Influence of Copper Coordination Spheres on Nitrous Oxide Reductase (N₂Or) Activity of a Mixed-Valent Copper Complex...

A new mixed-valent dicopper complex [5] was generated from ligand exchange by dissolving a bis(CH₃CN) precursor [3] in acetone. Introduction of a water molecule in place of an acetonitrile ligand was evidenced by base titration and the presence of a remaining coordinated CH₃CN by IR, ¹⁹F NMR, and theoretical methods. The proposed structure (CH₃CN-Cu-(SR)-Cu-OH₂) was successfully DFT-optimized and the calculated parameters are in agreement with the experimental data. [5] has a unique temperature-dependence EPR behavior, with a localized valence from 10 to 120 K that undergoes delocalized at room temperature. The electrochemical signatures are in the line of the other aquo parent [2] and sensibly different from the rest of the series. Similar to the case of [2], [5] was finally capable of single turnover N₂O reduction at room temperature. N₂ was detected by GC-MS, and the redox character was confirmed by EPR and ESI-MS. Kinetic data indicate a reaction rate order close to 1 and a rate 10 times faster compared to [2]. [5] is thus the second example of that kind and highlights not only the main role of the Cu-OH₂ motif, but also that the adjacent Cu-X partner (X = OTf^- in [2] and CH₃CN in [5]) is a new actor in the casting to establish structure/activity correlations.