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A general interest of the group is the role of transition metal ions in biology. We are particularly interested in the catalytic role of these metal ions in biology, i.e. in metalloenzymes. In addition, we are developing Fe-based catalysts derived from enzyme models for the use in organic synthesis.

The class of mono-nuclear non-heme iron enzymes comprising a so-called 2-His-1-carboxylate facial triad in their active site have recently attracted considerable attention. Whereas these enzymes share the same active site structural motif, they catalyze an astonishing wide variety of different (oxidative) transformations. In trying to understand and grasp the reactivity of these enzymes, we have designed a new class of tripodal, tridentate, mono-ionic, N,N,O ligands, the bis(1-alkylimidazol-2-yl)propionates. Initial studies have shown the accurate structural resemblance of synthetic Fe-complexes derived from these ligands with the enzyme active site and provide furher insight in the oxidative cleavage of catechols as carried out by some of these enzymes.

Modeling the 2-His-1-Carboxylate Facial Triad: Iron-catecholato Complexes as Structural and Functional Models of the Extradiol Cleaving Dioxygenases. P.C.A. Bruijnincx, M. Lutz, A.L. Spek, W.R. Hagen, B.M. Weckhuysen, G. van Koten, R.J.M. Klein Gebbink, J. Am. Chem. Soc. 2007, 129, 2275–2286.

Iron(III)-Catecholato Complexes as Structural and Functional Models of the Intradiol-Cleaving Catechol Dioxygenases. P.C.A. Bruijnincx, M. Lutz, A.L. Spek, W.R. Hagen, G. van Koten, R.J.M. Klein Gebbink, Inorg. Chem. 2007, 46, 8391–8402.

The versatility of the bis(1-alkylimidazol-2-yl)propionate ligands was further illustrated by the remarkable reactivity of its Zn complexes with pyruvate. It was found that these complexes are able to convert pyruvate in oxalate. Although not understood at this point, this reactivity pattern is of interest from both a synthetic and a biochemical point of view.

Zinc complexes of the biomimetic N,N,O ligand family of substituted 3,3-bis(1-alkylimidazol-2-yl)propionates: the formation of oxalate from pyruvate. P.C.A. Bruijnincx, M. Lutz, J.P. den Breejen, A.L. Spek, G. van Koten, R.J.M. Klein Gebbink, J. Biol. Inorg. Chem. 2007, 12, 1181–1196.

Besides trying to understand the reactivity of non-heme iron enzymes, we are also interested in trying to translate this reactivity into synthetically usefull reagents and catalysts. Within this realm we are studying a variety of (chiral) mixed N,O ligands in combination with Fe in several oxidative transformations, including alkane oxidation, alkene epoxidation and cis-hydroxylation, sulfide oxidation, etc.

Characterization and Alkane Oxidation Activity of a Diastereopure Seven-coordinate Iron(III) Alkylperoxo Complex. S. Gosiewska, H.P. Permentier, A.P. Bruins, G. van Koten, R.J.M. Klein Gebbink, Dalton Trans. 2007, 3365-3368.

Mononuclear Diastereopure Non-Heme Fe(II) Complexes of Pentadentate Ligands with Pyrrolidinyl Moieties: Structural Studies, and Alkene and Sulfide Oxidation. S. Gosiewska, M. Lutz, A.L. Spek, R.J.M. Klein Gebbink, Inorg. Chim. Acta 2007, 360, 405–417 (special issue ‘The Next Generation’).

Iron(II) Complexes with Bio-Inspired N,N,O Ligands as Oxidation Catalysts: Olefin Epoxidation and cis-Dihydroxylation. P.C.A. Bruijnincx, I.L.C. Buurmans, S. Gosiewska, M.A.H. Moelands, M. Lutz, A.L. Spek, G. van Koten, R.J.M. Klein Gebbink, Chem. Eur. J. 2008, 14, 1228–1237.

Inspired by metallo-enyzme active sites of higher nuclearity we are also studying multi-nuclear Fe-assemblies. One example is shown below; here, an iron bis(terpyridine) complexes bridges between two 3:1 sub-site differentiated [4Fe-4S] clusters.

A [4Fe-4S] Cluster Dimer Bridged by Bis(2,2':6',2''-Terpyridine-4'-Thiolato)iron(II). E.P.L. van der Geer, G. van Koten, R.J.M. Klein Gebbink, B. Hessen, Inorg. Chem. accepted for publication.