Mechanochemistry: Fundamentals, applications and future

Self-assembly of organometallic squares through mechanochemical activation of Re-CO bonds

Thomas Auvray , José G. Hernández, Tomislav Friščić* Department of Chemistry, McGill University, Montreal (Canada)

As an efficient methodology for rapid and environmentally-friendly synthesis, mechanochemistry is growing explosively, with notable applications in organic and polymer chemistry, and in the preparation of advanced materials such as metal-organic frameworks and pharmaceutical co-crystals. 1 One area that has been largely neglected until recently is organometallic chemistry. There is only a handful of reports on the mechanochemical formation of species containing metal-carbon bonds, including our own report on the multi-step and multi- component one-pot synthesis of monovalent group VII metal carbonyl complexes. 2 We have indeed shown than one can prepare [M(CO) 3 XL] complexes (where M is Mn(I) or Re(I)), X a halide and L a bidentate ligand such as 1,10-phenanthroline) via multistep, one-pot ball-milling reactions starting from zero-valent metal carbonyl precursors. Following the successful synthesis of these simple mononuclear species, we now turn to the synthesis of more complex organometallic architectures based on these group VII metal carbonyl units, motivated by previous report showing that solvent-free mechanochemical conditions drastically accelerate the formation of the desired self-assembled structure. 3 Rhenium carbonyl supramolecular assemblies have received a lot of attention since the initial report of Slone et al. of a luminescent molecular square. 4 Taking advantage of the redox- and photo- reactivity of rhenium carbonyl species, several synthetic strategies have been developed for the preparation in solution of self-assembled architectures of various shape and nuclearity. Over the course of our study, we showed that during neat milling, mechanochemical activation of the Re-CO bonds takes place and leads to the formation of pre-assembled linear oligomers, previously never isolated, that reorganize rapidly into the targeted molecular squares in solution. References

1. T. Friščić, C. Mottillo, H.M. Titi, Angew. Chem. Int. Ed. , 2020 , 59, 1018–1029 2. J.G. Hernández, I.S. Butler, T. Friščić, Chem. Sci. , 2014 , 5, 3576–3582 3. A. Orita, L. Jiang, T. Nakano, N. Ma, J. Otera, Chem. Commun. , 2002 , 1362–1363 4. V.Slone, J.T. Hupp, C.L. Stern, T.E. Albrecht-Schmitt, Inorg. Chem. , 1996 , 35, 4096-4097

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