Intimate mechanisms of ligand substitution

The sequential equilibria in Equation (4) are characterized by 12 = 12/ 21 (often denoted as K0) and K23 = k23/k32, respectively. When Kn cannot be directly determined it is often estimated using the electrostatic Fuoss equation.215 Usually, it is only possible to characterize the kinetics of the second equilibrium of Equation (4) so that the overall equilibrium is expressed as in Equation (5) irrespective of the intimate mechanism of ligand substitution. The pseudo-first-order rate constant for the approach to equilibrium, kabs, is given by Equation (6)... 

The Intimate Mechanism of Replacement in Square-Planar Complexes Platinum(II)-Catalyzed Substitutions of Platinum(IV) Complexes Kinetics of Nickel, Palladium and Platinum Complexes Isomerization Mechanisms of Square-Planar Complexes Anomalies in Ligand Exchange Reactions for Platinum(II) Complexes Inorganic Reaction Mechanisms The CIS and trans Efiects of Ligands... 

For M(H20)42+, substitution of an aqua ligand by Az takes place some 105-fold faster for M — Pd than for M = Pt typical rate constants are given in Table 8.9, which also shows that the charge on A is not important—the fastest reactions listed are with neutral thiourea—and hence ion pairing is not a prerequisite for reaction, in contrast to Ia processes. Recent evidence96 that at least one (and probably two) extra water molecule(s) is (are) located at relatively long M-OH2 distances above (and below) the MO4 plane in aqueous solution implies that the intimate mechanism may not be the simple A process that is commonly invoked. 

Demonstration of the nature of the intermediates is in general a very difficult experimental task, therefore most ligand substitution reactions are assumed to be interchange processes. Nonetheless, kinetic studies often permit us to establish the intimate reaction mechanism which assigns to the interchange pathways either an associative or a dissociative character. 

Marcus LFER. Oxidation-reduction reactions involving metal ions occur by (wo types of mechanisms inner- and outer-sphere electron transfer. In the former, the oxidant and reductant approach intimately and share a common primary hydration sphere so that the activated complex has a bridging ligand between the two metal ions (M—L—M ). Inner-sphere redox reactions thus involve bond forming and breaking processes like other group transfer and substitution rcaclions, and transition-state theory applies directly to them. In outer-sphere electron transfer, the primary hydration spheres remain intact. The... 

---