Abstract
The reduction of dinitrogen (N2) is essential for its incorporation into nucleic acids and amino acids, which are vital to life on earth. Nitrogenases convert atmospheric dinitrogen to two ammonia molecules (NH3) under ambient conditions. The catalytic active sites of these enzymes (known as FeM-cofactor clusters, where M = Mo, V, Fe) are the sites of N2 binding and activation and have been a source of great interest for chemists for decades. In this review, recent studies on nitrogenase-related synthetic molecular complexes and biological clusters are discussed, with a focus on their reactivity and spectroscopic characterization. The molecular models that are discussed span from simple mononuclear iron complexes to multinuclear iron complexes and heterometallic iron complexes. In addition, recent work on the extracted biological cofactors is discussed. An emphasis is placed on how these studies have contributed towards our understanding of the electronic structure and mechanism of nitrogenases.
Highlights
Iron sulfur cluster-containing proteins are found in all branches of life and carry out a wide range of essential processes, spanning from electron transfer to DNA repair toChen-Hao Wang completed hisB.Sc. in Chemistry (2012) at National Chung HsingUniversity, Taiwan and M.Sc.(2014) at National TaiwanUniversity under the supervision of Prof
The spectroscopic data revealed that the dinitrogen activation for [(SiPiPr3)Fe–N2]À followed a distal-like mechanism since the diazene adduct, which would represent the intermediate formed in an alternating mechanism, was not observed spectroscopically
We have discussed various synthetic models that have been used to understand the mechanism, potential intermediates, reactivity, and electronic properties of nitrogenases. Studies of these molecular models have provided key spectroscopic fingerprints which have been, and will continue to be, essential in correlated studies with the enzyme. These molecular model studies have shown that a single iron site is capable of catalytic N2 reduction,[48,51,52,53] albeit only at low temperature and under harsh reducing conditions
Summary
Iron sulfur cluster-containing proteins are found in all branches of life and carry out a wide range of essential processes, spanning from electron transfer to DNA repair to. [MoFe3S4]3+ and [VFe3S4]2+ cubanes have been shown to enable the catalytic conversion of hydrazine to ammonia, acetylene to ethylene and dimethyldiazene to methylamine, by utilizing cobaltocene and lutidinium chloride as the source of electrons and protons, respectively.[29] It is noteworthy to mention that most of these reactions cannot be enabled by Fe4S4 clusters, and even in cases where this can be achieved (e.g., for acetylene to ethylene conversion), the Fe4S4 clusters are much slower than the heterometal containing [MoFe3S4]3+ and [VFe3S4]2+ cubanes, suggesting a role of the heterometal in optimizing catalytic activity This parallels the observation that the Fe-only nitrogenases are by far the least efficient for N2 reduction.[4]. We place emphasis on the key role that spectroscopy has played in characterizing these complexes and providing key signatures for studies of the enzyme
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