Rhenium complexes cyclohexadienyl

The reaction of the rhenium complex XLII with lithium at 200°C is a special case, producing the dimeric )f -cyclohexadienyl species (XLIII) ... 

An interesting property of some cyclopentadiene- and cyclohexadienyl-metal complexes is the occurence of unusually broad, low frequency bands (2700 cm" ) which arise from a C—H stretch of the methylene carbon. The crystal structure of the rhenium complex, 7.21, which also has an unusually low C—H stretch, shows that the C—hydrogen is in the exoposition. It is reasonable to suppose that the unusual C—H stretches in the related complexes also arise from the C—H, bond. It has been suggested that the C—frequency is lowered as a result of direct interaction between the metal and the methylene carbon. 

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). 

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