Crystal‐to‐Crystal Synthesis of Photocatalytic Metal–Organic Frameworks for Visible‐Light Reductive Coupling and Mechanistic Investigations

Postmodification of reticular materials with well‐defined catalysts is an appealing approach to produce new catalytic functional materials with improved stability and recyclability, but also to study catalysis in confined spaces. A promising strategy to this end is the postfunctionalization of crystalline and robust metal–organic frameworks (MOFs) to exploit the potential of crystal‐to‐crystal transformations for further characterization of the catalysts. In this regard, two new photocatalytic materials, MOF‐520‐PC1 and MOF‐520‐PC2, are straightforwardly obtained by the postfunctionalization of MOF‐520 with perylene‐3‐carboxylic acid (PC1) and perylene‐3‐butyric acid (PC2). The single crystal‐to‐crystal transformation yielded the X‐ray diffraction structure of catalytic MOF‐520‐PC2. The well‐defined disposition of the perylenes inside the MOF served as suitable model systems to gain insights into the photophysical properties and mechanism by combining steady‐state, time‐resolved, and transient absorption spectroscopy. The resulting materials are active organophotoredox catalysts in the reductive dimerization of aromatic aldehydes, benzophenones, and imines under mild reaction conditions. Moreover, MOF‐520‐PC2 can be applied for synthesizing gram‐scale quantities of products in continuous‐flow conditions under steady‐state light irradiation. This work provides an alternative approach for the construction of well‐defined, metal‐free, MOF‐based catalysts.
We thank the ICIQ Foundation, the European Research Foundation for project ERC‐2014‐CoG 648304 (J.L.‐F.), MINECO (CTQ2016‐80038‐R; J.L.‐F.), and AGAUR 2017‐SGR‐1647 (J.L.‐F.) for funding. S.S.M. and N.K. are grateful to Marie‐Curie COFUND and JyC for postdoctoral scholarships, respectively.