Iridium Complexes in Water Oxidation Catalysis

Corbucci, Ilaria; Macchioni, Alceo; Albrecht, Martin

doi:10.1002/9781119007166.ch13

Cited by 17 publications

(18 citation statements)

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“…When tested with CAN, the first catalyst reported by Bernhard exhibited a TOF = 0.2 min -1 and a TON up to 2490. [35] At the present, there are catalysts reaching TOF values higher than 300 min -1 [77,63,68,72] and TON > 400000, [16] always with CAN. Generally speaking, Ir WOCs with Cp* show higher activity than those missing Cp*.…”

Section: Activity Of Ir Wocsmentioning

confidence: 93%

“…[37,40] Successively, many other molecular Ir WOCs were reported, [41][42][43][44][45][46][47][48][49][50][51] and many excellent and exhaustive reviews recently appeared in the literature. [3,52,16] Herein, the focus is on the stability and activity of Ir WOCs, two strictly interlocked and crucial aspects.…”

Section: Molecular Ir Wocsmentioning

confidence: 99%

“…The following catalysts were selected for this study (Figure 7): 1, [35] 3, [37,53,81] 4, [37,40] 6, [39,49,82] 7, [66,83] 12, [72,77] [Cp*Ir{P(O)-(OH) 2 } 3 ]Na (13), [24] which easily liberates up to three coordination sites by the oxidative expulsion of phosphate; mer-[IrCl 3 (pic)(HOMe)]K (14), [84] bearing the pic ligand as 12, thus potentially able to generate the same active species under the assumption that Cp* completely degrades; IrCl 3 ·nH 2 O (15) [85] and [Ir(OH) 6 ] 2- (16), prepared according to the procedure reported by Mallouk and co-workers. [86][87][88][89] Generally speaking, all WOCs exhibited high efficiencies with O 2 yield always approaching 100 %.…”

Section: Activity Of Ir Wocsmentioning

confidence: 99%

“…Iridium is, perhaps, the most efficient metal to be used in WOCs as demonstrated by the remarkable performances of both bulk and nanometric IrO 2 . [16][17][18][19][20][21] The strategies to minimize the contents of iridium foresee the exploitation of molecular Ir WOCs ( Figure 1A), under the assumption that all Ir-centers are catalytically active, differently from what happens in heterogeneous IrO 2 . Otherwise, it is conceivable to anchor a well-defined molecular Ir WOC onto a suitable support, thus obtaining a heterogenized WOC [22][23][24][25][26] (Figure 1B), combining the positive aspects of homogeneous and heterogeneous catalysis.…”

Section: Introductionmentioning

confidence: 99%

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The Middle‐Earth between Homogeneous and Heterogeneous Catalysis in Water Oxidation with Iridium

Macchioni

2018

Eur J Inorg Chem

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Water oxidation (WO) is considered the ideal reaction to provide electrons and protons for the photo‐ and electrosynthesis of renewable fuels, generating exclusively O2 as a benign by‐product. Besides being demanding from the thermodynamic point of view, WO is also extremely difficult from the kinetic one. This has caused an explosion of interest for developing efficient water oxidation catalysts (WOCs). WOCs based on noble metals usually exhibit much better performance. For that reason, parallel to the search for efficient non‐noble metal WOCs, many efforts are directed toward noble‐metal atom economy in WOCs. Three strategies have been proposed to minimizing the atomic contents of noble metals: (1) exploiting molecular WOCs, under the assumption that all metal centers are catalytically active, differently from what happens in heterogeneous WOCs; (2) anchoring a well‐defined molecular WOC onto a suitable support, thus obtaining a heterogenized WOC, combining the positive aspects of homogeneous and heterogeneous catalysis; (3) diluting active metal centers in a suitable material with features that maximize the metal‐accessibility and performance. Herein, the results of our efforts aimed at pursuing all three strategies for developing efficient WOCs based on iridium are reviewed.

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Section: Activity Of Ir Wocsmentioning

confidence: 93%

Section: Molecular Ir Wocsmentioning

confidence: 99%

Section: Activity Of Ir Wocsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Middle‐Earth between Homogeneous and Heterogeneous Catalysis in Water Oxidation with Iridium

Macchioni

2018

Eur J Inorg Chem

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“…The above considerations convinced us to perform ac omparative evaluation of the performances of molecular WOCs based on iridium,w hich has attracted much attention over the last ten years [21] owing to their remarkable TOF and TON values, under exactly the same experimental conditions. It was decided to test them using NaIO 4 as sacrificial oxidantbecause, being less aggressive than cerium ammonium nitrate (CAN) [22][23][24] and not showingb yi tself any tendency to form nanoparticles (NPs), as CAN does, it avoids complications in the kinetic studies.…”

Section: Introductionmentioning

confidence: 99%

Untitled

2017

ChemSusChem

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Iridium Water Oxidation Catalysts Based on Pyridine‐Carbene Alkyl‐Substituted Ligands

et al. 2019

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Iridium complexes bearing pyridine triazolylidene ligands with variable steric hindrance, derived by the presence of an R group (R=H, Me, Et, nPr, iPr, Bu, and Oct) onto the N1‐nitrogen, have been synthesized, fully characterized and tested as water oxidation catalysts (WOCs), using chemical sacrificial oxidants (CAN and NaIO4) or in photocatalytic experiments ([Ru(bpy)3]Cl2 as phosensitizer and Na2S2O8 as an electron acceptor). The catalytic activity is barely affected by the nature of R when WO is driven by NaIO4 (1 min−1<TOF<14 min−1) or light/[Ru(bpy)3]Cl2/Na2S2O8 (TOF≈0.15 min−1); on the contrary, a remarkable effect is observed with CAN. Particularly, in the latter case, complexes with R=H and Me exhibit similar activity (10 min−1<TOF<20 min−1), whereas all other complexes (R=Et, Pr, i‐Pr, Bu, and Oct) are significantly more active and exhibit comparable TOFs in the range 40–130 min−1. Thus, a marked discontinuity in performances occurs when passing from R=Me to R=Et. This can be hardly explained solely based on the previously proposed hypothesis, suggesting that an increased R‐dimension might favor the association of iridium complexes leading to the formation of highly active multimetallic species. An additional, more specific effect has to be present. It appears plausible that the steric hindrance introduced in close proximity of the iridium center, when R≥Et, hampers transfer of the hydroperoxo or peroxo moiety from iridium active species to cerium, a process that could slow down kinetics of O2 evolution.

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Iridium Complexes in Water Oxidation Catalysis

Cited by 17 publications

References 93 publications

The Middle‐Earth between Homogeneous and Heterogeneous Catalysis in Water Oxidation with Iridium

The Middle‐Earth between Homogeneous and Heterogeneous Catalysis in Water Oxidation with Iridium

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Iridium Water Oxidation Catalysts Based on Pyridine‐Carbene Alkyl‐Substituted Ligands

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