Cerium cyclooctatetraene

The synthesis and preliminary X-ray structure of the first organometallic Ce(IV) complex Ce(CsH8)2 was reported in 1976 [115] and reproduced in 1985 [116] by the reaction of cerium(IV) isopropoxide with triethylaluminum in the presence of cyclooctatetraene, as shown in Figure 8.35. The accurate sandwich molecule structure of cerocene has been eon-firmed by an X-ray structural study on the methyl substituted cerocene [Ce(MeCOT)2] [117], Subsequently, two more substituted cerocene analogs have been synthesized via a more efficient method, for example, controlled oxidation of cerium(III) precursors and one of these complexes has been structurally characterized [118],... 

Kilimann, U., Herbst-Inmer, R., Stalke, D. et al. (1994) An efficient access to organocerium(lV) complexes synthesis and structure of bis[l,3,6-tris(trimethylsilyl)cyclooctatetraene]cerium(lV). Angewandte Chemie International Edition, 33, 1618. 

The reduction of cerium tetra-isopropylate with triethyl aluminum in toluene in he presence of cyclooctatetraene at about 100°C yields cyclooctatetraenyl cerium... 

The di(cyclooctatetraenyl) cerium complex was prepared by the reaction of cerium tetra-iso-propoxide with triethyl aluminum in cyclooctatetraene at 140°C (Greco et al., 1976) ... 

A single lanthanide (IV) metallocene, i.e. bis(cyclooctatetraene)cerium(IV) Ce(C8Hg)2 or cerocene, has been studied theoretically. Rosch and Streitwieser (1978,1983) reported the results of nonrelativistic and quasirelativistic scattered-wave Xa calculations taking into account the scalar relativistic effects for cerocene, thorocene and uranocene at fixed idealized Dgh geometries (fig. 13). The authors discuss the participation of metal d and f... 

The reduction of Ce(0-i-C3H7)if with triethylaluminium in the presence of cyclooctatetraene yields a yellow colored cerium(lll) complex with two alkoxy-bridges between Ce and A1 (l62) ... 

The bis([8]annulene)lanthanate(III) anions which are complexed by an [8]annulenelanthanate(III) cation are the only other class of complexes which contain two [8]annulene dianions in a sandwich arrangement about a lanthanide(III) ion. This class was first reported for the cerium(III) ion, from the reduction of a cerium(IV) alkoxide with triethylaluminum in the presence of cyclooctatetraene.3 ... 

A bimetallic mono-[8]annulene complex containing cerium(lll) and aluminuro(III) has been synthesized.67 [8]Annulenecerium(III)-di-u isopropoxydiethylaluminum was synthesized by the reaction of cerium(IV) isopropoxide with triethylaluminum in the presence of cyclooctatetraene and toluene as the solvent. 

Bis([8]annulene) complexes, lanthanide 84 Bis(cyclooctatetraene) complexes, cerium 84,88 Bis([8]annulene) complexes, cerium 84,88 Bis(cyclooctatetraene) cerate anion 85,88 Bis([8]annulene) cerate anion 85,88 Molecular orbital calculations 86 Xa Scattered-wave calculations 86 Quasi-relativistic Xa Scattered-wave calculations 86... 

A number of interesting organometaUic compounds of cerium have also been reported as arising from the reactions of Ce(OPr )4.Pr OH or Ce(OIV)4 with cyclooctatetraene (CgHg) in the presence of AlEts. The composition of the final product depends on the reaction conditions (Eqs 2.308-2.310) ... 

C3 2H3 8B2Fe2N20ft, cis-Di-M carbonylbis[(1-t-butyl-3-methyl-2-phen-yl-7 -1, 2-azaborolinyl)carbonyliron) ], 46B, 935 C3 2HftoNd202, Cyclooctatetraenylbis(tetrahydrofuran)neodymium(III) bis(cyclooctatetraenyl)neodymate(lII), 42B, 710 44B, 791 C3 2Hft sCe2Cl20ft, Di-M-chloro-di(ir-cyclooctatetraene-bis(tetrahydro-furan)cerium), 38B, 811... 

Binuclear complexes of Ln(III) of general formula [(CgHg)2Ln][(CgHg)Ln(THF)2] (Ln Ce, Nd, Er) are formed on the condensation of these metal vapours at cyclooctatetraene at -196°C [24]. Besides, the cerium complex of the same structure has been prepared according to the reaction [35] ... 

The cerium-aluminium complex containing three types of ligands has been obtained on heating triethylaluminium at 100°C with Ce(OC3H7-i)4(L) (L = i-C3H70H, py) in toluene in presence of an excess of cyclooctatetraene [114] ... 

The assignment of oxidation states in cerium compounds is not always an easy task. A well-known case is that of cerocene, bis(cyclooctatetraene)cerium, Ce() -C8H8)2. This complex was originally formulated as a cerium(IV) compound with two (j -CsHs) " anions (Greco et al., 1976). Later calculations indicated that the stoichiometry of cerocene is better described as [Ce + ()] -C8H8)2 ] (Neumann and Fulde, 1989). Ab initio calculations showed that cerocene is in fact a mixed valent compound, with a ground state consisting of 83%... 

This chapter intends to remind the reader briefly of some important aspects of the shell structure, relativistic effects, and electron correlation effects for lanthanide and actinide atoms and molecules, mainly using the example of Ce and Th. It then turns to a discussion of the electronic structure of cerium-bis( 7 -cyclooctatetraene), cerocene, which fascinated this author for more than two decades, as well as a related cerium(III)-based molecular Kondo system, i.e., bis(r7 -pentalene)cerium. These systems feature many problems of an accurate relativistic correlated description of their electronic structure and moreover leave plenty of room for alternative interpretations of their electronic ground state as well as the involvement of 4f orbitals in chemical bonding. 

M. Dolg, P. Fulde, W. Ktichle, C.-S. Neumann, H. Stoll, Ground state calculations of di-tr-cyclooctatetraene cerium, J. Chem. Phys., 94, 3011-3017 (1991). 

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