in our recent studies, − owing to the difficulties in handling the positive charges during their synthesis. Significant bio-application is expected for cationic Au clusters since cellular proteins have higher affinity with cationic nanocomposites than neutral and anionic ones …”

“…26 ) x (4-PyET) 18−x (x ≈ 9) clusters were synthesized through the surface Menshutkin reaction on the Au 25 (4-PyET) 18 clusters as reported previously. 14 Au 25 (4-PyET) 18 clusters (5 mg, approximately 0.65 μmol) were dissolved in dehydrated DMF (5 mL), followed by the addition of liquid dimethyl sulfate (150 μL, approximately 1.57 mmol). The solution was allowed to react for 7 min while stirring at 400 rpm.…”

“…The Au 25 (4-PyET-CH 3 + ) x (4-PyET) 18−x (x ≈ 9) clusters were synthesized through the surface Menshutkin reaction on neutral Au 25 (4-PyET) 18 clusters and characterized by ESI-MS and UV−Vis absorption spectrum (Figure S1). 14 The number of methylated (cationized) ligands varied, and the average number (x) was calculated from the peak intensity ratio in ESI-MS, assuming that the mass spectral intensities were directly proportional to the solution concentrations of the corresponding cluster species and in good agreement with the 1 H NMR results (Figure S2).…”