KINETICS AND MECHANISM OF THE REACTIONS OF A PERCHLORATOIRIDIUM COMPLEX WITH NITRILES

A kinetic investigation of the replacement of ClO4- in the complex [Ir (ClO4)(CO)(PPh(3))(2)] with nitriles has shown somewhat different resu lts from those found for the rhodium analogue. The rates of substituti on reactions of Rh-I complexes are 10(2)-10(3) times faster than those of the corresponding Ir-I complexes. The entropies of activation are ca 60 J mol(-1) K-1 more negative for Ir-I complexes than for correspo nding Rh-I complexes, suggesting an associative mechanism through the formation of a five-coordinated intermediate [Ir(ClO4)(NCR)(CO)(PPh(3) )(2)] for the reaction. Copyright (C) 1996 Elsevier Science Ltd.