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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-η211 fashion by disulfide, [L3Cu33-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.