Substitution reactions at octahedral complexes: acid and base hydrolysis

1. Substitution reactions at octahedral complexes: acid and base hydrolysis

2. Acid hydrolysis • Protonation of a ligand which then dissociates from the metal See Questions 1-3

3. Electron rich metal PR3 stabilised by π back bonding from electron rich metal ion Acid hydrolysis • Protonation of an inert ligand labilises other ligands

5. Acid hydrolysis • Protonation of the metal itself leads to labilisation of a ligand

6. The experimental rate law is Dissociative Conjugate Base Base hydrolysis at a transition metal complex is based on the observation that reactions of the type are accelerated by increasing [OH-] [ML4(LH)(X)]n+ + OH- [ML4(LH)(OH)]n+ + X- and the saturation behaviour seen with acid-catalysed reactions (Chapter 2) does not occur Mechanism proposed by Garrick and called the DCB Mechanism

7. (1) Now

8. But

9. Since Substituting into (1)

10. Base hydrolysis is usually considerably faster than acid hydrolysis because of stabilisation of the transition state by the conjugate base. Hence a  donor ligand such as OH- or NH2- is required for this mechanism