J. Phys. IV France 7 (1997) C2-947-C2-948
EXAFS Investigations of Metal Organic Synthesis ToolsT.S. Ertel, W. Hörner, I. Abraham and H. Bertagnolli
Universität Stuttgart, Institut für Physikalische Chemie, Pfaffenwaldring 55, 70569 Stuttgart, Germany
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. From 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 cornpounds. 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-(R1R2)2-M (R=organic group ; M=metal, e.g. Li, Mg ; X=leaving group, e.g. Cl, Br, I, NO2) 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-CH2-C(H)Br]2 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 α-carbon atom.
© EDP Sciences 1997