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

Abstract

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.

Probing the electronic and mechanistic roles of the μ4-sulfur atom in a synthetic CuZ model system

“… 20 Here, the copper centers remained redox inactive while the μ 2 -sulfide ligand was not only the redox-active center but also acted as an oxygen atom acceptor. In another case, a phosphine-supported tetranuclear [Cu 4 S] cluster in its 4Cu I state showed reactivity towards N 2 O reduction, 21 but the cluster lost structural integrity during the reaction, losing the sulfur atom to unknown products in the reaction medium and thus limiting insight that can be gained about its role. Finally, a formamidinate-supported [Cu 4 S] cluster in its formally 3Cu I :1Cu II ([4Cu:1S] 1− ) state was found to reduce 15 N 2 O to 15 N 2 ( Scheme 1b ).…”

Synergy between metals for small molecule activation: Enzymes and bio-inspired complexes

“…the [Cu4(4-S)(2-dppa)4] 2+ cluster (Cu4S P , dppa = (Ph2P)2NH, see Fig. 16) that contains two NH groups as hydrogen-bond donors in its second coordination sphere [217]. Cu4S P mediates stoichiometric 2H + /2ereduction of N2O to N2 and H2O in the presence of cobaltocene, but only when specific hydrogen bond acceptor solvents (MeOH, acetone) are employed.…”

Progress toward the Isolation of Late Metal Terminal Sulfides

“…European Journal of Inorganic Chemistry [Cu(2,2′-bipy) 2 (S)]•CH 3 CH 2 OSO 3 H, is probably better formulated as a hydrosulfide complex. [117] Most copper sulfide chemistry has focused on the synthesis of models of the Cu z site in N 2 OR, [75,[118][119][120][121][122][123][124] and not necessarily on the synthesis of terminal copper sulfides. In this regard, several groups have successfully generated copper sulfide clusters that closely resemble the [Cu 4 (μ 4 -S)] core of the Cu z site, including [K(18-crown-6)][ NCN LCu 4 (μ 4 -S)] (67; NCN L = (2,4,6-Me 3 C 6 H 2 N) 2 CH), [17,125] which can reduce N 2 O in a stoichiometric fashion (Scheme 17).…”