Quantitative Analysis of Ligand Effects

The simplest form of regression is multiple linear regression (MLR), Y = XB + E. Here, X contains the descriptors, [di... dn] B contains the regression coefficients, Y contains the figures of merit and E contains the residuals. One well known example of MLR is the relationship shown in Equation (6.9). This model requires a few well-characterized parameters d. .. dn, which are usually derived from experimental measurements or from QM calculations. There are several applications of MLR in catalysis, eg., the quantitative analysis of ligand effects (QALE) model developed by Fernandez et al. [90]. 

Fernandez, A.L., Reyes, C., Prock, A. and Giering, W.P. (2000) The stereoelectronic parameters of phosphites. The quantitative analysis of ligand effects (QALE)./. Chem. Soc., Perkin Trans. 2, 1033. 

Giering and coworkers have combined electrochemical and spectroscopic analyses to develop a method, the quantitative analysis of ligand effects (QALE), for the separation of P-donor ligands into pure a donors and those with a significant degree of phosphorus n acceptor character (Figure 4). 

Application of standard quantitative analysis of ligand effects (QALE) methodology enabled the rate constants for the reactions of Ru3(GO)i2 with 32 phosphine ligands to be analyzed according to the electronic and steric properties of the nucleophiles. It was unexpectedly found necessary to include what has become known as the aryl effect in this analysis, together with a positive contribution to the rates due to the 7r-acidity of phosphite nucleo-philes. ... 

Heteroaromatic sulfoxides and sulfones ligand exchange and coupling in sulfuranes and //Avo-substitutions, 49, 1 Heteroaromatic systems, Claisen rearrangements in, 42, 203 Heteroaromatics, quantitative analysis of steric effects in, 43, 173 Heterocycles aromaticity of, 17, 255 chiral induction using, 45, 1 containing the sulfamide moiety,... 

The applications of EPR spectroscopy reviewed in the present chapter are based on the sensitivity of the spectrum displayed by iron-sulfur centers to various characteristics, such as the redox state of the center, the distribution of the valences on the iron ions, the nature and the geometry of the ligands, and the presence of nearby paramagnetic species. Although considerable progress has been made during the past few years in the quantitative analysis of these various effects in the case of the conventional iron-sulfur centers described in Section II, the discovery of centers exhibiting unusual EPR properties as... 

X -Ray powder pattern studies of the complexes [M(phen)2X2]" and [M(bipy)2YZ]"+ [M = Co, Rh, Ir, or Os X = Cl, H2O, or ox YZ = CI2 or (0H)(H20)] show that each metal in each series is isomorphous. A cis configuration is therefore assigned to all complexes. Luminescence quantum yields have been measured for a series of [IrCl2(N—N)2C1 complexes (N—N = phen or bipy, or diphenyl derivatives), permitting a quantitative estimate of the effect of ligand phenyl substituents.A normal-co-ordinate analysis (i.r. has been carried out for [Ir(NH3)5Cl]Cl2. ... 

Mixture B K[SiPh(3-fcat)2 and K[SiPh(dbcat)2] (3-fcat 2,3-dihydroxybenzaldehyde, dbcat 3,5-di-f-butylcatechol) contained two complexes with asymmetric catechols. Each complex showed the presence of two resonances due to the isomerism described above. The equilibrated mixtures showed the presence of two further species (Figure 9). These are attributed to isomers of the [SiPh(3-fcat) (dbcat)]- anion. Equilibrium was not established even after 8 weeks, whereupon decomposition prevented a more quantitative kinetic analysis. Flowever, it is apparent from the two experiments described that the kinetics of redistribution of ligands between complexes varies dramatically according to the cate-cholate involved. It is reasonable to conclude that the rate of redistribution decreases as the strength of the catecholate derivative increases. The nonstatistical distribution of complexes in a mixture indicates a thermodynamic stability of the complexes in Me2SO. The likely explanation lies in the electronic rather than the steric effects in the complex, since the live-coordination imposes little steric constraint. 

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