The preparation, spectroscopy, structure and electrochemistry of some [Co(η4-C4Ph4)(η5-C5H4R)] complexes

[Co(η4-C4Ph4)(η5-C5H4R)] (R = CO2Me, 2; and CHO, 3), prepared by the reactions of [Co(η5-C5H4R)(PPh3)2] with Ph2C2, were used as precursors for complexes where R = CH2OH, 4; CH2Cl, 5; CH2P(O)(OEt)2, 6; CH2PPh3+, [7]+; C(O)Fc, 8 (Fc = ferrocenyl); CFc2OH, 9; CHC(CN)2, 10; syn and anti-CHNNH–C6H3(NO2)2-2,4, 11; CH(Fc)OH, 12; CHFc+, [13]+; and CFc2+, [14]+. Most new compounds have been characterised by elemental analyses, and all by spectroscopy. Their spectra are consistent with their formulae; of particular interest is the UV–Vis spectrum of [14]+ which shows two very strong absorption bands at 389 and 835 nm. X-ray diffraction techniques were used to determine the structures of 1 (R = Me), 4, 6, [7]Cl, 8, 9, 10, 11a (syn isomer), and 12. All have the same basic structure with the Co atom sandwiched between ca. planar η5-C5H4R and η4-C4Ph4 rings. The Ph groups do not lie in the C4 planes, and the C4Ph4 ligands constitute four-bladed propellers. The two rings are close to parallel with interplanar angles of 0.4–4.4° except where R = CH(Fc)OH (6.6°) and CFc2OH (12°) which is attributed to steric crowding though this does not affect the ferrocenyl groups to the same extent. When the C atom α to the C5H4 ligand is sp3 hybridised, it is usually displaced out of the C5 plane away from Co, but when Cα is sp2 hybridised (in 8 and 10) it is displaced out of the C5 plane towards Co. This is attributed to the contribution that η6-fulvene mesomers make towards a description of the structure of the latter compounds but not the former. In the primary and secondary alcohols 4 and 12 there is H-O⋯H-O hydrogen bonding, but in the tertiary alcohol 9 there is evidence of an intramolecular Fe⋯HO bond to one ferrocenyl group Fe⋯H = 2.965(1) Å and an angle of 5.1° between its two cyclopentadienyl ligands. Electrochemical studies are reported for 8–11 and the known compound triferrocenylcarbinol; this last is compared with the mixed cobalt/ferrocenyl systems 8 and, particularly, 9. The Co(η4-C4Ph4)(η5-C5H4-) centre is always more difficult to oxidise than Fe(η5-C5H5)(η5-C5H4-).

Graphical abstract[Co(η4-C4Ph4)(η5-C5H4CHO)] and [Co(η4-C4Ph4)(η5-C5H4CO2Me)] are suitable precursors for a variety of compounds containing the Co(η4-C4Ph4)(η5-C5H4-) moiety such as the ferrocenyl (Fc) alcohols [Co(η4-C4Ph4){η5-C5H4C(OH)FcnH2−n}] (n = 1, 2). These can be converted to the [Co(η4-C4Ph4){η5-C5H4CFcnH2−n}]+ cations. The complexes are characterised by spectroscopy, X-ray diffraction and electrochemistry.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Preparation of Wittig and Horner–Wittig reagents & other useful precursor compounds. ► Preparation of triarylmethyl cation analogues. ► Solid state structural parameters of 10 new cobalt compounds. ► Electrochemistry of Fc3COH and 5 cobalt complexes.