N2O reduction at a dissymmetric {Cu2S}-containing mixed-valent center

Abstract

Through our bio-inspired approach toward replicating nitrous oxide reductase (N₂Or) activity, treatment of the L^Me(MAM)S–S ligand with [Cu(CH₃CN)₄](OTf) (OTf = trifluoromethanesulfonate ion) leads to the isolation of a new dissymmetric mixed-valent (MV) dicopper(II,I) [2·(H₂O)(OTf)]⁺ containing a {Cu₂S} core with labile triflate and water molecules at the copper centers. Whilst [2·(H₂O)(OTf)]⁺ is prone to ligand exchange under particular conditions, a raft of spectroscopic investigations, combined with theoretical calculations demonstrate that its structure is retained in acetone solution. Compared to our previously reported inactive parent complex [1] (Angew. Chem. Int. Ed., 2010, 49 (44), 8249–8252) featuring a symmetric and saturated coordination sphere (N and S atoms from the ligand), [2·(H₂O)(OTf)]⁺ is reactive towards nitrous oxide in acetone. Spectroscopic and theoretical studies combined with kinetic measurements show that exchangeable positions are required for N₂O interaction. The isolation of the final product and its characterization by X-ray crystallography as a doubly bridged (μ-thiophenolato)(μ-hydroxo) dicopper(II) species [3·(μ-OH)(OTf)₂] help to support the proposed reaction pathway. Implications for N₂Or mechanism are discussed.