Reactivity Studies of Chelated Maleate Ion: Stereoselectivity and Structural Correlations

Article abstract of DOI:10.1021/ja00322a016

cobalt(III) ion (Λ-⁺ (1)) undergoes parallel OH^- catalyzed reactions in aqueous solutions, first order in ->, to give stereospecific addition of a 2-aminoethaneaminato ion at the chelated olefin center and thereby (R)-N-(2-aminoethyl)aspartate (R-aea) bound as a quadridentate in Λ-mer(5,5)-⁺ (3) (k = 0.09 M^-1 s^-1, 25 deg C, μ = 1 M).The other path (k = 0.36 M^-1 s^-1) produced cis- and trans- complexes (19, 20) where the ring-opened monodentate ligand is unreactive.Similar stereoselectivity was observed for the reaction in liquid NH3 and dimethyl sulfoxide without ring opening.Equilibrium studies established that the fac(5,5)-⁺ isomer was more stable (96percent) than the mer isomer (4percent) produced by kinetic control.In the alkaline conditions the mer isomer also dissociates a carboxylate group and isomerizes about the cobalt center.The kinetics of this process were also followed.X-ray crystallographic analyses of the Λ-PF6*2H2O (I), racemic ClO4*2H2O (II), and Δ-fac(5,5)-BCS*3H2O (III) (BCS^- = (+)₅₈₉-α-bromocamphorsulfonate anion) salts were carried out to determine their connectivities and absolute configuration by the anomalous dispersion method.For I: space group P2₁; a = 11.629(6) Angstroem, b = 7.701(4) Angstroem, c = 9.379(4) Angstroem, β = 97.18(1) deg, Z = 2, 4336 reflections (F² >= 3.0?(F²)), residual R₁ = 0.045.For II: space group P2₁/c; a = 7.191(1) Angstroem, b = 10.915(2) Angstroem, c = 20.723(6) Angstroem, β = 91.41(1) deg, Z = 4, 4796 reflections (F² >= 3.0?(F²)), residual R₁ = 0.045.For III: space group P1; a = 6.976(1) Angstroem, b = 7.242(1) Angstroem; c = 14.248(2) Angstroem, α = 76.89(1) deg, β = 84.61(1) deg, γ = 70.86(1) deg, Z=1, 4731 reflections (F² >= 3.0?(F²)), residual R₁ = 0.040.The absolute configuration of the complex cation was also deduced from that of the BCS^- anion.The chiral N-(2-aminoethyl)aspartate was biologically inactive in an aspergillomarasmine sense, but the results in general provide some support for Glusker's ferrous wheel mechanism for aconitase.