Half-sandwich organometallic complexes with stereogenic metal centres: Synthesis and characterization of diastereomeric [(ηn-ring)M(Aa)X] (Aa = α-amino carboxylate) compounds

Diastereomeric mixtures of epimers at metal of the α-amino carboxylate compounds [(ηn-ring)M(Aa)Cl] [(ηn-ring)M = (η5-C5Me5)Rh(III), (η5-C5Me5)Ir(III), (η6-p-MeC6H4iPr)Ru(II); Aa = α-amino carboxylate] can be readily prepared from the corresponding acetylacetonate compounds [(ηn-ring)M(acac)Cl]. In general, even below 0 °C, these complexes epimerise at the metal. The absolute configuration at the metal has been determined by X-ray diffractometric methods and NMR and CD spectroscopies. The molecular structures of the complexes [(η5-C5Me5)M(Aa)Cl] [M(Aa) = Rh(l-Pro), Ir(l-Pro), Rh(MePro), Ir(MePro)] and [(η6-p-MeC6H4iPr)Ru(Aa)Cl] (Aa = Hyp, MePhe, MePro) are reported. Related iodide complexes, [(ηn-ring)M(Aa)I], can be prepared from the corresponding chlorides by halogen metathesis.

The determination of the absolute configuration of a family of half-sanwich α-amino carboxylates of Rh, Ir, or Ru indicate that the diastereomeric composition of these complexes is strongly influenced by the formation of intermolecular nets of hydrogen bonds.Figure optionsDownload as PowerPoint slideHighlights
► We prepare a family of half-sanwich α-amino carboxylates of Rh, Ir, or Ru.
► Amino acids govern the encountered diastereoselectivity.
► The absolute configuration is determined by X-ray, NMR and CD measurements.
► Intermolecular nets of hydrogen bonds control the diastereomeric composition.