Anation reactions of trans-Rh en2L(OH2)n+(where L = OH–, OH2, or NH3) have been studied over a temperature range. Consideration of the kinetic parameters enables a quantitative measure of the kinetic trans-effects of OH–, OH2, and NH3 to be obtained. These are compared with those of NH3 and the halide ions obtained previously. In terms of the enthalpies of activation, H2O has the lowest trans-effect yet found in these rhodium complexes, while OH– and NH3 have a trans-effect close to that of the chloride ion. The activation entropy for the anation of the diaquo-complexes is much more positive than that of the aquopenta-amminerhodium(III) complex, the latter being thought to react via an associative mechanism. Therefore, the trans-diaquo-complex, like the hexa-aquo-complex, probably reacts via a dissociative mechanism.
