Iodorhodium(III) tetramethylchiroporphyrin: potential reagent for chiral selection and analysis of amino compounds

The iodorhodium(III) complex of tetramethylchiroporphyrin was prepared and its X-ray structure was determined. With its single site available for coordination of an amine group, this chiral metallohost is a convenient reagent for the chiral analysis of amino compounds by 1H NMR. It affords a 1:1 adduct with (R)- or (S)-2-aminopropanol, and it binds rac-2-aminopropanol with an enantiomeric excess of 69% (enantioselective ratio 5.5) in favour of the (R)-enantiomer at the thermodynamic equilibrium after several days. When compared to analogous experiments with chlorocobalt(III) chiroporphyrin, these results show that enantiodiscrimination can be metal-dependent.