Base hydrolysis and mercury(II)-catalysed aquation of bis(ethylenediamine-NN′)(ethylenediamine-N)halogenocobalt(III) complexes
Abstract
The kinetics of base hydrolysis of the complexes cis-[CoX(en)2(en-N)]2+(X = Cl or Br) have been studied at 25 °C and I= 0.1M(Na[ClO4]) and kOHCl=(6.3 ± 0.3) and kOHBr=(4.1 ± 0.2)× 101 l mol–1s–1. The main product is [Co(en)2(en-N)OH]2+(ca, 97%) rather than [Co(en)3]3+. The ionization constants for the equilibria (i) and (ii) are pKlm 5.05 and pK2m 7.23. The mercury(II)-catalysed aquations have also been studied at 25 °C [Co(en)2(Hen-N)OH2]4+[graphic omitted][Co(en)2(Hen-N)OH]3++ H+(i), [Co(en)2(Hen-N)OH]3+[graphic omitted][Co(en)2(en-N)OH]2++ H+(ii)(I= 3.94M and [H+]= 0.94M) and kHgCl=(5.6 ± 0.3)× 10–3 and kHgBr=(5.0 ± 0.15)× 10–3 l mol–1 s–1. The major product (ca, 95%) is the complex [Co(en)2(Hen-N)OH2]4+. In dimethyl sulphoxide solution the complex [CoCl(en)2(en-N)]2+, in the presence of n-butylamine, undergoes cyclisation to [Co(en)3]3+. The reaction is first order in the complex and n-butylamine concentrations with k= 1.19 × 10–3 l mol–1 s–1 at 25 °C.
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