Acid, noncoordinating

The pH effect in Fenton reactions is due to the Fe speciation. In highly acidic solutions containing noncoordinating species, Fe exists as Fe(H20)f. The composition as function of the pH is represented in Figure 6.3a. At increasing pH, Fe undergoes hydrolysis forming FeOH +, Fe(OH)2+, and finally FeO via binuclear, Fe2(OH)4, and polynuclear species. The aim of optimization is to avoid Fe precipitation, either bi-, poly-, or precipitated Fe oxides that are aU inactive in... 

Reactions of P-halogen-NHPs with Lewis acids leading to halide abstraction, or metathetic replacement of the halide by a nucleofugic, noncoordinating anion form by far the most important routes to access phosphenium ions in general [51, 52] and also 1,3,2-diazaphospholenium cations in particular. As Lewis acid assisted P-X... 

In the latter bonding situation the overall rate enhancement over that for the noncoordinated ester will depend on the relative stabilities, and acidities, of tetrahedral intermediates, provided these are formed. There have been no detailed mechanistic studies on systems incorporating metals at a distance (23, 24 Scheme 21) but [(NH3)5Co(GlyOEt)]3+ undergoes hydrolysis some 102 times faster than free GlyOEt (44), and the effectiveness of the Co(III) center in this case is similar to that of protonation (see Table III). In other situations Co(III) centers are somewhat less effective than H+, but the sig-... 

The first hydration step was promoted by Bronsted acids containing weakly or noncoordinating anions. In the second step, an intramolecular hydrogen transfer in the secondary alcohol was catalyzed by ruthenium(III) salts with chelating bipyridyl-type ligands. The possible complexation of the latter with the diene did not inhibit its catalytic activity in the allylic rearrangements, under acid-catalyzed hydration conditions. 

The evaluation of catalysts typically uses two techniques. The first is evaluation as a thin layer on a bulk electrode (e.g., glassy carbon) in dilute liquid electrolyte (e.g., H2 4) either as a static electrode or an RDE. In the study of oxygen reduction, there has been much discussion as to the most appropriate electrolyte to use. In general, dilute perchloric acid (HCIOJ is preferred because of its noncoordinating nature, it is thus closest to the environment foxmd within a FEM catalyst layer with perfluorosulfonic acid ionomer. A possible alternative is trifluoromethylsulfonic acid (CF3SO3H), which mimics perfluorosulfonic acids closely, but there are relatively few studies with this acid. Rotating... 

Since the Tc complex of (95) proved to be a powerful radiopharmaceutical for the detection of bone cancer metastasis, considerable efforts have been made to provide the reasons for the specificity. In the preparation of the corresponding radiopharmaceuticals, all three stereoisomers are present from the reaction with meso-dmsa. The reason for the osteotropic behavior may arise from deprotonation of the noncoordinated carboxylic acid groups, and the active complex in solution therefore bears a 5— charge. 

The pH-neutral ionic liquids are highly polar and noncoordinating. These liquids have potential applications as solvents for metallic and organometallic reagents in two-phase reactions, and as replacements for polar, aprotic solvents like dimethyl-foimamide. The Lewis-acidic and superacidic ionic liquids are being investigated for use as catalytic solvents. 

Complexes with SBs from Hsal and ar-amino acids (glycine, l- and DL-alanine, L-methionine, L-valine, L-leucine, l- and DL-phenylalanine) were prepared and characterized.786 The complexes are bluish-grey and there is no appreciable interaction between V atoms. The compounds were [VO(SB)(H20)] (111), confirmed in an X-ray study of (111 R = Me, L-Ala derivative).787 v(V=0) was at —1000 cm-1 the compounds are not soluble in noncoordinating solvents, but when dissolved in py v(V=0) shifts to —970 cm-1 several orange py adducts (112) were isolated.686 Complexes (111) have electronic spectra that resemble those of... 

Trivalent yttrium and lanthanide metals, except for promethium, have been complexed to octaethylporphyrin by heating at 210 °C in an imidazole melt.17 The complexes obtained as hydroxides, Mm(OEP)(OH), are unstable in acidic media. As the charge radius ratio rule predicts, the early lanthanide metalloporphyrins, MIU(OEP)(OH) (M = La, Ce, PR, Nd), are demetallated during purification, and the middle series (M = Sm, Eu, Gd, Tb, Dy) in 1 % acetic acid in methanol, while the last five (M = Ho, Er, Tm, Yb, Lu) survive in 2% acetic acid in methanol but are dissociated in dilute hydrochloric acid. The Mnl(OEP)(OH) appears to coordinate more than one equivalent of pyridine and piperidine, and dimerizes in noncoordinating solvents such as benzene and dichloromethane at 10 4 M concentration. The dimer is considered to be a di-p-hydroxo-bridged species, different from the p-oxo dimer, Scin(OEP) 20 (Scheme 6). 

Use of noncoordinated donor centers of diazines, for instance in 775 [493], in reactions with Lewis acids (3.224) is widespread. A bridge joining the metal -carbonyl group, for example 776, as well as formation of the metal-cycle 777 was observed in these processes ... 

A related imidazole-appended zinc(II) porphyrin linked via an ethynylphenyl unit to a magnesium(II) phthalocyanine has recently been reported [38], The imidazole group binds to the magnesium center to form a stacked dimer in noncoordinating solvents such as chloroform even at submicromolar concentration (<10-6M). Upon addition of dimethyl sulfoxide, the stacked dimer transforms to an extended dimer in which the imidazole group binds to the zinc center on the basis of the hard and soft acid and base principle. The extended dimer exhibits a much stronger fluorescence (by a factor of 28) compared with the stacked dimer, and this coordination-induced sliding motion has been found to be reversible. 

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