EXAFS Investigations of Metal Organic Synthesis Tools

Grignard Compounds RMgX (R=organic group; X=Cl, Br, I) are common tools in inorganic and organic synthesis. The structure of these substances in solution, however, is unknown. To answer this question we performed EXAFS measurements at the Br-K-edge in absorption mode and at the Mg-K-edge in fluorescence mode. Rom these complementary data a consistent model of the structure of the investigated Grignard compounds in solution is deduced. A similar class of reagents are Reformatsky compounds RZnBr (R=organic group), which possess a very high chemical selectivity in contrast to the Grignard compounds. In order to determine the degree of association in solution we performed EXAFS measurements at the Zn-K-edge as well as at the Br-K-edge. To learn more about the chemical behavior we varied the organic residue and the solvent. Carbenoids of the general formula XC-(RIRz)z-M (R=organic group; M=metal, e.g. Li, Mg; X=leaving group, e.g. C1, Br, I, NOe) are modern tools in the synthesis of chiral organic compounds, but have the disadvantage to decompose at temperatures higher than -50°C. In detail we investigated Mg[Ph-CHz-C(H)Br]z disolved in THF. From the EXAFS spectroscopical determined data it was possible to derive a detailed structure model, especially to determine the geometry of the a-carbon atom.