Augmentation of Alkaline Earth Reactivity: An FLP Analogy

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Catalysis, the acceleration of chemical transformation, is the key to realising environmentally friendly and economical processes for the conversion of both conventional (fossil) and alternative (e.g. biomass and carbon dioxide) chemical feedstocks. Catalysts act by reducing the energy required for a reaction to proceed and will, thus, occupy a key role in the world's energy future. Many of the most useful soluble and solid catalysts incorporate precious metals such as rhodium, palladium, platinum and ruthenium. These metals are expensive and their supply is limited. There is, therefore, a need for the development of non-precious-metal catalysts as replacements.In response to these requirements, the last decade has seen emergence of s- and p-block compounds as inexpensive and ecologically benign catalytic reagents. The applicant's previous research has led the way in the development of group 2 reagents, particularly those based on magnesium and calcium (the eight and four most earth-abundant elements respectively) for a wide variety of catalytic transformations. Although this has included some of the most practically desirable transformations, the usefulness of currently available group 2 reagents is limited by their absolute reactivity. A detailed mechanistic approach to the study of these reactions has allowed the emergence of more generalised models for the chemical reactivity of these previously under-appreciated elements. This understanding is based on a polarisation model intrinsic to the bonding of most substrate molecules to a highly electropositive group 2 centre. The charge separation induced across a substrate molecule by these species may be viewed as resulting from reactivity closely related to another emerging field, 'frustrated' Lewis pair chemistry. In this latter case, a wide variety of small molecules may be activated through a cooperative interaction of a high energy vacant molecular orbital and a low energy filled atomic orbital. This proposal wishes to extrapolate this hydpothesis to apply the FLP concept to design new group 2 species of unparalleled reactivity. In so doing the new reagents will enable catalytic systems that combine the environmental and fiscal benefits of group 2 chemistry with the enhanced and readily manipulated FLP reactivity.