Metall-Oxo-Komplexe mit eta2-Pyrazolat-Liganden: Synthese und katalytische Sauerstoff-Transfer-Reaktionen
Final Report Abstract
We investigated the viability of sterically demanding pyrazolate compounds as functional models for oxotransferases, a class of enzymes that catalyze the transfer of an oxygen atom to and from a substrate. We found that dioxo complexes [Mo02X(tBu2pz)] (X = Cl, t-Bu2pz) as well as oxo imido complexes [MoO(NtBu)(tBu2pz)2] show interesting molecular structures as the distorted trigonal prism approaches the situation In the structure of DMSO reductase. An interesting feature of these compounds is their ability to catalyze oxygen atom transfer (OAT) from dimethylsulfoxide to triphenylphosphine, a reaction that has biological relevance to molybdenum-containing DMSO reductases, which are able to utilize a variety of dialkyl- and alkylarylsulfoxldes as oxo donors. Detailed mechanistic information was obtained by UV/Vis-spectroscopy. The obtained activation parameters point to an associative mechanism. The isolation and crystallographic characterization of a reduced molybdenum(IV) compound of the type [MoO(n2-tBu2pz)2(PEt3)2] represents an important step in the understanding of the mechanism. We developed molybdenum(VI) and tungsten(VI) dioxo compounds with a series of Schiff base ligands showing strictly octahedral geometries. Comparison of the kinetic data of these octahedral compounds to the trigonal prismatic [MoO(n2-pz)2] show the Schiff base system to be far less reactive towards OAT suggesting that a trigonal prismatic geometry accelerates OAT. This interesting result contributes to the widely discussed question of which geometry is involved in the enzyme's active site suggesting that a trigonal prism is Indeed favorable. An interesting and unexpected finding is the rare activation of molecular oxygen by molybdenum(IV) compounds employing Schiff base ligands leading to an isolable oxo peroxo species or to the reoxidation to the dioxo compound depending on the steric demand of the Schiff base. Activation of molecular oxygen represents a key step for its use in oxidation catalysis. Isoelectronic rhenlum(VII) compounds could be obtained with the n2-pyrazolate ligands that were found to be more reactive in OAT reactions than the Mo systems. With Schiff base ligands a series of rhenlum(V) compounds were accessible. Both systems, the pyrazolates and the Schiff bases proved to be catalysts in epoxidation of olefins.
Publications
- Molybdän- und Wolfram-Komplexe mit dem 3,5-Di-tert-butylpyrazolat-Liganden: Anwendungen in Sauerstoff-Transfer-Reaktionen, Georg-August-Universität Göttingen, Dissertation 2003
Kerstin Most
- Oxygen-transfer Reactions of Molybdenum- and Tungstendioxo Complexes Containing n2-Pyrazolate Ligands, Adv. Synth. Catal. 2005, 347, 463
Most, K.; Hoßbach, J.; Vidovic, D.; Magull, J.; Mösch-Zanetti, N. C.
- Rhenium oxo compounds containing n2-pyrazolate ligands, Dalton Trans. 2005, 2124
Mösch-Zanetti, N. C; Sachse, A.; Pfoh, R.; Vidovic, D.; Magull, J.
- Dioxomolybdenum(VI) and dioxotungsten(VI) complexes supported by an amido ligand, Dalton Trans. 2006, 1294
Lyashenko, G.; Jancik, V.; Pal, A.; Herbst-Irmer, R.; Mösch-Zanetti, N. C.
- Molecular oxygen activation by a molybdenum(IV) mono-oxo bis(ß-ketiminato) complex, Chem. Commun. 2007, 701
Lyashenko, G.; Saischek, G.; Pal, A.; Herbst-Irmer, R.; Mösch-Zanetti, N. C.
- Rhenlum(V) Oxo Complexes with Acetylacetone Derived Schiff Bases: Structure and Catalytic Epoxidation, Inorg. Chem. 2007,46,7129
Sachse, A ; Mösch-Zanetti, N. C.; Lyashenko, G.; Wielandt, J. W.; Most, K.; Magull, J.; Dall'Antonia, F.; Pal, A.; Herbst-Irmer, R.
- Molybdenum Oxo and Imido Complexes of ß-Diketiminate Ligands: Synthesis and Structural Aspects, Inorg. Chem. 2008, 47, 113
Lyashenko, G.; Herbst-Irmer, R.; Jancik, V.; Pal, A.; Moesch-Zanetti, N. C.
- Structural and functional model compounds of molybdenum and tungsten relevant to oxotransferases, Karl-Franzens-Universität Graz, Dissertation 2008
Ganna Lyashenko
