Fixing nitrogen with iron complexes

Abstract

Our group has suggested that a hemi-labile role may be played by the interstitial light X-atom of the FeMo-cofactor, most recently assigned as C. Such a role would enable a high degree of conformational and redox flexibility at a single iron N_2 binding site. A spring-like behavior of the interstitial atom would allow an iron binding site to modulate its local geometry by varying its degree of interaction with the light X-atom under crude local three-fold symmetry, possibly sampling trigonal bipyramidal, trigonal pyramidal, and/or pseudotetrahedral geometries as a function of the nature of the state of redn. of the nitrogenous ligand. To test these ideas, our group has been exploring a range of 4- and 5-coordinate iron model complexes that exhibit local three-fold symmetry and feature a host of nitrogenous ligands (e.g., N_2, N_2H_4, NH_3, NH_2-, NR^2-, N^3-) in an axial substrate-binding site. These inorg. model complexes will be discussed in the context of a single-iron site 'spring' hypothesis for nitrogen redn.