Crystal Structure of a Synthetic High-Valent Complex with an Fe2(μ-O)2 Diamond Core. Implications for the Core Structures of Methane Monooxygenase Intermediate Q and Ribonucleotide Reductase Intermediate X

Abstract

In our efforts to model high-valent intermediates in the oxygen activation cycles of nonheme diiron enzymes such as methane monooxygenase (MMOH-Q) and ribonucleotide reductase (RNR R2-X), we have synthesized and spectroscopically characterized a series of bis(μ-oxo)diiron(III,IV) complexes, [Fe2(μ-O)2(L)2](ClO4)3, where L is tris(2-pyridylmethyl)amine (TPA) or its ring-alkylated derivatives. We now report the crystal structure of [Fe2(μ-O)2(5-Et3-TPA)2](ClO4)3 (2), the first example of a structurally characterized reactive iron(IV)−oxo species, which provides accurate metrical parameters for the diamond core structure proposed for this series of complexes. Complex 2 has Fe−μ-O distances of 1.805(3) A and 1.860(3) A, an Fe−Fe distance of 2.683(1) A, and an Fe−μ-O−Fe angle of 94.1(1)°. The EXAFS spectrum of 2 can be fit well with a combination of four shells: 1 O at 1.82 A, 2−3 N at 2.03 A, 1 Fe at 2.66 A, and 7 C at 2.87 A. The distances obtained are in very good agreement with the crystal structure data ...