Selective Catalytic Olefin Epoxidation with Mn[superscript II]-Exchanged MOF-5

Abstract

Partial substitution of Zn[superscript II] by Mn[superscript II] in Zn₄O(terephthalate)₃(MOF-5) leads to a distorted all-oxygen ligand field supporting a single MnII site, whose structure was confirmed by Mn K-edge X-ray absorption spectroscopy. The Mn[superscript II] ion at the MOF-5 node engages in redox chemistry with a variety of oxidants. With [superscript t]BuSO₂PhIO, it produces a putative Mn[superscript IV]-oxo intermediate, which upon further reaction with adventitious hydrogen is trapped as a Mn[superscript III]–OH species. Most intriguingly, the intermediacy of the high-spin Mn[superscript IV]–oxo species is likely responsible for catalytic activity of the Mn[superscript II]-MOF-5 precatalyst, which in the presence of [superscript t]BuSO₂PhIO catalyzes oxygen atom transfer reactivity to form epoxides from cyclic alkenes with >99% selectivity. These results demonstrate that MOF secondary building units serve as competent platforms for accessing terminal high-valent metal–oxo species that consequently engage in catalytic oxygen atom transfer chemistry owing to the relatively weak ligand fields provided by the SBU. Keywords: alkene epoxidation; heterogeneous catalysis; manganese(III)−hydroxo; manganese(IV)−oxo; metal−organic framework; oxidation; tert-butylsulfonyl-2-iodosylbenzene