Halides of transition metals

Polymerization of olefins such as styrene is promoted by acid or base or sodium catalysts, and polyethylene is made with homogeneous peroxides. Condensation polymerization is catalyzed by acid-type catalysts such as metal oxides and sulfonic acids. Addition polymerization is used mainly for olefins, diolefins, and some carbonyl compounds. For these processes, initiators are coordination compounds such as Ziegler-type catalysts, of which halides of transition metals Ti, V, Mo, and W are important examples. 

The stereospecific polymerization of a-olefins takes place only in the presence of heterogeneous catalytic systems, including a crystalline substrate (formed by halides of transition metals, such as TiCb, TiCb, VCI3, CrCla, C0CI2, etc.) and a suitable metallorganic compound (5). 

The above-mentioned metallorganic compounds must have the property of forming complexes with the halides of transitions metals. It is required, in order to get catalytic complexes, that the metal of metallorganic compounds be able to create a strong localized electric field therefore, metals having a very small ionic diameter (below 1 A.) jointly with a very electropositive character are to be used. For such reasons, metals such as Ca,... 

There are also catalysts known in which ACs are formed during the direct interaction between the transition metal compound and the monomer without participation of special cocatalysts (so-called one-component catalysts). Examples of one-component catalysts are chromium oxide catalysts, lower halides of transition metals (titanium dichloride) and catalysts prepared by precipitating organometallic compounds of transition elements on oxide carriers... 

Nucleophilic displacement of halides of transition metal bonded compounds by organic nucleophiles... 

Aleskovsky, Kolstov, Volkova, and co-workers investigated the chemical modification of silica surfaces by inorganic compounds (274-281). The materials obtained are useful in heterogeneous catalysis, electronics, and so forth. The method for molecular lamination was developed (276-278) by interacting volatile and readily hydrolyzing halides of transitional metals with the surface of hydroxylated silica. This method makes it possible to modify the silica surface with mono- and polymolecular layers of V, Cr, Ti, Fe, Al, B, and so forth. 

Habeeb, J.J., Neilson, Lynn and Tuck, D.G. (1978) Electrochemical preparation of anhydrous halides of transition metals (Mn-Zn) , Inorg. Chem., 17, 306-310. 

Analogously, zinc reagents react with halides of various elements. They are particularly useful for the alkylation of halides of transition metals such as NbCls and TaCls that are too easily reducible by alkali metal alkyl reagents. Up to three halides can be substituted by alkyl groups R using ZnRj in these transition-metal halides. 

Ziegler-Natta catalysts are organometallic complexes prepared by reaction of an alkil of a metal from Groups I to III in the Periodic Table (e.g. A1(C2H5)3) with a halide of transition metal from Groups IV to VIII (e.g., TiCU) which are dissolved in a hydrocarbon solvent, such as toluene or n-heptane, at room temperature. The possible reactions, which take place during the preparation of a coordination complex catalyst from A1(C2H5)3 and TiCU, are reported in Fig. 1.7. 

Chlorine or bromine react with benzene in the presence of carriers, such as ferric halides, aluminum halides, or transition metal halides, to give substitution products such as chlorobenzene or bromobenzene [108-86-17, C H Br occasionally para-disubstitution products are formed. Chlorobenzene [108-90-7] ... 

As indicated by the title, these processes are largely due to the work of Ziegler and coworkers. The type of polymerisation involved is sometimes referred to as co-ordination polymerisation since the mechanism involves a catalyst-monomer co-ordination complex or some other directing force that controls the way in which the monomer approaches the growing chain. The co-ordination catalysts are generally formed by the interaction of the alkyls of Groups I-III metals with halides and other derivatives of transition metals in Groups IV-VIII of the Periodic Table. In a typical process the catalyst is prepared from titanium tetrachloride and aluminium triethyl or some related material. 

The highest halide of each metal is of course a fluoride Rep7 (the only thermally stable heptahalide of a transition metal), TcFg, and MnF4. This again indicates the diminished ability of manganese to attain high oxidation states when compared not only to Tc and Re but also to... 

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... 

Two commonly used synthetic methodologies for the synthesis of transition metal complexes with substituted cyclopentadienyl ligands are important. One is based on the functionalization at the ring periphery of Cp or Cp metal complexes and the other consists of the classical reaction of a suitable substituted cyclopentadienyl anion equivalent and a transition metal halide or carbonyl complex. However, a third strategy of creating a specifically substituted cyclopentadienyl ligand from smaller carbon units such as alkylidynes and alkynes within the coordination sphere is emerging and will probably find wider application [22]. 

