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...

A series of five ruthenium (II) complexes containing a tridentate CNC pincer ligand, a bidentate 2,2′-bipyridine (bpy) ligand, and a monodentate ligand (chloride, bromide, or acetonitrile) were synthesized. The CNC pincer ligands used imidazole or benzimidazole-derived N-heterocyclic carbenes (NHCs) as the C donors and a 4-methoxy-substituted central pyridyl ring as the N donor. All of the complexes were characterized by analytical, spectroscopic, and single-crystal X-ray diffraction methods. These complexes were used as catalysts for visible-light-driven CO2 reduction in the presence and absence of an external photosensitizer (PS). Notably, complex 4C with a benzimidazole-derived CNC pincer ligand and bromide as the monodentate ligand was the most active catalyst tested for both sensitized and self-sensitized CO2 reduction. Thus, this catalyst was the subject of further mechanistic studies using transient absorption spectroscopy (TAS), absorption spectroelectrochemistry (SEC), and computational studies. A mechanism has been proposed for self-sensitized CO2 reduction involving (1) light excitation of the catalyst, (2) reduction by sacrificial donors, (3) halide loss, and (4) CO2 binding to form [RuCO 2 ] + as the catalyst resting state. The timeline for these steps and the structures of key intermediates are all supported by experimental observations (including TAS and SEC) and supporting computational studies. Subsequent steps in the cycle past [RuCO 2 ] + were not experimentally observable, but they are supported by computations. Experiments were also used to explain the differences observed for sensitized catalysis. Catalyst 4C is an unusually active catalyst for both sensitized and self-sensitized CO2 reduction, and thus being able to understand how it functions and which steps are turnover-limiting is an important development facilitating the design of commercially viable catalysts for solar fuel formation.

Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C−H amination and olefin aziridination catalysis. The reactivity of the transient high‐valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of MnIII N‐haloamide complexes. The S=2 N‐haloamide complexes are characterized by 1H NMR, UV‐vis, IR, high‐frequency and ‐field EPR (HFEPR) spectroscopies, and single‐crystal X‐ray diffraction. Photolysis of these complexes results in the formal transfer of a nitrene equivalent to both C−H bonds, such as the α‐C−H bonds of tetrahydrofuran, and olefinic substrates, such as styrene, to afford aminated and aziridinated products, respectively. Low‐temperature spectroscopy and analysis of kinetic isotope effects for C−H amination indicate halogen‐dependent photoreactivity: Photolysis of N‐chloroamides proceeds via initial cleavage of the Mn−N bond to generate MnII and amidyl radical intermediates; in contrast, photolysis of N‐iodoamides proceeds via N−I cleavage to generate a MnIV nitrenoid (i.e., {MnNR}7 species). These results establish N‐haloamide ligands as viable precursors in the photosynthesis of metal nitrenes and highlight the power of ligand design to provide access to reactive intermediates in group‐transfer catalysis.

Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C−H amination and olefin aziridination catalysis. The reactivity of the transient high‐valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of MnIII N‐haloamide complexes. The S=2 N‐haloamide complexes are characterized by 1H NMR, UV‐vis, IR, high‐frequency and ‐field EPR (HFEPR) spectroscopies, and single‐crystal X‐ray diffraction. Photolysis of these complexes results in the formal transfer of a nitrene equivalent to both C−H bonds, such as the α‐C−H bonds of tetrahydrofuran, and olefinic substrates, such as styrene, to afford aminated and aziridinated products, respectively. Low‐temperature spectroscopy and analysis of kinetic isotope effects for C−H amination indicate halogen‐dependent photoreactivity: Photolysis of N‐chloroamides proceeds via initial cleavage of the Mn−N bond to generate MnII and amidyl radical intermediates; in contrast, photolysis of N‐iodoamides proceeds via N−I cleavage to generate a MnIV nitrenoid (i.e., {MnNR}7 species). These results establish N‐haloamide ligands as viable precursors in the photosynthesis of metal nitrenes and highlight the power of ligand design to provide access to reactive intermediates in group‐transfer catalysis.