Electrocatalytic reduction of CO to CO is reported for the complex, {fac-Mn([(MeO)Ph]bpy)(CO)(CHCN)}(OTf), containing four pendant methoxy groups, where [(MeO)Ph]bpy = 6,6'-bis(2,6-dimethoxyphenyl)-2,2'-bipyridine. In addition to a steric influence similar to that previously established [Sampson, M. D. et al. J. Am. Chem. Soc. 2014, 136, 5460-5471] for the 6,6'-dimesityl-2,2'-bipyridine ligand in [fac-Mn(mesbpy)(CO)(CHCN)](OTf), which prevents Mn-Mn dimerization, the [(MeO)Ph]bpy ligand introduces an additional electronic influence combined with a weak allosteric hydrogen-bonding interaction that significantly lowers the activation barrier for C-OH bond cleavage from the metallocarboxylic acid intermediate. This provides access to the thus far elusive protonation-first pathway, minimizing the required overpotential for electrocatalytic CO to CO conversion by Mn(I) polypyridyl catalysts, while concurrently maintaining a respectable turnover frequency. Comprehensive electrochemical and computational studies here confirm the positive influence of the [(MeO)Ph]bpy ligand framework on electrocatalytic CO reduction and its dependence upon the concentration and pK of the external Brønsted acid proton source (water, methanol, trifluoroethanol, and phenol) that is required for this class of manganese catalyst. Linear sweep voltammetry studies show that both phenol and trifluoroethanol as proton sources exhibit the largest protonation-first catalytic currents in combination with {fac-Mn([(MeO)Ph]bpy)(CO)(CHCN)}(OTf), saving up to 0.55 V in overpotential with respect to the thermodynamically demanding reduction-first pathway, while bulk electrolysis studies confirm a high product selectivity for CO formation. To gain further insight into catalyst activation, time-resolved infrared (TRIR) spectroscopy combined with pulse-radiolysis (PR-TRIR), infrared spectroelectrochemistry, and density functional theory calculations were used to establish the v(CO) stretching frequencies and energetics of key redox intermediates relevant to catalyst activation.

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A fast and reliable analytical method is reported for the quantitative determination of dissolved elemental sulfur in non-aqueous electrolytes for Li-S batteries. By using high performance liquid chromatography with a UV detector, the solubility of S in 12 different pure solvents and in 22 different electrolytes was determined. It was found that the solubility of elemental sulfur is dependent on the Lewis basicity, the polarity of solvents and the salt concentration in the electrolytes. In addition, the S content in the electrolyte recovered from a discharged Li-S battery was successfully determined by the proposed HPLC/UV method. Thus, the feasibility of the method to the online analysis for a Li-S battery is demonstrated. Interestingly, the S was found super-saturated in the electrolyte recovered from a discharged Li-S cell.

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The subject of this study [fac-Mn(bqn)(CO)3(CH3CN)]+ (bqn = 2,2′-biquinoline), is of particular interest because the bqn ligand exhibits both steric and electronic influence over the fundamental redox properties of the complex and, consequently, its related catalytic properties with respect to the activation of CO2. While not a particularly efficient catalyst for CO2 to CO conversion, in-situ generation and activity measurements of the [fac-Mn(bqn)(CO)3]− active catalyst allows for a better understanding of ligand design at the Mn center. By making direct comparisons to the related 2,2′-bipyridyl (bpy), 1,10-phenanthroline (phen), and 2,9-dimethyl-1,10-phenanthroline (dmphen) ligands via a combination of voltammetry, infrared spectroelectrochemistry, controlled potential electrolysis and computational analysis, the role of steric vs. electronic influences on the nucleophilicity of Mn-based CO2 reduction electrocatalysts is discussed.

Electrocatalytic CO2 reduction is demonstrated for the Mn and Re tricarbonyl complexes, [M­(Me2OQN)­(CO)3(CH3CN)] (M = Mn or Re) containing the 5,7-dimethyl-8-oxyquinolate (Me2OQN–) ligand. In comparison to the related 2,2′-bipyridyl (bpy) reference complexes, [M­(bpy)­(CO)3(CH3CN)]+ (M = Mn or Re), the Me2OQN–-based precatalysts exhibit an onset of catalytic current with the input of one less equivalent of electrons. This behavior is attributed to the formal Me2OQN(•/−) redox couple which contributes toward each catalytic cycle in tandem with the formal Mn(I/0) and Re(I/0) redox couples. In addition to computational support for synergistic metal–ligand redox cooperativity, electrochemistry (cyclic voltammetry and controlled potential electrolysis), spectroelectrochemistry (FTIR and EPR), and pulse radiolysis coupled with time-resolved infrared spectroscopy (PR-TRIR) provide structural insight into the electronic properties of the one-electron- and two-electron-reduced species..

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Super o xide reacts with carbonate solvents in Li-air batteries. Tris(pentafluorophenyl)borane is found to catalyse a more rapid superoxide (O 2-) disproportionation reaction than the reaction between superoxide and propylene carbonate (PC). With this catalysis, the negative impact of the reaction between the electrolyte and O 2 produced by the O 2 reduction can be minimized. A simple kinetic study using ESR spectroscopy was reported to determine reaction orders and rate constants for the reaction between PC and superoxide, and the disproportionation of superoxide catalyzed by Tris(pentafluorophenyl)borane and Li ions. The reactions are found to be first order and the rate constants are 0.033 s-1 M-1 , 0.020 s-1 M-1 and 0.67 s-1 M-1 for reactions with PC, Li ion and Tris(pentafluorophenyl)borane, respectively.