Nitrogen reduction by the Fe sites of synthetic [Mo3S4Fe] cubes

Abstract

N2 fixation by Nature, which is a crucial process to supply bio-available forms of nitrogen, is performed by nitrogenase. This enzyme employs a unique transition metal-sulfur-carbon cluster as its active-site cofactor ([(R-homocitrate)MoFe7S9C], FeMoco), 1,2 and the sulfur-surrounded Fe atoms have been postulated to capture and reduce N2. [3][4][5][6] Whereas synthetic counterparts of FeMoco, metal-sulfur clusters, have displayed binding of N2 in a few examples, 7,8 the reduction of N2 by any synthetic metal-sulfur clusters or even by the extracted form of FeMoco 9 have remained elusive despite a near-50-year history of research. Here we show that the Fe atoms in our synthetic [Mo3S4Fe] cubes 10,11 capture an N2 molecule and catalyze N2 silylation to form N(SiMe3)3 under treatment with excess Na and Me3SiCl. These results exemplify the first catalytic N2 reduction by a synthetic metal-sulfur cluster with an Fe center supported only by S ligands. This work demonstrates the N2-reducing capability of Fe atoms in a S-rich environment, which Nature has selected to accomplish a similar purpose. This work also suggests some critical features for successful N2 reduction by metal-sulfur compounds, which serve as clues to understand the origin of N2 fixation on Earth.

How Thermal Fluctuations Influence the Function of the FeMo-cofactor in Nitrogenase Enzymes

“…Apparently, H 2 formation greatly enhances the N 2 binding from a weak physical adsorption to a stronger chemical adsorption and further breaking its triple bond (see below), thus answering the long-standing unanswered question as to why H 2 formation is obligatory and how N 2 was activated 55 . Interestingly, this structure is in good agreement with the recent experimental observation of a synthetic [Mo 3 S 4 Fe] cube 56 , which proposed that the N 2 -reduction capability of Fe atoms is enhanced in a sulfur-rich environment. Overall the µ 2 − η 2 state is somewhere between end-on and side-on configurations, a point to which we return to in the next Section.…”

Iron‐Based Nanocatalysts for Electrochemical Nitrate Reduction

“…Adsorption of subsequent reactants can achieve the synergistic adsorption effect. [160][161][162] Lu et al designed and synthesized reductive sulfite synthetic metalloenzymes by introducing iron-sulfur cluster groups into cytochrome c peroxidase and modifying amino acids in the secondary coordination region of the metal-substrate binding site. [163] For many years, it has been a technical bottleneck in the field of biocatalysis, providing a new idea for the design of more enzymes.…”

CO Binding onto Heterometals of [Mo3S4M] (M = Fe, Co, Ni) Cubes

“…On the other hand, a direct incorporation of Fe-CO moiety to the incomplete-cubane [Mo3S4] platform was successful and led to the formation of [Cp XL 3Mo3S4Fe(CO)] (3) (Scheme 1, bottom). 7 Cluster 3 displayed a CO stretching frequency at 1877 cm -1 , which is significantly lower than the values for 2a and 2b. While it is reasonable that the more reduced cluster (3 in [Mo3S4Fe] 3+ state) exhibits stronger back donation than more oxidized species (2a and 2b in [Mo3S4M] 4+ states), these distinct differences over 100 cm -1 suggest effective interactions between Fe d orbitals and CO π* orbitals as further theoretical analyses given below.…”

“…5b CO-binding behaviors of clusters 1a-c were tested and discussed based on experimental and theoretical results and comparison with recently reported [Cp XL 3Mo3S4Fe(CO)] (3). 7 These results give a fundamental understanding of M-CO interactions in metal-sulfur clusters with iron triad metals (Fe, Co, Ni). This study will also be beneficial in developing molecular catalysts for the direct conversion of CO2 into fuels, as CO represents a key intermediate in this multi-step reaction.…”