Abstract
The kinetics of the formation/acid-catalysed aquation (SO2 elimination), CoIII-OSO2+→CoIII-SO3+ isomerization, intramolecular reduction and base hydrolysis of the O-bonded sulfito complexes, cis-[Co(en)2(RNH2) (OSO2)]+ (en=ethylenediamine; R=H, Me, Et, PhCH2 and C6H11) have been investigated. The spontaneous and base-catalysed isomerization involve loss of monodentate amine ligands from the CoIII centre to give trans-[Co(en)2(SO3-S)2]– (in excess SO32–) or trans-[Co(en)2(OH)(SO3-S)] (under base hydrolysis conditions). This result is presumably associated with a cis-labilizing action of the O-bonded sulfite. Steric retardation is observed for the formation and acid-catalysed aquation of the O-sulfito complex, the effect being relatively larger for the latter reaction. Steric acceleration is observed in the isomerization and intramolecular reduction and base hydrolysis of the O-sulfito complexes.¶ The trans-S-disulfito complex is prone to fast H+-catalysed aquation {k=(1.52±0.06)×104 dm3 mol–1 s–1, ΔH‡=81 ± 2 kJ mol–1, ΔS‡= 108 ± 5 J K–1 mol–1 at 25°C, I = 1.0 mol dm−3} yielding trans-[Co(en)2 (SO3-S)(OH2)]+.
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