Syntheses of Families of Enantiopure and Diastereopure Cobalt Catalysts Derived from Trications of the Formula [Co(NH2CHArCHArNH2)3]3

Abstract

Aerobic reactions of CoX₂ (X = OAc, Cl) or Co(ClO₄)₂ with (S,S)-1,2-diphenylethylenediamine [(S,S)-dpen] in CH₃OH, followed by HCl or HClO₄ additions, give the diastereomeric lipophobic salts Λ-[Co((S,S)-dpen)₃]³⁺3Cl^- [Λ-(S,S)-1³⁺3Cl^-] or Δ-(S,S)-1³⁺3ClO₄^- (60-65%) with high degrees of selectivity. Anion metatheses (room temperature) and equilibrations (charcoal, CH₃OH, 70 °C) show that the former is more stable than Δ-(S,S)-1³⁺3Cl^-, and the latter is more stable than Λ-(S,S)-1³⁺3ClO₄^-. Additional anion metatheses lead to large families of lipophilic salts Λ- and Δ-(S,S)-1³⁺2X^-X'^- [X/X' = Cl/BAr_f [BAr_f = B(3,5-C₆H₃(CF₃)₂)₄], PF₆/BAr_f, BF₄/BAr_f, PhBF₃/BAr_f, Cl/BAr_f20 [BAr_f20 = B(C₆F₅)₄], BAr_f/BAr_f, BAr_f20/BAr_f20, BF₄/BF₄, PF₆/PF₆]. Mixed salts of the formula Λ- and Δ-[Co((S,S)-NH₂CHArCHArNH₂)₃]³⁺2Cl^-BAr_f^- are similarly prepared (Ar = 4-C₆H₄n-Bu, 4-C₆H₄Cl, 4-C₆H₄CF₃, 4-C₆H₄OCH₃, α-naphthyl, β-naphthyl, 2-C₆H₄OBn). The diastereotopic NHH' protons exhibit different ¹H NMR signals; one shifts far downfield when X/X' = Cl/BAr_f (δ ca. 8.0 vs 4.0 ppm). This is believed to arise from hydrogen bonding between the two Cl^- anions and the two C₃ faces of the D₃-symmetric trication, each of which feature three synperiplanar NH groups. When all of the anions are poor hydrogen-bond acceptors (e.g., BAr_f^-, BF₄^-, ClO₄^-), equilibria favor Δ diastereomers.