Dynamic Topochemical Reaction Tuned by Guest Molecules in the Nanospace of a Metal–Organic Framework

Reaction
in well-designed solids allows yielding products with
high selectivity and unique compounds that cannot be obtained in solution.
However, the precise tuning of the arrangement of reactants in solids
for the versatile application of solid-phase reactions remains a challenging
subject. Here, a [2 + 2] photocyclization reaction at different positions
of the carbon–carbon bonds is described in which the spatial
arrangement of 4-styrylpyridines (4-spy) is changed by guest molecules
in a flexible metal–organic framework. The 4-spy molecules
undergo photodimerization between two carbon–carbon double
bonds in the guest-free framework, whereas a reaction between olefinic
and aromatic carbon–carbon bonds or the absence of reaction
takes place in the solvent-incorporated form. This reactivity, which
can be termed as “dynamic topochemistry” contributes
to enforce the applicability of solid-phase reactions in synthetic
chemistry.