Iron(II) complexes of sterically bulky α-ketocarboxylates. Structural models for α-ketoacid-dependent nonheme iron halogenases

Seth J. Friese, Benjamin E. Kucera, Victor G. Young, Lawrence Que, William B. Tolman

Research output: Contribution to journalArticle

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Abstract

Reaction of the sterically hindered α-ketocarboxylate 2,6-di(mesityl)benzoylformate (MesBF) with the iron(II) complexes LFeCl 2 [L = N,N,N′,N′-tetramethylpropylenediamine (Me 4pda) or 6,6′-dimethyl-2,2′-bipyridine (dmby)] yielded LFe(Cl)(MesBF) (1 or 2). X-ray crystal structures of these complexes showed that they closely model the active site structure of the nonheme iron halogenase enzyme SyrB2. A similar synthetic procedure using benzoylformate with L = dmby yielded (dmby)Fe[(O2CC(O)Ph)]2 (3) instead, demonstrating the need for the sterically hindered α-ketocarboxylate to assemble the halogenase model compounds. In order to make reactivity comparisons among the structurally related iron(II) complexes of benzoylformates of varying steric properties, the complexes [LFe(O2CC(O)Ar)]n (4-6) were prepared, where L′ = tris(pyridylmethyl)amine (tpa) and Ar = 2,6-dimesitylphenyl, 2,6-dip-tolylphenyl, or 2,4,6-trimethylphenyl, respectively. X-ray structures for the latter two cases (5 and 6) revealed dinuclear topologies (n = 2), but UV-vis and 1H NMR spectroscopy indicated that all three complexes dissociated in varying degrees to monomers in CH2Cl2 solution. Although compounds 1-6 were oxidized by O2, oxidative decarboxylation of the α-ketocarboxylate ligand(s) only occurred for 3. These results indicate that the steric hindrance useful for structural modeling of the halogenase active site prohibits functional mimicry of the enzyme.

Original languageEnglish (US)
Pages (from-to)1324-1331
Number of pages8
JournalInorganic chemistry
Volume47
Issue number4
DOIs
StatePublished - Feb 18 2008

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