Chemical behavior, cyclopentadienyl

The cyclopentadienyl rings in ferrocene display some of the same chemical behavior as benzene. For example, ferrocene undergoes Friedel-Crafts mono and di acylation reactions, but at different rates. 

The photochemical synthesis of the tungsten carbonyl metallocarborane [Eq. (18) ] is also effective in the preparation of the molybdenum carbonyl analog. The resulting air-sensitive complexes show chemical behavior similar to the cyclopentadienyl analogs, C5H5M(CO)3, in that they undergo protonation with anhydrous HOI and met.hylation with CH3I. They also react further with metal hexacarbonyls to afford bimetallic complexes 54) ... 

The chemistry of titanium and zirconium, bis(ij-pentamethylcyclopen-tadienyl) systems is essentially that of monomeric fo-CsfCH iM units. With the cyclopentadienyl systems, nearly all of the chemistry observed is that of dimers. Although the dimeric hydride fi-(tj5 tj5-C,0H8 )-/x(H2 C5H5)2Ti2 (3) is coordinatively saturated and relatively unreactive, the partially unsaturated, dimeric metallocene /t-( 1 i -C H )(,i>-CjH )3Ti1 (10) shows considerable chemical reactivity toward N2 (Section III,D) as well as interesting catalytic properties (Section VI). The behavior of dimer units in the cyclopentadienyl systems is exemplified by the unusual naphthalene ring binding in the naphthyl hydride zirconocene derivative... 

What is really key for the SSC family based on metallocenes and CGCs is the opportunity to have a catalyst precursor of defined chemical structure. Eor example, in the case of metallocenes, the n-bound cyclopentadienyl-type ligands remain coordinated to the transition metal atom during the course of polymerization. This allows for the following (1) the control of polymerization behavior and polymer microsttucture by modifying the structure of the ligands, and, as a consequence, (2) establishment of a correlation between ligand structure and polymer microstructure. 

This chapter outlines briefly the theory underlying the bonding between the cyclopentadienyl ligand and a typical rare earth ion, going on to discuss the relevance of structural studies then to mention in more detail some of the synthetic methods available and the general reactivity of the title complexes and then to present a more detailed discussion of structural, chemical, and catalytic behavior of the cyclopentadienyl complexes of rare earths. 

The coupling between electron transfer rates and solvent dynamics has also been the subject of reviews. Fleming and Wolynes have written a general overview of theoretical work and experimental observations concerning the effect of solvent dynamics on the kinetic behavior of very fast chemical processes.Weaver and McManis have reviewed their experimental investigations of the coupling between solvent frictional effects and the adiabaticity of electron transfer rates of ftw-cyclopentadienyl complexes. 

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