LIGAND SUBSTITUTION IN [RH(OH2)6]3-DIKETONES - APPLICABILITY OF LIGAND CONSTANTS( BY BETA)

The kinetics of anation of [Rh(OH2)6]3+ by beta=diketones has been fol lowed spectrophotometrically at different temperatures with different ligand concentrations. The reaction is pH dependent. The rate and acti vation parameters (calculated from Eyring plots), compared with H2O-ex change and other anation studies, indicate an associative mode of acti vation with the incoming ligand participation in the transition state. A correlation of rate constants with the ligand constant values (-1.8 2, -1.78 and -1.73 V for pentane-2,4-dione, 1-phenylbutane-1,3-dione a nd 1,3-diphenylpropane-1,3-dione respectively) has been attempted.