Chemical reactions are a vital process in the synthesis of products for a diversity of purposes. For the most part, these reactions are carried out in the liquid phase, by dissolving the reactants in a solvent. However, there are a significant number of chemicals that are partially or completely insoluble, and thus have not been used for synthesis. The starting materials required for the synthesis of many cutting-edge organic materials -- such as organic semiconductors and luminescent materials -- are often poorly soluble, leading to problems in solution-based synthesis. Therefore, the development of a solvent-independent synthetic approach to overcome these long-standing solubility issues in organic synthesis is highly desired to synthesize new valuable organic molecules.

In recent years, synthetic techniques using ball milling have been used to carry out solvent-free reactions in the solid phase. It has been proposed that the use of ball milling would potentially overcome the aforementioned solubility issues in synthetic chemistry, but a systematic study for such purpose has never been carried out.

A team of four scientists from Hokkaido University's Institute for Chemical Reaction Design and Discovery (WPI-ICReDD), led by Associate Professor Koji Kubota and Professor Hajime Ito, have developed a rapid, efficient, solvent-free protocol for Suzuki?Miyaura cross-coupling reaction of insoluble aryl halides. The protocol was published in theJournal of the American Chemical Society.

芳基卤化物材料th开始流行e synthesis of organic functional molecules, primarily by the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction -- for which Hokkaido University's Professor Emeritus Akira Suzuki shared the 2010 Nobel Prize in Chemistry. Although the cross-coupling reactions have been employed for the synthesis of a wide range of valuable molecules, insoluble aryl halides are not suitable substrates because Suzuki-Miyaura cross-coupling reactions have primarily been carried out in solution.

鉴于这种限制,科学家们集中在the development of an efficient solid-state Suzuki-Miyaura cross-coupling of a number of extremely unreactive insoluble aryl halides. The key equipment consisted of a ball mill, for mixing the reactants; a heat gun, to increase the temperature at which the reactions took place; and the use of a catalytic system composed of palladium acetate (the catalyst), SPhos (a high-performance ligand for Suzuki?Miyaura cross-coupling reactions) and 1,5-cyclooctadiene (dispersant and stabilizer).

The capstone of this study was the application of the solvent-free solid-state reaction to mostly-insoluble aryl halides. These reactants did not yield any products in conventional solution-based reactions. The solid-state reactions using the high-temperature ball milling, however, gave the desired products. Importantly, the team discovered a new strong photoluminescence material prepared from insoluble pigment violet 23.

"The high-temperature ball-milling technique and our catalytic system are essential for these cross-coupling reactions of insoluble aryl halides, and the protocol we have developed expands the diversity of organic molecules derived from insoluble starting materials," says Koji Kubota.