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Deactivation of the Chlorosulfonate Ion Coordinated to Pentaamminecobalt(III)

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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.

Keywords: Chlorosulfonate; Cobalt; Deactivation; Oxygen NMR; Synthesis

Document Type: Research Article


Publication date: January 1, 2002

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