Organometallic complexes cyclopentadienyl ligand

Many organometallic complexes carry ligands such as cyclopentadienyl, phenyl, methylene and methylidene groups, all of which are capable of... 

The stereochemical designations employed for organometallic complexes follow an extension of the CIP system2. In all cases, the chiral metal atom has a higher atomic number and thus receives priority. The main feature of this extension of the CIP system concerns treatment of polyhapto ligands such as cyclopentadienyl ... 

Bis(cyclopentadienyl) complexes are central to the organometallic chemistry of the early transition metals and feature in applications such as alkene polymerization chemistry. Parallels can be drawn between a porphyrin ligand and two cyclopentadienyl ligands, in that they both contribute a 2— formal charge and exert a considerable steric influence on other ligands in the same molecule. Several of the metalloporphyrin complexes discussed below have bis(cyclopentadienyl) counterparts, and authors in some ca.ses have drawn quite detailed comparisons, although these discussions will not be repeated here. 

In view of the ubiquity of the 5-cyclopentadienyl ligand in organometallic chemistry, and the reports in the literature of perchlorocyclopentadienyl analogues (56), it is both curious and unfortunate that attempts (85) to prepare complexes of the /5-pentafluorocyclopentadienyl ligand from the known C5F j anion (87,88) have failed. 

Hafner, A. and Okuda, J. (1993) Titanium NMR data for titanium half-sandwich complexes bearing substituted cyclopentadienyl ligands. Organometallics, 12, 949-950. 

There are major challenges to be tackled relating to the chemical and biochemical mechanisms of action of organometallic complexes, for example involving the mechanism of displacement and release of coordinated arenes and cyclopentadienyl ligands which can expose several reactive coordination positions on a metal ion. Also the metabolism of coordinated arene and Cp ligands (e.g. modification by P450 enzymes in the liver) may have a major effect on the biodistribution and excretion of complexes. 

Furthermore, we could show that this reaction mechanism to produce Cp-complexes of "mTc is not limited to carboxylate derivatives of Cp but that also further functionalities can be conjugated to receive, e.g., amides (49 and 50) [125]. This reactivity implies that, comparable to the SAAC approach, Thiele s acid derivatives can be incorporated in, e.g., a peptide strand and directly be labeled with [99mTc(OH2)3(CO)3]+. The preparation of cyclopentadienyl complexes with a variety of functionalities attached to the cyclopentadienyl ring stands for a more routine introduction of this important tridentate ligand in radiopharmaceutical organometallic complexes. 

Cyclopentadiene (1), a simple organic compound first found in the volatile parts of coal tar, has become one of the most important ligands used in organometallic chemistry. More than 80% of all known organometallic complexes of the transition metals contain the cyclopentadienyl fragment or a derivative thereof. 

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