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.

Graphical abstractThe 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 full-size imageDownload 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.