Octahedral cobalt(III) complexes in dipolar aprotic solvents. XI. Anation of cis-chlorodimethylformamidebisethylenediaminecobalt(III) by bromide ion, and solvolysis and isomerization of cis-and trans-bromochlorobisethylenediaminecobalt(III) ions in anhydrous N,N-dimethylformamide

Abstract

The anation of the cis-chlorodimethylformamidebisethylenediaminecobalt(III) ion (cis- [CoCl(DMF) en₂]²⁺) by bromide ion in N,N-dimethylformamide (DMF) has been studied. The reaction has an S_NIIP¹ mechanism, and when due allowance is made for ion association its activation parameters closely parallel those of other SNIIP anation reactions in DMF. The solvolysis and isomerization of the dichlorobisethylenediaminecobalt(III) ions (cis- and trans-[CoCl₂ en₂]+) and the bromochlorobisethylenediaminecobalt(III) ions (cis- and trans- CoBrCl en₂]⁺) in DMF have been examined over a range of anion concentration. In all cases solvolysis reactions are important, although direct isomerization appears to become an important path for the reaction of the trans complexes at high anion concentrations. Solvolysis of the cis-[CoCl₂ en₂]+ ion involves an S_N2 mechanism.¹ The cis-[CoBrClen₂]+, trans-[CoCl₂ en₂]⁺, and trans-[CoBrCl en₂]⁺ ions all react by an S_N1 mechanism.