Iridium‐EDTA as an Efficient and Readily Available Catalyst for Water Oxidation

Savini, Arianna; Bellachioma, Gianfranco; Bolaño, Sandra; Rocchigiani, Luca; Zuccaccia, Cristiano; Zuccaccia, Daniele; Macchioni, Alceo

doi:10.1002/cssc.201200067

Cited by 47 publications

(52 citation statements)

References 86 publications

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“…Citing just a small portion of the broad interest in molecular water oxidation: ruthenium dimers [9][10][11][12] and tetramers, [13][14][15] cobalt tetramers, 16,17 manganese dimers 18 along with recent work detailing single-site catalysts [19][20][21][22][23][24][25][26] all illustrate the diversity of successful catalysts. More recently, a variety of Cp*Ir complexes (Cp* = C 5 Me 5 -) have been shown to act as efficient water oxidation precatalysts.…”

Section: Introductionmentioning

confidence: 99%

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

Woods

Lalrempuia

Petronilho

et al. 2014

Energy Environ. Sci.

107

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Iridium complexes of Cp* and mesoionic carbene ligands were synthesized and evaluated as potential water oxidation catalysts using cerium ammonium nitrate as a chemical oxidant. Performance was evaluated by turnover frequency at 50% conversion and by absolute turnover number, and the most promising precatalysts were subjected to further study. Molecular turnover frequencies varied from 190 to 451 per hour with a maximum turnover number of 38,000. While the rate of oxygen evolution depends linearly on iridium concentration, 10 concurrent spectroscopic and manometric monitoring of stoichiometric additions of oxidant suggests oxygen evolution occurs as two sequential first order reactions. Under the conditions herein, the oxygen evolving species appears to be well defined and molecular based on the kinetic effects of careful ligand design, reproducibility, and the absence of persistent dynamic light scattering signals. Outside of these conditions, the complex mechanism is highly dependent on reaction conditions. While confident characterization of the catalytically active species is difficult, especially under high-turnover conditions, this work indicates IrOx is not essential for the 15 formation of catalytically active water oxidation species.

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Section: Introductionmentioning

confidence: 99%

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

Woods

Lalrempuia

Petronilho

et al. 2014

Energy Environ. Sci.

107

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“…5 Over the last few years, iridium complexes have emerged as very powerful catalysts for this water oxidation process. [6][7][8][9][10][11][12][13][14][15][16][17][18] Depending on the ligand design, very high turnover numbers have been achieved. 19 Moreover, kinetic and mechanistic studies have provide increasingly compelling evidence that some complexes are precursors for homogeneous rather than heterogeneous [20][21][22] water oxidation catalysts and that the oxidation therefore occurs at an iridium center that is in a well-defined environment.…”

Section: Introductionmentioning

confidence: 99%

Ligand Exchange and Redox Processes in Iridium Triazolylidene Complexes Relevant to Catalytic Water Oxidation

2014

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Iridium(III) complexes containing a bidentate spectator ligand have emerged as powerful catalyst precursors for water oxidation. Here we investigate the initial steps of transformation at the iridium center when using complex [IrCp*(pyr-trz)Cl] 1 (Cp* = pentamethylcyclopentadienyl, pyr-trz = 4-(2-pyridyl-)1,2,3-triazol-5-ylidene), a potent water oxidation catalyst precursor. Ligand exchange with water is facile and is reversed in the presence of chloride solutions, while MeCN substitution is only effective from the corresponding aqua complex. A pK a = 8.3 of the aqua complex was determined, which is in agreement with strong electron donation from the triazolylidene ligand that is comparable to aryl anions. Evaluation of the pH-dependent oxidation process in aqueous media reveals two regimes, between pH 4-8.5 and above 10.5, where proton-coupled electron transfer processes are occurring. These investigations will help to further optimize water oxidation catalysts and indicate that MeCN as a co-solvent has adverse effects for initiating water coordination in the oxidation process.3

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“…As a matter of fact, properly modulating the ancillary ligands coordinated at the iridium center, catalysts with very high TOF (≈ 5 s -1 , 4-6) 20 and remarkable TON (> 12000, 7) 21 were developed. In the case of catalysts bearing the Cp*Ir moiety, a transformation pathway leading to the gradual O-functionalization of Cp*, under strongly oxidative conditions, was delineated, by intercepting and characterizing several reaction intermediates.…”

Section: Discussionmentioning

confidence: 99%

“…Since the combination of nitrogen and carboxylate ligands afforded such remarkable results, we thought that the classical edta ligand could be successfully applied as supporting ligand for developing efficient iridium water oxidation catalysts 21 To our surprise, only a few papers in the literature deal with iridium edta complexes 22 and, interestingly, [IrCl(Hedta)]Na (7) seems to be the most stable species in which Hedta acts as a pentadentate ligand with the chloride coordinated in trans position with respect to the nitrogen atom having both acetate groups coordinated at iridium (Scheme 2). Furthermore, the presence of a pendant carboxylic acid moiety makes it particularly suitable to be heterogenized on solid supports (see below).…”

Section: New Iridium Water Oxidation Catalystsmentioning

confidence: 99%

Homogeneous and heterogenized iridium water oxidation catalysts

Macchioni

2014

SPIE Proceedings

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The development of an efficient catalyst for the oxidative splitting of water into molecular oxygen, protons and electrons is of key importance for producing solar fuels through artificial photosynthesis. We are facing the problem by means of a rational approach aimed at understanding how catalytic performance may be optimized by the knowledge of the reaction mechanism of water oxidation and the fate of the catalytic site under the inevitably harsh oxidative conditions. For the purposes of our study we selected iridium water oxidation catalysts, exhibiting remarkable performance (TOF > 5 s -1 and TON > 20000). In particular, we recently focused our attention on [Cp*Ir(N,O)X] (N,O = 2-pyridincarboxylate; X = Cl or NO 3 ) and [IrCl(Hedta)]Na water oxidation catalysts. The former exhibited a remarkable TOF whereas the latter showed a very high TON. Furthermore, [IrCl(Hedta)]Na was heterogenized onto TiO 2 taking advantage of the presence of a dandling -COOH functionality. The heterogenized catalyst maintained approximately the same catalytic activity of the homogeneous analogous with the advantage that could be reused many times. Mechanistic studies were performed in order to shed some light on the rate-determining step and the transformation of catalysts when exposed to "oxidative stress". It was found that the last oxidative step, preceding oxygen liberation, is the rate-determining step when a small excess of sacrificial oxidant is used. In addition, several intermediates of the oxidative transformation of the catalyst were intercepted and characterized by NMR, X-Ray diffractometry and ESI-MS.

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Iridium‐EDTA as an Efficient and Readily Available Catalyst for Water Oxidation

Cited by 47 publications

References 86 publications

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

Ligand Exchange and Redox Processes in Iridium Triazolylidene Complexes Relevant to Catalytic Water Oxidation

Homogeneous and heterogenized iridium water oxidation catalysts

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