Models for Single–Site Heterogeneous Catalysts on Carbon: MoO₂ Epoxidation Catalyst Anchored to a Fullerene

Single-site molybdenum dioxo catalysts, fullerenol/MoO₂, are prepared via grafting precursor (DME)MoO₂Cl₂ onto a highly polyhydroxylated fullerene (ful) and an isomerically-pure and well-defined fullerene (ful*). These catalyst structures are characterized by ICP-OES, XPS, XANES, EXAFS, DRIFT, Raman, and NMR spectroscopy, and DFT. Mo 3d_5/2 XPS and Mo K-edge XANES assign the oxidation state as Mo(VI). Mo EXAFS data fitting reveals two Mo=O double and two Mo–O single bonds at distances of 1.7 and 1.9 Å, respectively, while an Mo=O stretchingl mode is observed at ~950 cm^–1 by DRIFT and Raman spectroscopy. These data align well with DFT computational results, supporting the proposed catalyst structure as Fullerene(-μ-O-)₂M(=O)₂. Additionally, DFT provides insight into the energetically favorable grafting sites for an isomerically pure fullerenol. The scope of fullerenol/MoO₂ mediated alkene epoxidation includes abiotic alkenes, natural occurring terpenes, and conjugated olefins. For cyclooctene the rate law is first-order in [Mo], near first order in [olefin] and zero-order in [t-butyl hydroperoxide]. A plausible reaction mechanism involves peroxide addition first and then cyclooctene addition directly across the peroxo bond forming the epoxide product, consistent with DFT computation. Overall, fullerenol/MoO₂ shows promise as a sustainable and structurally well-defined system with versatile catalytic activity and good epoxidation recyclability.. Authors: Agarwal, Amol [Northwestern University, Evanston, IL (United States)]; Liu, Yiqi [Northwestern University, Evanston, IL (United States)]; Kraevaya, Olga A. [Russian Academy of Sciences, Chernogolovka (Russia)]; Alayoglu, Selim [Northwestern University, Evanston, IL (United States)]; Kratish, Yosi [Northwestern University, Evanston, IL (United States)]. DOE Contract: AC02-06CH11357; FG02-03ER15457; SC0001329; SC0024448. Subjects: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY