CO2 Utilisation and Transformation via Transition Metal Activation by Cobalt, Rhodium and Iridium

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Carbon dioxide is a rather unreactive compound of high thermodynamic and kinetic stability. Its abundance, non-toxicity, and simple manageability in connection with its low price make this substance a highly interesting alternative carbon source for chemical syntheses. Keeping the recent developments in CCS technologies (CCS = CO2 Capture and storage) as well as the European Union Emission Trading Scheme for CO2, launched in 2005, in mind, a further fall in price seems reasonable. This trend will lead to an increased economic interest in CO2 utilization in near future. Unfortunately, until now only a few chemical processes are known, in which carbon dioxide is utilized as an alternative carbon source in industrial scale. Prior to use, an activation of carbon dioxide is often necessary in such processes and can be achieved in different ways. Beside electrochemical methods or the use high energy substrates a variety of metal complexes can be applied to achieve activation in order to subsequently use CO2 in stoichiometric or catalytic transformations. In the simplest case, this activation proceeds via interaction of one carbon dioxide molecule and only one metal center leading to carbon dioxide complexes with varying coordination modes of the CO2 ligand in dependence of oxidation state of the metal and the co-ligands present. The main goals of this research project are the syntheses of such CO2 complexes of cobalt, rhodium and iridium and the investigation of their properties. These compounds will be evaluated in reactions with model substrates like hydrogen or alkenes to establish a relationship between their structures with respect to the coordination mode of the CO2 ligand and the resulting reactivity of the complexes in order to gain fundamental insights into the metal mediated CO2 activation process. For further information on the influence of auxiliary ligands and solvents, these parameters will be systematically varied. The information gained will help to develop novel tailor-made catalytic systems for CO2 transformations utilizing the metals cobalt, rhodium and iridium. In this connection, contributions to the development of improved protocols for the hydrogenation of carbon dioxide to formic acid and finally methanol as potential fuel are among the long term goal of this research project.