Centroids, cyclopentadienyl

Very recently, the synthesis and structure of pentamethylcyclopenta-dienylindium(I) have been reported (277). The golden yellow, very air-sensitive compound (CII) crystallizes in the form of monomeric units (indium-cyclopentadienyl centroid distance, 2.3 A) which are held together by an octahedral arrangement of indium atoms indicating weak indium-indium interactions (3.96 A). 

The Y complex with (/r-H) is characterized by nearly square planar geometry for the four cyclopentadienyl centroids [248]. The structure of the methoxy complex of Y is a triangular arrangement of three Cp2Y units bridged by methoxy groups [249]. 

In support of the electrochemical evidence, the molecular structure of the biferrocenium ion in [( -CsF Fe -CsfLOf -CsfLOFe -CsHs)] [I3] shows that both pairs of cyclopentadienyl rings have an eclipsed conformation, Figure 16. Furthermore, the mean Fe-Cp(Centroid) distance is equivalent in both the ferrocenyl units and equal to 1.68 A. Speculatively, this value is intermediate between the values previously observed for ferrocene and ferrocenium ions, thus supporting charge delocalization between the two centres.27... 

Finally, a molecule in which the two ferrocenyl subunits are separated by a C2H4 bridge is considered, namely l,2-bis(ferrocenyl)ethane. Its X-ray structure shows that the mean Fe-Cp(Centroid) distance in both the ferrocenyl subunits is 1.67 A and the cyclopentadienyl rings are slightly rotated (8.5°) with respect to the eclipsed conformation.31... 

It might be expected that the bond angle involving the centroids of the cyclopentadienyl rings and the metal center would anticipate the amount of space available to an incoming olefin and, therefore, reasonably expected to correlate with reactivity and/or selectivity of Ziegler-Natta processes. 

Figures 5-41 and 5-42 compare CpTiCp (centroid) bond angles in titanium cyclopentadienyl dichloride complexes from PM3 and BP/ 6-31G calculations, respectively, with experimental values for these and other compounds dealt with in this section from X-ray crystallography. Due to practical limitations, the data used for comparison with the density functional calculations are a subset of that used in comparison with PM3. Both models perform well in separating those systems where the cyclopentadienyl rings are spread far apart from those where they are closer together.

A number of cyclopentadienyl-ffee amidoAn -cyclooctatetraene complexes have been reported. Sattelberger s group found that [An(cot)Cl2(thf)2] with 2Na[N(SiMe3)2] in toluene yielded the crystalline [An(cot) N(SiMe3)2 2], which for An = Th was X-ray-characterised as a four-legged piano stool , with the Th- -Centroid distance of 2.04 A, each amido ligand having one short Th- - -C contact (3.15 or 3.04 A). The compounds [U(cot)-... 

Many investigations have been performed in order to elucidate the structure and bonding in cyclopentadienylthallium(I) compounds. Various bonding situations are found in this class. The parent compound, cyclopentadienyl-thallium (LHIa) is nearly unsoluble in polar solvents. It is rather stable to air and water and sublimable in a vacuum. The microwave spectrum (178) suggests a half-sandwich structure in the gas phase with a thallium to ring centroid distance of 2.41 A (see Fig. 11). The thallium-carbon distances of... 

The X-ray crystal structure of LXXa confirms the presence of isolated cations and anions in the solid state. In the cation, the pentamethylcyclo-pentadienyl n system is symmetrically pentahapto bonded to the tin atom (see LXX in Fig. 14). The tin-ring centroid distance is considerably shorter than in decamethylstannocene. The methyl groups are bent away from the plane of the cyclopentadienyl ring. 

The benzyl-substituted titanocene dichloride derivatives are well suited for X-ray diffraction studies Titanocene Y was found to crystallise in the orthorhombic space group Pbca ( 61) with eight molecules in the unit cell [13] as seen in Fig. 3. The molecules show a distorted tetrahedral coordination around the central titanium atom with a Ti-Cl bond length of 237 pm, while the Ti-Cp(centroid) length is found to be 206 pm. The Cl-Ti-Cl angle of the distorted tetrahedron is to be only 95.9°, while the Cp(centroid)-Ti-Cp(centroid) angle is widened to 130.7° due to bulkiness of the cyclopentadienyl group. 

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