Volume 14, Issue 30 p. 9377-9388
Full Paper

A Dinuclear Iron Complex Based on Parallel Malonate Binding Sites: Cooperative Activation of Dioxygen and Biomimetic Ligand Oxidation

Inke Siewert

Inke Siewert

Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 10829 Berlin (Germany), Fax: (+49) 30-2093-6966

Search for more papers by this author
Christian Limberg Prof. Dr.

Christian Limberg Prof. Dr.

Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 10829 Berlin (Germany), Fax: (+49) 30-2093-6966

Search for more papers by this author
Serhiy Demeshko Dr.

Serhiy Demeshko Dr.

Institut für Anorganische Chemie, Georg-August-Universität Göttingen, Tammannstrasse 4, 37077 Göttingen (Germany)

Search for more papers by this author
Elke Hoppe Dr.

Elke Hoppe Dr.

Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 10829 Berlin (Germany), Fax: (+49) 30-2093-6966

Search for more papers by this author
First published: 10 October 2008
Citations: 22

Graphical Abstract

Biomimetic O2 activation: A complex in which two iron centres are complexed by two ligands bearing parallel malonate binding pockets (see picture for crystal structure; Fe orange, O red, C grey, H omitted) activates O2 and then undergoes ligand oxidation to give alcohols, peroxides and α-keto esters. A reaction mechanism is suggested in which some steps mimic the proposed functioning of non-heme Fe enzymes.

Abstract

A ligand that offers two parallel malonate binding sites linked by a xanthene backbone, namely, Xanthmal2−, has been utilised to synthesise dinuclear FeII complex [Fe2(Xanthmal)2] (1). The reactivity of 1 in contact with O2 was investigated at −40 °C and room temperature. After activation of O2 through interaction with both iron centres the ligand is oxidised: at the Cα position monooxygenation and peroxide formation occur, partially accompanied by CC bond cleavage to yield α-keto ester groups. To reveal mechanistic details investigations concerning 1) peroxide decomposition, 2) the reactivity of a corresponding mononuclear complex, 3) the influence of monooxygenation of the ligand on the reactivity and 4) product formation in dependence on time were carried out. The results can be explained by postulating formation of high-valent Fe intermediates and ligand-to-metal electron transfer, and the mechanistic scheme derived includes several steps that mimic the (suggested) functioning of non-heme iron enzymes. In agreement with this proposal, ligand oxidation can also be performed catalytically. Furthermore, we show that via a competitive route [(Xanthmal)2Fe2O] (2) is formed, which is unreactive towards O2 and thus is a dead end with respect to ligand oxidation. Both compounds 1 and 2 were fully characterised, and their properties are discussed.