Synthesis, Characterization, and Oxygenation Studies of Carboxylate-Bridged Diiron(II) Complexes with Aromatic Substrates Tethered to Pyridine Ligands and the Formation of a Unique Trinuclear Complex

Abstract

In this study, diiron(II) complexes were synthesized as small molecule mimics of the reduced active sites in the hydroxylase components of bacterial multicomponent monooxygenases (BMMs). Tethered aromatic substrates were introduced in the form of 2-phenoxypyridines, incorporating hydroxy and methoxy functionalities into windmill-type diiron(II) compounds [Fe[subscript 2](μ-O[subscript 2]CAr[superscript R])[subscript 2](O[subscript 2]CAr[superscript R])[subscript 2](L)[subscript 2]] (1–4), where[superscript –]O[subscript 2]CAr[superscript R] is a sterically encumbering carboxylate, 2,6-bis(4-fluorophenyl)-, or 2,6-bis(p-tolyl)benzoate (R = 4-FPh or Tol, respectively). The inability of 1–4 to hydroxylate the aromatic substrates was ascertained. Upon reaction with dioxygen, compounds 2 and 3 (L = 2-(m-MeOPhO)Py, 2-(p-MeOPhO)Py, respectively) decompose by a known bimolecular pathway to form mixed-valent diiron(II,III) species at low temperature. Use of 2-(pyridin-2-yloxy)phenol as the ligand L resulted in a doubly bridged diiron complex 4 and an unprecedented phenoxide-bridged triiron(II) complex 5 under slightly modified reaction conditions.