The robust, readily available cobalt(iii) trication [Co(NH2CHPhCHPhNH2)3]3+ is a progenitor of broadly applicable chirality and prochirality sensing agents

Quang H Luu; Kyle G Lewis; Anik Banerjee; Nattamai Bhuvanesh; John A Gladysz

doi:10.1039/c8sc01510d

The robust, readily available cobalt(iii) trication [Co(NH₂CHPhCHPhNH₂)₃]³⁺ is a progenitor of broadly applicable chirality and prochirality sensing agents

Chem Sci. 2018 May 11;9(22):5087-5099. doi: 10.1039/c8sc01510d. eCollection 2018 Jun 14.

Authors

Quang H Luu¹, Kyle G Lewis¹, Anik Banerjee¹, Nattamai Bhuvanesh¹, John A Gladysz¹

Affiliation

¹ Department of Chemistry , Texas A&M University , P.O. Box 30012 , College Station , Texas 77842-3012 , USA . Email: gladysz@mail.chem.tamu.edu.

Abstract

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^-BAr_f^- (X = Cl, I; BAr_f = 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^-BAr_f^- 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.