Effect of Chelation

Tremendous effort has been made to develop ligands that control and improve the selectivity, stability, and reactivity of palladium and nickel complexes for cross coupling. Initially, ligandless palladium complexes and triphenylphosphine-palladium complexes were used for these processes. Subsequently, bidentate ligands and monodentate ligands have been developed that possess particular electronic and steric properties that increase reaction rates, scope, and turnover numbers. 

Although reductive elimination from the four-coordinate species tends to be slower than from related three-coordiante species, the wide bite angle of dppf helps to accelerate the rate of reductive elimination. Thus, reductive elimination occurs from the sec-butylpalladium complex to form the sec-butyl organic product without competing rearrangements to form -butyl products or butene. 

CHAPTER 19 TRANSITION METAL-CATALYZED COUPLING REACTIONS 

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RATE PARAMETERS FORREDUCTION OF SELECTED C ARBOX YLATOPENTA A MMINE Co(III) COMPLEXES BY Ct, SHOWING EFFECT OF CHELATION ... 

Wilson, A. D., Crisp, S. Ferner, A. J. (1976). Reactions in glass ionomer cements IV. Effect of chelating comonomers on setting behavior. Journal of Dental Research, 55, 489-95. 

A. Wallace, Effect of chelating agents on uptake of trace metals when chelating agents are supplied to soil in contrast to when they are applied to solution culture. J. Plant Niitr. 2 171 (1980). 

The effect of chelating polyamines on the rate and yield of benzylation of the lithium enolate of 1-tetralone was compared with HMPA and DMPU. The triamine... 

Effect of Chelate Ring Size on Complex Stability Comparison of Stabilities of Complexes of EDTA (Chelate Ring Size Five Involving the Two Nitrogens) and TMDTA (Analogous Chelate Ring Size Six ) ... 

Effect of Chelate Ring Size on Complex Stability with Metal Ions of Different Sizes Oxalate (Ring Size Five) and Malonate (Ring Size Six)°... 

Ercal N University of Missouri, Rolla, MO The adjunctive use of NAC to enhance the effectiveness of chelation-oriented therapies in lead poisoning National Institute of Environmental Health Sciences... 

Schwarz D Joseph Stokes Jr Research Institute Children s Hospital Philadelphia, PA Effects of Chelation With Succimer on Growth and Development of Children with Low Levels of Blood Lead National Center For Research Resources... 

Hammond PB. 1971. The effects of chelating agents on the tissue distribution and excretion of lead. Toxicol Appl Pharmacol 18 296-310. 

Essington, E., Nishita, H. and Wallace, A. (1963). Effect of chelating agents on the uptake of Y 1, Ru106, Ce144 and Pm147 by beans growing in a calcareous soil, Soil Sci. 95, 331. 

TPR and hydrogen uptake measurements were carried out to investigate the effect of chelating agents on the formation of metallic particles. Apparatus and procedures for TPR measurement were described in our previous paper.13 The... 

Effects of Chelating Agents on the Selectivity and Space-Time Yield of Hydrocarbon3... 

The beneficial effects of chelating ligands were also demonstrated by Hartwig, Ishiyama and Miyaura [62]. This group isolated the iridium(I) complex [lr(Bpin)3(COE)(DTBPY) modified with simple 2,2 -bipyridine ligands (such as 4,4 -di-tert-butyl-2,2 -bipyridine DTBPY), which seemed to be responsible for the first catalytic C—H borylation at room temperature (Scheme 7.30). An extension... 

Table 4.16 Consultants for Extraction of Actinide Amides from Nitrate Solutions into an Organic Solvent Showing the Effect of Chelate Ring Size...

Tried JF, Schubert J. 1961. Effect of chelating agent administration on the removal of monomeric and polymeric thorium. Rad Res 15 227-235. 

The reactions of fused and unfused a-pyrones with magnesium alkoxides, sodium alkoxides, and water as the nucleophile have been studied in depth, particularly with respect to the effects of chelation <1996J(P1)2715>. The annelation reactions of pyranose derivatives, with acetylacetone and ethyl acetoacetate, to give a variety of annelated fused pyrans have been reported, with the products obtained as single diastereoisomers (Scheme 13) <1997LA1019>. 

However, the effects of chelation allow the formation of one geometric isomer. One example, where the exclusive formation of the lithiated Z-isomer is due to chelation of lithium with an acetal oxygen is described in the asymmetric synthesis of vitamin E62. 

Dr. Anbar In the case where you examined the reaction of copper with hydrogen, what was the effect of chelation on this process ... 

Secondary antioxidants, i.e., sequestrants or chelators, are important compounds in the prevention of lipid oxidation. The effect of chelators tested varied with the different compounds. Of those chelators tested, ethylenediaminetetraacetic acid (EDTA, tetrasodium salt) and sodium phytate were the most effective inhibitors of lipid oxidation (so indicated by low hexanal and TEARS values) and MFD (as seen by high CBB and low PIT and CBD intensity values), see Table 5. Sodium phytate was previously shown to chelate iron and thus, was proposed as a food antioxidant(7J). Sodium citrate at a concentration of 500... 

Rogan WJ et al The effect of chelation therapy with succimer on neuropsychological development in children exposed to lead. N Engl J Med 2001 344 1421. [PMID 11346806]... 

A number of observations show the profound effect of chelation on the stability of Schiff bases and similar unsaturated nitrogen-containing ligands. Eichhorn and coworkers found that the Schiff base of bis(thiaphenal)ethylene-diimine is hydrolyzed in the presence of Cu+2, with the formation of the ethylene-diamine complex (Equation 18) (26, 28). 

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