Electrochemical Carbon Dioxide Reduction Catalyzed by a Dinuclear Ruthenium Complex with a Flexible Bridging Ligand

Abstract

A dinuclear Ru complex, [{Ru(tpy)Cl} 2 (¯-L)](PF 6 ) 2 (1), was synthesized by the reaction of the flexible bridging ligand L (= N,N¤-bis(5-bipyridylhexyl)-cis-1,4-cyclohexanediamine) with [Ru(tpy)Cl 3 ]. The complex contained two [Ru(tpy)(bpy)Cl] + moieties linked by L, and the reaction of 1 with AgNO 3 allowed for isolation of the ligand-exchanged product [{Ru(tpy)-(Solv.)} 2 (¯-L)](PF 6 ) 4 (2). The behavior of 2 as a CO 2 reduction electrocatalyst was investigated in acetonitrile. Under N 2 , two reduction peaks appeared at E p,c = ¹1.08 (tpy/tpy•¹ ) and ¹1.40 V (bpy/bpy•¹ ) vs. NHE. In a saturated CO 2 solution, a further reduction peak, at E p,c = ¹1.60 V, showed significant current enhancement consistent with electrocatalytic CO 2 reduction. The primary product of the CO 2 reduction was CO, and the turnover frequency was calculated to be ca. 1.4 s ¹1 .It is widely accepted that the increasing levels of CO 2 in the atmosphere are adversely affecting the global climate and that new technologies for the fixation and conversion of CO 2 are important goals in mitigating global warming. The electrochemical and photoelectrochemical reduction of CO 2 to provide C1 sources for chemical feedstock and fuels is a key target. CO 2 can be converted, by multielectron paths, to carbon monoxide (2e ¹ ), formate (2e, and methane (8e ¹ ), and the reduction can proceed via a protonassisted multiple-electron-transfer pathway. 15A variety of transition-metal complexes have been shown to be active catalyst precursors for the reduction of CO 2 , but typically at relatively negative potentials or at low reaction rates.612 One of the reasons for this is the stability of the CO 2 molecule, which ensures that a substantial activation energy barrier must be overcome to generate the anion radical. 15 As a result, the technologically and energetically viable electrochemical conversion of CO 2 to useful materials remains a challenging task.OH, CO, CHO, CH 2 OH, CH 3 , and C(O)CH 3 ; n = 0, 1, and 2) (bpy: 2,2¤-bipyridine), 13 illustrating the manner in which Ru centers could interact with CO 2 molecules. Going further, Meyer et al. reported the electrocatalytic reduction of CO 2 to CO using [Ru(tpy)(bpy)(Solv.)] 2+ (tpy: 2,2¤;6¤,2¤¤-terpyridine, Solv.: solvent), with the Ru center mediating the electron transfer from the tpy•¹ and bpy •¹ anion radicals to CO 2 at potentials below ¹1.5 V vs. NHE. 14 Coordination programming is an approach by which molecular design allows for the functionality of molecular species to be tuned though modulation of their coordinative or supramolecular interactions. 15 We hypothesized that dimerization of [Ru(tpy)(bpy)(Solv.)] 2+ units may lead to cooperative catalytic behavior such as multielectron processes, increasing the CO 2 reduction activity of the complex in comparison to the mononuclear species. To that end, we synthesized a dinuclear Ru complexes 1 and 2 and investigated their behavior as CO 2 reduction electrocatalysts (Figure 1).A novel flexible bridging ligand N,N¤-bis(5-bipyridylhexyl)-cis-1,4-...

Electronic Communication and Photoinduced Intramolecular Electron Transfer in Hybrid Ru(II)-Re(I) Complexes Using Eigenstate-Based and Diabatic-State-Based Models

“…1,2 The mixed-valence binuclear (or hybrid) complex has been widely used to speed up CO 2 reduction. [3][4][5] The previous study by Kuramochi et al reported that an electrochemical ruthenium (Ru) catalyst to yield the CO as well as rhenium (Re) complex also has been extensively used. 4 Suntharalingam et al studied the homogeneous metal complex and investigated mono-and bimetallic terpyridine complexes in DNA binding.…”

Electronics Communication and Photoinduced Intramolecular Electron Transfer in Hybrid Ru(II)-Re(I) Complexes Using Eigenstate-Based and Diabatic-State-Based Models

“…[3][4][5] The previous study by Kuramochi et al reported that an electrochemical ruthenium (Ru) catalyst to yield the CO as well as rhenium (Re) complex also has been extensively used. 4 Suntharalingam et al studied the homogeneous metal complex and investigated mono-and bimetallic terpyridine complexes in DNA binding. 6 They found that using two transition metals is better than one metal because of its strong corresponding to the photoexcitation properties.…”