title: Mechanism of Water Oxidation Catalyzed by a Mononuclear Manganese Complex.
abstract: The design and synthesis of biomimetic Mn complexes to catalyze oxygen evolution is a very appealing goal because water oxidation in nature employs a Mn complex. Recently, the mononuclear Mn complex [LMnII(H2O)2]2+[1, L=Py2N(tBu)2, Py=pyridyl] was reported to catalyze water oxidation electrochemically at an applied potential of 1.23 V at pH 12.2 in aqueous solution. Density functional calculations were performed to elucidate the mechanism of water oxidation promoted by this catalyst. The calculations showed that 1 can lose two protons and one electron readily to produce [LMnIII(OH)2]+(2), which then undergoes two sequential proton-coupled electron-transfer processes to afford [LMnVOO]+(4). The O-O bond formation can occur through direct coupling of the two oxido ligands or through nucleophilic attack of water. These two mechanisms have similar barriers of approximately 17 kcal mol-1. The further oxidation of 4 to generate [LMnVIOO]2+(5), which enables O-O bond formation, has a much higher barrier. In addition, ligand degradation by C-H activation has a similar barrier to that for the O-O bond formation, and this explains the relatively low turnover number of this catalyst.
authors.affiliation: Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Bioinorganic Chemistry and Materia Medica, Hubei Key Laboratory of Materials Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, 430074, P. R. China.
authors.forename: Ying-Ying
authors.initials: YY
authors.lastname: Li
authors.affiliation: Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Bioinorganic Chemistry and Materia Medica, Hubei Key Laboratory of Materials Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, 430074, P. R. China.
authors.forename: Ke
authors.initials: K
authors.lastname: Ye
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691, Stockholm, Sweden.
authors.forename: Per E M
authors.initials: PE
authors.lastname: Siegbahn
authors.affiliation: Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Bioinorganic Chemistry and Materia Medica, Hubei Key Laboratory of Materials Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, 430074, P. R. China.
authors.forename: Rong-Zhen
authors.identifier: 0000-0002-8989-6928
authors.initials: RZ
authors.lastname: Liao
mesh_terms: D002384:Catalysis; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D014867:Water / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D014867:Water; D008345:Manganese
keywords: density functional theory; manganese; oxidation; reaction mechanism; water splitting