Hydrogenation of Carbon Dioxide to Formate by Noble Metal Catalysts Supported on a Chemically Stable Lanthanum Rod-Metal-Organic Framework

Cyclometalated with platinum-groupmetals, the La-MOF JMS-5with a bipyridyl dicarboxylate linker gave a TON of over 5000 forIr-(III) and over 4000 for Rh-(III) in the catalytic hydrogenation ofcarbon dioxide to formate without any signs of nanoparticles. Fullcharacterization was performed including XPS, TEM, PXRD, and gas sorption.Single crystal diffraction revealed an unusual rod-MOF topology. The conversion of carbon dioxide to formate is of greatimportancefor hydrogen storage as well as being a step to access an array ofolefins. Herein, we have prepared a JMS-5 metal-organic framework(MOF) using a bipyridyl dicarboxylate linker, with the molecular formula[La-2(bpdc)(3/2)(dmf)(2)(OAc)(3)]center dot dmf. The MOF was functionalized by cyclometalation using Pd-(II),Pt-(II), Ru-(II), Rh-(III), and Ir-(III) complexes. All metal catalystssupported on JMS-5 showed activity for CO2 hydrogenationto formate, with Rh-(III)@JMS-5a and Ir-(III)@JMS-5a yielding 4319 and5473 TON, respectively. X-ray photoelectron spectroscopy of the mostactive catalyst Ir-(III)@JMS-5a revealed that the iridium binding energiesshifted to lower values, consistent with formation of Ir-Hactive species during catalysis. The transmission electron microscopyimages of the recovered catalysts of Ir-(III)@JMS-5a and Rh-(III)@JMS-5adid not show any nanoparticles. This suggests that the catalytic activityobserved was due to Ir-(III) and Rh-(III). The high activity displayedby Ir-(III)@JMS-5a and Rh-(III)@JMS-5a compared to using the Ir-(III)and Rh-(III) complexes on their own is attributed to the stabilizationof the Ir-(III) and Rh-(III) on the nitrogen and carbon atom of theMOF backbone.

Automated summary

By using the La-MOF JMS-5 with a bipyridyl dicarboxylate linker and cyclometalation with platinum-group metals, catalytic hydrogenation of carbon dioxide to formate was achieved with high TON values for Ir-(III) and Rh-(III) without nanoparticle formation. The MOF showed an unusual rod topology and was fully characterized. The conversion of carbon dioxide to formate is important for hydrogen storage and accessing olefins.