Arenes and Cyclopentadienyls

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. 

Isolobal analogy between organic and organometallic arene and cyclopentadienyl fragments and compounds (R. Hoffmann, 1975)... 

In the years following the discovery of bis(cyclopentadienyl), bis(arene) and cyclopentadienyl(arene) metal complexes, the structural feature of a sandwich was also established for compounds containing three-, four-, seven-, eight- and nine-membered ring systems. In these compounds the metal centre... 

The bridging chloride ligands in these [Ir(olefin)2Cl]2 compounds are susceptible to metathesis reactions, yielding new dimeric compounds of the form [Ir(olefin)2B]2 where B represents a new bridging ligand. AUcoxides, thiolates, and carboxylates have all been employed successfully in the replacement of chloride. The complexes with B = Br, I have also been prepared, both by metathesis reactions and by direct reaction of cyclooctene or cyclooctadiene with IrBrs or Iris The olefin complexes also provide excellent starting materials for the syntheses of arene and cyclopentadienyl iridium complexes, a subject that will be discussed in the next section. 

The crystal stmctures of a number of (arene)FeCp+ cations have been reported. In general, the planes defined by the arene and cyclopentadienyl ligands are essentially parallel. The Fe arene centroid distance is in the range 1.52-1.60 A, while the Fe-Cp centroid distance is 1.62-1.79 A. The arene C C bond distance increases upon complexation to 1.39 1.44 A. An upheld shift is observed for the C NMR signals of the complexed arene ring. ... 

The compound Na[Tc3(CO)9(OMe)4] prepared by the incomplete carbonylation of sodium pertechnetate in methanol shows promises as an important reagent for the future. It has been used to prepare LTc(CO)3, Tc2(CO)io, and various arene and cyclopentadienyl complexes (see Arene Complexes and Cydopentadienyl). The reaction conditions for these syntheses are moderately mild. 

Photosubstitution and Photoisomerization 13.2.5. with Other Organometallic Complexes 13.2.5.4. Containing Arenes and Cyclopentadienyls. 

They include, for example, arenes and cyclopentadienyl ligands and, especially in binuclear or cluster complexes, methylene (//-CH2) and methylidcne (/ij-CH) groups. Figure 5.5 depicts the p-CR2- OC and p CH- -OC bonding interactions in methylene and methylidene metal clusters. 

Ruthenium(II), d, is known as the binary bromide and as [RuCU] ". The richer complex chemistry involves stable compounds with cyanide, amines, halides, water, nitrosyl, carbonyl, hydride, phosphine, arsine, stibine, arene, and cyclopentadienyl ligands. [RuCl2(PPh3)2] is used as a catalyst. Ruthenium(II) is a good itt-donor and... 

Both arene and cyclopentadienyl 7i-complexes can undergo redistribution reactions. These reactions involve the exchange of ligands between two species possessing the same or different metal. For example, the reaction of dibenzenechromium with chromium hexacarbonyl provides a method for the preparation of benzenechromium tricarbonyl (2-6). A second example of a... 

As a group, substitution reactions provide the most widely applicable and general methods for the preparation of olefin (including 7r-allyl), arene, and cyclopentadienyl Ti-complexes. 

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