New Powerful and Oxidatively Rugged Dinuclear Ru Water Oxidation Catalyst: Control of Mechanistic Pathways by Tailored Ligand Design

Neudeck, Sven; Maji, Somnath; López, Isidoro; Meyer, S.; Meyer, Franc; Llobet, Antoni

doi:10.1021/ja409974b

Cited by 135 publications

(206 citation statements)

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“…Indeed a number of Ru [10][11][12][13][14][15][16][17] and Ir 18-22 complexes have been recently described as efficient catalysts for this reaction. Furthermore the understanding of the different mechanisms involved in these catalytic processes as well as the potential deactivation pathways, has been crucial for the development of the field.…”

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confidence: 99%

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

et al. 2017

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Section: Introductionmentioning

confidence: 99%

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

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“…4 Molecular transition metal complexes constitute an excellent platform to examine these factors since significant information based on an arsenal of spectroscopic, electrochemical and analytical techniques can be used together with the valuable complementary information provided by computational studies. 5,6,7,8,9,10,11,12,13,14 The best water oxidation catalysts reported today are based on seven coordinated Ru complexes containing dianionic ligands such as [2,2'-bipyridine]-6,6'-dicarboxylato (bda 2-) 15,16,17 and [2,2':6',2''-terpyridine]-6,6''-dicarboxylato (tda 2-) (see Figure 1 for drawn structures of these ligands). Particularly impressive is the seven coordinate complex [Ru IV (tda--N 3 O)(py)2(O) eq ], 4 IV (O), (the superscript in roman numbers indicates the formal oxidation state of Ru; py is pyridine; the "eq" superscript means equatorial) that is capable of oxidizing water to dioxygen at maximum turnover frequencies (TOFMAX) of 7,700 s -1 and 50,000 s -1 at pH = 7.0 and pH = 10.0 respectively.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Bonding Rescues Overpotential in Seven-Coordinated Ru Water Oxidation Catalysts

et al. 2017

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In this work we describe the synthesis, structural characterization and redox properties of two Ru complexes containing the dianionic potentially pentadentate [2,2':6',2''-terpyridine]-6,6''-dicarboxylate (tda 2-) ligand that coordinates Ru at the equatorial plane and with additional pyridine or dmso acting as monondentate ligand in the axial positions: [Ru II (tda--N 3 O)(py)(dmso)], 1 II and [Ru III (tda--N 3 O 2 )(py)(H2O) ax ] + , 2 III (H2O) + . Complex 1 II has been characterized by single crystal XRD in the solid state and in solution by NMR spectroscopy. The redox properties of 1 II and 2 III (H2O) + have been thoroughly investigated by means of cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Complex 2 II (H2O) displays poor catalytic activity with regard to the oxidation of water to dioxygen and its properties have been analyzed based on foot of the wave analysis (FOWA) and catalytic Tafel plots. The activity of 2 II (H2O) has been compared with related water oxidation catalysts (WOCs) previously described in the literature. Despite its moderate activity, 2 II (H2O) constitutes the cornerstone that has triggered the rationalization of the different factors that govern overpotentials as well as efficiencies in molecular water oxidation catalysts (WOCs). The present work uncovers the interplay between different parameters namely, coordination number, number of anionic groups bonded to the first coordination sphere of the metal center, water oxidation catalysis overpotential, pKa and hydrogen bonding and the performance of a given WOC. It thus establishes the basic principles for the design of efficient WOCs operating at low overpotentials.

