title: An anionic N-donor ligand promotes manganese-catalyzed water oxidation.
abstract: Four manganese complexes of pentadentate ligands have been studied for their ability to act as oxygen evolution catalysts in the presence of Oxone or hydrogen peroxide. The complexes [Mn(PaPy3)(NO3)](ClO4) (1) (PaPy3H = N,N-bis(2-pyridylmethyl)-amine-N-ethyl-2-pyridine-2-carboxamide) and [Mn(PaPy3)(μ-O)(PaPy3)Mn](ClO4)2 (2) feature an anionic carboxamido ligand trans to the labile sixth coordination site, while [Mn(N4Py)OTf](OTf) (3) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) and [Mn(PY5)(OH2)](ClO4)2 (4) (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)-pyridine) have neutral ligands of varying flexibility. 1 and 2 are shown to evolve oxygen in the presence of either Oxone or hydrogen peroxide, but 3 evolves oxygen only in the presence of hydrogen peroxide. 4 is inactive. The activity of 1 and 2 with Oxone suggests that the presence of an anionic N-donor ligand plays a role in stabilizing putative high-valent intermediates. Anionic N-donor ligands may be viewed as alternatives to μ-oxo ligands that are prone to protonation in low-valent Mn species formed during a catalytic cycle, resulting in loss of catalyst structure.
authors.affiliation: Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Karin J
authors.initials: KJ
authors.lastname: Young
authors.forename: Michael K
authors.initials: MK
authors.lastname: Takase
authors.forename: Gary W
authors.initials: GW
authors.lastname: Brudvig
mesh_terms: D000577:Amides / Q000737:chemistry; D000838:Anions / Q000737:chemistry; D002384:Catalysis; D056831:Coordination Complexes / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry*; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry; D013464:Sulfuric Acids / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D000577:Amides; D000838:Anions; D056831:Coordination Complexes; D008024:Ligands; C431605:N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide; D011725:Pyridines; D013464:Sulfuric Acids; D014867:Water; D008345:Manganese; D006861:Hydrogen Peroxide; C048813:potassium peroxymonosulfuric acid; D010100:Oxygen