Heterogenized water oxidation catalysts prepared by immobilizing Klaui-type organometallic precursors

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_TiO2 and 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'_TiO2 exhibits TOF values up to 23.7 min-1 in the oxidation of water to O2 driven by NaIO4 at nearly neutral pH, and a TON only limited by the amount of NaIO4 used, as indicated by multiple run experiments. Furthermore, while roughly 40¿% leaching is observed during the first catalytic run, 2'_TiO2 does 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_TiO2 occurs 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.Peer ReviewedPostprint (author's final draft

NMR investigation of non-covalent aggregation of coordination compounds ranging from dimers and ion pairs up to nano-aggregates

This review summarizes the results recently obtained by our research group investigating the non-covalent aggregation of coordination compounds in solution through NMR spectroscopy. First, systems that can undergo only weak non-covalent interactions, such as dispersive and dipole-dipole ones, are considered; successively, coordination compounds that are capable to establish more energetic non-covalent interactions, such as hydrogen bonding and/or extended π-π stacking interactions, are taken into account. The parallelism between the energy of non-covalent interactions and the level of aggregation is highlighted. The results concerning the latter are mainly obtained through diffusion NMR experiments. In some cases, information about the structure of non-covalent aggregation in solution, obtained through intermolecular NOE studies, is discussed and contrasted with that observed in the solid state (by means of X-ray single crystal investigations, mainly carried out by our group) and/or derived from theoretical calculations. © 2007 Elsevier B.V. All rights reserved

An Alternative Reaction Pathway for Iridium-Catalyzed Water Oxidation Driven by Cerium Ammonium Nitrate (CAN)

The generation of solar fuels by means of a photosynthetic apparatus strongly relies on the development of an efficient water oxidation catalyst (WOC). Cerium ammonium nitrate (CAN) is the most commonly used sacrificial oxidant to explore the potentiality of WOCs. It is usually assumed that CAN has the unique role to oxidatively energize WOCs, making them capable to offer a low-energy reaction pathway to transform H2O to O-2. Herein, we show that CAN might have a much more relevant and direct role in WO, mainly related to the capture and liberation of O-O-containing molecular moieties