Assignment of the absolute configuration of hydroxy and amino carboxylic acids by circular dichroism of their transition metal complexes

Optically active carboxylic acids can act as uni- or bidentante ligands in complexes of general formula [M2(O2CR)4] +k X-k (M = Mo, Rh or Ru). An in situ exchange of ligand(s) gives rise to several Cotton effects in the spectral range from 800 to 200 nm. In the case of molybdenum complexes with optically active hydroxy and amino acids a hexadecant rule is valid for the two Cotton effects between 400 and 300 nm. For rhodium and ruthenium complexes it was found that the sign of Cotton effects at around 600 nm can be correlated with the structure of investigated acids.