Cycloheptatrienyl complexes properties

Cycloheptatrienyl and cyclotatetraene complexes, like other sandwich compounds, and complexes [M(C H )L ] containing polyelectron ligands are thermally stable. Often, these compounds melt at higher temperatures without decomposition. Complexes with ligands which do not contain bulky substituents connected to the ring carbon atoms are usually very sensitive to oxidation and hydrolysis. The compounds of the type M(C0T)2 (M = U, Pa, Ce, etc.) are easily oxidized but are more resistant to water. Table 8.1 gives properties of some cycloheptatrienyl and cyclooctatetraene metal compounds. 

From 1971 to 1974 a group of Indian chemists published a series of papers in which the synthesis and the properties of more than 60 organo-Ce(IV) derivatives were described, including cyclopentadienyl, indenyl, fluorenyl, cycloheptatrienyl and cyclooctatetraenyl complexes (Table XLL). The structure of compounds was confirmed in the most cases by the data of elemental analysis (C, H, Ce), IR spectroscopy and chemical reactions. At the same time several attempts to repeat the described synthesis, which have been undertaken by other chemists, have failed, which gives the base for some doubts in reliability of the data of Kapur and coworkers. These reasons impelled us to collect all compounds of Ce(IV) described by the mentioned authors in a separate chapter. 

The reaction sequence includes a variety of different iron complexes and utilizes their specific nucleophilic and electrophilic properties. Nucleophilic addition ofri -allyl-Fp to a tricarbonyliron complexed cationic ri -cycloheptatrienyl system leads to an intermediate (Tj -cycloheptatriene)iron complex bearing an exocyclic cationic (Ti -alkene)iron unit. The latter is attacked by the uncomplexed alkene moiety with concomitant cyciization to leave an alkyl-Fp and an (ri -cycloheptadienylium)iron fragment in the molecule. Reduction with sodium borohydride and subsequent oxidative demetalation in the presence of carbon monoxide provides the hexahydroazulene derivative. 

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