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Reduction of nitrous oxide to dinitrogen by a mixed valent tricopper-disulfido cluster

Recent research from the groups of Professor Christopher Cramer and Professor William Tolman.

The greenhouse gas N2O is converted to N2 under mild conditions 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, Dr. Itsik Bar-Nahum and Aalo Gupta in Prof. Tolman’s group have prepared and fully characterized a localized mixed valent Cu(II)Cu(I)2 cluster bridged in μ-η211 fashion by disulfide, [L3Cu3(μ-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 by Dr. Stefan Huber and Mehmed Z. Ertem in Prof. Cramer’s group 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. This work is described in a communication just published online in the Journal of the American Chemical Society (DOI: 10.1021/ja808917k).

Structure of the new cluster that reduces N2O to N2.

Calculated structure of the transition state for N2O reduction by a dinuclear fragment of the tricopper cluster (ligand C atoms omittted for clarity).

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