Zr₆O₈ node-catalyzed butene hydrogenation and isomerization in the metal−organic framework NU-1000

Zirconium-based metal−organic frameworks (Zr-MOFs) have been increasingly studied over the past two decades as heterogeneous catalysts due to their synthetic tunability, well-defined nature, and chemical stability. In contrast to traditional zirconia-based heterogeneous catalysts, the community has assumed that Zr-MOFs are inert catalyst supports that do not participate directly in hydrocarbon transformations, such as olefin hydrogenation and isomerization. Here, we report that the Zr-MOF NU-1000 is capable of catalyzing olefin hydrogenation and isomerization, without any postsynthetic modifications, under a hydrogen atmosphere. We probe H₂ activation over the nodes of NU-1000 via spectroscopic and computational techniques revealing that H₂ dissociation can occur heterolytically across coordinatively unsaturated Zr sites and proximal hydroxide and μ₃-oxo ligands. These results, along with catalytic experiments, suggest that H₂ activation results in node-supported zirconium hydrides capable of the hydrogenation and isomerization of 1-butene. When examining rate dependence on the partial pressure of H₂, we observe first-order dependence for hydrogenation and half-order dependence for isomerization. Half-order H₂ rate dependence is consistent with a mechanism where both fragments of cleaved H₂ are active for 1-butene isomerization, suggesting that heterolytic cleavage generates acidic protons resulting in parallel, acid-, and hydride-catalyzed isomerization pathways. This work shows that Zr-MOFs have more diverse reactivity than the current literature may suggest and opens possibilities for ways in which Zr-MOFs can be used as heterogeneous catalysts and supports.