Asymmetric Catalysis with Alkaline Earth Metals: Towards Greener Chemical Processes

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Catalysts play an important role in chemical processes, both in academic research and on the worldwide industrial stage. Catalysts are not consumed by chemical reactions, but act by reducing the energy required for a reaction to proceed, thus reducing the reaction temperature, whilst at the same time increasing the selectivity of the reaction. In many cases chemical reactions are not possible without a catalyst. Catalysts are therefore an essential component of green chemical processes, increasing the efficiency of reactions and enabling new substances to be prepared. Catalysts are ubiquitous in commercial chemical production; with some 80% of feedstock chemicals produced using a catalyst. Many of the catalysts are based upon expensive rare metals, the use of which presents a number of problems. By virtue of their rarity, at the current rate of consumption many of these metals will become uneconomical to mine by the end of this century. In the short term, the mining and recycling costs associated with using these metals are significant, and can be prohibitive. This proposal aims to develop the emerging area of asymmetric catalysis using the inexpensive and environmentally benign Group 2 metals, particularly calcium, as a potential solution to this problem.Group 2 metals have shown much recent promise, with applications in catalysis showing their potential in this area. The Group 2 metals are therefore poised to make a significant contribution to Green Catalysis , as chemists seek to develop new and emerging technologies to render existing chemical processes cleaner whilst reducing costs. One of the main limitations associated with Group 2 metals is the stability of well-defined molecular species in solution; this has the tendency of rendering complexes either inactive or non-selective in catalysis. There have been important recent developments with non-stereoselective systems regarding the preparation of stable complexes. Our main objective is therefore to advance the catalytic applications of Group 2 metals beyond their current level, and into the arena of asymmetric catalysis.To this end, a series of chiral supporting ligands will be developed which are designed to increase the stability of Group 2 metal complexes. The complexes thus formed will enable the stereodirecting properties to be controlled as well independently controlling the ligand binding strength, such that an optimum binding strength can be found without compromising on catalytic activity. The coordination chemistry and reactivity of Group 2 complexes will be studies in order to assess their stability, and their reactivity towards unsaturated substrates which are pertinent to catalytic reactions.The catalytic applications described in this proposal will concentrate on the asymmetric hydroamination reaction, a 100% atom efficient synthetic route to a plethora of organic products and intermediates. Should the catalysts enable stereocontrol over the reaction products, this will open the door for further developments in asymmetric catalysis using Group 2 metals, moving a step closer to cleaner and inexpensive catalytic processes.