Syntheses of Families of Enantiopure and Diastereopure Cobalt Catalysts Derived from Trications of the Formula [Co(NH2CHArCHArNH2)3]3.
Aerobic reactions of CoX2(X = OAc, Cl) or Co(ClO4)2with (S,S)-1,2-diphenylethylenediamine [(S,S)-dpen] in CH3OH, followed by HCl or HClO4additions, 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/BArf[BArf= B(3,5-C6H3(CF3)2)4], PF6/BArf, BF4/BArf, PhBF3/BArf, Cl/BArf20[BArf20= B(C6F5)4], BArf/BArf, BArf20/BArf20, BF4/BF4, PF6/PF6]. Mixed salts of the formula Λ- and Δ-[Co((S,S)-NH2CHArCHArNH2)3]3+2Cl-BArf-are similarly prepared (Ar = 4-C6H4n-Bu, 4-C6H4Cl, 4-C6H4CF3, 4-C6H4OCH3, α-naphthyl, β-naphthyl, 2-C6H4OBn). The diastereotopic NHH' protons exhibit different1H NMR signals; one shifts far downfield when X/X' = Cl/BArf(δ ca. 8.0 vs 4.0 ppm). This is believed to arise from hydrogen bonding between the two Cl-anions and the two C3faces 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., BArf-, BF4-, ClO4-), equilibria favor Δ diastereomers.
Department of Chemistry, Texas A&M University , P.O. Box 30012, College Station, Texas 77842-3012, United States.
Subrata K
SK
Ghosh
Department of Chemistry, Texas A&M University , P.O. Box 30012, College Station, Texas 77842-3012, United States.
Kyle G
KG
Lewis
Department of Chemistry, Texas A&M University , P.O. Box 30012, College Station, Texas 77842-3012, United States.
Anil
A
Kumar
Department of Chemistry, Texas A&M University , P.O. Box 30012, College Station, Texas 77842-3012, United States.
John A
http://orcid.org/0000-0002-7012-4872
JA
Gladysz