Complexes predominant

In secondary wastewater treatment plants receiving silver thiosulfate complexes, microorganisms convert this complex predominately to silver sulfide and some metallic silver (see Wastes, INDUSTRIAL). These silver species are substantially removed from the treatment plant effluent at the settling step (47,48). Any silver entering municipal secondary treatment plants tends to bind quickly to sulfide ions present in the system and precipitate into the treatment plant sludge (49). Thus, silver discharged to secondary wastewater treatment plants or into natural waters is not present as the free silver ion but rather as a complexed or insoluble species. 

Figure 3. Distribution of uranyl complexes as a function of pH at 25°C in presence of typical ligands in surface and ground waters (PCO2 = 10 atm, E F = 0.3 ppm, E Cl = 10 ppm, E SO4 = 100 ppm, E PO4 = 0.1 ppm, E Si02 = 30 ppm). Below pH 4-5 uranyl (U02 ) ion and uranyl fluoride complexes predominate, at intermediaiy pHs (4.5 < pH < 7.5) U02(HP04)2 is the predominant species, whereas at higher pH uranyl is complexed with carbonates. [Used with permission of Elsevier Science, from Langmuir (1978) Geochim Cosmochim Acta, Vol. 42, Fig. 11, p. 558].

More mechanistic insight into the C-H functionalization process of arenes is provided by theoretical and experimental studies. Multifluorinated, electron poor, aromatic substrates readily undergo CH activation with coordina-tively unsaturated rhenium complexes, attributed to the stronger C-Re bond in the product, whereas with monofluorinated analogs, the if -complex predominates (Equation (60)).61... 

Polymer-bound reducing agents have received significantly less attention, presumably because main group metal hydride complexes predominate as reducing... 

A similar mechanism may occur for systems involving Cu(II) coordinated to ter-dentate or bidentate ligands in which the oxidized complex exists primarily as a 1 2 complex while, upon reduction, the 1 1 complex predominates. Kandegedara et al. [48] reported that the system involving copper and the terdentate ligand [9]aneS3 (LBE) appears to involve such a mechanism as illustrated in Scheme 4 ... 

Of the presently known reactions, production of the formate complex predominates. Catalysis of the hydrogen reduction of C02, which apparently involves insertion into a metal-hydrogen bond, is considered later. Here we consider the insertion reaction itself. 

Halpem and co-workers have carried out a detailed investigation of the mechanism of the asymmetric hydrogenation of methyl (MAC) and ethyl (EAC) (Z)-a-acetamidodnnamate by rhodium complexes of the ligands DIPAMP (50) and CHIRAPHOS (51).259 Coordination of alkene precedes the oxidative addition of hydrogen. For both ligands, one of the two possible diastereoisomers of the rhodium-diphosphine-alkene complex predominates in solution to a large extent. From the reaction of EAC with the S,S-CHIRAPHOS complex, this diastereoisomer has been isolated. Its structure is represented in (57).260... 

This C—H substitution process results in a Markovnikov orientation, with the H that is allylic to the more substituted end of the alkene preferentially abstracted. The stereochemistry of the resulting ir-allyl complex does not represent the stereochemistry of the starting alkene, as the complexes are capable of isomerization under the conditions in which they are formed. Typically, a thermodynamic mixture is obtained, with the syn form of the complex predominating over the anti form (equation 1). The syn form is more stable due to unfavorable steric interactions that the anti form encounters with the coordination sphere of the palladium. 

The kinetics of the Rh4(CO)i2-catalysed hydroformylation of 2-butenes are consistent with a mechanism involving fragmentation of the catalyst to the active mono- and nonactive bi-nuclear Rh-complexes. Interaction of the monomeric HRh(CO)3 with alkene appears to be the rate-limiting step. Binuclear Rh-complexes, predominating in the reaction mixture, serve as a reserve for the active monomeric complexes472. Amine-directed, Rh(I)-mediated hydrocarbonylation has been reported (347 —> 348)473. 

Although mixed carborane-cyclopentadienyl complexes, predominantly those of cobalt, are the metallocarboranes that have received the most... 

The same workers have reported245 that in three-ligand systems of zinc(n) or lead(n) and orthophosphate, cysteine, and a carboxylate, mixed-ligand complexes predominate at physiological pH. Such complexes solubilize lead(n). 

ATR-FTIR and the HF/3-21G(d,p) level of theory [103], it was predicted that salicylic acid is adsorbed strongly onto illite. Salicylate forms surface complexes predominantly with the Al3+ octahedra located on the edges of the illite grains. The authors of DFT studies [104, 105] show that the ordering for the best sorption of dioxine and furane on the surface of smectites follows the order Mg2+ > Fe2+ > Fe3+ > Li+, which was obtained also in the case of adsorption of nitrogen heterocyclics on smectites [106]. 

