TRANSITION-METAL ORGANIC COMPOUNDS

Chapter 14 (Organometallic Compounds) has been a prominent part of our text since the first edition and, owing to Nobel-worthy advances based on organic compounds of transition metals, has steadily increased in importance. The chemistry of these transition-metal organic compounds has been expanded in 9e to where it now comprises approximately one-half of the chapter. 

PO can be made degradable by means of additives. The types of additives include aromatic ketones (benzo-phenone and substituted benzophenones [47], qui-none), aromatic amines (trisphenylamine), polycyclic aromatic hydrocarbons (anthracene, certain dyes such as xanthene dyes), or transition metal organic compounds. The transition metal compounds of Fe, Co, Ni, Cr, Mn are widely used. Organo-soluble acetyl acetonates of many transition metals are photooxidants and transition metal carboxylates are also thermal pro-oxidants. Co acetylacetonate appears to be an effective catalyst for chemical degradation of PP in the marine environment. The preferred photoactivator system is ferric dibutyldithiocarbamate with a concentration range of 0.01. 1%. Scott has patented the use of organometallic compounds hke iron (ferric) dibutyldithiocarbamate or Ni-dibutyl-dithiocarbamate [48]. Cerium carboxylate [49] and carbon black are also used in such materials [50]. 

Indeed, these reactions proceed at 25 °C in ethanol-aqueous media in the absence of transition metal catalysts. The ease with which P-H bonds in primary phosphines can be converted to P-C bonds, as shown in Schemes 9 and 10, demonstrates the importance of primary phosphines in the design and development of novel organophosphorus compounds. In particular, functionalized hydroxymethyl phosphines have become ubiquitous in the development of water-soluble transition metal/organometallic compounds for potential applications in biphasic aqueous-organic catalysis and also in transition metal based pharmaceutical development [53-62]. Extensive investigations on the coordination chemistry of hydroxymethyl phosphines have demonstrated unique stereospe-cific and kinetic propensity of this class of water-soluble phosphines [53-62]. Representative examples outlined in Fig. 4, depict bidentate and multidentate coordination modes and the unique kinetic propensity to stabilize various oxidation states of metal centers, such as Re( V), Rh(III), Pt(II) and Au(I), in aqueous media [53 - 62]. Therefore, the importance of functionalized primary phosphines in the development of multidentate water-soluble phosphines cannot be overemphasized. 

Gray, G. M. Lawson, C. M. Structure-Property Relationships in Transition Metal-organic Third-order Nonlinear Optical Materials. In Optoelectronic Properties of Inorganic Compounds, Roundhill, D. M., Fackler, J. P., Jr., Eds. Plenum New York, 1999 pp 1-27. 

Wilkinson s catalyst after its discoverer, G. Wilkinson. In 1973, the Nobel Prize in chemistry was awarded jointly to Wilkinson and E. O. H. Fischer for their respective contributions to the field of organometallic chemistry. As you will see in this and later chapters, compounds with carbon-metal bonds (organometallic compounds) are extremely useful reagents, reactive intermediates, or catalysts in organic reactions. To a very large extent, the work of Fischer and Wilkinson created the current interest and developments in the field of transition-metal organic chemistry, which will be discussed in Chapter 31. 

Concomitant with continued olefin insertion into the metal-carbon bond of the titanium-aluminum complex, alkyl exchange and hydrogen-transfer reactions are observed. Whereas the normal reduction mechanism for transition-metal-organic complexes is initiated by release of olefins with formation of hydride followed by hydride transfer (184, 185) to an alkyl group, in the case of some titanium and zirconium compounds a reverse reaction takes place. By the release of ethane, a dimetalloalkane is formed. In a second step, ethylene from the dimetalloalkane is evolved, and two reduced metal atoms remain (119). 

Ziegler-Natta catalysts generally consist of a metal organic compound involving a metal from groups I-ffl of the periodic table, such as triethyl aluminium, and a transition metal compound (from groups IV-VIII), such as titanium tetrachloride (Figure 3-37). 

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