Ligand exchange rates

In line with expectations of kinetic inertness for third-row transition metals, little interest has been vested in the development of osmium anticancer drugs, as ligand-exchange rates did not seem favorable on the timescale of cellular processes. Our work, however, shows that the kinetic lability of such complexes can be timed to such extent that anticancer activity comes within range. We have demonstrated how rational chemical design can thus be applied to osmium-arene complexes resulting in specific... 

Surface speciation can be expected to have a tremendous impact on rates of precursor complex formation. Rj, the rate of precursor complex formation, may depend upon the extent of surface protonation, since ligand exchange rates of >MeOH2, >MeOH, and >MeO may vary substantially ... 

The variable-temperature NMR spectra help to explain the catalytic properties of the dppp complex system which were outlined previously in Table I. The reduced catalytic activity compared with the tris(triphenylphosphine) complex system is apparently due to the reduced dissociation of the cyclic complexes. For example, the 90°C spectra of Figures 3 and 13, clearly show that the ligand-exchange rate is much slower in the case of dppp. However, temperature-dependent ligand exchange of the monocyclic complex occurs and leads to cis-bisphosphine species that catalyze the hydroformylation of olefins at minimal partial pressures of CO. The hydroformylation rate of the dppp system is faster at 1 atm CO pressure than that of the dppe system. Of course, such hydroformylations are nonselective due to the cis-stereochemistry. 

Mn (0.97, 0.81) Co (0.72) Mg (0.86), and Al (0.58). The solvent exchange rates (Kex S 1) for inner-sphere water molecules in metal ions are Al(10°) Mg (105) Co (105 5), and Mn(106 7) [21].The order of increasing rate constants in acidic solution is, Al exchange rate over Al. These differential characteristics of the metals play a crucial role in metal-DNA interactions. 

The spectral-kinetic method has been proposed for studying ligand exchange rates [130], Consider the case of Eu(III) and the spectroscopic excited state is 5Do and this state is selectively excited by a pulsed dye laser. Let us consider the equilibrium... 

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