N2O reduction at a dissymmetric {Cu2S}-containing mixed-valent center
Résumé
Through our bio-inspired approach toward replicating nitrous oxide reductase (N(2)Or) activity, treatment of the LMe(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 center dot(H2O)(OTf)](+) containing a {Cu2S} core with labile triflate and water molecules at the copper centers. Whilst [2 center dot(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 center dot(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 (mu-thiophenolato)(mu-hydroxo) dicopper(II) species [3 center dot(mu-OH)(OTf)(2)] help to support the proposed reaction pathway. Implications for N(2)Or mechanism are discussed.