Chiral metal complexes. 48. Stereoselectivity in ternary Co(III) complexes of N,N′-di (2S-pyrrolidin-2-yl)-1R, 2R-diaminocyclohexane

The ternary complexes Δ-β₁-, Δ-β₂- and Δ-β₂-[Co(S,R,R,S-pychxn)(S-ala)]²⁺ have been synthesised and characterised using electronic and CD spectroscopy and X-ray diffraction methods (S,R,R,S-pychxn = N,N′-di(2S-pyrrolidin-2-yl)-1R, 2R-diaminocyclohexane; S-alaH = S-alanine). A single-crystal X-ray structural study of the diperchlorate monohydrate salt of the Δ-β₁ diastereoisomer has been undertaken. The complex is orthorhombic, space group P2₁2₁2₁, with a = 9.607(3), b = 11.803(5) c = 23.936(7)Å, Z = 4. The structure was refined by full-matrix least-squares methods to R = 0.061 and R_w = 0.060 for 2648 reflections with I > 3σ(I). Both nitrogen atoms of the coordinated pyrrolidyl groups adopt S configurations but the two internal nitrogen donors have opposite configurations, with that at the fold of the tetradendate being R. It is apparent that S,R,R,S-pychxn is not stereospecific in its coordination to octahedral transition metal ions, as has been previously claimed.