MOLECULAR ORGANIC FRAMEWORKS

Selectivity in one click

J. Am. Chem. Soc. http://doi.org/cpz7 (2018)

It is notoriously difficult to react only one alkyne moiety of a symmetric dialkyne with an azide, as both alkynes are likely to undergo a [3+2] cycloaddition reaction (a click-chemistry reaction) and form a bis-triazole. As a result, lengthy chemical protection and deprotection procedures have been developed. Now, Huxley et al. have reported a direct synthetic strategy to convert a symmetric dialkyne into an alkyne-functionalized triazole by taking advantage of the steric constrains that a metal–organic framework (MOF), used as a nanovessel, imposes on the reaction pathway.

Credit: American Chemical Society

The researchers first prepare a Mn-based MOF in which the Mn atoms are about 13 Å apart. They then substitute the bromine atoms, which are attached to each Mn, with an azide moiety, therefore creating an environment in which the azides are uniformly spaced within the pores of the MOF. When reacting the MOF with a short dialkyne, the only product of the reaction is a mono-triazole. This is because the dialkyne is shorter than the distance between the azides. When using a longer dialkyne, the researchers find a mixture of products including a bis-triazole. Finally, to release the product, they add methyl bromide, which displaces the alkyne-functionalized triazole and regenerates the initial Mn-based MOF.

All reactions are in the solid state and the crystallinity of the MOF is maintained throughout the process, thus providing researchers with a reliable ruler to control the selectivity of the reaction.

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Correspondence to Alberto Moscatelli.

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Moscatelli, A. Selectivity in one click. Nature Nanotech 13, 436 (2018). https://doi.org/10.1038/s41565-018-0173-4

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