Deactivation of the Chlorosulfonate Ion Coordinated to Pentaamminecobalt(III)
The synthesis and properties of [(NH3)5CoOSO2Cl](ClO4)2 are described. This complex is one of the most reactive cobalt(III) species ever isolated (t1/2 10 s; 25°C; 0.1 M HClO4). In water it yields [(NH3)5CoOSO3]+, [(NH3)5CoOH2]3+ and [(NH3)5CoCl]2+. The first two of these products come from the expected direct S-Cl and Co-O cleavages. The chloro complex arises via intramolecular linkage isomerisation to the transient [(NH3)5Co-ClSO3]2+ species which then cleaves the S-Cl bond. Considerable attention is given to the characterisation of the Co-O3SCl species, including reaction in 17O-H2O where the NMR spectra confirm Co-17OSO3, Co-17OH2 and free 17OSO32− products. The reactions have been studied also in aqueous base, 0.1 M HClO4 and Me2SO where the same reactions are observed but in quite different proportions. In liquid ammonia, with or without added NH4+, no O-bonded sulphamate complex [(NH3)5CoOSO2NH2]2+ arising from direct S-Cl cleavage is observed. The linkage isomerisation pathway is more pronounced in the absence of base, and this is usual. Mechanisms are discussed in relation to the analogous Co(III)-FSO3− chemistry and to the hydrolysis reactions of the free FSO3− and ClSO3− anions. The most remarkable result is that the ClSO3− ion (and likely FSO3− as well) is substantially deactivated on coordination to Co(III), and such protection is most unusual and no doubt the reason for a successful isolation of the complex of a ligand which hydrolyses in millisec. It can be recovered substantially intact by rapid recrystallisation from water.
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