An SN2 Mechanism for the Aquation of the trans Dichloro Triethylenetetramine Cobalt (III) Ion

Abstract

THE aquation of the first chloride ion in dichlorobis-(ethylenediamine)cobalt(III) ions [Co en₂ C1₂]⁺ is characterized by retention of configuration in the cis¹ and extensive isomerization in the trans isomer². A similar pattern has now been observed for the aquation of the dichloro triethylenetetramine cobalt (III) isomers cis α, cis β and trans [Co trien Cl₂]⁺ (Fig. 1). The cis isomers lost one Cl⁻ at the same rate as the cis chloroaquo ions were formed and as mutarotation occurred (Table 1 (a) (rates c, s and p respectively)). These results implied full retention of configuration during the aquation process and the retention was verified by converting the chloroaquo products to the carbonate isomers with NaHCO₃ (ref. 3). The rotations observed, cis α, [M]_D = +4,700° cis β, [M]_D= −3,000°, agreed with those obtained for the fully resolved carbonate ions, α, [M]_D= +4,730°; β,[M]_D= −2,990°.