Question

State the effect on the rate of dissociatively activated reactions of Rh(III) complexes of (a) an increase in the overall charge on the complex, (b) changing the leaving group from NO3 ‐ to Cl‐ , (c) changing the entering group from Cl‐ to I‐ , and (d) changing the cis ligands from NH3 to H2O.

Answer 1

Effect on rate of dissociateve mechanism of Rh(III) complexes of

(a) Increasing +ve charge increases M-L bond strength and so will decrease an dissociative meachnism rate

(b) NO3 - is a better leaving group, so rate is slower

(c) Little effect, since an dissociative meachnism reaction is not sensitive to the nucleophile

(d) NH3 is a better σ donor and so increases electron density at the metal. H2O gives lower electron density at the metal, and the leaving group X binds more strongly in the H2O complex, which will react more slowly.