Thermodynamic and kinetic studies of the equilibration between the sulfur- and carbon-bonded forms of a cobalt(III) complex with the ligands 2-aminoethyl-3-aminopropyl sulfide and 1,1,1-tris(aminomethyl)ethane

A thermodn. and kinetic study of the equilibration between the Co-S bonded complex Co(tame)(S-aeaps)3+ and the Co-C bonded complex Co(tame)(C-aeaps)2+ is reported (tame = 1,1,1-tris(aminomethyl)ethane, aeaps = 2-aminoethyl-3-aminopropyl sulfide = 3-thiahexane-1,6-diamine and C-aeaps = 1,6-diamine-3-thia-hexan-4-ide anion). Kinetic and thermodn. data were obtained using UV-visible spectroscopy, IE-HPLC and 13C NMR ([OH-] = 4 * 10-5-1.0 M, T = 25.0-100 Deg, I = 1.0 M). The kinetic data were interpreted in terms of different reactivity of ion pairs with perchlorate and hydroxide, resp. Rate consts. and activation parameters for the formation of the Co-alkyl complex from ion pairs with perchlorate and hydroxide, resp. (composite terms), and for the reformation of the Co-S complex from ion pairs with perchlorate are given, together with thermodn. data. The data were interpreted in terms of the intermediate formation of a carbanion, and this was strongly supported by 13C NMR CH/CD-exchange studies. The Co(tame)(aeaps)3+ cation exchanges one C-H proton, and only one, prior to the formation of the Co-alkyl complex. The subsequent reaction of the partially C-deuterated (-N-CH2-CH2-CHD-S-) Co-S complex to form the Co-alkyl complex gave complete loss of D. From the kinetic data it is estd. that the carbanion reacts with H2O 170 times faster than it is captured by Co(III).