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.