Cobalt(III) Complexes with 4-Methyldiethylene-triamine[2,2'-Methyliminodi(ethylamine)]: Their Separation, Characterization and Reactions

An efficient synthesis of 2,2'-methyliminodi(ethylamine) trihydrochloride (medien,3HCl) from diethylenetriamine (dien) is described. The reactions [CO(NH3)5Cl] C12+2medien, and oxygen-oxidation of cobalt(II)+2medien, with charcoal give only the s-fac isomer of [Co(medien)]3+. A little s-fac-[Co(dien)(medien)]3+ is also always formed, and this arises by demethylation of s-fac-[Co(medien)2]3+ with oxygen on charcoal. The substitution reaction [Co(NH3)5Cl] Cl2 + 1.6 medien + 0.4 dien produces a complicated mixture of s-fac-[Co(medien)2]3+, all three isomers s-fac, u-fac and mer of [Co(dien)(medien)]3+, and all three isomers of [Co(dien)2]3+. A procedure using exchanges of the counter-ions, crystallization, and chromatography on SP-Sephadex cation-exchange resin is described for separating and isolating the products, and pure s-fac-[Co(dien)(medien)] (ClO4)3 is obtained preparatively by this means. From isomerization of this complex in water the pure u-fac and mer [Co(dien)(medien)]3+ isomers are isolated. 13C and 1H N.M.R. and visible spectra of the compounds are reported. The equilibrium isomer proportions of [Co(dien)2]3+, [Co(dien)(medien)]3+ and [Co(medien)2]3+ are discussed. Some particular charcoal samples, which lack catalytic activity towards cobalt(III) equilibrations, effect the unusual conversion of s-fac-[Co(medien)2]3+ into u-fac-[Co(arnam)]3+ (amam = 2,3-bis[(2-aminoethyl)(methyl)amino-ethylimino]-1-methylpiperazine).