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.

于精心构筑的固体介质中开展反应，可得到高选择性产物与无法在溶液体系中获取的独特化合物。然而，为实现固相反应（solid-phase reactions）的多场景应用，精准调控固体中反应物的排布仍属一项颇具挑战性的课题。本文报道了一类发生于碳-碳键不同位点的[2+2]光环化反应（[2+2] photocyclization）：在柔性金属有机框架（flexible metal–organic framework）中，客体分子可改变4-苯乙烯基吡啶（4-styrylpyridines, 4-spy）的空间排布。在不含客体分子的框架内，4-苯乙烯基吡啶分子会在两条碳-碳双键之间发生光二聚反应；而在负载溶剂客体的框架中，则会发生烯烃与芳香碳-碳键之间的反应，或不发生任何反应。这种可被称为"动态拓扑化学（dynamic topochemistry）"的反应特性，有助于推动固相反应在合成化学领域的应用拓展。