1083100-07-5Relevant academic research and scientific papers
Synthesis, characterization and diastereoselective coordination of a planarly chiral, hybrid ferrocene ligand, (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid
Stepnicka, Petr
, p. 567 - 575 (2007/10/03)
Hydrolytic cleavage of the dihydrooxazole ring in (Sp)-2-{2-(diphenylphosphino)ferrocenyl}-4-(1-methylethyl)-4, 5-dihydrooxazole affords the planarly chiral functionalized phosphine, (Sp)-2-(diphenylphosphino)-ferrocenecarboxylic acid, (Sp)-Hpfc, in two steps and 65% yield. (Sp)-Hpfc, all intermediates and the corresponding phosphine oxides were characterized by elemental analysis, multinuclear NMR and IR spectroscopy, and by optical rotation measurements. Solid-state structures of the phosphine oxides were further studied by X-ray crystallography to reveal extensive hydrogen bonding of various types. Neutralization of (Sp)-Hpfc with tert-BuOK followed by metathesis of the in situ obtained salt with [{RuCl(μ-Cl)(η6-p-cymene)}2] gives a chelate complex [RuCl(pfc-k2O,P)(η6-p-cymene)], 5, as a kinetic 1:1 mixture of diastereoisomers. Upon standing in solution, the diastereomeric mixture undergoes a spontaneous resolution to yield the thermodynamically preferred diastereoisomer (RRu,Sp)-5 whose configuration was corroborated by X-ray crystallography; the (RRu,Sp)-5 diastereoisomer was obtained in 82% yield by crystallization. The epimerization is likely initiated by a reversible Ru-O bond cleavage and suggests a hemilabile coordination of the (Sp)-pfc- anion. However, according to NMR spectra pure (RRu,Sp)-5 does not undergo diastereoisomer interconversion in a solution, which is in agreement with an unfavourable geometric arrangement of the (SRu)-epimer.
