Copper oxide clusters synthesized via atomic layer deposition on the nodes of the metal-organic framework (MOF) NU-1000 are active for oxidation of methane to methanol under mild reaction conditions. Analysis of chemical reactivity, in situ X-ray absorption spectroscopy, and density functional theory calculations are used to determine structure/activity relations in the Cu-NU-1000 catalytic system. The Cu-loaded MOF contained Cu-oxo clusters of a few Cu atoms. The Cu was present under ambient conditions as a mixture of ∼15% Cu and ∼85% Cu. The oxidation of methane on Cu-NU-1000 was accompanied by the reduction of 9% of the Cu in the catalyst from Cu to Cu. The products, methanol, dimethyl ether, and CO, were desorbed with the passage of 10% water/He at 135 °C, giving a carbon selectivity for methane to methanol of 45-60%. Cu oxo clusters stabilized in NU-1000 provide an active, first generation MOF-based, selective methane oxidation catalyst.

Molybdenum(VI) oxide was deposited on the Zr node of the mesoporous metal-organic framework NU-1000 via condensed-phase deposition where the MOF is simply submerged in the precursor solution, a process named solvothermal deposition in MOFs (SIM). Exposure to oxygen leads to a monodisperse, porous heterogeneous catalyst, named Mo-SIM, and its structure on the node was elucidated both computationally and spectroscopically. The catalytic activity of Mo-SIM was tested for the epoxidation of cyclohexene. Near-quantitative yields of cyclohexene oxide and the ring-opened 1,2-cyclohexanediol were observed, indicating activity significantly higher than that of molybdenum(VI) oxide powder and comparable to that of a zirconia-supported analogue (Mo-ZrO) prepared in a similar fashion. Despite the well-known leaching problem of supported molybdenum catalysts (i.e., loss of Mo species thus causes deactivation), Mo-SIM demonstrated no loss in the metal loading before and after catalysis, and no molybdenum was detected in the reaction mixture. In contrast, Mo-ZrO led to significant leaching and close to 80 wt % loss of the active species. The stability of Mo-SIM was further confirmed computationally, with density functional theory calculations indicating that the dissociation of the molybdenum(VI) species from the node of NU-1000 is endergonic, corroborating the experimental data for the Mo-SIM material.

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Zr-based metal-organic frameworks (MOFs) are promising supports for copper-based catalysts able to activate methane. Homo- and heterobimetal-functionalized NU-1000 MOF nodes were selected to computationally screen the effect of ancillary metals for C-H bond activation, allowing us to correlate activation free energies with chemical descriptors.

Evidence for key σ-complex intermediates in the hydrogenolysis of the iridium-methyl bond of (PONOP)Ir(H)(Me)(+) (1) [PONOP = 2,6-bis(di-tert-butylphosphinito)pyridine] has been obtained. The initially formed η(2)-H(2) complex, 2, was directly observed upon treatment of 1 with H(2), and evidence for reversible formation of a σ-methane complex, 5, was obtained through deuterium scrambling from η(2)-D(2) in 2-d(2) into the methyl group of 2 prior to methane loss. This sequence of reactions was modeled by density functional theory calculations. The transition state for formation of 5 from 2 showed significant shortening of the Ir-H bond for the hydrogen being transferred; no true Ir(V) trihydride intermediate could be located. Barriers to methane loss from 2 were compared to those of 1 and the six-coordinate species (PONOP)Ir(H)(Me)(CO)(+) and (PONOP)Ir(H)(Me)(Cl).