A (μ-oxo)bis(μ-carboxylato)diiron(III) complex with a tethered phenoxyl radical as a model for the active site of the R2 protein of ribonucleotide reductase

David P. Goldberg, Dionysios Koulougliotis, Gary W Brudvig, Stephen J. Lippard

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We have designed and synthesized a novel bidentate nitrogen donor ligand, 1,1-bis(2-(1-methylimidazolyl))-1-(3,5-di-tert-butyl-4-hydroxyphenyl)ethane (BIDPhEH) (2). The phenoxyl radical form of this ligand, BIDPhE (3), was prepared and isolated as a stable solid. BIDPhEH was used in the synthesis of the mononuclear ferric complex, [Fe(BIDPhEH)2Cl2]X (X = Cl (5a), FeCl4 (5b). The crystallographic characterization of 5b is reported. Use of the solvente complex [Fe2O(XDK)(MeOH)5(H2O)](NO3) 2, where XDK is m-xylenediaminebis(Kemp's triacid)-imide, a pre-organized, cleft-shaped dicarboxylate ligand, facilitated preparation of the phenoxyl radical (μ-oxo)-bis(μ-carboxylato)diiron(III) complex [Fe2O(XDK)(BIDPhE)2(NO3)2] (6), a new model for the tyrosyl radical containing active site of the R2 protein of E. coli ribonucleotide reductase. Magnetic susceptibility studies of 6 revealed overall magnetic behavior quite similar to that of the protein. The iron atoms are antiferromagnetically coupled, and a theoretical fit of the data determined the J value (ℋ= -2JS1·S2) to be -117 cm-1. Pulsed saturation-recovery EPR experiments conducted on 6 provided an independent measure of J, the value of which was in excellent agreement with the magnetic susceptibility measurements. Comparisons are made to the saturation-recovery EPR results for the R2 protein.

Original languageEnglish
Pages (from-to)3134-3144
Number of pages11
JournalJournal of the American Chemical Society
Issue number11
Publication statusPublished - Mar 22 1995


ASJC Scopus subject areas

  • Chemistry(all)

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