Revealing Catalyst Self-Adjustment in C–S Cross-Coupling through Multiscale Liquid-Phase Electron Microscopy

Abstract

Carbon−carbon and carbon−heteroatom bond formation mediated by transition metals is a powerful and convenient methodology for organic synthesis. To effectively meet the demands of catalyst design, an in-depth understanding of the reaction mechanisms and pathways of active species evolution is essential. Advances in electron microscopy now offer unprecedented multilevel visualization of liquid-phase chemical systems, providing a powerful tool for mechanistic studies. In this work, we found that the use of either nickel-or copper-based catalyst precursors with preinstalled thiolate groups in combination with pyridinium ionic liquid as the reaction medium leads to a positive synergistic effect, resulting in the formation of transition metal species with high catalytic activity in the C−S cross-coupling reaction between aryl halides and thiols or disulfides. Through multiscale in situ and operando electron microscopy in the liquid phase, we elucidated the self-adjustment of the catalytic system and revealed the simultaneous emergence of metallic nanoparticles and corresponding thiolate species, leading to the independent activation of the C-and S-substrates and the subsequent elimination of the product via organic group metathesis. The proposed methodology for the catalytic preparation of aromatic organosulfides was used for the design of synthetic routes to pharmacologically important substances.