Yuzo Yoshikawa

Chromatographic separation of geometric isomers of lambda(OB)-tris-(1-propylenediamine)cobalt(III) ion

(Received 19 February 1973) There are four possible isomers for trls(l-propylenedlamine)cobalt(lll) ion, A(lel)(fac), A(lel)(mer), /k(ob)(fac) and A(ob)(mer). Among them the ~(lel)(fac) isomer has been well studied for various properties including the absolute conflguration(1). In 1968 MacDermott(2) separated the A (lel)(mer) isomer from the ~(lel)(fac) isomer by fractional crystallizatlon, but the former was isolated only as amorphous glasses, and it was not possible to determine its crystal structure(3). We have isolated the A(ob)(fac) and A (ob)(mer) isomers in pure states by the column chromatography on ion-exchange Sephadex(4)(FIG.l). The [Co(l-pn)3]3+ ion was prepared by reacting 1 mole of [CoBr(NH3)5]Br 2 and 3 moles of l-propylenediamlne(l-pn) in the presence of active charcoal, and the resulted solution was subjected to column chromatography after removal of charcoal. One to two milllmoles of the prepared complex was adsorbed on a column (@2.7 x 135 cm) of SP-Sephadex and eluted with a 0.18M solution 2~. (mer) j~. (fac)

15N NMR studies of cobalt(III) complexes: [Co(NH3)5(15NH3)]3+ and [Co(15NH2CH2CH215NH2)3]3+

Abstract 15 N Fourier-transform nuclear magnetic resonance spectroscopy enabled the determination of spin-spin coupling constants 1 J ( 59 Coue5f8 15 N) and spin-lattice relaxation times T 1 ( 59 Co) for hexaamminecobalt(III) complex [Co(NH 3 ) 5 ( 15 NH 3 )] 3+ and tris-(ethylenediamine[ 15 N, 15 N])cobalt(III) complex. The obtained values are as follows: 1 J ( 59 Coue5f8 15 N) = 62.5 (± 1.0)Hz, T 1 ( 59 Co) = 38 msec for the hexaamminecobalt complex, and 1 J ( 59 Coue5f8 15 N) = 63.8 (± 1.0)Hz, T 1 ( 59 Co) = 13 msec for the tris(ethylenediamine)cobalt(III) complex. These T 1 ( 39 Co) values are well consistent with the values obtained from multi-pulse spin-echo measurement.

Geometrical and optical isomers of diethylenetriaminemonoacetato(ethylene-diamine)cobalt(III) ion and their isomerism

Abstract Two isomers of the complex ion in the title were obtained and each isomer was resolved chromatographically into its antipodes. The two isomers with their isomer proportion of 27.9 and 72.1% in the equilibrium mixture were assigned to α and β( mer -N) isomers, respectively, of three possible geometrical isomers, from the measurements of their absorption, circular dichroism, and NMR spectra. Preference of the β( mer -N) to the isomer and very poor yield of an expected β( fac -N) isomer were confirmed by conformational analyses carried out for each structure of the isomers of Λ configuration, with possible configurations around nitrogen atoms and conformations of chelate rings. They gave minimized total strain energies of 43.13, 44.24, and 52.63 kJ/mol for the Λ- R , R (en:λ) structure of a β( mer -N) isomer, the Λ- S , R (δ,δ) structure of an α isomer, and a Λ- R , S (λ,λ) structure of a β( fac -N) isomer, respectively. From the results, configurations and conformations of the enantiomers of the resolved β( mer -N) and its isomers were deduced. An unfound isomer, β( fac -N) isomer, is thought to be very unstable; it would exist as less than 2% of the amount of β( mer - N) isomer, even if it were present in the reaction mixture.