Controlled Synthesis of Cluster Mimics of Nitrogenase FeMo-cofactor

Catalytic conversion of atmosphere dinitrogen into ammonia by nitrogenase is one of the most important chemical processes in nature. FeMo-cofactor (FeMoco), the key active site of this conversion in the Mo-based nitrogenase, is one of the most complicated metalloenzyme molecules. The synthesis of FeMoco cluster holds the key to elucidating the mechanism of nitrogen fixation, but the complex framework with a unique sextuply-bridged carbide in FeMoco cluster dictates its synthesis to be an extreme challenge that remains unsolved for several decades. In this work, two cluster models have been synthesized as the first highly analogous mimics of FeMoco using a precisely-designed cluster-coupling strategy. A carbide ligand has been introduced into M-Fe-S (M = Mo or W) clusters and the characteristic triangular prismatic [Fe6(µ6-C)] moiety of FeMoco has been synthesized for the first time. The structural parameters of the two mimics match well with those of FeMoco identified in natural nitrogenase. Quantum chemical studies reveal that the electronic ground states of the mimics resemble those observed for FeMoco, with maximized antiferromagnetic coupling among the iron centers. The clusters synthesized in this work represent the only highly analogous synthetic mimics of FeMoco. The cluster-coupling reaction is a versatile strategy that allows the synthesis of more analogous mimics of FeMoco. These mimics and the cluster-coupling strategy provide an excellent platform for studying the function and behavior of FeMoco, and also pave the way for elucidating the mechanism of nitrogen fixation by nitrogenase.