Reusable
Oxidation Catalysis Using Metal-Monocatecholato
Species in a Robust Metal–Organic Framework
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Abstract
An
isolated metal-monocatecholato moiety has been achieved in a
highly robust metal–organic framework (MOF) by two fundamentally
different postsynthetic strategies: postsynthetic deprotection (PSD)
and postsynthetic exchange (PSE). Compared with PSD, PSE proved to
be a more facile and efficient functionalization approach to access
MOFs that could not be directly synthesized under solvothermal conditions.
Metalation of the catechol functionality residing in the MOFs resulted
in unprecedented Fe-monocatecholato and Cr-monocatecholato species,
which were characterized by X-ray absorption spectroscopy, X-band
electron paramagnetic resonance spectroscopy, and <sup>57</sup>Fe
Mössbauer spectroscopy. The resulting materials are among the
first examples of Zr(IV)-based UiO MOFs (UiO = University of Oslo)
with coordinatively unsaturated active metal centers. Importantly,
the Cr-metalated MOFs are active and efficient catalysts for the oxidation
of alcohols to ketones using a wide range of substrates. Catalysis
could be achieved with very low metal loadings (0.5–1 mol %).
Unlike zeolite-supported, Cr-exchange oxidation catalysts, the MOF-based
catalysts reported here are completely recyclable and reusable, which
may make them attractive catalysts for ‘green’ chemistry
processes