Cyclopentadienyl and related complexes

NMR spectroscopy is a useful new tool to investigate kinetic problems. Attention has been focused on cyclopentadienyl and related complexes, and in a number of cases thermodynamic parameters have been derived in spite of experimental difficulties. First, in a typical experiment, on increasing the temperature, two or more sharp signals broaden, vanish into the noise, then a broad singlet appears and sharpens. Thus from line shape analysis it is possible to determine rates of exchange near the slow and fast exchange limits, but not in the tem-... 

XIII. Transition Metal ry -Cyclopentadienyl and Related Complexes. .. 97... 

Evans S, Green MLH, Jewitt B, Orchard AF, Pygall CF (1972) Electronic spectra of metal complexes containing 7t-cyclopentadienyl and related ligands part I. - He(I)... 

The chemistry of rhenium(I) is dominated by organometallic compounds which are not covered by this review. Thus, cyclopentadienyl and related compounds, where the organometallic part of the molecule dominate the properties will generally not be considered. Nevertheless, compounds with carbonyl or isocyanide co-ligands will be treated when they can be regarded as constituents of a typical coordination compound or the compounds are of fundamental interest in a radiopharmaceutical context such as the hexakis(isocyanide)rhenium(I) cations. For the same reason a separate section has been included which gives a brief summary of recent attempts to develop synthetic routes to tiicarbonylrhenium(I) complexes for nuclear medical applications. 

In this chapter we will review the synthesis, structural aspects, and basic chemical properties of formally divalent and trivalent titanium and zirconium metallocene complexes. We have restricted our coverage to the low-valent bis(rj-cyclopentadienyl) and related metallocenes metal halide complexes and organometallic mixed metal systems will not be discussed here. We have not attempted to present an exhaustive coverage of the field. Rather, our aim has been to describe critically and to evaluate the often confusing chemistry that has been reported for the reactive low-valent titanium and zirconium metallocenes. More general reviews (7) and a book (2) on the organometallic chemistry of titanium, zirconium, and hafnium have been published. 

Complexes containing cyclopentadienyl and related ligands are considered in Section B. 

The lanthanide halides are usually bi(cyclopentadienyl) and related lanthanide complexes M is an alkali metal or silver, and A is an anionic transition metal carbonyl compound or tetraphenyl borate. The formation of the insoluble salt MX is a driving force for this reaction. 

RUTHENOCENYL DERIVATIVES AND OTHER COMPLEXES OF r/ -CYCLOPENTADIENYL AND RELATED LIGANDS... 

Several metallocene complexes of cobalt and rhodium have been studied in which one cyclopentadienyl ring is replaced by a diborole moiety133. Under suitable conditions, auration of the C-2 carbon atom occurs (equation 29). Cyclopentadienyl and related gold(I) complexes are given in Table 5. 

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