Organometallic cerium compound

Some of the applications of the organometallic compounds of lanthanides are as catalysts for (i) stereo specific polymerization of diolefins and in particular to obtain high yields of 1,4-ci.v-polybutadiene and 1,4-cw-polyisoprene and copolymer of the two monomers. The order of effectiveness of the rare earths as catalysts is Nd > Ce, Pr < Sm, Eu. The nature of halogen of the Lewis acid affecting the catalytic activity is in the order Br > Cl > I > F. Detailed work on the activity of cerium octanoate-AlR3-halide showed stereo specificity with cerium as the primary regulator. Cerium is thought to form jr-allyl or 7r-crotyl complexes with butadiene. 

Smoke suppressants are combustion catalysts. This class of additives is usually composed of organometallic compounds. Adding these compounds to fuel can reduce the emissions of pollutants that result from incomplete combustion. Smoke suppressants that are based on organometallic compounds of iron, cerium, platinum are in common use. 

In this article the term organometallic compound includes alkyl and aryl derivatives of the rare earths—the transition metals of group III, scandium, yttrium, lanthanum and the lanthanides cerium to liitetium with covalent metal-to-carbon a-bonds, as well as the so-called 77-complexes with more than monohapto metal-to-carbon bonds, for example cyclopentadienyl and olefin complexes, metal acetylides, but not carbonyls, cyanides and isocyanide complexes. Derivatives of scandium, yttrium and lanthanum are included and discussed together with the compounds of the lanthanides, because of many similarities in the synthesis and the chemistry of these organometallic derivatives of the rare earths. 

If there is any chance to isolate organometallic compounds of the lan-thanoides in the oxidation state Ln ", it should be possible in the case of cerium because of the electron configuration of the rare gas xenon for the ion The first paper published in 1971 reported the success-... 

Even flien well-characterized coordination compoimds are limited to only a few classes of compounds. Notable are, e.g., halogeno complexes and complexes of oxo acids, p-diketonates and related SchifF-base complexes, as well as porphyrinates and related complexes. Two other important classes of cerium(lV) compounds, the alkoxides and amides of Ce" +, can be regarded as pjewfifo-organometallics and are discnssed together with the organocerium(IV) complexes in Tetravalent Chemistry OrganometalUc. 

The Ln oxidation state in organometallic compounds is known only for cerium. It should be noted, however, that in some cases offered pathways to Ce complexes are apparently wrong and give in reality compounds with Ce. Only alkoxides (RO)4Ce, CpjCeOR and cyclooctatetraenyl complex (CgH8)2Ce are well-defined compounds of Ce. ... 

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]. 

Borsini, et al.,f ] reported the use of a redox catalyst system for the polymerization of ethylene and chlorotrifluoroethylene. One advantage of this catalyst system was that it permitted operation at lower temperatures than with peroxides. It allowed production of polymers with a linear chain, an orderly distribution of the asymmetric points. This process had favorable economics due to the possibility of the recovery of the catalyst, followed by its oxidation and recycle. The catalytic system was comprised of an organometallic compound and tetravalent cerium salt in quantities ranging from 0.01 to 2 of the former and 0.001 to 1 of metallic cerium part by weight per hundred parts by weight of the monomer mixture. This catalyst allowed the polymerization reaction to be conducted in the range of -60 to 20°C. Examples of the catalytic system include Pb(C2H5)4 and (NH4)2Ce(N03)g. 

Cerium is the only lanthanide element forming tetravalent compounds, stable in aqueous solutions, because the ion Ce + has the electron configuration of the ideal gas xenon. Despite the very strong oxidizing power of the Ce cation, several organometallic compounds have been reported to have an astonishingly high stability. 

Boussie, T.R., Eisenberg, D.C., Rigsbee, J. et al. (1991) Structures of organo-f-element compounds differing in the oxidation state of the central metal crystal structures of bis([8]annulene) complexes of cerium(lV), ytterbium(III), and uranium(III). Organometallics, 10, 1922. 

The alkoxides Ce(OR)4 are another well-developed class of Ce compounds. The alkoxide group plays an important role in stabilising the Ce(IV) state, witness the existence of [CeCp2(OBuOz] and [CeCp3(OBu )], when other Ce(IV) organometallics cannot be isolated. The isopropoxide is volatile in vacuo below 200 °C (its bis (isopropanol) adduct has six-coordinate cerium). General methods are available to... 

Reviews of carbanionic reactions in synthesis have addressed the use of organo-cerium compounds and ketone formation by reactions of acyl chlorides with organometallic reagents. ... 

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