Pyridones can also be converted to 2-chloropyridines by exchanging the carbonyl functionality using phosphoroxychloride (POCI3) [72]. A combination of N-halosuccinimides and triphenylphosphine has also been applied to introduce halogens in this position [73]. The carbonyl functionality in 2-pyridones makes these systems reactive towards nucleophiles as well, which add in 1,4-reactions with displacement of halides [74]. The use of transition metal mediated couplings like Heck, and Suzuki have also been successfully applied on halogenated 2-pyridones (d. Scheme 10) [36,75]. 

The synthesis of (hetero)aryl cyanides from (hetero)aryl halides via transition-metal catalysis is a very valuable reaction since a nitrile can be easily transformed into several other functional groups. Not until 2000 were the first examples on microwave-assisted cyanation reported in the literature. Alter-man and Hallberg found that 3-bromopyridine and 3-bromothiophene were... 

Hydrogen reduction has a major advantage in that the reaction generally takes place at lower temperature than the equivalent decomposition reaction. It is used extensively in the deposition of transition metals from their halides, particularly the metals of Groups Va, (vanadium, niobium, and tantalum) and Via (chromium, molybdenum, and tungsten). The halide reduction of Group IVa metals (titanium, zirconium, and hafnium) is more difficult because their halides are more stable. 

Metallo-organics are compounds in which the atom of an element is bound to one or more carbon atoms of an organic hydrocarbon group. Many of the elements used in MOCVD are the metals of groups Ila, Ilb, Illb, IVb, Vb, and VIb, which are non-transitional. The metallo-organics thus complement the halides and carbonyls, which are the precursors for the deposition of transition metals (Groups IVa, Va, and Via) and their compounds. 

Reactions between anionic species containing one or more group-IIIB elements (particularly boron) and complexes of transition-metal halides are used to produce an immense number of ionic boron-containing compounds. For this reason a strong selection factor must be made. 

A60. J. P. Candlin, K. A. Taylor, and D. T. Thompson, "Reactions of Transition-Metal Complexes. Elsevier, Amsterdam, 1968. A review of types of reactions of metal complexes (e.g., substitution, combination, redox) reactions with various reagents (e.g., hydrocarbons, halides, carbon monoxide, and isonitrile) and preparation of new stabilised organic systems (e.g., metallocenes, carbenes). Intended for research workers, consequently written at a fairly high level, with emphasis on organometallics. A61. H. J. Keller, NMR-Untersuchungen an Komplexverbindungen. Springer, Berlin, 1970. Expansion of review article 37.1. 

Based on the concept of mixed-framework lattices, we have reported a novel class of hybrid solids that were discovered via salt-inclusion synthesis [4—7]. These new compounds exhibit composite frameworks of covalent and ionic lattices made of transition-metal oxides and alkali and alkaline-earth metal halides, respectively [4]. It has been demonstrated that the covalent frameworks can be tailored by changing the size and concentration of the incorporated salt. The interaction at the interface of these two chemically dissimilar lattices varies depending upon the relative strength of covalent vs. ionic interaction of the corresponding components. In some cases, the weak interaction facilitates an easy... 

Ames Laboratory (Iowa State University, USA) investigating new solid state phases based on reduced rare earth halides. Since 1993, she has held a position at the University Jaume 1 of Castello (Spain) and became Associate Professor of Physical Chemistry in 1995. During the second semester of 2005, she held a visiting professor position at the Laboratory of Chemistry, Molecular Engineering and Materials of the CNRS-Universtity of Angers (France). Her research has been focussed on the chemistry of transition metal clusters with special interest in multifunctional molecular materials and the relationship between the molecular and electronic structures of these systems with their properties. She is currently coauthor of around 80 research papers on this and related topics. 

Although naturally occurring compounds of transition metals are restricted in scope, a wide variety of compounds can be synthesized in the laboratory. Representative compounds appear in Table 20-2. These compounds fall into three general categories There are many binary halides and oxides in a range of oxidation numbers. Ionic compounds containing transition metal cations and polyatomic oxoanions also are common these include nitrates, carbonates, sulfates, phosphates, and perchlorates. Finally, there are numerous ionic compounds in which the transition metal is part of an oxoanion. 

The presence of transition metal ions has a catalytic effect on reduction of halides and tosylates by LiAlH4.166 Various copper hydride reducing agents are effective for removal of halide and tosylate groups.167 The primary synthetic value of these reductions is for the removal of a hydroxy function after conversion to a halide or tosylate. 

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