Abstract
The model complex [Cu(4) (μ(4) -S)(dppa)(4) ](2+) (1, dppa=μ(2) -(Ph(2) P)(2) NH) has N(2) O reductase activity in methanol solvent, mediating 2 H(+) /2 e(-) reduction of N(2) O to N(2) +H(2) O in the presence of an exogenous electron donor (CoCp(2) ). A stoichiometric product with two deprotonated dppa ligands was characterized, indicating a key role of second-sphere N-H residues as proton donors during N(2) O reduction. The activity of 1 towards N(2) O 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 [Cu(4) S] 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.