Transition metal salts/complexes

Extraction of uncharged species into organic media by onium salts. These include transition metal salts (complex formation with, e.g. CuX, PdCy, and acids, H2O2 and amines which form weakly hydrogen-bonded complexes with quats... 

Several methods have been developed to generate the transient highly reactive o-QMs. In addition to thermal and base initiation, some Lewis acids and transition-metal salts/complexes of Os, Rh, Ir, Mn, and Pd have been reported to mediate the generation of o-QMs. The resulting 2-aryl-chromans can be functionalized to provide the core structures of natural and synthetic compounds exhibiting a wide array of biological properties (Scheme 7.56). 

Nikje MMA, Mozaffari Z. Polybutadiene and hydroxyl-terminated polybutadiene epoxidation using in situ-generated dimethyl dioxirane (DMD)/transition metal salts complex. Des Monomers Polym. 2008 11 271-281. 

We have already seen that in the aquo-complex which is usually formed when a simple transition metal salt dissolves in water, the... 

Alkali or alkaline-earth salts of both complexes are soluble in water (except for Ba2[Fe(CN)g]) but are insoluble in alcohol. The salts of hexakiscyanoferrate(4—) are yellow and those of hexakiscyanoferrate(3—) are mby red. A large variety of complexes arise when one or more cations of the alkah or alkaline-earth salts is replaced by a complex cation, a representative metal, or a transition metal. Many salts have commercial appHcations, although the majority of industrial production of iron cyanide complexes is of iron blues such as Pmssian Blue, used as pigments (see Pigments, inorganic). Many transition-metal salts of [Fe(CN)g] have characteristic colors. Addition of [Fe(CN)g] to an unknown metal salt solution has been used as a quaUtative test for those transition metals. 

Other miscellaneous compounds that have been used as inhibitors are sulfur and certain sulfur compounds (qv), picryUiydrazyl derivatives, carbon black, and a number of soluble transition-metal salts (151). Both inhibition and acceleration have been reported for styrene polymerized in the presence of oxygen. The complexity of this system has been clearly demonstrated (152). The key reaction is the alternating copolymerization of styrene with oxygen to produce a polyperoxide, which at above 100°C decomposes to initiating alkoxy radicals. Therefore, depending on the temperature, oxygen can inhibit or accelerate the rate of polymerization. 

Guo et al. [70,71,73] recently attempted to hydrogenate NBR in emulsion form using Ru-PCy complexes. However, successful hydrogenation can only be obtained when the emulsion is dissolved in a ketone solvent (2-butanone). A variety of Ru-phosphine complexes have been studied. Crosslinking of the polymer could not be avoided during the reaction. The use of carboxylic acids or first row transition metal salts as additives minimized the gel formation. The reactions under these conditions require a very high catalyst concentration for a desirable rate of hydrogenation. 

Thermolysis rates are enhanced substantially by the presence of certain Lewis acids (e.g. boron and aluminum halides), and transition metal salts (e.g. Cu ", Ag1).46 There is also evidence that complexes formed between azo-compounds and Lewis acids (e.g. ethyl aluminum scsquichloridc) undergo thermolysis or photolysis to give complexed radicals which have different specificity to uncomplexed radicals.81 83... 

Finally, chain polymerisation can occur via coordination, as is the case for polymerisation involving Ziegler-Natta catalysts. These catalysts are complexes formed between main-group metal alkyls and transition metal salts. Typical components are shown in Table 2.1. 

Polysulfides have been prepared with many different types of cations, both monoatomic Hke alkah metal ions and polyatomic Hke ammonium or substituted ammonium or phosphonium ions. In this chapter only those salts will be discussed in detail which contain univalent main-group cations although a large number of transition metal polysulfido complexes have been prepared [7-9]. 

Activation of Silicon Bonds by Transition Metal Salts and Complexes... 

In addition to activation of sihcon bonds by fluoride ions as discussed in Section 2.4, silicon-silicon, silicon-carbon, silicon-hydrogen, and silicon-nitrogen bonds are activated by transition metal salts and transition metal complexes. Thus, hydrolysis of silicon-carbon bonds such as in phenyltrimethylsilane 81 can be induced by... 

