Iron cycloheptatrienyl complexes

Initial attempts to prepare 7r-cycloheptatrienyl-iron tricarbonyl complexes were not successful—the products often being 7r-cycloheptadienyl-iron tricarbonyl derivatives (60). In 1964 Mahler, Jones, and Pettit (162) reported the synthesis of a complex [(C7H7)Fe(CO)3] BF4 by the following route ... 

The reaction of the iron-carbene complex [[Bu C CC(OEt)=)Fe(CO)4] with 1,3-cyclohexadiene afforded223 (32), which was characterised by X-ray diffraction. The addition of the anionic derivatives of i-(diphenylmethane)-il-fluorene- and ii-(9,10-dihydroanthracene)-bis tricarbonylchromium to the hydrocarbon moiety (alkene, benzene, cyclohexadienyl, cycloheptadienyl and cycloheptatrienyl) in various cationic compounds of manganese, rhenium, iron, chromium, molybdenum, tungsten and cobalt was reported224 to provide a new route to hydrocarbon-bridged heteronuclear species such as (33). 

Reactions of anionic metal complexes with halide-bridged dimers can also be used to form a bond between two different metal atoms. Reaetion of (/j -C7H7)Fe(CO)3 with Mn2(CO)gBr2 gives ()j -C7H7)MnFe(CO)6 in which the cycloheptatrienyl ligand coordinates as a diolefin to manganese and as an allyl toward iron . 

Two heterobimetallic complexes with a Pd-Fe bond supported by a bridging cycloheptatrienyl group have been reported (Scheme 41). In both cases, the cycloheptatrienyl group binds iron as 77 -allyl. For R = Tj -cyclopentadienyl, the complex formed is [ OC)3Fc (p2W 7 -C7H7 Pd( 7 -CsHs)], with Pd-C distances to the two carbons of the... 

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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