Metal Complexes of Peptides. VI. Di-μ-hydroxo–Dicobalt(III) Complexes Containing Peptides

Two isomers of the dinuclear complex with β-alanyl-L-aspartate (β-ad), glycinate (gly), and ethylenediamine (en), [Co(β-ad)Co(gly)(en)(μ-OH)2]+, were prepared by treating an aqueous solution containing [Co(β-ad)(OH2)2] and [Co(gly)(en)(OH2)2]2+ under basic conditions. The geometrical structures and absolute configurations of these isomers were assigned on the basis of the NMR, UV, and CD spectral data; the assignments were confirmed on the basis of the spectral data of the mononuclear species that were obtained by the acid hydrolysis of the isomers. The faster eluted isomer (eluted with H2O on an SP-Sephadex (K+ form) column) consists of [Co(β-ad)(μ-OH)2] (β-ad coordinates to cobalt(III) as a tetradentate) and Δ-fac(O)-[Co(gly)(en)(μ-OH)2] moieties, and the later consists of [Co(β-ad)(μ-OH)2] and Λ-fac(O)-[Co(gly)(en)(μ-OH)2]. Another di-μ-hydroxo–dicobalt(III) complex containing β-alanyl-L-histidinate (car), [Co2(car)2(μ-OH)2], was also prepared by treating an aqueous solution containing [Co(car)(OH2)2]+ under basic conditions. The dinuclear structures of these complexes are stable for several days in the neutral aqueous solutions.