Ligand cyclopentadienyl, modification

Modification of the acceptor properties of the metal atom may be achieved by using complexes containing 7r-cyclopentadienyl ligands. 

Modification of the cyclopentadienyl ligands has led to a very rich chemistry and today a great variety of microstructures and combination thereof can be synthesised as desired including isotactic polymer with melting points above 160 °C, syndiotactic polypropene [16], block polymers, hemi-isotactic polymers etc. 

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. 

In addition to the many functionalized cyclopentadienyl ligands shown in Figures 7.23 and 7.30, a vast array of possible variants are accessible via modification of free cyclopentadienes. This is fortunate, in that ferrocene is unique in its versatility towards functionalization. The majority of other metallocenes, once constructed, are not as tolerant of such subsequent transformations. 

Modification of the Cyclopentadienyl Ligands, The results described so far suggest that the MX2 moiety within the metallocene dihalides represents the active center of the molecules. However, modification of the cyclopentadienyl rings in (C5H5)2TiCl2 as the model system also has a significant influence on the tumor-inhibiting potency of titanocene dichloride. 

In continuation of the modification of the cyclopentadienyl ligands, one or two of these can be replaced by the related vr-bound systems indenyl or tetrahydroindenyl. The tested compounds of this type include (C9H7)2TiCl2, (C9H7)(CqH pTiCl2, and (C9H7)(C5H5)TiCl (Table V). Whereas for the mixed cyclopentadienyl complex, which reveals a maximum cure rate of 100 %, no di-... 

The chemistry of complexes having achiral ligands is based solely on the geometrical arrangement on titanium. Optically active alcohols are the most favored monodentate ligands. Cyclopentadienyl is also well suited for chiral modification of titanium complexes. 

Cyclopentadienyl ring, 16 79 modifications of, 16 80 Cyclopentadienylsilylamido ligand, 16 81 Cyclopentadienylthallium, 24 635 ... 

Any modification of a complex, in order to increase or decrease its reactivity towards a substrate for catalytic purposes, can be easily accomplished by modulating the steric effects, even though modification of the electronic properties of the reactive site may also be necessary to render the catalyst more efficient. The evaluation of such electronic influence requires a comparison of complexes bearing ligands of the same size (isosteric ligands) but different in their chemical nature. The organometallic chemistry of the hard lanthanide elements is dominated by the soft cyclopentadienyl type ligands, while the number of non cyclopentadienyl hydrides is really modest. Due to the paucity of the published syntheses of... 

Another chelated system was obtained after an in situ modification of ligand 102 via 100 and 101 by introduction of a trimethylsilyl group at the cyclopentadienyl ring to give 254, which was not isolated but treated with FeCh to produce a 30% yield of multiply chelated complex 255 (Scheme 47). If the reaction was performed with FeCl2(CO)4 under irradiation instead of FeCF, the yield increased to 40%."... 

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