Iron complexes azulene

It might be expected that azulenes would be able to act as 7-electron ligands. In those complexes whose crystal structures have been determined this is not so. In the binuclear iron complex, (azuIenejFe CCOjj, for example, azulene acts as a 5 + 3 electron ligand while in the similar molybdenum compound, (azulenejMo CCO), it is a 2 x 5 electron ligand. 

The mass spectra of binuclear iron carbonyl complexes of acenaphthylene and azulene have been briefly reported 26). The acenaphthylene complex previously 43> reported as Ci2H8Fe2(CO)6 exhibits Ci2H8Fe2 (CO)5 as the highest m/e ion the implied pentacarbonyl formulation was later 44> confirmed by X-ray crystallography which indicated structure 16. The reaction between azulene and Fe(CO)s has been reported 45> to give dark red CioHgFegfCOJs this formulation was confirmed by... 

Formally there are five nonequivalent double bonds and, as a consequence, a number of different coordination modes have been reported [51]. The complexes are usually obtained by reaction of the ligand with metal complexes such as iron carbonyls. For example, the constitution of the dinuclear iron azulene complex 131 has been identified on the basis of its crystal structure analysis [138]. The interesting complex 132 with two azulene moeties was obtained by the reaction of triisopropyliron (from isopropylmagnesium bromide and FeClj) and azulene (Scheme 10.46) [139]. 

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