Structure and Reactivity of Single-Site Vanadium Catalysts Supported on Metal-Organic Frameworks

Mandal, M.; Cramer, C. J.; Truhlar, D. G.; Sauer, J.; Gagliardi, L.
ACS Catal. 2020, 10, 10051 (doi:10.1021/acscatal.0c02300).

Single-site catalysts with active species anchored over metal-organic framework (MOF) supports have garnered significant interest in recent years. Catalysts with vanadium oxide (VOx) species immobilized over Zr-NU-1000 and Hf-MOF-808 (which have nodes containing six Zr(IV) or Hf(IV) ions, respectively) were recently characterized experimentally (Otake et al. J. Am. Chem. Soc. 2018, 140, 8652) and were reported to be active for selective oxidation of benzyl alcohol to benzaldehyde. Here we report a detailed computational investigation of these VOx incorporated MOF catalysts (V-MOF) by employing density functional theory. Based on the mode of VOx attachment, various structures are explored, and their relative stabilities and computed IR spectral features are reported. Mechanisms for the selective oxidation reaction are investigated. Analysis of electron flow in the turnover-limiting C-H activation step shows that the hydrogen-atom abstraction process involves a concerted proton-coupled electron transfer mechanism. The results of this study suggest that in addition to the identity of the metal constituting the node cluster, the MOF node architecture plays a crucial role in driving catalytic activities of V-MOFs.