Nitrogen reduction by the Fe sites of synthetic [Mo 3 S 4 Fe] cubes.

Nitrogen (N 2 ) fixation by nature, which is a crucial process for the supply of bio-available forms of nitrogen, is performed by nitrogenase. This enzyme uses a unique transition-metal-sulfur-carbon cluster as its active-site co-factor ([(R-homocitrate)MoFe 7 S 9 C], FeMoco) 1,2 , and the sulfur-surrounded iron (Fe) atoms have been postulated to capture and reduce N 2 (refs. 3-6 ). Although there are a few examples of synthetic counterparts of the FeMoco, metal-sulfur cluster, which have shown binding of N 2 (refs. 7-9 ), the reduction of N 2 by any synthetic metal-sulfur cluster or by the extracted form of FeMoco 10 has remained elusive, despite nearly 50 years of research. Here we show that the Fe atoms in our synthetic [Mo 3 S 4 Fe] cubes 11,12 can capture a N 2 molecule and catalyse N 2 silylation to form N(SiMe 3 ) 3 under treatment with excess sodium and trimethylsilyl chloride. These results exemplify the catalytic silylation of N 2 by a synthetic metal-sulfur cluster and demonstrate the N 2 -reduction capability of Fe atoms in a sulfur-rich environment, which is reminiscent of the ability of FeMoco to bind and activate N 2 .