Cationic half-sandwich quinolinophaneoxazoline-based (η6-p-cymene)ruthenium(ii) complexes exhibiting different chirality types: synthesis and structural determination by complementary spectroscopic methods

Abstract

Novel, optically pure 2-{4-methyl[2]paracyclo[2](5,8)quinolinophan-2-yl}-4-aryl/alkyloxazolines (QUIPHANOX) exhibiting both planar and central chirality have been prepared by reacting (R_p)- and (S_p)-2-cyano-4-methyl[2]paracyclo[2](5,8)quinolinophane with 2-aryl/alkyl-2-aminoethanols. The reaction of each of the above N,N-ligands with [Ru(η⁶-p-cymene)Cl₂]₂ in methanol, in the presence of either NH₄PF₆ or NaBPh₄, gave the corresponding half-sandwich [(η⁶-p-cymene)Ru(QUIPHANOX)Cl]⁺Y⁻, (Y⁻ = PF₆⁻, BPh₄⁻) as stable complex salts exhibiting planar and carbon- and metal-centered chirality. The unknown absolute configuration (AC) at the metal was determined by ¹H NMR and by theoretical calculations of electronic circular dichroism (ECD) spectra and subsequently confirmed by crystallographic X-ray analysis. (R_p) and (S_p)-ligands afforded (R_Ru)- and (S_Ru)-configured complexes, respectively, independent of the AC at the chiral carbon of the oxazoline moiety.