Structure-function studies of tetranuclear iron clusters with a variable interstitial μ4-atom as models of biological active sites

Abstract

Multinuclear first-row transition metal clusters contg. bridging one-atom ligands to three or more metal ions are found in complex biol. active sites including the Oxygen Evolving Complex in Photosystem II (μ_3- and μ_4-oxo ligands), and the iron-molybdenum cofactor in nitrogenase (μ_6-carbide). Synthetic tetranuclear clusters have been studied with the goal of understanding how an interstitial atom can affect the chem. of the cluster. These model complexes are composed of a trimetallic core which is connected to an apical metal center by three pyrazolate ligands, and a μ_4-atom (μ_4-F and μ_4-O). The apical metal center possesses a trigonal pyramidal geometry with an open coordination site. The intermol. chem. of these bio-inspired clusters has been investigated to understand the effect of the neighboring metals and bridging atom. When the pyrazolate ligands display Ph substituents, intramol. C-H and C-F bond functionalization occurs upon reaction with oxygen atom transfer (OAT) reagents. More sterically open tetrairon clusters with μ_4-F and μ_4-O interstitial ligands and no Ph substituents have been synthesized. Reactions with OAT reagents suggest the formation of terminal iron-oxo intermediates. The reactivity and properties of these clusters as a function of the μ_4-interstitial atom will be discussed.