Complexes of cerium

Mononuclear monopentamethylcyclopentadienyl complexes of cerium and yttrium were obtained according to Eq. (18) and are isostructural (Table 14)... 

Fig. 4.31. Structures of two complexes of cerium with octaethylporphyrin double-decker (or sandwich) CeIV(EtgPor)2 (left) and triple-decker Ce ,11 (EtgPor)3 (right). Redrawn from J.W. Buchler et al., J. Am. Chem.

Oxidation of 1-(4-methoxyphenyl)-2-( -substituted phenyl) et hands, 6, by Cerium(IV). Dehydration prevented the oxidative-cleavage study of l-(4-hydroxyphenyl)-2-(4,-substituted phenyl)ethanols, 4, (8). As an alternative study, the oxidation of these phenolic compounds using the homolytic oxidant ceric ammonium nitrate (CAN) in an acidic environment was initiated. However, preliminary oxidations of these compounds were unsuccessful due to the apparent formation of complexes of cerium(IV) with the phenolic hydroxyl groups. 

Greco, A., Cesca, S., and Bertolini, G. (1976) New 7r-cyclooctateTraenyl andiT-cyclopentadienyl complexes of cerium. Journal of Organometallic Chemistry, 113, 321. 

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. 

TRIPHENYLPHOSPHINE OXIDE AND BIPYRIDINE DIOXIDE COMPLEXES OF CERIUM(IV)... 

Several other cations, such as calcium, barium, cadnium, nickel, magnesium, and mangane(II), are capable of forming a complex analogue to (Figure 6.5.3) thereby changing the color from yellow to red. But only the complex of cerium(lll) will form by fhe addition of fluoride. 

The closest redox-stable analogue of Ce(IV) is thorium(IV), for which a large data base of thermodynamic parameters is available for the carboxylic add complexes (Martell and Smith 1977). Using the ionic radii of Shannon (1976) and recalling that the stability of lanthanide and actinide complexes is derived almost exclusively from electrostatics, we can estimate that a 16% increase in the log of the stability quotients for thorium (since AG oc Z /r oc log should provide a reasonable estimate for the corresponding complexes of cerium(IV) [rce(CN = 8) = 0.97 A, r iCN = 10) = 1.13 A, (l/rce)/(l/ xh) = 116, CN = coordination number]. 

Figure 12.2 TG and DTG curves of complex of cerium bromide with glycine [21...

Table 2.11 Volatilities and molecular complexities of cerium and thorium alkoxides...

Quite in contrast to the alkoxides and simple silox-ides, related disiloxanediolate complexes of cerium(rv) form spontaneously upon treatment of cerium(III) precursors with... 

Dicyclooctatetraenylcerium has been prepared by the interaction of the same pyridine complex of cerium hexachloride with dipotassium cyclooctatetraenide in THF at room temperature [15]. Kalsotra and coworkers described the complex as a greenish-yellow crystalline substance, decomposing without melting in the narrow temperature range 114-115°C. Water, acetic acid and NaOH do not decompose the product. 

Notice that chloro complexes of cerium(IV) are much less stable than the corresponding nitrato or sulfato complexes, due to the oxidation of the chlorides to molecular chlorine by cerium(IV). For instance, cerium(IV) chloride, CeCU, is an unstable compound. 

The Ce + ion is one of the most active catalysts for peptide hydrolysis. Its activity is much higher than that of the trivalent lanthanide ions and other transition metal ions. In particular, Ce + is far superior to other tetravalent ions like Zr" or Hf +. Yashiro et al. (1994) reported that dipeptides and tripeptides were efficiently hydrolyzed under neutral conditions by the y-cyclodextrin complex of cerium(IV). Komiyama and coworkers (Takarada et al., 2000) studied the catalytic hydrolysis of oligopeptides by cerium(IV) salts. The hydrolysis is fast, especially when the oligopeptides contain no metal-coordinating side-chains. The hydrolysis rates of the dipeptides, tripeptides and tetrapeptides is similar. The hydrolysis reaction was performed at pH 7 and 50 °C and under these conditions, the half-life of the amide bond was only a few hours. The authors found that ammonium hexanitratocerate(IV) is more active than other cerium(IV) compounds like ammonium cerium(IV) sulfate, cerium(IV) sulfate and cerium(IV) hydroxide. The lower reactivity of ammonium cerium(IV) sulfate is ascribed to the competitive inhibition by sulfate ions, while the low reactivity of cerium(IV) sulfate and cerium(IV) hydroxide can be explained by their poor solubility in water. However, in the reaction mixtures at the given reaction conditions, most of the cerium(IV) consists in a gel of cerium(IV) hydroxides. No oxidative cleavage has been observed. 

Greco A, Cesca S, Bertolini G. New pi-cyclooctatretraenyl and pi-cyclopentdienyl complexes of cerium. J Organomet Chem. 1976 113 321-30. 

Kragten, J. and Decnop-Weever, L.G. (1978) Hydroxide complexes of cerium(lll). Talanta, 25, 147-150. 

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