Transition metals, chlorides

A series of solid transition-metal chlorides can be used as positive electrodes in cells with sodium as the negative electrode. The various metal chlorides form electrochemical pairs with sodium showing different emf values (Table 1 ). 

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. 

Transition-metal chlorides react with the anion [G4H4B2(NMe2)2l to produce novel 1,2-diborabenzene complexes . 

As shown in Table IV, the highest catalytic activity of metal halides used as Lewis acid for the alkylation reaction of ferrocene with 2 was observed in methylene chloride solvent. Among Lewis acids such as aluminum chloride, aluminum bromide, and Group 4 transition metal chlorides (TiCl4, ZrCU, HfCU), catalytic efficiency for the alkylation decrea.ses in the following order hafnium chloride > zirconium chloride > aluminum chloride > aluminum bromide. Titanium chloride... 

By using a transition metal chloride catalyst and an iodine modified cocatalyst, ring-opening polymerization of C5 and C8 monocyclic olefins is controlled to prepare either cis polymers or trans products that are crystallizable. In copolymerization, the cis/trans units in the copolymers are regulated by adjusting the C5/C8 olefin monomer ratio. As the comonomer is increased, the copolymer becomes less crystalline and then completely amorphous at equal amounts of cis/trans units. Polymerization results are reported from WC16 and MoCl5 catalysts. 

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... 

Aromatic halides such as chlorobenzene and p-fluorololuene were rapidly hy-drogenolyzed in 100% conversion by NaH of nanometric size in the presence of homogeneous catalysts. One- or two-component (e.g., Ni(OAc)2/TiCl4) systems were effective. The combination of ytterbium chloride and a transition-metal chloride showed a remarkable synergistic effect [37, 38]. 

In this chapter, we describe the design and important properties of supra-molecularly organized dye molecules in the channels of hexagonal nanocrystals. We focus on zeolite L as a host. The principles, however, hold for other materials as well. As an example, we mention ZSM-12 for which some preliminary results have been reported [55], We have developed different methods for preparing well-defined dye-zeolite materials, working for cationic dyes, neutral dyes, and combinations of them [3, 22, 25, 52], The formula and trivial names of some dyes that so far have been inserted in zeolite L are reported in Section II.C. The properties of natural and commercially available zeolites can be influenced dramatically by impurities formed by transition metals, chloride, aluminiumoxide, and others. This fact is not always sufficiently taken care of. In this chapter, we only report results on chemically pure zeolites, the synthesis of which is described in [53]. 

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]. 

Titanocene and zirconocene dichlorides (Cp2MtCl2 with Mt = Ti, Zr) were the first metallocenes studied [Breslow and Newburg, 1957 Natta et al., 1957a], The metallocene initiators, like the traditional Ziegler-Natta initiators, require activation by a Lewis acid coinitiator, sometimes called an activator. AIRCI2 and A1R3 were used initially, but the result was initiator systems with low activity for ethylene polymerization and no activity in a-olefin polymerization. The use of methylaluminoxane (MAO), [A1(CH3)0] , resulted in greatly improved activity for ethylene polymerization [Sinn and Kaminsky, 1980], The properties of MAO are discussed in Sec. 8-5g. MAO has two functions alkylation of a transition metal-chloride bond followed by abstraction of the second chloride to yield a metallocenium... 

In this category, the most convenient living catalysts are group 6 transition metal chloride or oxychloride, generally expressed as MO Clj -co-catalyst-ROH (M = Mo or W, = 0 or 1, ot = 5 or While quantitative initiation... 

The cyclopropane 1 reacts with none of the group 1 and 2 metal chlorides. Among early transition metal chlorides, NbCl reacted with i in moderate yield to give the same homoenolate obtained by the reaction of equimolar amounts of titanium homoenolate 2 and NbCl (Scheme 2). TaCl5, CrCl3, MoCls, and WC15 did not give any characterizable products. 

The catalysts were synthesized either from the reaction of transition metal chlorides, WCle, M0CI5, OSCI3, R11CI3, IrClj, ReCls with the monomers, or generated by reactions of the transition metal chlorides with alkylating agents, such as Pl Sn, Bu4Sn, (CFh Sn, etc. 

One problem with chloroaluminate melts is that aluminum chloride and most transition metal chlorides (cf. Eqs. 10.99 to 10.101) are hygroscopic, and even if very carefully handled will hydrolyze from any moisture in the atmosphere ... 

One of the problems encountered with the Werth cell was an increase in resistance with cycling. This may have been caused in part by the /3-alumina reacting with the acidic sodium chloroaluminate melt. Coetzer had the idea of using transition metal chlorides as a positive electrode and chose a basic sodium chloroaluminate melt as the liquid electrolyte. This is compatible with /3-alumina, and a new class of secondary cells based upon the reaction between sodium metal and transition metal chloride has resulted from this work. Collectively, the term Zebra battery is used to describe this new class of cell. 

Several of the first row transition metal chlorides offer attractive voltages versus sodium in the cell arrangement ... 

A battery system closely related to Na-S is the Na-metal chloride cell. The cell design is similar to Na-S however, iu addition to the /3-alumina electrolyte, the cell also employs a sodium chloroaluminate, NaAlCL . molten sail electrolyte. Tlie positive electrode active material consists of a transition metal chloride such as iron(II) chloride, FeCL, or nickel chloride, NiCty, in lieu of molten sulfur. This technology is in a younger state of development than the Na-S. 

There are also catalysts that lack any apparent source of metal-carbon bonds. These catalysts include the aforementioned alumina- and silica-sup-ported transition metal oxides (which, in principle, do not demand any activation by organometallic compounds), and also several group 6-8 transition metal chlorides (soluble in hydrocarbons or chlorohydrocarbons), most typically RuC13. Some of these transition metal halides require activation by a cocatalyst of the Lewis acid type (e.g. A1C13, GaBr3, TiCU) [66,67], Noble metal chlorides may be used in alcoholic solvents or in water containing emulsifiers [68]. 

GICs have been first discovered from the reaction of graphite with sulfuric acid more than 150 years ago.30 In the long history of GICs research, a huge number of compounds have been yielded with a large variety of donors and acceptors, in which alkali metals, alkaline earth metals, transition metal chlorides, acids, and halogens are involved as typical intercalates. 

Zang L, Macyk W, Lange C, et al. Visible light detoxification and charge generation by transition metal chloride modified titania. Chem Ear J 2000 6 379-84. 

Alkynes are reduced preferentially to alkenes with preferred Z-selectivity with molar mixtures of LiAlH4 and several transition metal chlorides such as TiCh. 

Most transition metal chlorides undergo only partial alcoholysis leading to chloroalkoxides MCl j(OR) j. Therefore the reaction has to be driven to completion by adding a base such as ammonia or sodium alkoxide. 

The first group of catalysts is just MoCls and WC16. These metal chlorides polymerize various monosubstituted acetylenes. Table 4 demonstrates that WC16 and MoCl5 are specifically effective for phenylacetylene polymerization among various transition metal chlorides. It is noted that NbCl5 and TaCl5 selectively cyclotrimerize phenylacetylene, and that other metal chlorides hardly induce any reactions. 

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