Heterogenized Water Oxidation Catalysts Prepared by Immobilizing Kläui-Type Organometallic Precursors

Abstract

An efficient heterogenized water oxidation catalyst (2_TiO2) has been synthesized by immobilizing the Kläui-type organometallic precursor [Cp*Ir{P(O)(OH)2}3]Na (2, Cp*=1,2,3,4,5-pentamethylcyclopentadienyl ligand) onto rutile TiO2. Iridium is homogeneously distributed at the molecular and atomic/small cluster level in 2_TiO2and 2′_TiO2(solid catalyst recovered after the first catalytic run), respectively, as indicated by STEM-HAADF (scanning transmission electron microscopy - high angle annular dark field) studies. 2′_TiO2exhibits TOF values up to 23.7 min−1in the oxidation of water to O2driven by NaIO4at nearly neutral pH, and a TON only limited by the amount of NaIO4used, as indicated by multiple run experiments. Furthermore, while roughly 40 % leaching is observed during the first catalytic run, 2′_TiO2does not undergo any further leaching even when in contact with strongly basic solutions and completely maintains its activity for thousands of cycles. NMR studies, in combination with ICP-OES (inductively coupled plasma optical emission spectrometry), indicate that the activation of 2_TiO2occurs through the initial oxidative dissociation of PO43−, ultimately leading to active centers in which a 1:1 P/Ir ratio is present (derived from the removal of two PO43−units) likely missing the Cp* ligand.