Employing Ag2Cu2O3, a mixed metal oxide, as a template catalyst material for electrochemical reduction of CO enables generation of multi-carbon products with a faradaic efficiency of close to 92%, at a current density of 600 mA cm−2.

Enantioselective desymmetrization by direct monofunctionalization of prochiral diols is a powerful strategy to prepare valuable synthetic intermediates in high optical purity. Boron acids can activate diols toward nucleophilic additions; however, the design of stable chiral catalysts remains a challenge and highlights the need to identify new chemotypes for this purpose. Herein, the discovery and optimization of a bench-stable chiral 9-hydroxy-9,10-boroxaro­phenanthrene catalyst is described and applied in the highly enantioselective desymmetrization of 2-aryl-1,3-diols using benzylic electrophiles under operationally simple, ambient conditions. Nucleophilic activation and discrimination of the enantiotopic hydroxy groups on the diol substrate occurs via a defined chairlike six-membered anionic complex with the hemiboronic heterocycle. The optimal binaphthyl-based catalyst 1g features a large aryloxytrityl group to effectively shield one of the two prochiral hydroxy groups on the diol complex, whereas a strategically placed “methyl blocker” on the boroxarophenanthrene unit mitigates the deleterious effect of a competing conformation of the complexed diol that compromised the overall efficiency of the desymmetrization process. This methodology affords monoalkylated products in enantiomeric ratios equal or over 95:5 for a wide range of 1,3-propanediols with various 2-aryl/heteroaryl groups.

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In CO 2 electroreduction it is common to use cation exchange membranes in combination with high-molar electrolytes. In a model polymer electrolyte membrane (PEM) water electrolysis setup, which mimics CO 2 electrolysis in a mixed (mode mix ) and in a separate electrolyte mode (mode sep ), this study investigates how K + -sulfonate interactions increase membrane resistance dependent on the electrolyte concentration. K + -based electrolytes (KHCO 3 , K 2 SO 4 ) are used instead of ultrapure water in the PEM-model electrolyzer. At 1.0 M KHCO 3 , the membrane resistance is increased by 1.7 Ω cm 2 (cathode side only) to 4.2 Ω cm 2 (mode mix ), causing a significant voltage increase that needs to be invested for K + transport over a PFSA membrane. We quantify the underlying ionic interactions to 527-545 mV and observed a further effect, namely a space-charge limitation expressed by a strongly increased voltage, occurring in the case of K + overload when lacking hopping centers for cation transport. Beginning at ca. 300 mA/cm 2 , the current density gets high enough to drive K + back to the cathode side and low enough to prevent large resistive contributions and K + overload. Along with thermodynamic considerations and pHinduced intrinsic operational contributions, the membrane resistance was found to have a significant impact contributing to the total cell voltage V total and proved that current research towards green and scalable CO 2 electrolysis is on a promising way towards broad application.[a] K.