Mechanistic analysis of water oxidation catalyzed by mononuclear copper in aqueous bicarbonate solutions

Abstract

We characterize a mechanism for a monomeric copper catalyst reported to oxidize water in bicarbonate solution when subject to sufficiently high external potentials at near neutral pH values.

Electrocatalytic Water Oxidation by a Dinuclear Copper Complex in a Neutral Aqueous Solution

“…On the basis of these calculations,t he first scenario (3!Int1!Int2,a s shown in Figures 5a nd 6) is proposed to be the most likely pathway for OÀObond formation enabled by the present catalyst, in which the cooperation of two Cu centers plays av ital role.I mportantly,t his dinuclear Cu II catalyst avoids the access of the high-oxidation state,C u IV = O. Theb est pathway for Cu IV =Oi sanucleophilic water attack on the oxo group,a si nt he case of Cu II polypeptide catalyst reported by Meyer et al, [3b] but this pathway is not preferred in the present case.T his is also different from the very recent proposal of water-oxidation catalyzed by mononuclear Cu bicarbonate complex, in which O À Ob ond formation takes place by coupling of Cu IV -OH and carbonate. [15] We further investigated the O 2 release from Int2 using DFT calculations ( Figure S26-S31). [16] Three possibilities have been considered.…”

Structural, electronic and acid/base properties of [Ru(bpy)(bpy(OH)2)2]2+ (bpy=2,2′-bipyridine, bpy(OH)2=4,4′-dihydroxy-2,2′-bipyridine)

“…As the number of bpy(OH) 2 ligands increases the destabilization of the HOMO increases, resulting in proportional decreases in Ru III/II potential. Abiding by the trend, each bpy(OH) 2 ligand provides a more favorable oxidation potential by $0.13-0.15 V. The reductive scan of [Ru(bpy) (bpy(OH) 2 ) 2 ] 2+ is dwarfed by proton reduction, arising from the addition of HPF 6 to the solution (Supporting materials). Since the addition of HPF 6 is necessary for solubility of the complex, no ligand redox potentials can be reported for protonated 2À in acetonitrile with n Bu 4 NOH gives a reversible Ru III/II wave at 0.05 V versus SCE, which is shifted 0.96 V lower than the protonated form of the complex, Fig.…”

“…The complex was then dissolved in approximately 40 mL 0.1 M HCl then precipitated out with NH 4 PF 6 , which was collected and rinsed with water followed by Table 9 Luminescence data of complexes in a 1:1 water:acetonitrile mixture (n = +2, 0, À2, or À4). 6 À anions. One PF 6 À anion was rotationally disordered and modeled over two positions with the aid of similarity restraints on 1,2-and 1,3-distances as well as restraints/constraints on the anisotropic displacement parameters of nearby atoms.…”

“…UV-Vis spectra of [Ru(bpy)(bpy(OH) 2 ) 2 ] 2+ and [Ru(bpy)(bpy (OMe) 2 ) 2 ] 2+ were collected in acetonitrile and a 1:1 water:acetonitrile mixture with either 10 mM NaOH or 10 mM HPF 6 . No significant shift was observed in the spectrum of [Ru(bpy)(bpy (OMe) 2 ) 2 ] 2+ with the addition of acid or base, (Supporting materials).…”

“…Mechanistic studies of such catalysts have revealed the complexity involving many proton-coupled electron transfer (PCET) events [4][5][6][7][8][9][10][11]. In single site mononuclear ruthenium catalysts, such as [Ru(tpy)(bpm)(OH 2 )] 2+ (tpy = 2,2 0 ;6 0 ,2 00 -terpyridine, bpm = 2,2 0 -bipyrimidine) [12][13][14][15][16], oxidation of the Ru II metal center to a more Lewis acidic Ru III metal center substantially increases the acidity of the coordinated water molecule, resulting in the loss of a proton.…”