title: Redox-inactive metal ions promoted the catalytic reactivity of non-heme manganese complexes towards oxygen atom transfer.
abstract: Redox-inactive metal ions can modulate the reactivity of redox-active metal ions in a variety of biological and chemical oxidations. Many synthetic models have been developed to help address the elusive roles of these redox-inactive metal ions. Using a non-heme manganese(II) complex as the model, the influence of redox-inactive metal ions as a Lewis acid on its catalytic efficiency in oxygen atom transfer was investigated. In the absence of redox-inactive metal ions, the manganese(II) catalyst is very sluggish, for example, in cyclooctene epoxidation, providing only 9.9% conversion with 4.1% yield of epoxide. However, addition of 2 equiv. of Al(3+) to the manganese(II) catalyst sharply improves the epoxidation, providing up to 97.8% conversion with 91.4% yield of epoxide. EPR studies of the manganese(II) catalyst in the presence of an oxidant reveal a 16-line hyperfine structure centered at g = 2.0, clearly indicating the formation of a mixed valent di-μ-oxo-bridged diamond core, Mn(III)-(μ-O)2-Mn(IV). The presence of a Lewis acid like Al(3+) causes the dissociation of this diamond Mn(III)-(μ-O)2-Mn(IV) core to form monomeric manganese(iv) species which is responsible for improved epoxidation efficiency. This promotional effect has also been observed in other manganese complexes bearing various non-heme ligands. The findings presented here have provided a promising strategy to explore the catalytic reactivity of some di-μ-oxo-bridged complexes by adding non-redox metal ions to in situ dissociate those dimeric cores and may also provide clues to understand the mechanism of methane monooxygenase which has a similar diiron diamond core as the intermediate.
authors.affiliation: School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Key Laboratory for Large-Format Battery Materials and System, Ministry of Education, Luoyu Road 1037, Wuhan 430074, PR China. zqchen@hust.edu.cn ligxabc@163.com gyin@hust.edu.cn.
authors.forename: Cholho
authors.initials: C
authors.lastname: Choe
authors.forename: Ling
authors.initials: L
authors.lastname: Yang
authors.forename: Zhanao
authors.initials: Z
authors.lastname: Lv
authors.forename: Wanling
authors.initials: W
authors.lastname: Mo
authors.forename: Zhuqi
authors.initials: Z
authors.lastname: Chen
authors.forename: Guangxin
authors.initials: G
authors.lastname: Li
authors.forename: Guochuan
authors.initials: G
authors.lastname: Yin
mesh_terms: D000475:Alkenes / Q000737:chemistry; D000535:Aluminum / Q000737:chemistry*; D002384:Catalysis; D004852:Epoxy Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D058116:Lewis Acids / Q000737:chemistry; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*
chemical_list: D000475:Alkenes; D004852:Epoxy Compounds; D007477:Ions; D058116:Lewis Acids; D008024:Ligands; D009942:Organometallic Compounds; D008345:Manganese; D000535:Aluminum; D010100:Oxygen