Thermodynamic and kinetic studies of the equilibration reaction between the sulfur and carbon bonded forms of a cobalt(III) complex with the ligands 2-aminoethyl-3-aminopropylsulfide 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).
Acta Chemica Scandinavica, 1996, Vol 50, Issue 6, p. 531-536
Carbanions Role: FMU (Formation, unclassified), FO; Equilibrium (equilibration between sulfur- and car; Ion pairs (in relation to equilibration of cobalt; Kinetics; Thermodynamics (thermodn. and kinetics of the equi