title: Determining the Fate of a Non-Heme Iron Oxidation Catalyst Under Illumination, Oxygen, and Acid.
abstract: We analyze the stability of the non-heme water oxidation catalyst (WOC), Fe(bpmcn)Cl2toward oxygen and illumination under nonaqueous and acidic conditions. Fe(bpmcn)Cl2has been previously used as a C-H activation catalyst, a homogeneous WOC, and as a cocatalyst anchored to WO3for photoelectrochemical water oxidation. This paper reports that the ligand dissociates at pH 1 with a rate constant k = 19.8(2) × 10-3min-1, resulting in loss of catalytic activity. The combination of UV-vis experiments,1H NMR spectroscopy, and cyclic voltammetry confirm free bpmcn and Fe2+present in solution under acidic conditions. Even under nonaqueous conditions, both oxygen and illumination together show slow oxidation of iron over the course of a few hours, consistent with forming an Fe3+-O2-intermediate as corroborated by resonance-enhanced Raman spectroscopy, with a rate constant of k = 3.03(8) × 10-3min-1. This finding has implications in both the merits of non-heme iron complexes as WOCs as well as cocatalysts in photoelectrochemical schemes: the decomposition mechanisms may include both anchoring group hydrolysis and instability under illumination.
authors: Department of Chemistry, University of Michigan , 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
authors: Samuel L
authors: SL
authors: Esarey
authors: Department of Chemistry, University of Michigan , 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
authors: Joel C
authors: JC
authors: Holland
authors: Department of Chemistry, University of Michigan , 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
authors: Bart M
authors: BM
authors: Bartlett