Transition metal ions addition complexes

Many of these complexes are more stable than those formed with the corresponding open-chain ligands. This macrocyclic effect is determined by enthalpic as well as by entropic contributions. Still higher stability constants are obtained when side chains with additional donor groups are attached to the macrocycle thus, tetraacetic acid 22 forms complexes with most metal ions, including alkaline earth ions and transition metal ions these complexes show stabilities among the highest known. 

The mechanism of catalytic hydrosilylation involves oxidative addition of a silicon-hydrogen bond to a metal complex as an essential step since it is here the activation of hydrosilane by the catalyst takes place. Thus, many transition metal ions and complexes, especially group VIII metals in low oxidation state containing ir-acid ligands such as CO, tertiary phosphines or olefins display catalytic activity. The sequence of unit reactions in a typical d -metal complex-catalyzed hydrosilylation is summarized as ... 

The use of microporous solid catalysts such as zeolites and related molecular sieves has an additional benefit in organic synthesis. The highly precise organization and discrimination between molecules by molecular sieves endows them with shape-selective properties [12] reminiscent of enzyme catalysis. The scope of molecular sieve catalysis has been considerably extended by the discovery of ordered mesoporous materials of the M41S type by Mobil scientists [13,14]. Furthermore, the incorporation of transition metal ions and complexes into molecular sieves extends their catalytic scope to redox reactions and a variety of other transition metal-catalyzed processes [15,16]. 

There are several typical oxidation products from alkenes, which can be reached via catalytic routes using molecular oxygen as terminal oxidant. We are only considering liquid phase processes catalyzed by transition metal ions or complexes typically below 100-150 C. Many of these homogeneous catalytic reactions occur at or around room temperature. In addition to a single solvent containing the dissolved catalyst complex, phase-transfer conditions involving liquid-liquid or solid-liquid systems will in some cases be described. Likewise,... 

Two possible reasons may be noted by which just the coordinatively insufficient ions of the low oxidation state are necessary to provide the catalytic activity in olefin polymerization. First, the formation of the transition metal-carbon bond in the case of one-component catalysts seems to be realized through the oxidative addition of olefin to the transition metal ion that should possess the ability for a concurrent increase of degree of oxidation and coordination number (177). Second, a strong enough interaction of the monomer with the propagation center resulting in monomer activation is possible by 7r-back-donation of electrons into the antibonding orbitals of olefin that may take place only with the participation of low-valency ions of the transition metal in the formation of intermediate 71-complexes. 

The coordination of transition metal ions in acidic chloroaluminate melts has not been firmly established. However, in the case of AICb-EtMelmCI. the E0 values of simple redox systems that are electrochemically accessible in both acidic and basic melt, e.g., Hg(II)/Hg [51], Sb(III)/Sb [52], and Sn(II)/Sn [53] exhibit a large positive potential shift on going from basic melt, where metal ions are known to exist as discrete anionic chloride complexes, to acidic melt. Similar results were observed for Cu(I) in AlCh-NaCl [48]. This dramatic decrease in electrochemical stability isprima facie evidence that metal ions in acidic melt are probably only weakly solvated by anionic species such as AICI4 and AECI-. Additional evidence for this is derived from the results of EXAFS measurements of simple metal ions such Co(II), Mn(II), and Ni(II) in acidic AlCh-EtMelmCl, which indicate that each of these ions is coordinated by three bidentate AICI4 ions to give octahedrally-coordinated species such as [ M (AIC14) 2 ] [54]. Most transition metal chloride compounds are virtually... 

In real systems (hydrocarbon-02-catalyst), various oxidation products, such as alcohols, aldehydes, ketones, bifunctional compounds, are formed in the course of oxidation. Many of them readily react with ion-oxidants in oxidative reactions. Therefore, radicals are generated via several routes in the developed oxidative process, and the ratio of rates of these processes changes with the development of the process [5], The products of hydrocarbon oxidation interact with the catalyst and change the ligand sphere around the transition metal ion. This phenomenon was studied for the decomposition of sec-decyl hydroperoxide to free radicals catalyzed by cupric stearate in the presence of alcohol, ketone, and carbon acid [70-74], The addition of all these compounds was found to lower the effective rate constant of catalytic hydroperoxide decomposition. The experimental data are in agreement with the following scheme of the parallel equilibrium reactions with the formation of Cu-hydroperoxide complexes with a lower activity. 