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“…etal-complex catalyzed water oxidation continues to evolve with new catalysts and new mechanistic insights (1)(2)(3)(4)(5)(6)(7)(8)(9) [Mebimpy is 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy is 2,2′-bipyridine; Fig. 1], both in solution and on surfaces, reveal mechanisms in which stepwise oxidative activation of aqua precursors to Ru V =O is followed by rate-limiting O-O bond formation (10)(11)(12)(13)(14)(15).…”

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Base-enhanced catalytic water oxidation by a carboxylate–bipyridine Ru(II) complex

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et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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In aqueous solution above pH 2.4 with 4% (vol/vol) CH 3 CN, the complex [Ru II (bda)(isoq) 2 ] (bda is 2,2′-bipyridine-6,6′-dicarboxylate; isoq is isoquinoline) exists as the open-arm chelate, [Ru II (CO 2 -bpy-CO 2 − )(isoq) 2 (NCCH 3 )], as shown by 1 H and 13 C-NMR, X-ray crystallography, and pH titrations. Rates of water oxidation with the open-arm chelate are remarkably enhanced by added proton acceptor bases, as measured by cyclic voltammetry (CV). In 1.0 M PO 4 3-, the calculated half-time for water oxidation is ∼7 μs. The key to the rate accelerations with added bases is direct involvement of the buffer base in either atom-proton transfer (APT) or concerted electron-proton transfer (EPT) pathways. [Mebimpy is 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy is 2,2′-bipyridine; Fig. 1], both in solution and on surfaces, reveal mechanisms in which stepwise oxidative activation of aqua precursors to Ru V =O is followed by rate-limiting O-O bond formation (10-15). The results of kinetic and mechanistic studies have revealed the importance of concerted atom-proton transfer (APT) in the O-O bond-forming step. In APT, the O-O bond forms in concert with H + transfer to water or to an added base (11,12,(16)(17)(18)(19). APT can promote dramatic rate enhancements. In a recent study on surface-bound [Ru(Mebimpy)(4,4′-((HO) 2 OPCH 2 ) 2 bpy)(OH 2 )] 2+ [4,4′-((HO) 2 OPCH 2 ) 2 bpy is 4,4′-bis-methlylenephosphonato-2,2′-bipyridine] stabilized by atomic layer deposition, a rate enhancement of ∼10 6 was observed with 0.012 M added PO 4 3− at pH 12 compared with oxidation at pH 1 (20).Sun and coworkers (21, 22) have described the Ru single-site water oxidation catalysts, [Ru II (bda)(L) 2 ] (H 2 bda is 2,2′-bipyridine-6,6′-dicarboxylic acid, HCO 2 -bpy-CO 2 H; L is isoquinoline, 4-picoline, or phthalazine). They undergo rapid and sustained water oxidation catalysis with added Ce IV . A mechanism has been proposed in which initial oxidation to seven coordinate Ru IV is followed by further oxidation to Ru V (O) with O-O coupling to give a peroxo-bridged intermediate, Ru IV O-ORu IV , which undergoes further oxidation and release of O 2 (21, 22). We report here the results of a rate and mechanistic study on electrochemical water oxidation by complex [1], [Ru II (CO 2 -bpy-CO 2 )(isoq) 2 ] (isoq is isoquinoline) (Fig. 1). Evidence is presented for water oxidation by a chelate open form in acidic solutions. The chelate open form displays dramatic rate enhancements with added buffer bases, and the results of a detailed mechanistic study are reported here. − /HPO 4 2− phosphate buffer, I = 0.5 M (NaClO 4 )] in 4% (vol/vol) CH 3 CN at a glassy carbon electrode (GC) (0.071 cm 2 ). The Ag/AgCl [3 M NaCl, 0.21 V vs. normal hydrogen electrode (NHE)] reference electrode was isolated with an electrolyte filled bridge to avoid chloride ion diffusion into the anode compartment. The sample was purged with argon to remove O 2 before each scan, with only O 2 freshly produced in oxidative scans detected on reverse scans at -0.3 V vs. NHE, a...

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New Powerful and Oxidatively Rugged Dinuclear Ru Water Oxidation Catalyst: Control of Mechanistic Pathways by Tailored Ligand Design

Cited by 135 publications

References 29 publications

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

Hydrogen Bonding Rescues Overpotential in Seven-Coordinated Ru Water Oxidation Catalysts

Base-enhanced catalytic water oxidation by a carboxylate–bipyridine Ru(II) complex

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