Characterization of Structurally Unusual Diiron N_xH_y Complexes

Abstract

Mechanistic proposals concerning the pathway of N_2 reduction in biology at the MoFe-cofactor of nitrogenase continue to be advanced. In addition to nitrogen, hydrazine2 and diazene1a are nitrogenase substrates, and recent DFT calculations and spectroscopic studies suggest that whereas initial N_2 binding may occur at one iron center, diiron pathways may be involved at certain N_xH_y intermediate stages en route to ammonia formation. In this broad context, recent work has explored the synthesis and spectroscopic characterization of structurally unusual mono- and bimetallic iron complexes featuring nitrogenous ligand functionalities. The demand for such model complexes continues in light of recent ENDOR and ESEEM spectroscopic data that has been obtained under turnover conditions at the cofactor. To date, there are few synthetic iron systems that feature parent hydrazine (N_2H_4), hydrazido (N_2H_2^(2-)), diazene (N_2H_2), amide (NH_(2)^-), and imide (NH^2-) ligands. Herein we describe the synthesis and characterization of a series of structurally distinct diiron complexes that feature each of these ligand types.

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