Small molecule redox mediators convey interfacial electron transfer events into bulk solution and can enable diverse substrate activation mechanisms in synthetic electrocatalysis. Here, we report that 1,2-diiodo-4,5-dimethoxybenzene is an efficient electrocatalyst for C−H/E−H coupling that operates at as low as 0.5 mol % catalyst loading. Spectroscopic, crystallographic, and computational results indicate a critical role for a three-electron I−I bonding interaction in stabilizing an iodanyl radical intermediate (i.e., formally I(II) species). As a result, the optimized catalyst operates at more than 100 mV lower potential than the related monoiodide catalyst 4iodoanisole, which results in improved product yield, higher Faradaic efficiency, and expanded substrate scope. The isolated iodanyl radical is chemically competent in C−N bond formation. These results represent the first examples of substrate functionalization at a well-defined I(II) derivative and bona f ide iodanyl radical catalysis and demonstrate one-electron pathways as a mechanistic alternative to canonical two-electron hypervalent iodine mechanisms. The observation establishes I−I redox cooperation as a new design concept for the development of metal-free redox mediators.
The reactivity of three ruthenium electrocatalysts is shown to be modulated through the addition of anions for more selective and faster electrocatalysis. Controlled potential electrolysis studies confirm the generation of CO from CO 2. The Faradaic efficiency increased for the three ruthenium catalysts studied through the introduction of Clto the reaction solution. Interestingly, a neutral ruthenium coordination complex with an associated chloride also gave equal or faster rates of catalysis upon Cl À addition. In this report, a systematic study on the effects of added halides (I À , Br À , Cl À , and F À) with varied counter cations (K + and TBA +) with and without water is examined. Computational analysis provides insights into this interesting increase in FE based on anion addition. These results show anion addition to electrocatalysis reaction mixtures add an additional parameter to increase both rate and selectivity of catalysis with one example improving from 19 % FE to 91 % FE for CO production.
Seven ruthenium catalysts with the general formula [(CNC)Ru(CH 3 CN) 2 Cl]OTf have been used to understand structure function relationships in the sensitized photocatalytic CO 2 reduction reaction. Herein, CNC is a pincer ligand containing imidazole-based N-heterocyclic carbenes (NHCs) attached to a central pyridyl ring with R groups at the 3-or 4-position. Two new complexes (R = 3-OMe, 4-NPh 2) have been fully characterized by analytical and spectroscopic methods and single-crystal X-ray diffraction. Furthermore, three previously synthesized complexes (R = 4-Me, 4-NMe 2 , and 4-OH) are used for photoca-[a
A new method to synthesize complexes of the type [(CNC)Ru II -(NN)L] n + has been introduced, where CNC is a tridentate pincer composed of two (benz)imidazole derived NHC rings and a pyridyl ring, NN is a bidentate aromatic diimine ligand, L = bromide or acetonitrile, and n = 1 or 2. Following this new method a series of six new complexes has been synthesized and characterized by spectroscopic, analytic, crystallographic, and computational methods. Their electrochemical properties have been studied via cyclic voltammetry under both N 2 and CO 2 atmospheres. Photocatalytic reduction of CO 2 to CO was performed using these complexes both in the presence (sensitized) and absence (self-sensitized) of an external photosensitizer. This study evaluates the effect of different CNC, NN, and L ligands in sensitized and self-sensitized photocatalysis. Catalysts bearing the benzimidazole derived CNC pincer show much better activity for both sensitized and self-sensitized photocatalysis as compared to catalysts bearing the imidazole derived CNC pincer. Furthermore, self-sensitized photocatalysis requires a diimine ligand for CO 2 reduction with catalyst 2 ACN being the most active catalyst in this series with TON = 85 and TOF = 22 h À 1 with an electron donating 4,4'-dimethyl-2,2'-bipyridyl (dmb) ligand and a benzimidazole derived CNC pincer.
We demonstrate that sequential disproportionation reactions can enable selective aggregation of two- or four electron-holes at a hypervalent iodine center. Disproportionation of an anodically generated iodanyl radical affords an iodosylbenzene...
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