[superscript 19]F NMR Study of Ligand Dynamics in Carboxylate-Bridged Diiron(II) Complexes Supported by a Macrocyclic Ligand

Abstract

A series of asymmetrically carboxylate-bridged diiron(II) complexes featuring fluorine atoms as NMR spectroscopic probes, [Fe[subscript 2](PIM)(Ar[superscript 4F-Ph]CO[subscript 2])[subscript 2]] (10), [Fe[subscript 2](F[subscript 2]PIM)(Ar[superscript Tol]CO[subscript 2])[subscript 2]] (11), and [Fe[subscript 2](F[subscript 2]PIM)(Ar[superscript 4F-Ph]CO[subscript 2])[superscript 2]] (12), were prepared and characterized by X-ray crystallography, Mössbauer spectroscopy, and VT [superscript19]F NMR spectroscopy. These complexes are part of a rare family of syn-N diiron(II) complexes, [Fe[subscript 2](X[subscript 2]PIM)(RCO[subscript 2])[superscript 2]], that are structurally very similar to the active site of the hydroxylase enzyme component of reduced methane monooxygenase (MMOH[subscript red]). Solution characterization of these complexes demonstrates that they undergo intramolecular carboxylate rearrangements, or carboxylate shifts, a dynamic feature relevant to the reactivity of the diiron centers in bacterial multicomponent monooxygenases