The robust readily available cobalt(iii) trication Co(NH2CHPhCHPhNH2)33+ is a progenitor of broadly applicable chirality and prochirality sensing agents

摘要

When NMR spectra of chiral racemic organic molecules containing a Lewis basic functional group are recorded in the presence of air and water stable salts of the cobalt(iii) trication [Co((S,S)-NH2CHPhCHPhNH2)3]³⁺ (>2³⁺), separate signals are usually observed for the enantiomers (28 diverse examples, >12 functional groups). Several chiral molecules can be simultaneously analyzed, and enantiotopic groups in prochiral molecules differentiated (16 examples). Particularly effective are the mixed bis(halide)/tetraarylborate salts Λ->2³⁺ 2X^–BArf^– (X = Cl, I; BArf = B(3,5-C6H3(CF3)2)4), which are applied in CD2Cl2 or CDCl3 at 1–100 mol% (avg 34 and 14 mol%). Job plots establish 1 : 1 binding for Λ->2³⁺ 2Cl^–BArf^– and 1-phenylethyl acetate (>4) or 1-phenylethanol (>10), and ca. 1 : 2 binding with DMSO (CD2Cl2). Selected binding constants are determined, which range from 7.60–2.73 M^–1 for the enantiomers of >10 to 28.1–22.6 M^–1 for the enantiomers of >4. The NH moieties of the C₂ faces of the trication are believed to hydrogen bond to the Lewis basic functional groups, as seen in the crystal structure of a hexakis(DMSO) solvate of Λ->2³⁺ 3I^–. These salts rank with the most broadly applicable chirality sensing agents discovered to date.