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|Title:||Reactions of oxygen-bonded and sulphur-bonded (sulphito) pentaminecobalt(III) complexes in solution|
|Authors:||Dash, Anadi C|
Padhy, Bishnu P
|Abstract:||The reactions of cis-[Co(en)2(B)OH]2+ (B = NH3, imidazole) and trans-[Co(en)2(NH3)OH]2+ with aqueous sulphur dioxide instantaneously generate the corresponding oxygen-bonded sulphito species, N5CoOSO, as intermediates which undergo slow intramolecular isomerisation to the stable S-bonded sulphito species as the major product. Strong trans activation of S-bonded sulphite results in fast substitution of NH3 in trans-[Co(en)2(NH3)SO3]+ by SO resulting in trans-[Co(en)2(SO3)2]- in which both the SO are S-bonded to Co (III). On the other hand the species, cis-[Co(en)2(NH3/imH)SO3]+ are stable towards further replacement of imH or NH3 by SO in the time scale of measurement. Simultaneously intramolecular reduction of O-bonded sulphito species, a process which is relatively more facile for the cis-complexes, also occurs to the extent of ~30%. The kinetics of intramolecular isomerisation and reduction of these in situ generated oxygen-bonded sulphito complexes have been investigated over the temperature range of 30-45°C (I = 0.3 mol dm-3).The rates and activation parameters of these reactions are reported and compared with previously published related data. It is worth noting that while increasing chelation of Co (III) centre by multidentate amine ligand enhances rate of isomerisation of N5CoO-SO to S-bonded sulphito species, reverse trend in reactivity is observed for intramolecular reduction of O-bonded sulphito complexes; kred follows the sequence: (NH3)5CoOSO> cis-[Co(en)2 (B)OSO2]+ (B = NH3, imH) > trans-[Co(en)2NH3OSO] > > (tetren)CoOSO, (tetren =tetraethylenepentamine), the last mentioned complex being totally inert to reduction.|
|Appears in Collections:||IJC-A Vol.28A(12) [December 1989]|
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