title: Mechanism of Oxidation of Ethane to Ethanol at Iron(IV)-Oxo Sites in Magnesium-Diluted Fe2(dobdc).
abstract: The catalytic properties of the metal-organic framework Fe2(dobdc), containing open Fe(II) sites, include hydroxylation of phenol by pure Fe2(dobdc) and hydroxylation of ethane by its magnesium-diluted analogue, Fe0.1Mg1.9(dobdc). In earlier work, the latter reaction was proposed to occur through a redox mechanism involving the generation of an iron(IV)-oxo species, which is an intermediate that is also observed or postulated (depending on the case) in some heme and nonheme enzymes and their model complexes. In the present work, we present a detailed mechanism by which the catalytic material, Fe0.1Mg1.9(dobdc), activates the strong C-H bonds of ethane. Kohn-Sham density functional and multireference wave function calculations have been performed to characterize the electronic structure of key species. We show that the catalytic nonheme-Fe hydroxylation of the strong C-H bond of ethane proceeds by a quintet single-state σ-attack pathway after the formation of highly reactive iron-oxo intermediate. The mechanistic pathway involves three key transition states, with the highest activation barrier for the transfer of oxygen from N2O to the Fe(II) center. The uncatalyzed reaction, where nitrous oxide directly oxidizes ethane to ethanol is found to have an activation barrier of 280 kJ/mol, in contrast to 82 kJ/mol for the slowest step in the iron(IV)-oxo catalytic mechanism. The energetics of the C-H bond activation steps of ethane and methane are also compared. Dehydrogenation and dissociation pathways that can compete with the formation of ethanol were shown to involve higher barriers than the hydroxylation pathway.
authors.affiliation: †Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, United States.|∥Nanoporous Materials Genome Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Pragya
authors.initials: P
authors.lastname: Verma
authors.affiliation: †Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, United States.|∥Nanoporous Materials Genome Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Konstantinos D
authors.initials: KD
authors.lastname: Vogiatzis
authors.affiliation: †Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, United States.|∥Nanoporous Materials Genome Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.|⊥Department of Chemistry, University of Wisconsin-Eau Claire, Eau Claire, Wisconsin 54702, United States.
authors.forename: Nora
authors.initials: N
authors.lastname: Planas
authors.affiliation: †Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, United States.|∥Nanoporous Materials Genome Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Joshua
authors.initials: J
authors.lastname: Borycz
authors.affiliation: ‡Department of Chemistry, University of California, Berkeley, California 94720, United States.|∥Nanoporous Materials Genome Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Dianne J
authors.initials: DJ
authors.lastname: Xiao
authors.affiliation: ‡Department of Chemistry, University of California, Berkeley, California 94720, United States.|§Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California 94720, United States.|∥Nanoporous Materials Genome Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Long
authors.affiliation: †Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, United States.|∥Nanoporous Materials Genome Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Laura
authors.initials: L
authors.lastname: Gagliardi
authors.affiliation: †Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, United States.|∥Nanoporous Materials Genome Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Donald G
authors.initials: DG
authors.lastname: Truhlar
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D056831:Coordination Complexes / Q000737:chemistry*; D004980:Ethane / Q000737:chemistry*; D000431:Ethanol / Q000138:chemical synthesis* / Q000737:chemistry; D058085:Iron Compounds / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D056831:Coordination Complexes; D058085:Iron Compounds; D000431:Ethanol; D008274:Magnesium; D004980:Ethane; D010100:Oxygen