Kinetics simple ligand-exchange constants

If the metals bound in complexes exchange with biological ligands, the dissociation kinetics of these complexes, the ligand-exchange kinetics and the association kinetics with the biological ligands must be considered. Simple dissociation kinetics of complexes are related to their thermodynamic stability constants by the relationship ... 

To investigate the origin of the very high hydroformylation and isomerization activity of ligand 33, we measured the rate of CO dissociation from the HRh(dipho-sphine)(CO)2 complex using labeling in rapid-scan IR experiments [54]. The CO dissociation rate constants, ki, can be obtained by exchanging CO for CO in the HRh(diphosphine)( CO)2 complexes [52].The CO dissociation proceeds via a dissociative mechanism and consequently obeys simple first-order kinetics. The rate constants kj can, therefore, be derived from Eqs. (5) and (6). 

Dale Margerum Ralph Wilkins has mentioned the interesting effect of terpyridine on the subsequent substitution reaction of the nickel complex. I would like to discuss this point—namely the effect of coordination of other ligands on the rate of substitution of the remaining coordinated water. However, before proceeding we should first focus attention on the main point of this paper-which is that a tremendous amount of kinetic data for the rate of formation of all kinds of metal complexes can be correlated with the rate of water substitution of the simple aquo metal ion. This also means that dissociation rate constants of metal complexes can be predicted from the stability constants of the complexes and the rate constant of water exchange. The data from the paper are so convincing that we can proceed to other points of discussion. 

The observed rale constants, ki, are listed in Table 7. It is commonly accepted that CO exchange in (diphosphine)Rh(CO)2H complexes proceeds via the dissociative pathway. The decay of the carbonyl resonances of the (diphosphine)Rh( CO)2H complexes indeed followed simple first-order kinetics. The experiments with ligand 31 at different CO partial pressure show that the rate of CO displacement is independent of the CO pressure. Furthermore, the rate is also independent of the (diphosphine)Rh( CO) H complex concentration, as demonstrated by the experiments with ligand 29. It can therefore be concluded that CO dissociation for these complexes obeys a first-order rate-law and proceeds by a purely dissociative mechanism. 

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