Cyclopentadienyl, indenyl, and fluorenyl complexes

Cyclopentadienyl complexes of the alkali metals are of fundamental importance as reagents in organometallic chemistry [13]. The structural chemistry of these species 

Related chain polymers have also been found in several Lewis-base adducts of alkali metal cyclopentadienyl, indenyl, and fluorenyl complexes. Such adducts with ethers or amines have been thoroughly investigated because they form stable, crys- 

Closely related is the unusual mixed-hgand cesium cyclopentadienyl/penta-methy Icyclopentadienyl complex [ Cs(l 8-crown-6) 2 (fi-Cs Mc5)][ Cs( 18-crown- 

6)(C5Me5) 2 Cs2(C5H5)3 ], 23 [23]. The anion consists of a central Cs2(C5H5)3 core to which two Cs(18-crown-6)(C5Me5) units are attached. All interactions between cesium and the cyelopentadienyl ring systems involve pentahapto coordination. Most recently these investigations have been extended to mixed-metal alkali cyclo- 

The dianion of dihydroacepentalene is of considerable interest as a potential precursor for the elusive hydrocarbon acepentalene, CioHe, which has been predicted to have a triplet diradical ground state. The corresponding dianion, CioHe , is significantly more stable and can be generated in solution by treating triquinacene with a superbasic mixture of n-butyllithium and potassium t-pentoxide in the presence of tmeda [27]. More recently a crystalline sample of the dimethoxyethane solvate [ Li(DME) 2CioH6]2, 33, has been successfully prepared according to Eq.(l) by means of a transmetallation reaction between 4,7-bis(trimethylstannyl)-dihydroacepentalene and methyllithium in DME solution at -60 °C [28]. 

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Organic fragments which can serve as n ligands include cyclopentadienyl, indenyl, and fluorenyl systems as well as polynuclear aromatic anionic and dianionic species. From IR and NMR data it has been concluded that the bonding in these complexes may be regarded as fully ionic. 

The interaction of bis(pyridinium)cerium hexachloride with Na[Cp] was claimed to produce Ce(Cp)4 and similar reactions afforded the indenyl and fluorenyl complexes. Tris(cyclopentadienyl)cerium chloride and bis(indenyl)cerium dichloride were also claimed. This work is not repeatable and the Ce(Cp)4 has been shown to be Ce(Cp)3(THF). 

CpLi exists in ethers as a contact ion pair, in which the lithium ion is located above the cyclopentadienyl ring. The crystal structure of CpLi(12-crown-4) reveals analogous structural features. This complex has a sandwich-type structure in which the lithium ion is coordinated to the four oxygen atoms of the crown ether on one side and to the Cp ring on the other. Several X-ray structures of alkali metal cyclopentadienyl compounds containing silyl substitution of the Cp ligand have been reported. The structures of fluorenyl alkali metal complexes (Li-Cs) stabilized by diglyme have also been reported. The crown-ether-stabilized compounds of cyclopentadienyl, indenyl, and fluorenyl with the heavier metals, Rb and Cs, have also been reported. " A common structural feature is the rf coordination of... 

Copper N-heterocyclic carbene complexes in catalysis 13CST912. Cyclopentadienyl-, indenyl- and fluorenyl-fimctionalized N-hetero-cyclic carbene metal complexes Synthesis and catalytic applications 12EJI1309. 

Several types of supramolecular self-assembly are found in indenyl and fluorenyl complexes of the alkali metals. It has recently become possible for the first time to elucidate the crystal structures of unsolvated lithium indenide, [LiC9H7] , 26, and sodium fluorenide, [NaCoHgjn, 27 [24]. The crystal structure of 26 closely resembles that of unsolvated lithium cyclopentadienide because it also consists of a polymeric multidecker array in which the Li atoms are symmetrically coordinated by two rj -cyclopentadienyl rings of the indenyl ligands. In contrast, unsolvated sodium fluorenide, 27, forms a two-dimensional supramolecular structure in the solid state (Figure 7.3). In this unusual coordination polymer both the five- and six-membered rings of the fluorene system participate in coordination to sodium via and rj -interactions, respectively. 

Figure 7. Structures of cyclopentadienyl, indenyl, and fluorenyl cation complexes with metal carbonyls (48). (Reprinted with permission from ref 32. Copyright 1999 American Chemical Society.)...

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]. 

In most cases the catalyst precursor is a metallocene dichloride complex consisting of two aromatic five-membered ring systems that can be tethered by a bridging unit ansa metallocene complexes) or not. The two aromatic ligands at the metal can be of the same type. i.e.. cyclopentadienyl. indenyl. or fluorenyl. The introduction of substituents at certain positions of the two aromatic ligands and/or the bridge modifies not only the steric and electronic conditions in the molecule but also the symmetry of such a metallocene dichloride complex. Another variable parameter is the metal M = Ti. Zr. Hf. 

Fig. 5 Reaction scheme of the alkylation, complexation and ion pair formation of zirconocene dichloride and MAO. L cyclopentadienyl, indenyl, or fluorenyl...

Germanium-bridged complexes, with Zr(IV) and Hf(IV) cyclopentadienyl complexes, 4, 967 fluorenyl complexes, 4, 974 indenyl complexes, 4, 972... 

Organometallic complexes such as tris, bis and monocylopentadienyl complexes, cyclooctatetraenyl complexes, cyclopentadienyl-cyclooctatetraenyl complexes, indenyl complexes, fluorenyl complexes, complexes with other aromatic ligands, callixerene complexes, NMR spectroscopy of organometallic complexes, vibrational spectra, and catalytic applications form the theme of the sixth chapter. 

Hydrocarbon anions such as fluorenyl, indenyl, and cyclopentadienyl substitute for fluoride, leading, for example, to (phenylindene)Cr(CO)3 complex (20) [36,37]. 

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