Evolution of strategies to prepare synthetic mimics of carboxylate-bridged diiron protein active sites

Abstract

We present a comprehensive review of research conducted in our laboratory in pursuit of the long-term goal of reproducing the structures and reactivity of carboxylate-bridged diiron centers used in biology to activate dioxygen for the conversion of hydrocarbons to alcohols and related products. This article describes the evolution of strategies devised to achieve these goals and illustrates the challenges in getting there. Particular emphasis is placed on controlling the geometry and coordination environment of the diiron core, preventing formation of polynuclear iron clusters, maintaining the structural integrity of model complexes during reactions with dioxygen, and tuning the ligand framework to stabilize desired oxygenated diiron species. Studies of the various model systems have improved our understanding of the electronic and physical characteristics of carboxylate-bridged diiron units and their reactivity toward molecular oxygen and organic moieties. The principles and lessons that have emerged from these investigations will guide future efforts to develop more sophisticated diiron protein model complexes.

Intermediate P* from Soluble Methane Monooxygenase Contains a Diferrous Cluster

“…5–7 The unique reactivity of sMMO has spurred research into its chemical mechanism and led to extensive efforts to mimic the chemistry using synthetic model compounds. 6–12 We have studied the mechanism of sMMO using the enzyme from the Type II methanotroph Methylosinus trichosporium OB3b ( M. t. OB3b), while others have used the enzyme from the Type X methanotroph Methylococcus capsulatus Bath ( M. c. Bath) with similar results. 6–8,13 …”

19F NMR study of ligand dynamics in carboxylate-bridged diiron(ii) complexes supported by a macrocyclic ligand

“…12,13 The rational synthesis of carboxylate-bridged dinuclear metal complexes is challenging, owing to the propensity of these ligands to form polymers. Reliable strategies involve the use of sterically demanding ligands such as m -terphenyl carboxylates or dinucleating ligand frameworks.…”

Triptycene‐Based, Carboxylate‐Bridged Biomimetic Diiron(II) Complexes

“…11–17 In addition to providing a platform for studying the mechanisms of natural systems, biomimetic models may also function as catalysts to perform similar chemical transformations. Over the past three decades, many different ligands have been employed to mimic the diiron cores of BMMs.…”

“…22 We have prepared and reported several ligands with the goal of modeling this structural feature. 14,16,17,36 1,2-Diethynylbenzene-based scaffolds were effectively employed for this purpose. 37–41 The low-energy barrier to rotation about the alkynyl C–C bond, however, led to the formation of undesired metallopolymers and bis(ligand) iron complexes.…”