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

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 the 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. The 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 in the node, the MOF node
architecture plays a crucial role in driving the catalytic activities
of V-MOFs.