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In this report, we present intricate pathways for the synthesis of linear nickel­(I) silylamide K­{m}­[Ni­(NR2)2] (NR2 = −N­(SiMe3)2). This is achieved first via the reduction of nickel­(II) trisamide Li­(donor)4[Ni­(NR2)3] (Li­(thf) x [1]) with KC8 in the presence of 18-crown-6 or crypt.222. In due course, the behavior of Li­(donor)4[Ni­(NR2)3] as a source of masked two-coordinate nickel­(II) hexamethyldisilazanide is explored, leading to the formation of nickel­(I) and nickel­(II) N-donor adducts, as well as metal–metal-bonded dinickel­(I) trisamide K­(toluene)­[Ni2(NR2)3] (K­(toluene)­[5]). Finally, a convenient and reliable synthesis of K­{m}­[Ni­(NR2)2] by ligand exchange of phosphines in [Ni­(NR2)­(PPh3)2] with K­{m}­(NR2) is presented. This allows for the comprehensive analysis of its electronic properties which reveals a fluxional behavior in solution with tight anion/cation interactions.

A pair of trigonal imido iron complexes ([Fe(NMes)L2]0,−) in two oxidation states is reported. The anionic complex K{crypt.222}[Fe(NMes)L2] is best described as an iron(ii) imide.

We report on the synthesis of a variety of trigonal imido cobalt complexes [Co(NAryl)L 2 ] À , (L= N-(Dipp)SiMe 3 ), Dipp = 2,6-diisopropylphenyl) with very long CoÀN Aryl bonds of around 1.75 . Their electronic structure was interrogated using a variety of physical and spectroscopic methods such as EPR or X-Ray absorption spectroscopy which leads to their description as highly unusual imidyl cobalt complexes. Computational analyses corroborate these findings and further reveal that the high-spin state is responsible for the imidyl character. Exchange of the Dipp substituent on the imide by the smaller mesityl function (2,4,6-trimethylphenyl) effectuates the unexpected Me 3 Si shift from the ancillary ligand set to the imidyl nitrogen, revealing a highly reactive, nucleophilic character of the imidyl unit.

Among the numerous homogeneous electrochemical CO2 reduction catalysts, [Ni­(cyclam)]2+ is known as one of the most potent catalysts. Likewise, [Ni­(isocyclam)]2+ was reported to enable electrochemical CO2 conversion but has received significantly less attention. However, for both catalysts, a purposeful substitution of a single nitrogen donor group by chalcogen atoms was never reported. In this work, we report a series of isocyclam-based Ni complexes with {ON3}, {SN3}, {SeN3}, and {N4} moieties and investigated the influence of nitrogen/chalcogen substitution on electrochemical CO2 reduction. While [Ni­(isocyclam)]2+ showed the highest selectivity toward CO2 reduction within this series with a Faradaic efficiency of 86% for the generation of CO at an overpotential of −1.20 V and acts as a homogeneous catalyst, the O- and S-containing Ni complexes revealed comparable catalytic activities at ca. 0.3 V milder overpotential but tend to form deposits on the electrode, acting as precursors for a heterogeneous catalysis. Moreover, the heterogeneous species generated from the O- and S-containing complexes enable a catalytic hydride transfer to acetonitrile, resulting in the generation of acetaldehyde. The incorporation of selenium, however, resulted in loss of CO2 reduction activity, mainly leading to hydrogen generation that is also catalyzed by a heterogeneous electrodeposit.

In many metalloenzymes, sulfur‐containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S‐ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four‐nitrogen bound [Co(cyclam)]2+ (1; cyclam=1,5,8,11‐tetraaza‐cyclotetradecane) and the S‐containing analog [Co(S2N2‐cyclam)]2+ (2; S2N2‐cyclam=1,8‐dithia‐5,11‐diaza‐cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the CoII centers in 1 and 2 point to the involvement of sulfur in the O2 reduction process as the key for the improved catalytic ORR capabilities of 2.

Controlling the electronic spin state in single molecules through an external stimulus is of interest in developing devices for information technology, such as data storage and quantum computing. We report the synthesis and operation mode of two all-organic molecular spin-state switches that can be photochemically switched from a diamagnetic [electron paramagnetic resonance (EPR)-silent] to a paramagnetic (EPR-active) form at cryogenic temperatures due to a reversible electrocyclic reaction of its carbon skeleton. Facile synthetic substitution of a configurationally stable 1,14-dimethyl-[5]­helicene with radical stabilizing groups at the 4,11-positions afforded two spin-state switches as 4,11-dioxo or 4,11-bis­(dicyanomethylidenyl) derivatives in a closed diamagnetic form. After irradiation with an LED light source at cryogenic temperatures, a stable paramagnetic state is readily obtained, making this system a bistable magnetic switch that can reversibly react back to its diamagnetic form through a thermal stimulus. The switching can be monitored with UV/vis spectroscopy and EPR spectroscopy or induced by electrochemical reduction and reoxidation. Variable-temperature EPR spectroscopy of the paramagnetic species revealed an open-shell triplet ground state with an experimentally determined triplet–singlet energy gap of ΔE T–S < 0.1 kcal mol–1. The inherent chirality and the ability to separate the enantiomers turns this helical motif into a potential chiroptical spin-state switch. The herein developed 4,11-substitution pattern on the dimethyl[5]­helicene introduces a platform for designing future generations of organic molecular photomagnetic switches that might find applications in spintronics and related fields.