A Ru(II) Bis-terpyridine-like Complex that Catalyzes Water Oxidation: The Influence of Steric Strain

Kaveevivitchai, Nattawut; Kohler, Lars; Zong, Ruifa; Ojaimi, Maya El; Mehta, Nirja; Thummel, Randolph P.

doi:10.1021/ic4016383

Cited by 33 publications

(33 citation statements)

References 54 publications

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“…As reported earlier for other single-site, polypyridyl Ru V (O) oxidants with added buffer bases (17,20), the rate law is consistent with rate-limiting O-atom transfer from Ru V (O) to a water molecule with O-O bond formation. In this interpretation, O-O bond formation is dominated by APT with proton transfer occurring to added proton acceptor bases as illustrated for HPO 4 2− in Eq. 5 (17).…”

Section: Resultsmentioning

confidence: 98%

“…In these experiments, the pH was held constant at 7.0 while the total concentration of buffer, H 2 PO − 4 + HPO 2− 4 , was increased. The ionic strength was maintained at I = 0.5 M with added NaClO 4 . Variations in peak currents for water oxidation at E p = 1.08 V and O 2 reduction are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…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).…”

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

Song

Concepcion

Binstead

et al. 2015

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

136

168

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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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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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

Song

Concepcion

Binstead

et al. 2015

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

136

168

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“…Firstly, one of the tpy ligand in [Ru(tpy) 2 ] 2+ in the arbitrarily defined equatorial plane lacks sufficient angle strain, impeding the attack of a water molecule in this plane. Secondly, the other tpy ligand is not able to provide a nearly linear axial arrangement required by the formation of a heptacoordinate pentagonal bipyramid, thereby making the formation of the prerequisite seven-coordinate geometry impossible [76 ]. This problem can be overcome by employing the 2-(quinol-8′-yl)-1,10-phenanthroline (phenq) ligand [77] to produce the heteroleptic complex [Ru(phenq)(tpy)] 2+ .…”

Section: Chart 11mentioning

confidence: 99%

Role of ligands in catalytic water oxidation by mononuclear ruthenium complexes

Zeng

Lewis

Harwood

et al. 2015

Coordination Chemistry Reviews

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“…This process produces the oxidized Ru IV @O and Ru V @O species [8,[15][16][17][18]. However, some water oxidation catalysts have been reported which are seemingly incapable of PCET as they lack a ligand suitable for deprotonation, such as water [3,19]. For instance, [Ru(bpy)(tpy)I]I catalyst lacks an H 2 O bound to Ru but evolves more oxygen than the parent [Ru II (bpy)(tpy)H 2 O] 2+ complex [3].…”

Section: Introductionmentioning

confidence: 99%

Unexpected ligand lability in condition of water oxidation catalysis

Yan

Zong

Pushkar

2015

Journal of Catalysis

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a b s t r a c tIn the search for rational design of improved water oxidation catalysts, enhanced catalytic activities were reported for single site Ru catalysis with Ru-iodide coordination. As these complexes are not initially capable of proton coupled electron transfer (PCET) and Ru@O formation, a proposal was put forward on the generation of catalytically active 7-coordinate Ru species. We tested this hypothesis by EPR and X-ray spectroscopy and found that [Ru II (bpy)(tpy)I] + only serves as a precursor for the formation of [Ru IV (bpy)(tpy)@O] 2+ . Upon oxidation with excess of Ce IV the RuAI bond quickly dissociates with the formation of [Ru III (bpy)(tpy)H 2 O] 3+ and [Ru IV (bpy)(tpy)@O] 2+ complexes. The catalytic steady state was composed of 95% [Ru IV (bpy)(tpy)@O] 2+ species. Thus, introducing the RuAI bond into initial catalysts does not serve to improve catalyst design. This manuscript also shows how EXAFS can directly probe transition metal-halogen interaction for in situ catalysis.

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A Ru(II) Bis-terpyridine-like Complex that Catalyzes Water Oxidation: The Influence of Steric Strain

Cited by 33 publications

References 54 publications

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

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

Role of ligands in catalytic water oxidation by mononuclear ruthenium complexes

Unexpected ligand lability in condition of water oxidation catalysis

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