Parameters ligand

A particularly simple type of chirality function is a polynomial in one or more ligand parameters, such as the two functions of Eq. (III-I). Maximum simplicity is obtained if one requires each component of the qualitatively complete x to be a polynomial of lowest possible order in the parameter(s). We first consider the case <3 = <3 . 

As Figure 6 shows there is a good linear correlation between the formal electrode potentials and the sum of the ligand parameters. Such a linear trend obeys the expression ... 

The transition metal catalysed addition of HCN to alkenes is potentially a very useful reaction in organic synthesis and it certainly would have been more widely applied in the laboratory if its attraction were not largely offset by the toxicity of HCN. Industrially the difficulties can be minimised to an acceptable level and we are not aware of major accidents. DuPont has commercialised the addition of HCN to butadiene for the production of adiponitrile [ADN, NC(CH2)4CN], a precursor to 1,6-hexanediamine, one of the components of 6,6-nylon and polyurethanes (after reaction with diisocyanates). The details of the hydrocyanation process have not been released, but a substantial amount of related basic chemistry has been published. The development of the ligand parameters % and 0 by Tolman formed part of the basic studies carried out in the Du Pont labs related to the ADN process [1],... 

Typically, in vitro tests are cell- or tissue-based experiments. The aim is to study the biochemical functions of the target as a result of binding to potential drug ligands. Parameters such as ionic concentrations, enzyme activities, and protein expression profiles are studied. 

IV. Variation of Thermodynamic Quantities with Ligand Parameters. 170... 

Scheme 3.5-2. Ligand property-specific control as a function of the electronic (xj) and steric (0j) ligand parameters for the system COD2Ni/P-ligands/butadiene (1.0 1.0 170),...

Dependence of the Ligand Parameter Pl on the Binding Metal Center 91... 

Tab. 1 General relationship between the electrochemical Pi ligand parameter and the electronic properties of the ligand (L) and its coordination M —L bond...

Hence, the Pi ligand parameter reflects, in an overall way, the combined a- and Tt -electronic properties of the coordination M—L bond. It is noteworthy to mention that it relates to the variation of the free-energy difference of the redox processes (consider the known expression AG = —nFE, in which n is the number of electrons transferred and F is the Faraday constant). It has analogies with the Hammett Up constant [11, 12] defined as og[Kx/Kh), that is, log Kx - log K, in which Kx and ATh are the acidic constants of the p-substituted benzoic acid HOOCCg H4X-4 and of benzoic acid itself, respectively [13] (consider also the known relationship AG = —RT nK). 

I 3 Redox Potential-structure Relationships in Coordination Compounds Tab. 2 Values of the Pi ligand parameter for ligand L ... 

Tab. 4 Values of the Pl ligand parameter for organonitriles (N=CR) at metal centers Ms with a different electron-richness (Es) [24]...

Dependenceofthe Ligand Parameter Pi on the Binding Metal Center In... 

The dependence of the Pi ligand parameter on the type of binding metal center is a limitation of the Pickett s model, but a similar difficulty is encountered for the Ei Lever parameter (see in the following) for which the need for corrections has been recognized for ligands such as CO and CNR. Such a type of limitation is inherent to any additive model that tries to separate the effects of ligands and metal centers on the redox potential, and add them as independent components, in contrast with the situation of the real molecule in which those effects are mutually dependent. 

The P i ligand parameter is then the shift in the oxidation potential resulting from the replacement of n CO ligands in [Cr(CO)g] by L ligands, and should reflect the overall effect of these ligands, that... 

Hence, these models are somehow of complementary characters and efforts should be directed toward their developments and wider applications, including those situations in which the additivity fails. Extensions of the Pickett s and Lever s models have already been proposed to overcome their limitations, as discussed above, and in some cases the dependency of the ligand parameters on the metal centers and generalizations to types (with different electron-counts, structures, compositions, etc.) of complexes, metal centers and ligands not included in the original proposals, have already been successfully treated. 

Fig. 2 Plots of ° for Tc ", Tc " ", and Tc"/ redox couples versus the sum of ligand parameters, accordingto Eq. (4) (reprinted with permission from Ref 29, Copyright 1990 American Chemical Society).

The bite angle makes the difference A practical ligand parameter for diphosphine ligands./. Chem. Soc., Dalton Trans., 1519-1529. 

Wayland and coworkers have recently prepared a novel diporphyrin linked dirhodium(II) bimetallo radical complex whose ligand parameters preclude a strong metal-metal interaction but allow binuclear activation of methane and methanol. 

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