Our general experience with the application of high pressure techniques in the elucidation of inorganic, organometallic and bioinorganic reaction mechanisms is offered as a service to all other participating groups in this network. We have equipment available with which UV-Vis, NMR (1H, 7Li, 13C, 17O, 19F and 31P), stopped-flow, T-jump, flash-photolysis and electrochemical measurements can be performed at pressures up to 200 MPa. This enables the determination of thermodynamic and kinetic data as a function of pressure with which a volume profile for the studied reaction can be constructed. This volume profile reveals information on intrinsic and solvational volume changes in going from the reactant and product (in the case of a reversible process) to the transition state, and so reveals unique mechanistic information. Such measurements can be applied to a variety of mechanistic questions dealing with solvent exchange, ligand substitution, electron transfer, oxidative addition/reductive elimination and activation of small molecule processes.
Solvent exchange and complex-formation reactions are the most fundamental chemical processes in aqueous phase chemistry. On dissolution of a metal salt, spontaneous dissociation leads to aquation of the metal ion to produce various aqua and hydroxo (monomeric or dimeric) species in solution that all exhibit different water exchange rates and mechanisms. The mechanistic understanding of such processes is essential in order to understand subsequent ligand substitution processes like the binding of small molecules (O2, NO, CO2, alkanes) to such metal centers. The rate and mechanism of such reactions can be controlled by the ligand environment by introducing steric hindrance, -donor and -acceptor effects on the spectator ligands. The Work from our group cited below, has clearly demonstrated our ability to control such processes by selective tuning of the mentioned properties.
3. Activation of hydrogen peroxide by model iron porphyrins for the oxidation and hydroxylation of alkanes
There is presently a significant interest in the activation of hydrogen peroxide by heme and non-heme Fe(III) complexes for the selective oxidation and hydroxylation of alkanes and environmentally hazardous compounds. The first reaction step involves the direct coordination of hydrogen peroxide to the Fe(III) center, which is accompanied by deprotonation to form an intermediate hydroperoxo complex. The latter species can be stabilized by ring-closure or undergo homolysis or heterolysis of the O-O bond to initiate the subsequent oxidation and hydroxylation reactions. The mechanistic details of such reactions are essential in order to be able to tune the oxidation/hydroxylation reactions in a specific direction. Furthermore, the gained mechanistic insight is of fundamental interest to the understanding of biological oxidation/hydroxylation reactions such as catalyzed by cytochrome P450.
1. Effect of pressure on inorganic reactions. Introduction and mechanistic applications, R. van Eldik and C.D. Hubbard in "High Pressure Chemistry: Synthetic, Mechanistic and Supercritical Applications", R. van Eldik and F.-G. Klärner (Eds.), VCH-Wiley, Weinheim, Germany, 2002, p. 3-40.
2. Water exchange controls the complex-formation mechanism of water-soluble iron(III) porphyrins. Conclusive evidence for dissociative water exchange from a high pressure 17O NMR study, T. Schneppensieper, A. Zahl and R. van Eldik, Angew. Chem. Int. Ed., 40, 1678 (2001).
3. Kinetics and mechanism of the reversible binding of nitric oxide to reduced cobalamin B12r, M. Wolak, A. Zahl, T. Schneppensieper, G. Stochel and R. van Eldik, J. Am. Chem. Soc., 123, 9780 (2001).
4. Kinetics, mechanism and spectroscopy of the reversible binding of nitric oxide to aquated iron(II). An undergraduate text book reaction revisited, A. Wanat, T. Schneppensieper, G. Stochel, R. van Eldik, E. Bill and K. Wieghardt, Inorg. Chem., 41, 4 (2002).
5. To be or not to be NO in coordination chemistry? A mechanistic approach, M. Wolak and R. van Eldik, Coord. Chem. Rev., 230, 263 (2002).
6. Activation volume measurement for C-H activation. Evidence for associative benzene substitution at a platinum(II) center, J. Procelewska, A. Zahl, R van Eldik, H.A. Zhong, J.A. Labinger and J.E. Bercaw, Inorg. Chem., 41, 2808 (2002).
7. Electronic tuning of the lability of Pt(II) complexes through -acceptor effects. Correlations between thermodynamic, kinetic and theoretical parameters, A. Hofmann, D. Jaganyi, O.Q. Munro, G. Liehr and R. van Eldik, Inorg. Chem., 42, 1688 (2003).
8. Cyclometallated analogues of platinum terpyridine complexes: Kinetic study of the strong -donor cis and trans effects of carbon in the presence of a -acceptor ligand backbone, A. Hofmann, L. Dahlenburg and R. van Eldik, Inorg. Chem., 42, 6528 (2003).
9. The profound influence of a single metal-carbon bond on the reactivity of bio-relevant cobalt(III) complexes, M.S.A. Hamza and R. van Eldik, Dalton Trans., 1 (2004).
One doctoral position
Starting date November 2006, duration 12 months
- self contained furnished flat, 400-600 €/month
- furnished room in a shared flat, from 3 to 4 people, range 150-250 €/month
A number of university guest houses offer temporary accommodation.
Other living expenses
Around 500 €/month.
Institute for Inorganic Chemistry
University of Erlangen-Nürnberg
Home page: www.anorganik.uni-erlangen.de
Magic Show: www.zaubervorlesung.de