Nucleophilic reactivity and electrocatalytic reduction of halogenated organic compounds by nickel o-phenylenedioxamidate complexes

Abstract

A growing number of halogenated organic compounds have been identified as hazardous pollutants. Although numerous advanced oxidative processes have been developed to degrade organohalide compounds, reductive and nucleophilic molecular approaches to dehalogenate organic compounds have rarely been reported. In this manuscript, we employ nickel(ii)-ate complexes bearing the o-phenylenebis(N-methyloxamide) (Me2opba) tetraanionic ligand as nucleophilic reagents that can react with alkyl halides (methyl up to the bulky isobutyl) by O-alkylation to give their respective imidate products. Four new nickel(ii) complexes have been characterized by X-ray crystallography, and the salient structural parameters and FT-IR vibrational bands (∼1655 cm(-1)) concur with their assignment as the imidate tautomeric form. To the best of our knowledge, this is the first report on the nucleophilic reactivity of Ni(II)(Me2opba) with halogenated organic compounds. The parent nickel(ii) Me2opba complex exhibits reversible electrochemical oxidation and reduction behavior. As a proof of concept, Ni(II)(Me2opba) and its alkylated congeners were utilized for the electrocatalytic reduction of chloroform, as a representative, simple polyhalogenated organic molecule that could arise from the oxidative treatment of organic compounds by chlorination. Modest turnover numbers of up to 6 were recorded, with dichloromethane identified as one of the possible products. Future efforts are directed towards bulkier -ate complexes that possess metal-centered instead of ligand-centered nucleophilic activity to create more effective electrocatalysts for the reduction of halogenated organic compounds.

Cold Crystallization and the Molecular Structure of Imidazolium-Based Ionic Liquid Crystals with a p-Nitroazobenzene Moiety

“…Most materials that exhibit cold crystallization have a slow rate of crystallization from the liquid to the solid phase. Previous studies have typically investigated polymeric materials, − but recent research has focused on smaller molecular materials, such as ionic liquids, , liquid crystals, − organic materials, ,− and metal complexes. ,− Most of these studies focus on the thermal behavior of these materials (e.g., macroscopic heat absorption and emission), and only a few studies have investigated the molecular structural features associated with such thermal behavior or presented guidelines for designing molecules applicable for thermal energy storage. ,,, …”

Kinetics and DFT Studies of Photoredox Carbon–Carbon Bond Cleavage Reactions by Molecular Vanadium Catalysts under Ambient Conditions

“…[19][20][21] Our team has been active in creating the constituents of artificial photosynthetic constructs, including multielectron (photo)catalysts for both reduction and oxidation processes, with exclusive use of only earth-abundant elements. [22][23][24] For instance, we have employed nickel complexes in their reduced -ate forms for the electrocatalytic reduction of CHCl 3 and also the evolution of H 2 from seawater in separate studies. To achieve an integrated artificial photosynthetic unit without sacrificial reagents, the electrons needed for the reduction processes can be derived from commensurate (photo)catalytic oxidative half reactions (Figure 1a).…”

Electrocatalytic Dechlorination of Dichloromethane in Water Using a Heterogenized Molecular Copper Complex

“…In contrast, molecular catalysts are attractive due to (1) facile property tuning from ligand modification, (2) easy selectivity and activity evaluation by incorporation of various types of metal to the catalysts, and (3) low metal content used. The catalysts for these systems typically contain ligands, such as salen, , alamin, − tetrapyrrole, − and polypyridyl family, , that are utilized in coordination complexes with metal centers such as cobalt, iron, and nickel. ,− Salen-containing metal complexes such as nickel­(I) salen and cobalt­(I) salen ( MSalen in Chart ) have been reported to facilitate the electron transfer reaction during dehalogenation. , The nickel­(II) tetraazamacrocyclic complex ( NiTAM in Chart ) also presented dehalogenative activity toward various bromo- and iodo- compounds . Dobson and Saini developed a Co­(II)-porphyrin complex ( CoPor in Chart ) for the detection and quantification of a series of organohalides via an electrocatalytic dehalogenation mechanism. ,, Although most molecular catalytic systems are homogeneous, molecular catalysts can also be heterogenized to reduce the amount of catalyst needed compared to a homogeneous system, which also facilitate catalyst recycling.…”