A Strongly Coupled Biruthenium Complex as Catalyst for the Water Oxidation Reaction

Abstract

Dedicated to Prof. José A. Olabe on occasion of his 80th birthdayThe catalytic activity towards water oxidation of a strongly coupled bimetallic ruthenium complex, trans-[Ru(tpy)(bpy)(μ-CN)Ru(py) 4 (OH 2 )] 3 + (RuIIRuIIOH2), where tpy = 2,2':6',2''-terpyridine, bpy = 2,2'-bipyridine and py = pyridine are presented. At pH 1 the first two oxidation reactions are centred at the aquo fragment and result in the Ru II Ru III OH 2 and Ru II Ru IV O redox states as confirmed by its spectroscopy and DFT calculations. Oxidation by an additional electron is followed by an irreversible step and a catalytic wave associated with the water oxidation reaction. At pH 1 the reaction with an excess of Ce(IV) results in the generation of an stoichiometric amount of oxygen based on molar amounts of the added Ce(IV). The dominant species during the catalytic cycle is the three-electron oxidized product, Ru III Ru IV O. The reduction of the concentration of Ce(IV) monitored at 370 nm follow the rate equation, À d[Ce(IV)]/dt = k ox [Ce(IV)][Ru II Ru II OH 2 ] with a k ox = 82 � 3 M À 1 s À 1 at T = 298 K. The Ru III Ru IV O species is not stable and reacts to give Ru II Ru IV O.

Coupling between two Ru(bda) catalysts bridged by a trans-dicyano complex

“…Inspired by our previous experience in the synthesis and physicochemical properties of cyanide-bridged Ru( ii ) polypiridyl complexes, 21–24 we have prepared and characterized two cyanide-bridged triruthenium oligomers of the general formula trans -[{Ru(bda)(DMSO)(μ-CN)} 2 Ru(L) 4 ] (with L = pyridine, [RuRu(py) 4 Ru] , or 4- tert -butylpyridine, [RuRu( t bupy) 4 Ru] ) (Scheme 1). The presence of central Ru( ii ) donors in these systems results in a rich spectrum that allows us to identify their different redox states and their role in the mechanism of WO catalyzed by [RuRu(py) 4 Ru] .…”

“…However, recently the Würthner group has characterized a family of oligomeric {Ru(bda)} complexes which react through the water nucleophilic attack (WNA) mechanism. [15][16][17][18][19][20] Inspired by our previous experience in the synthesis and physicochemical properties of cyanide-bridged Ru(II) polypiridyl complexes, [21][22][23][24] we have prepared and characterized two cyanide-bridged triruthenium oligomers of the general formula trans-[{Ru(bda)(DMSO)(μ-CN)} 2 Ru(L) 4 ] (with L = pyridine,…”

Exploring the interfacial behavior of ruthenium complexes in ionic liquids: implications for supported ionic liquid phase catalysts

“…15 The unique properties of the Ru(II) polypyridine complexes, such as their strong light absorption in the visible range, longlived excited states, and good chemical stability, resulted in their application in various fields, including photochemotherapy, 16 multicomponent devices, 17 dye-sensitized solar-cells, 18,19 and catalysts for the water oxidation reaction. 20 Furthermore, Ru complexes have demonstrated success as catalysts in ILs. [21][22][23][24][25] More recently, the SILP concept has been employed to immobilize Ru complexes for the conversion of CO 2 into value-added compounds.…”