Tackling Solubility Issues in Organic Synthesis: Solid-State Cross-Coupling of Insoluble Aryl Halides

Conventional organic synthesis generally relies on the use of liquid organic solvents to dissolve the reactants. Therefore, reactions of sparingly soluble or insoluble substrates are challenging and often ineffective. The development of a solvent-independent solid-state approach that overcomes this longstanding solubility issue would provide innovative synthetic solutions and access to new areas of chemical space. Here, we report extremely fast and highly efficient solid-state palladium-catalyzed Suzuki-Miyaura cross-coupling reactions via a high-temperature ball-milling technique. This solid-state protocol enables the highly efficient cross-couplings of insoluble aryl halides with large polyaromatic structures that are barely reactive under conventional solution-based conditions. Notably, we discovered a new luminescent organic material with a strong red emission. This material was prepared via the solid-state coupling of Pigment violet 23, a compound that has so far not been involved in molecular transformations due to its extremely low solubility. This study thus provides a practical method for accessing unexplored areas of chemical space through molecular transformations of insoluble organic compounds that cannot be carried out by any other approach.