Installing Heterobimetallic Cobalt–Aluminum Single Sites on a Metal Organic Framework Support

A heterobimetallic
cobalt–aluminum complex was immobilized
onto the metal organic framework NU-1000 using a simple solution-based
deposition procedure. Characterization data are consistent with a
maximum loading of a single Co–Al complex per Zr6 node of NU-1000. Furthermore, the data support that the Co–Al
bimetallic complex is evenly distributed throughout the NU-1000 particle,
binds covalently to the Zr6 nodes, and occupies the NU-1000
apertures with the shortest internode distances (∼8.5 Å).
Heating the anchored Co–Al complex on NU-1000 at 300 °C
for 1 h in air completely removes the organic ligand of the complex
without affecting the structural integrity of the MOF support. We
propose that a Co–Al oxide cluster is formed in place of the
anchored complex in NU-1000 during heating. Collectively, the results
suggest that well-defined heterobimetallic complexes can be effective
precursors for installing two different metals simultaneously onto
a MOF support. The CoAl-functionalized NU-1000 samples catalyze the
oxidation of benzyl alcohol to benzaldehyde with tert-butyl hydroperoxide as a stoichiometric oxidant. Density functional
theory calculations were performed to elucidate the detailed structures
of the Co–Al active sites on the Zr6-nodes, and
a Co-mediated catalytic mechanism is proposed.