N2O Reductase Activity of a [Cu4S] Cluster in the 4CuI Redox State Modulated by Hydrogen Bond Donors and Proton Relays in the Secondary Coordination Sphere

• Published in: Angewandte Chemie International Edition 2020-01, Vol.59 (2), p.627-631
• Main Authors: Hsu, Chia‐Wei, Rathnayaka, Suresh C., Islam, Shahidul M., MacMillan, Samantha N., Mankad, Neal P.
• Format: Article
• Language: English
• Subjects: bioinorganic chemistry; cluster compounds; Computer applications; Coordination compounds; Electron density; Hydrogen; Hydrogen bonding; Hydrogen bonds; Localization; Nitrous oxide; Protons; Redox properties; Reductase; Reductases; Reduction; second sphere; Solvents
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201906327

The model complex [Cu4(μ4‐S)(dppa)4]2+ (1, dppa=μ2‐(Ph2P)2NH) has N2O reductase activity in methanol solvent, mediating 2 H+/2 e− reduction of N2O to N2+H2O in the presence of an exogenous electron donor (CoCp2). A stoichiometric product with two deprotonated dppa ligands was characterized, indicating a key role of second‐sphere N−H residues as proton donors during N2O reduction. The activity of 1 towards N2O was suppressed in solvents that are unable to provide hydrogen bonding to the second‐sphere N−H groups. Structural and computational data indicate that second‐sphere hydrogen bonding induces structural distortion of the [Cu4S] active site, accessing a strained geometry with enhanced reactivity due to localization of electron density along a dicopper edge site. The behavior of 1 mimics aspects of the CuZ catalytic site of nitrous oxide reductase: activity in the 4CuI:1S redox state, use of a second‐sphere proton donor, and reactivity dependence on both primary and secondary sphere effects. N2O reductase activity of a synthetic model compound [Cu4S(dppa)4]2+ (dppa=(Ph2P)2NH) relies on both primary and secondary coordination sphere effects. It mediates the 2 H+/2 e− reduction of N2O to N2 and H2O in the presence of an exogenous electron donor (CoCp2).