Complexation rate constants

First, solvent molecules, referred to as S in the catalyst precursor, are displaced by the olefinic substrate to form a chelated Rh complex in which the olefinic bond and the amide carbonyl oxygen interact with the Rh(I) center (rate constant k ). Hydrogen then oxidatively adds to the metal, forming the Rh(III) dihydride intermediate (rate constant kj). This is the rate-limiting step under normal conditions. One hydride on the metal is then transferred to the coordinated olefinic bond to form a five-membered chelated alkyl-Rh(III) intermediate (rate constant k3). Finally, reductive elimination of the product from the complex (rate constant k4) completes the catalytic cycle. 

Complex rate constant (M-1 s-1) Self-exchange rate (M-1 s-1) AG (kJ mol ) Geometrya E°... 

A variety of N-O-chelated glycine amide and peptide complexes of the type [CoN4(GlyNR R2)]3+ have been prepared and their rates of base hydrolysis studied.169 The kinetics are consistent with Scheme 8. Attack of solvent hydroxide occurs at the carbonyl carbon of the chelated amide or peptide. Amide deprotonation gives an unreactive complex. Rate constants kOH are summarized in Table 16. Direct activation of the carbonyl group by cobalt(III) leads to rate accelerations of ca. 104-106-fold. More recent investigations160-161 have dealt with... 

Figure 5. The mechanism of RNA replication by means of viral-specific RNA repli-cases. The sketch shows a simplified version of the mechanism of RNA replication by QP replicase. The mechanism within each of the two cycles consists of binding of the RNA (l+ and I" standing for plus- or minus-strand respectively) to the enzyme (E), elongation of the growing chain (see Figure 2) and, eventually, dissociation of the enzyme-RNA complexes. Rate constants for association, elongation and dissociation are indicated by kX, kf, kp, k), ki and kp, respectively. According to complementar-...

The equilibrium constant, K, is related to the rates for the complexation (7q) and decomplexation ( i) reactions by the equation K = kxlk i (Section 1.4). The forward and reverse complexation rate constants for three types of complex are given in Table 3.9. In general, it is found that the rates of both the forward and reverse reactions decrease in the order perching > nesting > capsular. 

Again, the same general trends as were found for MeOH, AcOH, n-BuNII2 and MeOTMS are observed in the temperature dependences for reaction of the two silenes, 19a and 19e, with acetone. In both solvents, the differences are consistent with the efficiency of product formation from the intermediate complex, being greater for 19e than for 19a. Interestingly, the curvature observed in the temperature dependence for silene 19e in hexane solution indicates a turnover temperature of ca —15 °C, and the calculated complexation rate constant at this temperature, kc 1.5 x 1010 M-1 s 1, is identical to the diffusional rate constant within experimental error (fcdiff = 1.3 x 1010 M s-1). 

With a rate law having this form, the pseudo first-order (with respect to the complex) rate constants can be written as... 

This review is concerned with the quantitative aspects of metal-catalysed oxyradical reactions. As such one will find discussions of structures of metal complexes, rate constants and reduction potentials, not unlike our review of 1985 [34], Two areas related to the role of transition metals in radical chemistry and biology have been reviewed recently these are the metal-ion-catalysed oxidation of proteins [35] and the role of iron in oxygen-mediated toxicities [36]. These topics will not be discussed in detail in this review. Related to this work is a review on the role of transition metals in autoxidation reactions [37]. Additional information can be obtained from Afanas ev s two volumes on superoxide [38,39], This subject is also treated in a more general and less quantitative manner by Halliwell and Gutteridge [40],... 

Complexation rate constants for tervalent lanthanide-acylpyrazolone complexes in the toluene-water phase pair... 

The adsorption constants (K ) of the neutral forms were all of the order of 10 cm and the complexation rate constants of the dissociated form with the Ni(II) ion at the interface were of the order of 10 M s for the three extractants, whereas the... 

The complexation proceeded almost completely at the interface. The values of the interfacial complexation rate constants are listed in Table 10.3. The rate constant, k = 5.3 X 10 M- -s", was determined in the aqueous solution using stopped-flow spectrometry in the region where the formation rate was independent of pH. The conditional interfacial rate constants represented by k, = k ki y L i/ k2 -I- ) were... 

There is a large amount of kinetic data available for the substitution, of different ligands by H2O in ammine complexes rate constants, activation energies, and preexponential factors have been obtained in many cases. Tobe and co-workers have obtained a fairly comprehensive set of data for the bisethylenediamine complexes, which, together with some results of other workers are given in Tables XI and XII. These data provide information on the trans effect of different ligands X and a comparison of cis and trans effects. For the explanation of base hydrolysis see Section IV, A. For other data on ammine complexes see recent reviews (31, 46, 174, 175). Table XIII includes all the kinetic data available for the bisdimethylglyoxime complexes. Certain other quantitative data and some qualitative observations will be mentioned in later sections. 

Ligand Stability Constant (log K) of Fe-Ligand Complex Rate Constant" (min X 10 )... 

Here k and k are complex rate constants containing the rate constants associated with all three steps in the isomerisation mechanism above. The important point, though, is that Sr, the total number of active sites at the surface is contained in the rate equation, hence the need for high surface area to maximise Sr- In some cases (especially in selective oxidations) it is necessary to limit Sr and surface area to avoid further reaction/ decomposition of a desired intermediate product. 

For the hydrolysis of bis-4-nitrophenylphosphate hydrolysis promoted by zinc complexes of L5-L14, kinetic studies were carried out at pH = 11 to ensure full deprotonation of the Zn-OH2 moiety of the complexes. Rate constants obtained at 25 °C were used in the preparation of a Bronsted plot. In this plot, reactivity differences as a function of the type of chelate ligand present are clearly evident. Zinc complexes supported by L5-L7 and L9 exhibit the highest reactivity and the... 

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