Title
Preparative resolution of stable enantio-enriched POCOP-based planar chiral pincer complexes
Author
Noel Angel Espinosa-Jalapa, Manuel Alejandro Roque Ramires, Rubén Alfredo Toscano, Jean-Pierre Djukic, Ronan Le Lagadec
Year
2017
Journal
Journal of Organometallic Chemistry
Abstract
The η6-coordination of the [CpRu]+ fragment to the aromatic ring of non-symmetric POCOP pincer derivatives of palladium and platinum based on a naphthoresorcinate backbone afforded in one step racemic rac-2a and rac-2b complexes (a = Pd, b = Pt) and the planar-chiral nature of the compounds was demonstrated by metathesis of the achiral PF6− counterion by enantiomerically pure Δ-tris(tetrachloro-1,2-benzenediolato)phosphate(V) chiral anion (Δ-TRISPHAT), followed by the physical separation of the diastereomers. The absolute configuration of one enantiomer of each pair was established by a single-crystal X-ray diffraction and was found to be pR according to the extended Cahn-Ingold-Prelog rules. Upon release of the chiral auxiliary (metathesis of [Δ-TRISPHAT]- by PF6−), the pairs of enantiomers pR-2a/pS-2a and pR-2b/pS-2b were fully characterized. Each pair of enantiomers exhibits opposite (+)/(−) optical rotation and afforded reciprocal circular dichroism with Cotton effect of similar absolute intensity. Each enantiomer was obtained in an enantiomeric excess (ee) > 90% with retention of their absolute configuration confirmed by X-ray diffraction crystallographic analysis of pR-2a and pR-2b. This report represents an unprecedented study in which the resolution of the racemic compound into its enantiomers was achieved in a preparative manner and the absolute configuration as well as the planar-chiral nature of the heterobimetallic complex were unambiguously demonstrated.
Instrument
J-810
Keywords
Circular dichroism, Stereochemistry