Iron clusters perform many functions in biological systems, such as catalysis (e.g., dinitrogen fixation), and electron transfer. Despite the significant progress made in understanding the fundamental aspects of these clusters, there still remain many questions regarding the reactivity of iron clusters supported by weak-field donors. For example, ENDOR studies on hydride bridged iron cluster found in nitrogenases support iron hydrides that are unreactive towards adventitious protons but undergo reductive elimination of dihydrogen and subsequent coordination of dinitrogen. More broadly, reduction of iron-sulfur clusters in [Fe-S] proteins is proposed to be coupled to the protonation of a sulfide bridge; yet, the only evidence in support of this phenomenon is pKa measurements of molecular [4Fe-4S] clusters and ENDOR measurements on the reduced states of the nitrogenase cofactors. To expand our understanding of the chemistry of iron clusters in the weak-field regime, we have synthesized hydrido- and sulfido-bridged diiron complexes employing a macrocyclic ligand to enforce a target cluster nuclearity and ligand field while also conferring structural stability to investigate reactivity. The hydride cluster shows diverse reactivity, such as intermolecular H/D and H/Cl ligand exchange with another iron cluster, and H-atom transfer to generate low valent iron. The relevance of this reactivity to enzymatic systems will be discussed.

Reactivity of diiron clusters containing sulfide and hydride bridges

255th National Meeting (2018)

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