Apart from the hardness and softness, two reactivity-related features need to be pointed out. First, iron salts (like most transition metal salts) can operate as bifunctional Lewis acids activating either (or both) carbon-carbon multiple bonds via 71-binding or (and) heteroatoms via a-complexes. However, a lower oxidation state of the catalyst increases the relative strength of coordination to the carbon-carbon multiple bonds (Scheme 1). 

The fourth chapter gives a comprehensive review about catalyzed hydroamina-tions of carbon carbon multiple bond systems from the beginning of this century to the state-of-the-art today. As was mentioned above, the direct - and whenever possible stereoselective - addition of amines to unsaturated hydrocarbons is one of the shortest routes to produce (chiral) amines. Provided that a catalyst of sufficient activity and stabihty can be found, this heterofunctionalization reaction could compete with classical substitution chemistry and is of high industrial interest. As the authors J. J. Bmnet and D. Neibecker show in their contribution, almost any transition metal salt has been subjected to this reaction and numerous reaction conditions were tested. However, although considerable progress has been made and enantios-electivites of 95% could be reached, all catalytic systems known to date suffer from low activity (TOP < 500 h ) or/and low stability. The most effective systems are represented by some iridium phosphine or cyclopentadienyl samarium complexes. 

Stable transition-metal-alkene complexes can be obtained readily from their salts and alkenes in water.141... 

The basic idea was to randomly acylate polyallylamine (MW = 50,000-65,000) all at once with eight different activated carboxylic acids. The relative amounts of acids used in the process was defined experimentally. Since the positions of attack could not be controlled, a huge family of diverse polymers (4) was formed. In separate runs the mixtures were treated with varying amounts of transition metal salts and tested in the hydrolysis reaction (1) —> (2) (Equation (1). The best catalyst performance was achieved in a particular case involving Fe3+, resulting in a rate acceleration of 1.5 x 105. The weakness of this otherwise brilliant approach has to do with the fact that the optimal system is composed of many different Fe3+ complexes, and that deconvolution and therefore identification of the actual catalyst is not possible. A similar method has been described in other types of reaction.30,31... 

As with other first-row transition metals, copper complexes are not expected to be satisfactory singlet oxygen photogenerators, because of the rapid deactivation of excited states in the presence of partially filled d-orbitals. The exceptional case of the copper(II) benzochlorin iminium salt ((18), M = Cu) has already been referred to (Section 9.22.5.6) this showed bioactivity, although the nickel(II) complex ((18), M = Nin) was inactive.195... 

In spite of the fact that silver(i) X-heterocyclic carbene complexes were widely employed as carbene-transfer reagents for the synthesis of other transition metal carbene complexes, their synthesis could also be achieved by the reaction of silver salts with relatively more labile carbene metal complexes, albeit rare. Complexes 71a-71c were reported to be synthesized from the reaction of the corresponding pentacarbonyl(carbene)chromium(i) complexes with silver(i) hexafluorophosphate in CDC13 under inert atmosphere (Scheme 17).117... 

The metamagnetic behavior of [Fe(Cp )2] [Ni(a-tpdt)2] is attributed to the AF coupling between the FM coupled D+A D+A chains within the chain layers, as predicted from the application of the McConnell I model and spin density calculations, in a similar way to other salts also based on decamethylmetallocenes and other transition-metal bisdichalcogenate complexes with a type I structural motive such as [Mn(Cp )2][M(tdt)2] (M = Ni, Pd, Pt). 

Nothing has been found in the published literature about what takes place during the induction period. We believe that an active catalytic species is formed during this period, and that its formation requires reduction of chloroplatinic acid, or of whatever transition metal salt or complex one uses. 

The route to carbene initiation for systems catalyzed solely by transition metal salts (55, 54), or their combinations with Lewis acids such as A1C13 (55), is not well established. Nevertheless, some evidence suggests reduction of the metal by the olefinic substrate (55). Zero-valent (56) and hexavalent (57, 55) tungsten complexes that promote metathesis when activated by UV radiation are the least-understood metathesis systems. 

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