Bis(phosphane oxide) Adducts of Rh2(MTPA)4 — Kinetics and Chirality Discrimination

The symmetrical bis(phosphane oxide) 1 and its chiral derivatives 2 and 3 form a variety of adduct species with the dirhodium complex [Rh−Rh] which can be identified by low-temperature 1H and 31P NMR spectroscopy by using varying [Rh−Rh]:ligand ratios. The asymmetric bis(phosphane oxide) 3 shows a distinct preference for binding through the Ph2P=O (Pa) as compared to the tBu(Ph)P=O (Pb) functionality due to the bulky tert-butyl group. The chiral bis(phosphane oxides) 2 and 3 form complex mixtures of various adduct species. Nevertheless, it is possible to monitor enantiomeric compositions from various NMR signal duplications at 213 K and even at room temperature or slightly elevated temperatures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)