Chiral Tricationic Tris(1,2-diphenylethylenediamine) Cobalt(III) Hydrogen Bond Donor Catalysts with Defined Carbon/Metal Configurations; Matched/Mismatched Effects upon Enantioselectivities with Enantiomeric Chiral Counter Anions
Connor Q. Kabes, William J. Maximuck, Subrata Ghosh, Anil Kumar, Nattamai Bhuvanesh, John A. Gladysz
Abstract
The enantiopure and diastereopure salts Λ- or Δ-[Co((S,S)-dpen)3]3+ 2Cl–BArf– (Λ- or Δ-(S,S)-13+ 2Cl–BArf–; dpen/BArf = 1,2-diphenylethylenediamine/B(3,5-C6H3(CF3)2)4) and Λ-(S,S)-13+ 3Cl– are treated with salts of the enantiopure chiral monoanions (A–) or dianions (A2–) 3-bromocamphor-8-sulfonate (camphSO3–), 1,1′-binaphthyl-2,2′-diyl phosphate (and three 3,3′-disubstituted derivatives), a related biphenanthryl species, tartrate, and Sb2(tart′)22– (tart′ = [−O2C–CHO––CHO––CO2–]). The lipophilic salts Λ- or Δ-(S,S)-13+ 2A–BArf–, Λ-(S,S)-13+ A2–BArf–, and Λ-(S,S)-13+ 3A– are isolated as hydrates and characterized by NMR and microanalyses. In the presence of tertiary amines, many of these are highly enantioselective catalysts for additions of 1,3-dicarbonyl compounds to trans-β-nitrostyrene and di-tert-butylazodicarboxylate. The ee values for diastereomeric salts can exhibit significant differences (avg/high/median Δ%ee = 10/63/6; matched/mismatched effect), and in a few cases, they are better than those obtained with Λ- or Δ-(S,S)-13+ 2Cl–BArf–. The crystal structure of Δ-(S,S)-13+ 2(1S)-camphSO3–BArf– shows that the two sulfonate moieties hydrogen-bond to opposite (idealized) C3-symmetric faces of the trication, with a separate oxygen atom associated with each of the three synperiplanar NH groups.