The titration of metal ions in alcohol solvents28 follows the same sort of rules as titrations of metal ions in water29 but poses additional problems due to the lower polarity that increases ion pairing and oligomerization of the metal ions. We have performed several such titrations with the analysis of the potentiometric data depending on the level of information one requires. More complete and time-consuming analyses are reserved for the most effective catalytic metals, namely La3 +, and for the transition metal ion Zn2+ and Cu2+ along with some simple complexes of the latter two which we describe a little later. For the other metal ions described in our titration papers,7,8 we only present the data in terms of the... 

The primary, secondary, and tertiary aliphatic amines do not form simple addition complex ions with bare transition metal ions. Only Ag+ reacts with MeNH2 to form a simple addition product [AgMeNH2]+ (107). The Pb+ ion also forms addition products, [PbMeNH2]+ and [Pb(MeNH2)2]+, with methylamine (143). Other bare transition metal ions (144) react with amines via removal of one hydrogen to form the metal hydride and the amine cation with one hydrogen removed [RR N]+. 

An extensive study of the reactions of the bare transition metal ions with phosphine (PH3) has been undertaken (111). Although a few metals formed addition complexes [M(PH3) ]+, most transition metal ions first reacted by a dehydrogenation reaction. As an example of addition reactions, Cu+ and Ag+ reacted very slowly with PH3 (incomplete reactions after 50 s with PH3 at a pressure of 1 x 10 5 Pa in a FT-ICR) sequentially forming [M(PH3)]+ and [M(PH3)2]+. 

Many carbon compounds have been reacted with bare transition metal ions (9) but in most studies C-C or C-H scission was the desired process under investigation. Simple addition complex ions with hydrocarbons have been observed but only a few complexes with benzene and C60 will be mentioned here. 

The presence of residual unbound transition-metal ions on a dyed substrate is a potential health hazard. Various eco standards quote maximum permissible residual metal levels. These values are a measure of the amount of free metal ions extracted by a perspiration solution [53]. Histidine (5.67) is an essential amino acid that is naturally present as a component of perspiration. It is recognised to play a part in the desorption of metal-complex dyes in perspiration fastness problems and in the fading of such chromogens by the combined effects of perspiration and sunlight. The absorption of histidine by cellophane film from aqueous solution was measured as a function of time of immersion at various pH values. On addition of histidine to an aqueous solution of a copper-complex azo reactive dye, copper-histidine coordination bonds were formed and the stability constants of the species present were determined [54]. Variations of absorption spectra with pH that accompanied coordination of histidine with copper-complex azo dyes in solution were attributable to replacement of the dihydroxyazo dye molecule by the histidine ligand [55]. 

There are many ligands in addition to water, for example Cl , NH3, CN , N02, and transition metal ions, in particular, form a large number of complex ions with different ligands. The number of ligands surrounding the central atom, or ion, is called the coordination number. The numerical value of the co-ordination number depends on a number of factors, but one important factor is the sizes of both the ligands and central atom, or ion. A number of complex ions are given below in Table 2 9. The shape of complex... 

Preliminary heats of solution of C0CI2 and CuCl2 have been measured up to 300 C by Cobble and Murray (50). Hydrolysis was suppressed by HC1 addition so that when the work is completed and when the extent of Cl complexing (and Cu + reduction) can be allowed for the data will prove extremely valuable. Preliminary concentration cell studies on the Cl complexing of Cd + and Ni + up to 170 C (51) support the conclusions given earlier that such complexing with first row transition metal ions is likely to be significant by 300°C. 

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