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A Dinuclear Iron Complex Based on Parallel Malonate Binding Sites: Cooperative Activation of Dioxygen and Biomimetic Ligand Oxidation
Author(s) -
Siewert Inke,
Limberg Christian,
Demeshko Serhiy,
Hoppe Elke
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800955
Subject(s) - chemistry , reactivity (psychology) , ligand (biochemistry) , malonate , peroxide , xanthene , stereochemistry , yield (engineering) , photochemistry , medicinal chemistry , organic chemistry , receptor , materials science , medicine , biochemistry , alternative medicine , pathology , metallurgy
A ligand that offers two parallel malonate binding sites linked by a xanthene backbone, namely, Xanthmal 2− , has been utilised to synthesise dinuclear Fe II complex [Fe 2 (Xanthmal) 2 ] ( 1 ). The reactivity of 1 in contact with O 2 was investigated at −40 °C and room temperature. After activation of O 2 through interaction with both iron centres the ligand is oxidised: at the C α 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) 2 Fe 2 O] ( 2 ) is formed, which is unreactive towards O 2 and thus is a dead end with respect to ligand oxidation. Both compounds 1 and 2 were fully characterised, and their properties are discussed.