Kinetics and mechanism of the ligand hydrolysis of (hexafluoroacetylacetonato)(tetraamine)cobalt(III) complexes. Reactivity pattern

The kinetics of the ligand hydrolysis of (hexafluoroacetylacetonato)(tetraamine)cobalt(III) perchlorate complexes, [Co(N4)(hfac)](ClO4)2, where N4=(NH3)4, (en)2, (tn)2, tren and trpn, and hfac=hexafluoroacetylacetonate anion were examined by stopped-flow at 25 °C and 1.0 M ionic strength (NaClO4). Each system was studied in two different basic buffer media. The rate constants for OH− addition to the carbonyl carbon of the coordinated hfac ligand (k1) were almost independent on the nature of the coordinated amine(s), except for N4=trpn, and rates showed no correlation with neither the average basicity of the amines nor the equilibrium constant (K1). The results are discussed in terms of distortion and ring strain in the hfac chelate, induced by the requirement of the amine chelates, especially with tripod trpn amine.