The phenomenon of catalyst-inhibitor conversion1 2,143,356 may be understood and critical concentration of metal can be deduced by reference to Eq. (280). If decomposition of the hydroperoxide is the source of initiation, it must be formed as rapidly as it is consumed to maintain a steady rate. If termination by metal complex predominates, a steady state occurs when the right-hand side of Eq. (280) equals unity. No oxidation will occur when this quantity is less than unity. Hence, catalyst-inhibitor conversion is observed as the metal concentration is increased to the point that the chain length becomes less than unity. If termination occurs by the bimolecular reaction of peroxy radicals, a chain length of less than unity will result in the depletion of the hydroperoxide until the rate of initiation has decreased to the point where the chain length is unity again. No inhibition is expected or observed. 

As we have already mentioned, ruthenium complexes predominantly catalyze the dehydrogenative silylation of alkenes but competitively with the hydrosilylation so the reaction usually gives a mixture of the dehydrogenative silylation and hydrosilylation products. Ru3(CO)12 appears to be a very active catalyst for the dehydrogenative silylation of styrene, para-substituted styrenes [ 19, 20],trifluoropropene and pentafluorostyrene [21] by trialkyl-, phenyldialkyl-silanes (but also triethoxysilane) (Eq. 10). 

Aluminum binds to nucleoside phosphates mainly through the basic terminal phosphate groups. Nucleosides mono-, di-, and triphosphates demonstrate similar phosphate basicity. Aqueous solutions of Al3+ and nucleoside phosphates have a tendency to form ternary complexes with hydroxide in a pH-dependent manner. In addition, there is a possibility of Al3+-bridged complexes being formed. Fig. 3 shows the species distribution for the A13+-ATP system. At physiological pH the merged hydroxo mono complexes predominate [9, 18]. 

As found with H2P20 and H2P30 hydrolysis of ATP and ADP can be accelerated by [Co(OH)(OH2)(N)4]2+ species570,571 and by the hydrolysis products of [Co(Cl)3(dien)].572 The (N)4 = (tn)2 complex shows no acceleration for a 1 1 ratio, but the 2 1 metal ATP mixture (0.1-0.01 mol dm 3 ATP) shows 105 enhancement at pH 7. Scheme 63 summarizes these findings. At high pH hydrolysis of the Coin complex predominates. [Co(cyclen)(H20)2]3+ also catalyzes the hydrolysis of [Co(NH3)4(ATP)] at pH 8-9, and (168) has been claimed as the reactive species.581 In all these studies however no intermediates have been positively identified, and the immediate products, coordinated or otherwise, also lack definition. 

The formation of copper(II) complexes with terpy has been investigated fairly intensively. The interaction is pH dependent, and numerous hydroxy, aqua, and polynuclear species are present in aqueous solution 94, 245,278). In general, an Eigen-Wilkins mechanism appears to be operative, although the kinetics are complicated by ligand-protonation equilibria 263,390,391). In acidic solution, 1 1 complexes predominate (567). A number of substituted terpyridine ligands have been evaluated as potential colorimetric reagents for copper 400). The adsorption behavior of copper(II)-terpy complexes at silica surfaces has been studied 499). Such complexes are reasonably active as catalysts for the hydrolysis of fluorophosphate esters 456). 

The obtained amino functionalised imidazolium salts could be used to generate the corresponding palladium(ll) carbene complexes using the silver(l) complexes as carbene transfer agents. Application of these palladium(ll) complexes (predominantly in situ) in asymmetric allylic alkylation reactions between ( )-l,3-diphenylprop-3-enyl acetate and dimethyl malonate (a standard reaction for this catalytic process [145]) gave up to 80% ee,... 

When alkali metal bases are used to raise the solution pH to moderate levels, the uranium will precipitate from the solution in the form of hydrous uranyl hydroxides or uranates, for example, Na2U207. However, through judicious choice of a base, for example, tetramethylammonium hydroxide, (TMA)OH, or tetramethylaimnoirium trifluoromethansulfonate, the study of the amphoteric behavior of uranyl hydroxides can be undertaken. Polynuclear anions of the form (U02)3(0H)7, (U02)3(0H)g, and (U02)3(OH)io are examples of soluble species in solutions where the pH < 14. When the concentration of the (TMA)OH is increased (>0.6 M OH ), highly soluble ( 0.1M) monomers ofthe form U02(0H) "(n = 3, 4,5) have been reported. These three species are in equilibrium with each other however, in solutions where the [OH ] is greater that 1M, the pentahydroxo complex predominates the speciation. 

Dinuclear and trinuclear compounds represent a new class of platinum anticancer complexes and are among the most studied platinum compounds in antitumor chemistry. Many of these complexes circumvent cisplatin-resistance mechanisms. In contrast to cisplatin, the polynuclear complexes predominantly form interstrand cross-links. The dinuclear complex [ tranx-PtCl(NH3)2 2 /u.-(H2N(CH2) NH2) ]2+ (l,l/t,t) (17, Figure 9) is antitumor-active and shows no cross-resistance in cisplatin-resistant cell fines. Binding studies sfiowed tfiat DNA binding for this compound is different from that for cisplatin, as illustrated by the increased interstrand cross-linking. However, clinical testing was abandoned because of severe neurotoxicity. 

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