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

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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).…”

mentioning

confidence: 99%

See 2 more Smart Citations

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.

134

168

View full text Add to dashboard Cite

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...

show abstract

Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

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.

134

168

View full text Add to dashboard Cite

show abstract

“…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

View full text Add to dashboard Cite

“…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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

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

Contact Info

Product

Resources

About