Dr Stephen Best
Position: Senior lecturer in Chemistry
Affiliation: School of Chemistry, University of Melbourne
The change in reactivity of transition metal complexes accompanying a change in redox state is a key distinguishing characteristic of the d-block elements. It is this characteristic that is pivotal to their remarkable ability to act as catalysts for an extraordinary range of reactions and explains the high incidence of transition metal compounds / clusters at the active sites of many enzymes.
In the broadest sense our work is driven by a desire to better understand the interplay between structural and electronic interactions that leads to the changes in structure, reactions and reactivity of metal complexes with a change in redox state. In some cases we take our inspiration from the metal complexes revealed by structural characterisation of metalloproteins but in others the focus is clearly on abiological systems.
An important strategy that we have pursued in recent years has been to develop techniques that permit spectroscopic examination of reactive electrogenerated species particularly using techniques such as infrared or UV-visible spectroscopy, an area of research known as spectroelectrochemistry (SEC).
Since our interests include the activation of gaseous species such as H2, CO, CO2, C2H2 etc. it has been necessary to develop techniques that permit our SEC experiments to be carried out at moderate gas pressures (0.1 to 1.o MPa). This provides a means of controlling the concentration of those species in our experiments and permits the systematic study of the coordination chemistry of gaseous molecules with metal complexes and clusters over a range of redox states.
Iron sulfur clusters are found at the active sites of numerous enzymes where they commonly facilitate electron transfer and substrate transformations. Processes involving assembly, rearrangement, degradation and ligand substitution are often triggered by a change in redox state. In addition to the more conventional spectroscopic techniques (IR, UV-Vis, EPR) used in these studies we have recently developed approaches that permit the extraction of structural information from transiently stable electrogenerated complexes using XAFS techniques.
The recent elucidation of the structure of the all-iron hydrogenase enzymes has lead to renewed interest in classical binuclear diiron compounds both as models of the H-cluster and as proton reduction catalysts. The reduction chemistry of these compounds is complex, but may be brought under a level of control using p(CO).