Ferrocenic acid derivatives: towards rationalizing changes in the electronic and geometric structures

Using calculations based on Density functional theory (DFT), we optimized the geometry of three compounds containing the ferrocenoyl moiety, ferrocene aldehyde (I), ferrocene carboxylic acid (II), ferrocene amide (III) and the parent ferrocene. The calculated results were compared to experimental structural data. General trends have emerged: the carbonyl C-O distance increases in the order aldehyde < ketones < amides < acid. The O-C-X (X = O, N, C) angles are less responsive to substituents and seem to be more a reflection of packing forces. Expectedly the distance between carbonyl carbon and the organic group R (R = OH (acid), NR2 (amide), CR3 (ketone) increases in the order acid < amides < ketones. Maximization of electron delocalization involving the C(O)-X (X = O, N, C) and the Cp ring will force the Cp ring and the C(O)-X substituent to be co-planar. However, steric interference between the Cp ring and the substituent can result in a significant deviation from co-planarity and can give rise to a significant twist. (C) 1998 Elsevier Science S.A. All rights reserved.