Iron(II) Complexes Featuring a Redox-Active Dihydrazonopyrrole Ligand

Nature uses control of the secondary coordination sphere to facilitate an astounding variety of transformations. Similarly, synthetic chemists have found metal-ligand cooperativity to be a powerful strategy for designing complexes that can mediate challenging reactivity. In particular, this strategy has been used to facilitate two electron reactions with first row transition metals that more typically engage in one electron redox processes. While NNN pincer ligands feature prominently in this area, examples which can potentially engage in both proton and electron transfer are less common. Dihydrazonopyrrole (DHP) ligands have been isolated in a variety of redox and protonation states when complexed to Ni. However, the redox-state of this ligand scaffold is less obvious when complexed to metal centers with more accessible redox couples. Here, we synthesize a new series of Fe-DHP complexes in two distinct oxidation states. Detailed characterization supports that the redox-chemistry in this set is still primarily ligand based. Finally, these complexes exist as 5-coordinate species with an open coordination site offering the possibility of enhanced reactivity.