Organometallic compounds of transition elements

The catalysts formed by the support of organometallic compounds of transition elements are also of great interest for nonpolymerization reactions. Generally speaking, these catalysts can be used in three various states (a) in the initial state, (b) after reduction, and (c) after oxidation... 

YU. I. Yermakov, Supported catalysts obtained by interaction of organometallic compounds of transition elements with oxide supports, Catal. Rev. Sci. Eng. 13(1), 77-120 (1976). 

The most important complexes involving carbon-containing ligands in which carbon is bound to the metal are discussed separately those of carbon monoxide in Chapter 16, organometallic compounds of transition elements, and organometallic compounds of the main group elements in the corresponding chapters. 

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... 

Y. I. Yermakov and B. N. Kuznetzov, Supported Metallic Catalysts Obtained via Organometallic Compounds of Transition Elements, Kinet. Catal., 18, pp. 955-65, 1977. 

An already large and steadily increasing number of organometallic compounds of transition elements is known, and their applications in both laboratory and industrial processes has transformed synthetic organic chemistry. They not only make it possible to carry out reactions that are difficult to do otherwise but in many cases do so as catalysts rather than reactants. Before we look at the reactions of transition-metal organometallics in this and subsequent sections, some structural background is in order. 

Sigma-bonded Organometallic Compounds of Transition Elements of Groups III A to VIIA... 

This monograph contains enthalpies of formation, heat capacities, entropies, and metal-ligand bond dissociation enthalpies of organometallic compounds of transition and main group elements. 

In this chapter, we introduce the chemistry of organic compounds that contain transition metals elements. The chemistry of organometallic compounds lies at the interface of inorganic chemistry and organic chemistry. As a prelude to this discussion, we will briefly introduce some basic principles and nomenclature. Then, we will be able to describe the tremendous versatility of organometallic compounds of transition metal elements in organic synthesis. We wfll focus upon a small number of organometaUic reactions and emphasize the basic principles that reach far beyond these reactions. 

The fundamental Ziegler-Natta recipe consists of two components the halide or some other compound of a transition metal from among the group IVB to VIIIB elements and an organometallic compound of a representative metal from groups lA to IIIA. Some of the transition metal compounds that have been... 

Nomenclature of organometallic compounds of the transition elements (lUPAC recommendations) 99PAC1557. 

An area of current development is the nomenclature of organometallic compounds. Organometallic compounds of Main Group elements can, to a first approximation, be considered to be derivatives of hydrides, and the methods of substitutive nomenclature can be applied. Even then, the accessibility of different oxidation states, as with phosphorus(iii) and phosphorus(v), introduces complications. Transition metal organometallic compounds are even more difficult to treat, and the development of a unified, self-consistent and accepted and applied nomenclature is not easy. Witness the different ways (k, t and italicised symbols) for denoting donor atoms in ligands. 

The low-pressure polymerization of olefins using Ziegler-Natta catalysts, i.e., mixtures of compounds of transition groups IV to VI of the periodic table of the elements together with organometallic compounds of groups I to III is widely applied. Such catalysts, consist of titanium alkyl compounds and aluminum alkyl compounds or alkylaluminum halides. 

In another recent study of CO reduction using organometallic compounds of the early transition elements, Caulton et al. report that CH4 is evolved when toluene solutions of (C5H5)2Ti(CO)2 are heated at 150°C under H2 or H2 -l- CO atmospheres (55). When deuterium is used, the observed product is CD4, although some deuteration of the cyclopentadienyl rings is noted. Caulton does not report the percent yield of methane, but does state that the reaction is not catalytic. One of the most novel aspects of this investigation is the isolation of a blue Tig cluster that is inert to further reaction... 

Organometallic chemistry does have its own distinctive flavour. Organometallic compounds are often (but not invariably) air- and moisture-sensitive and their handling requires much care and skill. In the interplay between kinetic and thermodynamic considerations, organometallic chemistry falls somewhere between inorganic and organic chemistry. Most organometallic compounds of the transition elements can also be classified as coordination compounds, and are dealt with in more detail in Chapter 8. (See also Section 10.5.)... 

All the standard texts listed in Section A.3 of the Appendix have lengthy sections on coordination and organometallic compounds of the transition elements. See also the books listed in Sections A.10 and A.ll. Bell (1977) gives the fullest account of the chelate effect. Cotton and Wilkinson (1988) (Section A.3) is best for the catalytic applications of complexes. Jolly (1984) (Section A.3) discusses electron-counting in polynuclear carbonyls in some depth. 

To date, the only trifluoromethyl migrations that have been observed in compounds of the elements that are located in the third row of the transition metals occur in the two Ir(I) complexes which, as noted in Table I, retain the CO linkage after alkyl migration, in CF3CORe(CO)5 (38), and in the platinum(II) species for which a temperature of 210°C was required to initiate the decarbonylation. While the conditions of the last reaction clearly indicate that CF3-Pt bonds are very stable, many if not most organometallic species cannot survive this type of treatment, and the application of the technique to the heavier transition metals is therefore expected to be quite limited. 

Davidson G (1989) Vibrational spectra of transition-element compounds. In Davidson G, Ebswonh EAV (eds) Spectroscopic properties of inorganic and organometallic compounds, vol 22, The Royal Society of Chemistry, Cambridge, p 278 Davies B, Poliakoff M, Smith KP. Turner JJ (1978) J Photochem 1978 2 Davies JP, Pachuta SJ, Cooks RG, Weaver MI (1986) J Analyt Chem 58 1290 Davies PB, Moiton-Joncs AJ (1987) AppI Phys B 42 35 de Abney W. Resting RE (1881) Phil Trans Royal Soc (London) 172 887 Decius JC (1949) J Chem Phys 17 1315... 

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