Syntheses and Vibrational Circular Dichroism Spectra of the Complete Series of [Ru((−)- or (+)-tfac) n (acac)3−n ] (n = 0 ∼ 3, tfac = 3-Trifluoroacetylcamphorato and acac = Acetylacetonato)

Twenty four kinds of Ru(III) complexes expressed by the formula of Δ- or Λ-[Ru((−)- or (+)-tfac)n(acac)3−n ] (n = 1, 2, and 3, (−)- or (+)-tfac = (−)- or (+)-3-trifluoroacetylcamphorato and acac = acetylacetonato) were prepared in a pure diastereomeric form. The separation of these diastereomers was accomplished chromatographically by rational use of two antipodal chiral columns. The separated complexes were identified by means of mass spectra, 1H NMR, electronic circular dichroism, and partly X-ray diffraction analyses. When a pair of Δ- and Λ-[Ru(acac)3] (n = 0) was added to this group, they constituted the complete series of mixed ligand complexes including ligand chirality under the condition of no mixing of chiral ligands. The vibrational circular dichroism (VCD) spectra of their CDCl3 solutions were recorded in the wavenumber region of 1000∼1800 cm−1. The results provided a benchmark for systematically examining the effects of the stereochemical properties on VCD spectra such as the degree of ligand substitution, ΔΛ configurations, geometrical isomerism, and ligand chirality. As a result, the geometrical isomers of trans- or cis-[Ru((−)- or (+)-tfac)2(acac)] and mer- or fac-[Ru((−)- or (+)-tfac)3] were clearly differentiated by their VCD signals, which was hardly possible from their IR spectra alone.