Metallocenes crystal structures

The structure of the metallocene cation energy minimised with the Car-Parrinello method agrees well with the experimentally obtained crystal structures of related complexes. Typical features of the structure as obtained from X-ray diffraction on crystals of very similar neutral complexes (e.g., the dichlorides), such as small differences in distances between C atoms within a cyclopentadienyl (Cp) ring, as well as differences in distances between the C atoms of the Cp ring and the Zr atom, were revealed from the simulations. 

Prior to this 1996 study, there had been no reports of boratabenzene complexes of early transition metals.42 An X-ray crystal structure of the catalyst revealed a C2-symmetric geometry that resembles Cp2Zr-based bent metallocenes. The bond lengths suggest a strong B-N it interaction (rotational barrier measured by NMR 18 kcal/mol) and a very weak Zr B interaction ( t 5 coordination of the boratabenzene ring). 

As discussed in more detail in Section 2.02.4.2.2.(iii), almost all the metallocenes of calcium, strontium, or barium are bent, even when unsolvated. The only exception to this so far is the sterically crowded (CsPr Ba 152 (Figure 79),348 whose X-ray crystal structure reveals a linear geometry with Ba-C = 2.997(4)A. All three... 

Some exchange reactions of complexes 112 and 115 have been studied. From the X-ray crystal structure analyses, it appears that trimethylgallium is rather loosely bound to the (r 2-aryne)- and (r 2-cydohexyne) metallocene building blocks in the dimetalla-bicyclic complexes 112 and 115, respectively (Scheme 7.34). Therefore, it was tempting to investigate whether it was possible to reverse the reactions depicted in Schemes 7.32 and 7.33 using these specific examples to carry out thermally induced exchange reactions. 

Since the discovery of ferrocene and the development of metallocene chemistry, the compound cyclopentadienyllithium, C5H5Li, has been of considerable interest to both experimentalists and theoreticians. In its physical properties cyclopentadienyllithium qualitatively behaves like a typical salt. It is nearly insoluble in noncoordinating solvents and possesses a high melting (decomposition) point and a very low volatility. To our knowledge the crystal structure of C5H5Li is unknown. 

Macrocyclic calix[4]arene metallocene hosts have been prepared by our laboratory (138, 146) (Schemes 35, 36) and the crystal structures of (109) and the dimeric host (110) are shown in Figs. 25 and 26. Preliminary solution H NMR and electrochemical inclusion studies in solvents such as acetonitrile, chloroform, and dichloromethane showed... 

The complex SmCpj was synthesized by metal vapour reaction of samarium with Cs(CH3)5H as a green product or by desolvation of the red SmCpj 2THF by sublimation. The crystal structure of the complex SmCpj shows it to be decamethyl samarocene with bent metallocene disposition [138], The Cg-Sm-Cg angle of 140.1° is greater than 136.7 in the desolvated analogue. The Sm-C bond distance is reduced, 2.79(1) A compared to 2.86 (3) A and the structure of SmCpj is shown in Fig. 6.12. 

X-Ray crystal structures of the metallocene diselenolate chelates 13-15 were reported <1996ZFA1979>. 

Emily Maverick and Jack Dunitz used the anisotropic displacement parameters from crystal structure analyses of metallocenes at various temperatures to estimate the barriers for the rotation of an individual C5H5 ring in the crystal about its five fold axis. The average mean-square amplitude of libration ( ) is is found to be 28° at 101 K, corresponding to an energy barrier of approximately 2 kcal moE (9.3 kJ... 

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