A comprehensive mechanistic study of N2 activation and splitting into terminal nitride ligands upon reduction of the rhenium dichloride complex [ReCl2(PNP)] is presented (PNP– = N(CH2CH2PtBu2)2–). Low-temperature studies using chemical reductants enabled full characterization of the N2-bridged intermediate [{(PNP)ClRe}2(N2)] and kinetic analysis of the N–N bond scission process. Controlled potential electrolysis at room temperature also resulted in formation of the nitride product [Re(N)Cl(PNP)]. This first example of molecular electrochemical N2 splitting into nitride complexes enabled the use of cyclic voltammetry (CV) methods to establish the mechanism of reductive N2 activation to form the N2-bridged intermediate. CV data was acquired under Ar and N2, and with varying chloride concentration, rhenium concentration, and N2 pressure. A series of kinetic models was vetted against the CV data using digital simulations, leading to the assignment of an ECCEC mechanism (where “E” is an electrochemical step and “C” is a chemical step) for N2 activation that proceeds via initial reduction to ReII, N2 binding, chloride dissociation, and further reduction to ReI before formation of the N2-bridged, dinuclear intermediate by comproportionation with the ReIII precursor. Experimental kinetic data for all individual steps could be obtained. The mechanism is supported by density functional theory computations, which provide further insight into the electronic structure requirements for N2 splitting in the tetragonal frameworks enforced by rigid pincer ligands.

Herein, we present a detailed kinetic and thermodynamic analysis of the anodic allylic esterification of alkenes as well as the bulk application of the anodic amination and esterification of nonactivated alkenes catalyzed by diselenides. The electrochemical study led to a comprehensive picture of the coupled electrochemical and chemical reaction steps. Cyclic voltammetry measurements are consistent with a bimolecular step after initial electrochemical 1e − oxidation of the diphenyl diselenide catalyst, 1a, and therefore we postulate a dimerization of the cation, which reacts very rapidly with the alkene, forming the addition product, i.e. the selenolactone 2a. Subsequent electrochemical oxidation of 2a occurs at a slightly higher potential than initial oxidation of 1a. The second oxidation is also followed by a bimolecular process and we hypothesize a dimerization of the cation, which finally eliminates 1a and protons in the rate-determining step, forming the product. Electrochemical analysis of various catalysts, i.e. nonsterically demanding diaryl diselenides with electron withdrawing and donating substituents, revealed that the oxidation potential of the catalyst and the intermediate can be readily tuned by the substituents, thus, prospectively allowing for a wide application of olefinic and nucleophilic substrates. The substituent pattern at the alkene has a smaller influence on the redox potential of the adduct. Controlled potential electrolysis experiments employing different nucleophiles proved that the reaction can be run electrochemically. The functionalization of unactivated alkenes with N-and O-nucleophiles was successfully demonstrated in several bulk electrolysis experiments, and the products were isolated in good yields.

A Co(III) complex with a mesoionic pyridylcarbene ligand is presented. This complex is an efficient electrocatalyst for H2 production at very low overpotential and high turnovers when using a (glassy carbon) GC electrode. The corresponding triazole complexes display no catalytic activity whatsoever under identical conditions. The remarkable robustness of the Co-C(carbene) bond towards acids is likely responsible for the high efficiency of this catalyst. The present results thus open new avenues for carbene-based ligands for generating functional models for hydrogenases.

The development of new solar-to-fuel scenarios is of great importance, but the construction of molecular systems that convert sunlight into chemical energy represents a challenge. One specific issue is that the molecular systems have to be able to accumulate redox equivalents to mediate the photodriven transformation of relevant small molecules, which mostly involves the orchestrated transfer of multiple electrons and protons. Disulfide/ dithiol interconversions are prominent 2e − /2H + couples and can play an important role for redox control and charge storage. With this background in mind, a new photosensitizer [Ru( S−S bpy)-(bpy) 2 ] 2+ (1 2+ ) equipped with a disulfide functionalized bpy ligand ( S−S bpy, bpy = 2,2′-bipyridine) was synthesized and has been comprehensively studied, including structural characterization by X-ray diffraction. In-depth electrochemical studies show that the S−S bpy ligand in 1 2+ can be reduced twice at moderate potentials (around −1.1 V vs Fc +/0 ), and simulation of the cyclic voltammetry (CV) traces revealed potential inversion (E 2 > E 1 ) and allowed to derive kinetic parameters for the sequential electron-transfer processes. However, reduction at room temperature also triggers the ejection of one sulfur atom from 1 2+ , leading to the formation of [Ru( S bpy)(bpy) 2 ] 2+ (2 2+ ). This chemical reaction can be suppressed by decreasing the temperature from 298 to 248 K. Compared to the archetypical photosensitizer [Ru(bpy) 3 ] 2+ , 1 2+ features an additional low energy optical excitation in the MLCT region, originating from charge transfer from the metal center to the S−S bpy ligand (aka MSCT) according to time-dependent density functional theory (TD-DFT) calculations. Analysis of the excited states of 1 2+ on the basis of ground-state Wigner sampling and using charge-transfer descriptors has shown that bpy modification with a peripheral disulfide moiety leads to an energy splitting between charge-transfer excitations to the S−S bpy and the bpy ligands, offering the possibility of selective charge transfer from the metal to either type of ligands. Compound 1 2+ is photostable and shows an emission from a 3 MLCT state in deoxygenated acetonitrile with a lifetime of 109 ns. This work demonstrates a rationally designed system that enables future studies of photoinduced multielectron, multiproton PCET chemistry.