Studies of the bonding in iron(II) cyclopentadienyl and arene sandwich compounds. Part 4. A survey of the effect of methyl substitution on the bonding in some iron sandwich complexes

A series of methylated benzene complexes of the type [Fe(η6-C6HnMe6–n)(η5-C5H4X)]PF6(n= 0–6) have been synthesised where X = H, Me or COPh. Iron-57 Mossbauer data are presented and quadrupole splittings (q.s.) correlated with the degree of methylation (n) of the arene moiety. Fox X = H, a linear correlation between q.s. and n was found. For X = Me, a similar correlation was obtained but with a significantly lower slope whereas for X = COPh the plot showed a minimum at n= 1. These results are discussed in relation to the bonding in other iron sandwich complexes {ferrocenes and [Fe(η6-arene)2]2+ salts}. This has enabled a rationalisation of Mossbauer parameters for a wide range of iron sandwich complexes to be made.