Related Compounds Written with Prof. Jack R. Norton

Cyclopentadienyl and Related Compounds (Written with Prof. Jack R. Norton) 

The cyclopentadienyl ligand, generally abbreviated as Cp, is a common anionic ancillary ligand in organometallic chemistry. Complexes of this ligand or its substituted derivatives are known for all transition metals and for most /-block metals. - Ferrocene is the classic cyclopentadienyl compound, and the identification of the structure of this species by Woodward, Wilkinson, and co-workers, after initial misassignment, is legendary7 ° 

Cyclopentadienyl ligands are present on some of the most active catalysts for olefin polymerization, on the first complexes to add alkanes and on the first catalysts to functionalize the terminal position of alkanes regiospecifically. They are ancillary ligands on complexes that undergo all of the classes of reactions described in later chapters of this book, and for these reasons many derivatives of Cp ligands have been prepared. Section 3.6 describes the thermodynamic, electronic, and steric properties of cyclopentadienyl ligands, the synthesis of cyclopentadienyl complexes, and some fundamental reactivity of the Cp ligand. 

The Ti -cyclopentadienyl ligand is an L X-type ligand, and can be considered to occupy three facially oriented coordination sites. The molecular orbitals of the TT-system of a cyclopentadienyl ligand were shown in Chapter 1. These orbitals consist of one filled orbital of cr-symmetry and two filled orbitals of ir-symmetry, along with two imoccupied orbitals of 8-symmetry that can act as electron acceptors. 

Cyclopentadienyl complexes are usually prepared by taking advantage of the acidity of cyclopentadiene (pK = 16.0). By one method, Cp compounds are prepared by combining salts of its anion (usually NaCp) with metal halides, as shown for ferrocene in Equation 3.81/38,239,248,249 Reactions of the toxic, air-stable TlCp have been used to prepare metal-cyclopentadienyl complexes when side reactions such as electron transfer limit 

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