Chloride of transition metals

A third type of material is the chlorides of transition metals, such as ZnCl2 and SnCl4 (36, 37). This group of catalysts works in molten state in contrast to the solid state of the previous two groups. The corrosive nature and instability may excludes their practical application. No details are reviewed here. 

In view of the above-said it is necessary to investigate oxide solubilities in the melts based on alkali-metal halides and to establish regularities in metal-oxide-ionic melt systems . Such data are required for predicting the stability of melts doped with additions of metal cations, and of electrochemical cells containing chlorides of transition metals, under the action of oxide ions formed in the melt owing to oxidation or pyrohydrolysis of its constituent parts. 

Acetoxyvinylphosphonates are formed as the main products (along with acylphos-phonates as byproducts) in the reactions of dialkyl phosphite with acetic anhydride in MeCN, in the presence of chlorides of transition metals such as iron (II), iron (III) or cobalt. The same chlorides also catalyse the transformation of acylphosphonates into enol acetates by treatment with AC2O in MeCN ... 

Products from reactions of trivalent alkoxy chlorides of transition metals with certain halogen-fi-ee organoaluminum compounds, e.g., triisobutylaluminum. Such catalysts are used without any support. 

The active components are usually oxychlorides or chlorides of transition metals, particularly copper. The promotional effect of rare earth chlorides has been known for some time (15) and the Shell catalyst used in a fluid bed process contains rare earth and alkali metal chlorides in addition to copper chloride. The (SLP) nature of the catalyst is clearly spelt out in the patents (16). A large surface area of the support may increase the activity but only insofar as the reactant can easily enter the pellet. Excessive catalyst loading can lead to pore blocking and an anticipated maximum activity for a specific loading is noted. 

Recently, Deligoz and Yilmaz [51] prepared three polymeric calix[4]arenes, which were synthesized by reacting chloromethylated polystyrene with 25,26,27-tribenzoyloxy-28-hydroxy calix[4]arene (2a, 3a) and po-lyacryloyl chloride with 25,26,27,28-tetraacetoxy ca-lix[4]arene (4a). After alkaline hydrolysis of the polymers, they were utilized for selective extraction of transition metal cations from aqueous phase to organic phase. 

The formation of high polymers of olefins in the presence of titanium halogenides with no specially added organometallic co-catalysts was discovered long ago [see (147), and the references therein], A complete description of various alkyl-free polymerization catalysts based on the use of transition metal chlorides may be found in the review by Boor (17), where a comparison of these catalysts with traditional two-component systems is given. 

With regard to the mechanism of these Pd°-catalyzed reactions, little is known in addition to what is shown in Scheme 10-62. In our opinion, the much higher yields with diazonium tetrafluoroborates compared with the chlorides and bromides, and the low yields and diazo tar formation in the one-pot method using arylamines and tert-butyl nitrites (Kikukawa et al., 1981 a) indicate a heterolytic mechanism for reactions under optimal conditions. The arylpalladium compound is probably a tetra-fluoroborate salt of the cation Ar-Pd+, which dissociates into Ar+ +Pd° before or after addition to the alkene. An aryldiazenido complex of Pd(PPh3)3 (10.25) was obtained together with its dediazoniation product, the corresponding arylpalladium complex 10.26, in the reaction of Scheme 10-64 by Yamashita et al. (1980). Aryldiazenido complexes with compounds of transition metals other than Pd are discussed in the context of metal complexes with diazo compounds (Zollinger, 1995, Sec. 10.1). 

Colour - A striking feature of transition-metal compounds is their colour. Whether it is the pale blue or pink hues of copper(ii) sulfate and cobalt(ii) chloride, or the intense purple of potassium permanganate, these colours tend to be associated most commonly with transition-metal compounds. It is rare for compounds of main group metals to be highly coloured. 

Activation methods can be divided into two groups. Activation by addition of selected metals (a few wt%), mainly transition metals, e.g., fine powders of Fe, Ni, Co, Cr, Pt, Pd, etc. ", or chlorides of these metals when these are reducible to the metal by hydrogen during presintering. The mechanism of activation is not understood (surface tension, surface diffusion, etc.) but is related to the electronic structure of the metal additive. Activation by carbon is also effective. Alternatively, activation utilizes powders in a specially activated state, e.g., very fine (submicronic) powders. ... 

Trimethylchlorosilane TCS 14 readily transforms metal oxides such as ZnO, MgO, MnO, BeO, AI2O3, or Ti02 and oxides of transition metals such as SmO or Iu203 into the corresponding reactive anhydrous chlorides and volatile HMDSO 7 (b.p. 100°C) (Scheme 13.6). 

Early attempts by Asinger to enlarge the scope of hydroalumination by the use of transition metal catalysts included the conversion of mixtures of isomeric linear alkenes into linear alcohols by hydroalumination with BU3AI or BU2AIH at temperatures as high as 110°C and subsequent oxidation of the formed organoaluminum compounds [12]. Simple transition metal salts were used as catalysts, including tita-nium(IV) and zirconium(IV) chlorides and oxochlorides. The role of the transition metal in these reactions is likely limited to the isomerization of internal alkenes to terminal ones since no catalyst is required for the hydroalumination of a terminal alkene under these reaction conditions. 

