Mechanochemical synthesis, usually performed by the grinding or milling of reagents with little or no solvent, presents an opportunity to investigate the preparation of compounds under conditions that complement those encountered in solution-based routes. It enjoins a rethinking of the “parameter space” of synthetic methodology, e.g., the suitability of starting materials and the range of products that can be expected from a given reaction. In organometallic chemistry, for instance, useable solvents may interfere with the interaction of reagents, or solvent molecules may bind strongly to the products, and change their structure and reactivity. Conversely, some reactions that proceed easily in organic media may result in decomposition if the dry reactants are simply ground together. Metal complexes with sterically demanding allyl ligands, specifically those of the form A′xM (A´= [1,3-(SiMe3)2C3H3]–), starkly illustrate these points. Thus the unsolvated species A´3Al can be prepared through the milling of AlX3 and K[A´], although attempts to prepare the compound in solution are not successful (Organometallics, 2014, doi: 10.1021/om5009204). In contrast, the reaction of NiBr2(dme) with K[A´] in THF readily yields the nickel complex A´2Ni, whereas milling the reagents results in decomposition and the formation of the substituted hexadiene {A´}2. Opportunities and limitations of mechanochemical activation in this area of organometallic synthesis will be discussed, including computational investigations of the reactivity differences.

Synthesis without the solvent: Mechanochemical approaches to organometallic complexes

249th National Meeting (2015)

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