Synthetic and spectroscopic characterization of Rh(I)-( S )-amino acid complexes with diphosphine and triphosphine ligands

Abstract

Reaction of [Rh(η⁴-cod)(S)-amino-acidato] ((S)-amino acidate = (S)-O₂C-CHR-NH₂; cod = cycloocta-1,5-diene) with 1,2-bis(diphenylphosphino)ethane (dppe) affords the ionic [Rh(dppe)₂]{(S)-O₂C-CHR-NH₂} (R = Me, I; Ph, II) complexes. Reactions with 1,3-bis(diphenylphosphino)propane (dppp) or 2,2,2-tris(diphenylphosphinomethyl)ethane (triphos) give the neutral [Rh(dppp){(S)-O₂C-CHR-NH₂}] (R = Me, III; Ph, IV) or [Rh(η²-triphos){(S)-O₂C-CHR-NH₂}] (R = Me, V; Ph, VI) complexes. The complexes are characterized by elemental analysis, UV–Vis-, IR-, ¹H/³¹P{¹H} NMR- and mass-spectroscopy. Two molecules of dppe coordinate to the Rh(I) symmetrically by replacing both cod and (S)-amino acidate to give I–II. Only one molecule of dppp (or triphos) coordinate to the Rh(I) asymmetrically by replacing only cod to give III–VI. Two diastereomeric Rh(I)-complexes are present in V and VI. The results further suggest that the ligands are arranged in a distorted square planar geometry around the Rh(I) centre. The use of triphos instead of dppe or dppp yields the same coordination sphere.