Guiding the High-Yield Synthesis of NHC-Ligated Gold Nanoclusters by 19 F NMR Spectroscopy.

Optimizing the synthesis of atomically precise metal nanoclusters by virtue of molecular tools is highly desirable but quite challenging. Herein we report how 19 F NMR spectroscopy can be used to guide the high-yield synthesis of N-heterocyclic carbene (NHC)-stabilized gold nanoclusters. In spite of little difference, 19 F NMR signals of fluoro-incorporated NHCs ( F NHC) are highly sensitive to the tiny change in their surrounding chemical environments with different N-substituents, metals, or anions, thus providing a convenient strategy to discriminate species in reaction mixtures. By using 19 F NMR, we first disclosed that the one-pot reduction of F NHC-Au-X (X is halide) yields multiple compounds, including cluster compounds and also a large amount of highly stable [Au( F NHC) 2 ] + byproduct. The detailed quantitative 19 F NMR analyses over the reductive synthesis of NHC-stabilized Au nanoclusters reveal that the formation of the di-NHC complex is deleterious to the high-yield synthesis of NHC-stabilized Au nanoclusters. With the understanding, the reaction kinetic was then slowed by controlling the reduction rate to achieve the high yield of a [Au 24 ( F NHC) 14 X 2 H 3 ] 3+ nanocluster with a unique structure. The strategy demonstrated in this work is expected to provide an effective tool to guide the high-yield synthesis of organic ligand-stabilized metal nanoclusters.