Although transition-metal precatalysts play a critical role in sustainable synthesis, their preparative routes, from ligand synthesis, to formation of metal coordination complex, employ multiple solvent, time, and energy intensive steps. This is often justified by the notion that catalysts are sufficiently value-added to justify their preparative means. In an effort to expand the scope of sustainable synthesis to include the preparation of the catalysts themselves, our group has recently reported the mechanochemical (via vibratory ball milling) preparation of acetyl- and bis(imino)pyridine ligands; a ubiquitous ligand class for numerous catalytic applications. By judicious experimental design, we were able to access this important ligand class via a solvent-free synthetic, and solvent-minimal workup procedure, all with very short reaction times (4 h), and competitive yields. We further expanded this methodology to the one-pot, one-step synthesis of an acetyl(imino)pyridine cobalt species, where the ligand itself was formed in situ (4 h, 86% yield).<br/>To better understand this exciting process, with the aim of developing rapid, sustainable routes to catalytically relevant organometallics/inorganic complexes, we expanded our study in two directions. #1 we broadened our ligand functionality scope with cobalt species to delineate effects of sterics and electronics. #2 we studied this process with several zinc halides. Due to removal of the constraints of paramagnetism, the zinc species afforded us the opportunity to monitor reaction progress by <sup>1</sup>H NMR (in addition to UV-Vis and FTIR), thus leading to a deeper mechanistic understanding. The results from these two avenues of investigation will be presented.

Developing one-pot, one-step routes to transition metal imino-pyridine complexes

2019 Spring National Meeting

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