Web Release Date: March 11,
Iron Complexes of Dendrimer-Appended Carboxylates for Activating Dioxygen and Oxidizing Hydrocarbons
and
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Department of Chemistry, University of California, Berkeley, and Division of Materials Sciences, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460, and Department of Chemistry and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, California 94305
Received September 9, 2007
Abstract:
The active sites of metalloenzymes are often deeply buried inside a hydrophobic protein sheath, which protects them from undesirable hydrolysis and polymerization reactions, allowing them to achieve their normal functions. In order to mimic the hydrophobic environment of the active sites in bacterial monooxygenases, diiron(II) compounds of the general formula [Fe2([G-3]COO)4(4-RPy)2] were prepared, where [G-3]COO- is a third-generation dendrimer-appended terphenyl carboxylate ligand and 4-RPy is a pyridine derivative. The dendrimer environment provides excellent protection for the diiron center, reducing its reactivity toward dioxygen by about 300-fold compared with analogous complexes of terphenyl carboxylate ([G-1]COO-) ligands. An FeIIFeIII intermediate was characterized by electronic, electron paramagnetic resonance, Mössbauer, and X-ray absorption spectroscopic analyses following the oxygenation of [Fe2([G-3]COO)4(4-PPy)2], where 4-PPy is 4-pyrrolidinopyridine. The results are consistent with the formation of a superoxo species. This diiron compound, in the presence of dioxygen, can oxidize external substrates.
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