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

摘要

The model complex [Cu-4(mu(4)-S)(dppa)(4)](2+) (1, dppa=mu(2)-(Ph2P)(2)NH) has N2O reductase activity in methanol solvent, mediating 2 H+/2 e(-) reduction of N2O to N-2+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 Cu-Z catalytic site of nitrous oxide reductase: activity in the 4Cu(I):1S redox state, use of a second-sphere proton donor, and reactivity dependence on both primary and secondary sphere effects.