Cerium complexes tetrakis

Tetrakis-cyclopentadienyl cerium (CeCp4) has been reported to be formed by the reaction of bis(pyridinium) hexachlorocerate with sodium cyclopentadienide [17]. Similarly indenyl and fluorenyl derivatives were prepared. Later work showed the same reactants in tetrahydrofurane to yield, Ce(Cp3), tricyclopentadienyl cerium complex instead of Ce(Cp4) [18]. 

Metal salts or complexes have a role in promoting dehydration of nitro compounds. Thus, 5-phenylisoxazole has been obtained in low yield from the lithium salt of phenylacetylene with nitromethane in dioxan at room temperature [24]. The complex tetrakis(triphenylphosphane) platinum(O) on treatment with nitromethane leads to fulminatobis(triphenylphosphane)platinum(II), possibly via CT-nitromethyls [25-27]. Cerium and other metal nitrates have been claimed to promote condensation of nitro compounds with alkenes [28]. More examples of condensations caused by transition metal salts are reported in Section 8.2.4. 

Tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)cerium(IV) has been found to have antiknock properties for petrol.153 Other lanthanide complexes of the same ligand are also effective and mixtures may be used, especially those rich in cerium.154... 

To construct such a porphyrin-based positive allosteric system, we chose a cerium(iv) bis(porphyrinate) double decker compound 184-861 namely the tetrakis(4-pyridyl)porphyrin derivative 38.[871 This molecule satisfies the aforementioned requirements firstly, slow rotation of the two porphyrin planes with respect to one another should be possible at room temperature,1881 in analogy to similar cerium(iv) bis(diarylporphyrin) and bis(tetraarylporphyrin) complexes studied by Aida et al/861 Secondly, tilting of two porphyrin planes is more difficult than in 37, and thirdly, four pairs of 4-pyridyl groups are available as hydrogen bond acceptor sites for diols, hydroxycarboxylic acids, and dicarboxylic acids. Compound 39, which has only one pair of pyridyl groups, was used as a reference. 

High-coordination-number complexes of 0-keto-enolates continue to be obtained with the metals such as zirconium(IV),8 hafnium(IV),8 cerium(IV),9 and the lanthanons(III),10 the last being tetrakis anionic species. At least one example of a volatile tetrakis 0-keto-enolate salt has been reported,11 Cs[Y(CF3-COCHCOCF3)4]. The ionic charge on the 0-keto-enolate complex has been shown to produce12 a high field nuclear magnetic resonance for anions and low field shifts for cations, relative to the positions observed for the neutral species. 

In the complex NH4 [Ho(tropolanto)4] m edges are spanned since the complex has a small bite [125]. A similar situation of sharing m edges is encountered in isoquinolinium tetrakis[4,4,4-trifluoro-l-(2-thienyl)-l,3-butanedione]cerium(III) and the dodecahedron is... 

Cerium tetrakis(acetylacetonate), 1114 Cesium complexes crown ethers, 40 Chevrel phases, 1321 Chlorella vulgaris nitrate reductase structure, 1438 Chlorine cations... 

Cerium(IV) forms tetrakis complexes with y3-diketonates. Two monoclinic polymorphs are known for [Ce(acac)4] Q -[Ce(acac)4] and j0-[Ce(acac)4]. The a-form has been isolated after reaction between cerium(IV) hydroxide and an excess of acetylacetone (Matkovic and Gr-denic, 1963 Titze, 1974). Addition of benzene to the same reaction mixture resulted information of the jS-form (Titze, 1969) (fig. 16). The formation of the a- or /3-form is solvent dependent. Behrsing et al. (2003) obtained o -[Ce(acac)4] by aerial oxidation of [Ce(acac)3(H20)2] in dichloromethane, and j0-[Ce(acac)4] by the same reaction in toluene. In both cases, one has to made sure that besides [Ce(acac)3(H20)2] an excess of acetylacetone is present in the reaction mixture. Attempts to convert the jS-form into the Q -fonn by reciystallization in dichloromethane, resulted in significant reduction of cerimn(IV) to cerium(III). The coordination polyhedron of cerium(IV) in o -[Ce(acac)4] has both been described as a distorted square antiprism (Titze, 1974), a dodecahedron (Allard, 1976) or a bicapped square antiprism (Steffen and Fay, 1978). The coordination polyhedron in /3-[Ce(acac)4] is a square antiprism (Allard, 1976). The main difference between the a- and the /3-form is the more pro-notmced folding of the acetylacetonate ligand in the /3-form. Neutralization of a ntixture of... 

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