The presence of salts and additives can have an important influence on the performance of an FBA. Traces of transition-metal ions such as iron and copper have an adverse effect on fluorescence [30], but this can be controlled using conventional polyphosphate or EDTA-type sequestering agents [31]. Other salts, even sodium sulphate or sodium chloride, have been claimed to enhance the fluorescence of FBAs in solution [32]. Apart from the normal... 

Recent trend in the synthesis of olefinic pheromones is the use of transition metal-catalyzed cross coupling reaction for carbon-carbon bond formation. Scheme 8 summarizes a synthesis of the termite trail marker pheromone, (3Z,6Z)-3,6-dodecadien- l-ol (2) by Oehlschlager [19]. The key-step is the palladium-catalyzed cross-coupling of allylic chloride A and alkenylalane B. 

The activity of transition metal allyl compounds for the polymerization of vinyl monomers has been studied by Ballard, Janes, and Medinger (10) and their results are summarized in Table II. Monomers that polymerize readily with anionic initiators, such as sodium or lithium alkyls, polymerize vigorously with allyl compounds typical of these are acrylonitrile, methyl methacrylate, and the diene isoprene. Vinyl acetate, vinyl chloride, ethyl acrylate, and allylic monomers do not respond to these initiators under the conditions given in Table II. 

Relatively little attention has been devoted to the direct electrodeposition of transition metal-aluminum alloys in spite of the fact that isothermal electrodeposition leads to coatings with very uniform composition and structure and that the deposition current gives a direct measure of the deposition rate. Unfortunately, neither aluminum nor its alloys can be electrodeposited from aqueous solutions because hydrogen is evolved before aluminum is plated. Thus, it is necessary to employ nonaqueous solvents (both molecular and ionic) for this purpose. Among the solvents that have been used successfully to electrodeposit aluminum and its transition metal alloys are the chloroaluminate molten salts, which consist of inorganic or organic chloride salts combined with anhydrous aluminum chloride. An introduction to the chemical, electrochemical, and physical properties of the most commonly used chloroaluminate melts is given below. 

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 many ways, chloroaluminate molten salts are ideal solvents for the electrodeposition of transition metal-aluminum alloys because they constitute a reservoir of reducible aluminum-containing species, they are excellent solvents for many transition metal ions, and they exhibit good intrinsic ionic conductivity. In fact, the first organic salt-based chloroaluminate melt, a mixture of aluminum chloride and 1-ethylpyridinium bromide (EtPyBr), was formulated as a solvent for electroplating aluminum [55, 56] and subsequently used as a bath to electroform aluminum waveguides [57], Since these early articles, numerous reports have been published that describe the electrodeposition of aluminum from this and related chloroaluminate systems for examples, see Liao et al. [58] and articles cited therein. 

The use of transition metals for the facilitation of substitution reactions on vinylic carbon has proven to be quite successful. For example, vinylic chlorides in the presence of nickel(II) chloride react with trialkyl phosphites to substitute phosphorus for the halide (Figure 6.17j.71-72 While reminiscent of a direct Michaelis-Arbuzov reaction, including final dealkylation by a chloride ion, the reaction actually involves an addition-elimination process. It appears that chloride provides a more facile reaction than bromide, a characteristic noted in several reaction systems. 

The development of G. N. Lewis s octet rule for the s/p-block elements was strongly influenced by the stoichiometric ratios of atoms found in the common compounds and elemental forms (CH4, CCI4, CO2, CI2, etc.). Let us therefore begin analogously by examining the formulas of the common neutral binary chloride, oxide, and alkyl compounds of transition metals. (Here we substitute alkyl groups for hydrogen because only a small number of binary metal hydrides have been well characterized.)... 

To avoid the necessity of memorizing a separate name for each ion, we can use the Stock system. In the Stock system, the charge of the cation appears as a Roman numeral immediately after the name of the element. Using the Stock system, we write Fe2+ as the iron(II) ion, and Cu+ as the copper(I) ion. Other than the necessity of indicating the charges, there are no differences between the naming of transition metal compounds and other compounds of the metals. So while KC1 is potassium chloride, CuCl is copper(I) chloride. 

The reaction of propargyl chloride 83 and trichlorosilane 84 showed two different regioselectivities depending on the choice of transition metal catalysts [88]. Whereas the Sn2 substitution proceeded to give the propargylsilane 85 with 94% selectivity using a CuCl catalyst, the silylallene 86 was obtained via an SN2 pathway with >97% selectivity with 3mol% of Ni(PhCOCHCOPh)2 (Scheme 3.42). 

The synthesis of polyhalide salts, R4NX , used in electrophilic substitution reactions, are described in Chapter 2 and H-bonded complexed salts with the free acid, R4NHX2, which are used for example in acid-catalysed cleavage reactions and in electrophilic addition reactions with alkenes, are often produced in situ [33], although the fluorides are obtained by modification of method I.I.I.B. [19, 34], The in situ formation of such salts can inhibit normal nucleophilic reactions [35, 36]. Quaternary ammonium chlorometallates have been synthesized from quaternary ammonium chlorides and transition metal chlorides, such as IrClj and PtCl4, and are highly efficient catalysts for phase-transfer reactions and for metal complex promoted reactions [37]. 

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