Reduction of Nitrous Oxide to Dinitrogen by a Mixed Valent Tricopper-Disulfido Cluster

Bar-Nahum, I.; Gupta, A. K.; Huber, S. M.; Ertem, M. Z.; Cramer, C. J.; Tolman, W. B.
J. Am. Chem. Soc. 2009, 131, 2812.

The greenhouse gas N₂O is converted to N₂ by a μ-sulfido-tetracopper active site in the enzyme nitrous oxide reductase (N₂OR) via a process postulated to involve μ-1,3 coordination of N₂O to two Cu(I) ions. In efforts to develop synthetic models of the site with which to test mechanistic hypotheses, we have prepared a localized mixed-valent Cu(II)Cu(I)₂ cluster bridged in μ-η²:η¹:η¹ fashion by disulfide, [L₃Cu₃(μ³-S₂)]X₂ (L = 1,4,7-trimethyl-triazacyclononane, X = O₃SCF₃^– or SbF₆^–). This cluster exhibits spectroscopic features similar to those of the active site in N₂OR and reacts with N₂O to yield N₂ in a reaction that models the function of the enzyme. Computations implicate a transition state structure that features μ-1,1-bridging of N₂O via its O-atom to a [L₂Cu₂(μ-S₂)]⁺ fragment and provide chemical precedence for an alternative pathway for N₂O reduction by N₂OR.