Due to their extensive tunability, and ability to act as both neutral or charged “non-innocent” pincer-type ligands, bis(imino)pyridines have become a ubiquitous ligand class for broad ranging applications in organometallic, synthetic inorganic, and polymer chemistry1. Since their inception, they have primarily been synthesized through Schiff base condensations, often via lengthy reflux at elevated temperatures2. Such conditions may be conducive to unwanted side reactions, require higher energy input, and often utilize large volumes of toxic, and expensive solvent. Using a mechanochemical approach with a vibratory ball mill, we eliminate solvent from the reaction equation and cut the reaction time on average to 4 h. The resulting product is purified by dissolution in minimal methanol (or pentane), filtration, and subsequent fractional crystallization, ultimately affording pure product in excellent yield. We can additionally operate this process in the presence of CoCl2 ● 6H2O to synthesize, in only 3 h, the respective bis(imino)pyridine-CoCl2 species with excellent yields. This is promising for the future development of rapid, green routes to transition-metal species for catalytic application. Finally, by restricting the initial aniline stoichiometry (1.2 vs 3), we can readily isolate mono-substituted 2-imino,6-acetyl-pyridine in good yield. The resulting species can then be subjected to similar mechanochemical processing with a different aniline to generate unsymmetrically substituted ligands. Such species are valuable for the development of highly selective catalysts and frame the focus of our future studies.

Mechanosynthesis of bis(imino)pyridine ligands and related compounds

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.