X-Ray studies on constrained ferrocene derivatives. Part I. Crystal structure of 1,12-dimethyl[1,1]ferrocenophane (1,1″:1′,1‴-diethylidendiferrocene)

Abstract

The crystal and molecular structure of the title compound has been detrmined by X-ray diffraction methods. Crystals are monoclinic with a= 18·14(3), b= 6·10(2), c= 18·67(3)Å, β= 119° 40′(10′), space group P2/c, and Z= 4; each molecule has C₂ crystallographic symmtry. The structure was refined to R 0·083 on 1765 nonzero structure amplitudes collected photographically. The molecules exist in the eclipsed-form with an exo-methyl configuration. The cyclopentadienyl rings bonded to one iron atom are twisted with respect to each other by 21·5 and 23·9° in the two independent molecules, while the angle of tilt between such rings in slight (2–3°). There are dihedral angles of 30° 10′ and 31° 28′ between cyclopentadienyl rings in the same ligand in the two molecules. There is considerable geometric evidence that the molecular conformation is dictated by intramolecular H ⋯ H contacts, both within ligands and between ligands. The Fe ⋯ Fe distances are 4·620(2) and 4·595(2)Å.