Stepwise N–H bond formation from N2-derived iron nitride, imide and amide intermediates to ammonia. Issue 9 (14th June 2016)

• Record Type: Journal Article
• Authors: MacLeod, K. Cory; McWilliams, Sean F.; Mercado, Brandon Q.; Holland, Patrick L.
• Is Part Of: Chemical science. Volume 7:Issue 9(2016:Sep.)
• Page Start: 5736
• Page End: 5746
• Publication Date: 2016-06-14
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c6sc00423g
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The pathway from N2 to NH3 at low-coordinate iron complexes is shown through crystallographic and spectroscopic characterization of intermediates, including bridging nitride, imide, and amides. Proton-coupled electron transfer plays a key role in the transformations. Abstract : Reduction of N2 to ammonia in nature and in electrocatalysis takes place through 1-proton/1-electron steps, motivating efforts to experimentally study the steps during proton/electron transfer to well-characterized N2 -derived species with bridging nitrides. We report here the protonation and reduction reactions of an N2 -derived iron bis(nitride) complex (Rodriguez et al., Science, 2011, 334, 780). We isolate and definitively characterize triiron imido and amido intermediates that lie along the path to ammonia formation, and Mössbauer spectroscopy shows the oxidation level of iron atoms in these mixed-valence clusters. The first two H atoms add to one of the two nitrides of the bis(nitride) complex, and the proton-coupled electron transfer in the second step can be concerted or stepwise depending on the sources of protons and electrons. The characterization of partially protonated nitrides and their mechanisms of formation are expected to guide efforts to convert N2 to ammonia with mild acids.